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EXPERIMENTAL STUDY ON THE PROPERTIES OF A NEW ROTATION-MAGNIFIED VISCOELASTIC DAMPER
Hong-nan LI, Yuan-long LI, Zhou HUANG, Xing FU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0213
Abstract:
This paper develops a new rotation-magnified viscoelastic damper, and the leverage principle is used to magnify the relatively small rotation angle at the beam-column joint of a structure. By magnifying the rotation angle, the energy dissipation capacity of the damper is fully utilized to achieve a more ideal vibration control effect. First, the basic structure and working principle of the damper are introduced, and a physical model is manufactured. Then the frequency dependency, deformation dependency and fatigue performance loading tests of the damper have been performed to investigate the change law of its mechanical performance indexes, such as the maximum damping force, equivalent shear stiffness, energy consumption per cycle and equivalent viscous damping ratio. Finally, the mechanical properties of the traditional angle damper without amplification function are tested to validate the energy consumption amplification ability of the proposed damper. Results show that: the hysteresis curve of the damper is plump with stable hysteresis performance, and the anti-fatigue performance is good; compared with traditional angle damper without amplification function, its energy consumption capacity can be increased by up to 4.42 times.
EXPERIMENTAL INVESTIGATION AND FINITE ELEMENT MODELING OF INTERFACE BOND-SLIP BEHAVIOR BETWEEN SHAPE STEEL AND ECC
Liang BAI, Miao ZHANG, Lei YANG, Shuai HU, Zheng-fu BAO
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0265
Abstract:
In order to study the interface bond-slip behavior between shape steel and Engineered Cementitious Composites (ECC), the shape steel-ECC specimens were designed to conduct push-out testing. The influences of the volume fraction of PVA fiber, stirrup reinforcement ratio, ECC cover thickness and shape steel embedment length on the failure modes, on the load-slip curves and on the bond stress of shape steel-ECC specimens were analyzed, also the bond stress distribution along steel embedded length was proposed. The result shows that the volume fraction of PVA fiber and ECC cover thickness have great influences on bond stress. The maximum bond stress occurred near the loading end, and the equivalent bond stress increased with the increase of the load. According to the test results, the expression of bond stress in different states were established, and the bond-slip constitutive laws were proposed. On this basis, the finite element model of shape steel-ECC specimens was established by using a nonlinear spring to simulate the interface bond-slip behavior between shape steel and ECC. The finite element analysis results were compared with the test results, which indicated that the finite element simulation method proposed could accurately analyze the interface bond-slip behavior of shape steel-ECC.
NUMERICAL MODEL FOR THE RESIDUAL SEISMIC CAPACITY OF SEISMICALLY DAMAGED REINFORCED CONCRETE COLUMNS
Lei LI, Guang-xi LUO, Zhuo-han WANG, Shan-suo ZHENG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0789
Abstract:
Based on the reinforced concrete (RC) column test data in the Pacific Earthquake Engineering Research Center (PEER) database and the existing seismic damage index models, the damage characteristics of the RC columns at different damage levels were summarized. Damage evaluation criteria for damaged columns were proposed. The evolutionary damage to the sectional materials, including the cover concrete, confined concrete and longitudinal reinforcement, during the earthquake damage process was investigated. Evolutionary damage models for the sectional materials were proposed, where the uneven damage to the materials at different positions of the plastic hinge zone of the RC column was considered. Based on the OpenSees platform and the fiber model, a numerical model of the seismic damaged RC frame columns was established, which was directly based on the constitutive relationship of materials. The model considered the damage difference of materials in different positions of the damage area and the damage difference of materials in different positions of the same section. The test data of 13 existing RC frame columns were randomly selected to verify the numerical model calculation results of seismic damaged RC frame columns. The results show that the model accurately predicted the post-earthquake behavior of the RC columns. These results provide an analytical model for the performance evaluation of and retrofitting decisions for RC structures after an earthquake.
STUDY ON THE FIRE PERFORMANCE OF CONCRETE-FILLED DOUBLE-SKIN TUBULAR COLUMNS WITH EXTERNAL STAINLESS STEEL TUBES
Jia-qi LI, Rui WANG, Hui ZHAO, Hui-wen WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0679
Abstract:
To investigate the fire performance of concrete-filled double-skin tubular (CFDST) columns with external stainless steel tubes, the fire resistance of this kind of composite members was analyzed by ABAQUS. The differences in the fire mechanisms between CFDST columns with external stainless steel tubes and those with external carbon steel tubes were studied. The effects of the cross-sectional dimension, hollow ratio, load ratio and material strength on the fire resistance of components were analyzed. The results show that the CFDST columns with external stainless steel tubes present better fire resistance than those with external carbon steel tubes. The fire resistance of members was greatly affected by the cross-sectional dimension and load ratio. The hollow ratio and material strength had a moderate influence on the fire resistance of the members. Based on a parametric analysis, a design method for the fire safety of CFDST columns with external stainless steel tubes was suggested.
ANALYTICAL SOLUTION FOR NONLINEAR CONSOLIDATION OF SAND-DRAINED GROUND WITH EXPONENTIAL FLOW UNDER VACUUM COMBINED SURCHARGE PRELOADING
Wen-hao JIANG, Liang-tong ZHAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0190
Abstract:
Based on an exponential flow law for soft soil, e-lgσ′ and e-lgk logarithmic models are introduced to consider the nonlinear consolidation characteristics of soil, the characteristics of the vacuum negative pressure decreasing along the depth are also considered, and an analytical solution for nonlinear consolidation of sand-drained ground is derived under vacuum combined surcharge preloading. By comparing the analytical solution with the existing one, the correctness of the analytical solution is verified. According to the analytical solution, the consolidation behaviors of sand-drained ground are analyzed. The analysis shows that in the initial stage of consolidation, the larger the seepage index m, the faster the consolidation rate of sand well foundation, but in the later stage of consolidation, the larger m is, the slower the consolidation rate of sand well foundation is. The negative pressure transfer coefficient kz has little effect on the consolidation rate of sand-drained ground, but the decrease of kz will reduce the settlement rate and final settlement of sand-drained ground. The higher the ratio of compression index to permeability index, the slower the consolidation rate of sand-drained ground is. When m<1, the larger the surcharge loading, the smaller the consolidation rate of sand-drained ground; When m>1, the larger the surcharge loading, the higher the consolidation rate of sand-drained ground.
CALCULATION OF THE UNSTEADY AERODYNAMIC FORCES ON MOVING TRAINS UNDER CROSSWINDS
Zhi-yong YAO, Nan ZHANG, Ze-nong CHENG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0730
Abstract:
We investigate the effect of crosswinds on the unsteady aerodynamic forces of moving trains. Two methods are introduced to simulate the fluctuating wind velocity at the position of a moving vehicle. Using the quasi-steady theory and aerodynamic weighting function approach, a calculation formula of the unsteady forces on moving trains is established by considering the nature of different turbulent components and various wind directions. A numerical example is given to explore the effect of different parameters on the simulated results. The results show that the filtering and time-lag effects are observed in the weighting function approach. As additional wind turbulences from different directions are considered, there are greater fluctuations in the force. The mean value and coefficient of variance of the unsteady forces are affected by the various wind directions and lateral turbulences, respectively.
STUDY ON THE INTERACTION MECHANISM BETWEEN SURROUNDING ROCK AND LINER WITH HIGHLY DEFORMABLE ELEMENTS IN SQUEEZING TUNNELS
Kui WU, Zhu-shan SHAO, Su QIN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0013
Abstract:
As a type of circumferential yielding supports, liner embedded with highly deformable elements can achieve the release of rock deformations through the compressible deformation of highly deformable elements. The paper aims to investigate the interaction mechanism between surrounding rock and liner with highly deformable elements. In this paper, the improved fractional Burgers model is established to describe the time-dependent behavior of rock, and then the analytical solutions for tunnel displacement and support pressure are derived taking into account the tunnel face advancement effect and the installation delay of support. In addition, the reliability and effectiveness of analytical solutions are well validated by comparing the monitoring data in Lyon-Torino Base tunnel. Furthermore, based on the analytical solutions proposed in this paper, a comprehensive parametric investigation including the influences of fractional order of rock constitutive model, supporting time and yield stress of highly deformable elements is carried out. The main conclusions are made as follows: The deforming ability of surrounding rock becomes stronger as fractional order of Burgers model increases, and the tunnel displacement and support pressure also exhibit an increasing trend; Supporting time has a great influence on tunnel performance. On the one hand, in order to keep rock stability it is recommended to install support structures as early as possible. On the other hand, the optimal number and length of highly deformable elements should be determined for ensuring that the support pressure varies within a range of bearing capacity of liner; The yield stress of highly deformable elements does not pose a significant effect on tunnel displacement and support pressure. However, this does not mean the yield stress of highly deformable elements can be determined randomly. There should be an appropriate range for this yield stress, where the purposes for both the tunnel stability and the release of rock deformation can be achieved.
STUDY ON PERFORMANCE OF COUPLED LOW YIELD POINT STEEL PLATE SHEAR WALLS AFFECTED BY THE INTERACTION OF INFILL PLATES AND BOUNDARY FRAME
Meng WANG, Yong-chao GUO
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0640
Abstract:
In order to satisfy the requirements on seismic behavior and spatial flexibility of high-rise buildings, based on the combination of high-performance materials and high-performance structures, the low yield point (LYP) steel plate shear wall structure with coupling beams was proposed. The finite element models of steel plate shear wall structures were established by ABAQUS, which were proved accurate through a comparison with the published tests. Using the verified numerical method, five coupled and uncoupled LYP steel plate shear wall structure models with different degrees of coupling were established. These models were subjected to static pushover loads and cyclic loads to compare their failure modes, lateral load carrying-capacities, hysteretic behaviors and energy dissipation performances. The influence of the interaction between infill plates and boundary frame on the mechanical properties of the structures and their members was discussed, and some suggestions were proposed for the design of coupled steel plate shear wall structures. The analysis results show that the interaction between infill plates and boundary frame can effectively improve the bearing capacity, bearing efficiency and energy dissipation capacity of the whole structure. Considering the material efficiency, bearing capacity and energy dissipation capacity, it is suggested that the coupling degree of the connecting beam should be controlled within 0.45. With the increase of coupling degree, the shear force shared by the boundary frame increases to 60%, the axial forces of the internal frame columns significantly decreases, and the rotation of coupling beams keeps decreasing. Therefore, the interaction between infill plates and boundary frame should be fully considered in the design of coupled shear wall structures, which is able to effectively reduce the design thickness of infill plates and the section size of boundary frame, and improves the material efficiency and design economy. At the same time, compared with the pure frame, the interaction between infill plates and boundary frame effectively improves the initial lateral stiffness and bearing capacity of the boundary frame.
DETECTION OF STRUCTURAL DEFECT AND DEFORMATION BASED ON MULTI-VIEW GEOMETRIC THREE-DIMENSIONAL RECONSTRUCTION METHOD
Yu-fei LIU, Jian-sheng FAN, Si-yu KONG, Xiao-chen WEI
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0598
Abstract:
Surface damage and deformation are important indicators for testing, appraisal and monitoring of structural safety. The adoption of digital image method can effectively overcome the shortcomings of current manual inspection methods. However in engineering practice, challenges are encountered such as the difficulty in correcting the geometric deformation of the image during quantitative detection, the difficulty of damage localization of images in the overall structure, and the inability to measure the spatial deformation of the steel structure. By combining the research and application of multi-view geometric 3D reconstruction method, the above problems can be effectively solved. This paper discusses the principle and algorithm for the implementation of multi-view geometric 3D reconstruction, and introduces the classic and efficient algorithms for practice. Aiming at the problem of the digital image detection method in engineering practice, a surface projection method for the correction of imaging geometric deformation and damage localization, and a reverse engineering modeling and feature extraction method for the geometric deformation damage detection are proposed. Through three application studies including structural surface crack identification, large structure surface damage localization and steel structure component deformation identification, the specific operation methods and comparative advantages of multi-view geometric 3D reconstruction method for structural surface damage and deformation identification are discussed. The multi-view geometry three-dimensional reconstruction method has the benefits of low equipment requirements, convenient operation, rich model color and relatively high point cloud precision, After combined with the digital image method, it shows great research and application potential in the field of engineering structure inspection and monitoring.
SEISMIC DAMAGE ASSESSMENT OF COMPOSITE FRAME WITH REINFORCED CONCRETE COLUMNS AND STEEL BEAMS BASED ON IMPROVED PARK-ANG DOUBLE PARAMETER MODEL
Jin-jie MEN, Qian ZHANG, Chao XU, Qing-xuan SHI
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0604
Abstract:
To evaluate the damage degree of Composite Frame with Reinforced Concrete Column and Steel Beam after the earthquake, the seismic damage model of RCS composite frame structure was established by modifying the relevant parameters of the Park-Ang double parameter seismic damage model. By analyzing the influence of the slab on the key parameters of the model, the formula to calculate the ultimate deformation capacity of the composite beam members under the influence of the slab space combination effect was given. The formula was verified. Based on the test results, the parameter β under the influence of cyclic loading of the composite beam member was obtained by inverting the component at a damage index equal to 1 at the point of failure. The range of damage index corresponding to the degree of damage of the structure was given, and a seismic damage assessment method for this structure was proposed. The seismic damage assessment of a 4-layer RCS composite frame structure under the action of El-Centro wave shows that the seismic damage model proposed in this paper can better reflect the damage evolution process and degree of RCS composite frame structure. The research results provide a theoretical basis for seismic damage assessment and performance-based seismic design of RCS composite frame structures.
PASSIVE VIBRATION REDUCTION OF SPACE TRUSS STRUCTURES BASED ON NES
Gen LIU, Gong-fa CHEN
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0617
Abstract:
The discrete linear spatial truss structure composed of many bar members is taken as a continuous beam by using an equivalent method. The transient vibration suppression of the truss structure is studied by adding nonlinear energy sinks (NES) to the equivalent beam. The lattice structure of the beam is modeled as an equivalent linear continuous system (finite length beam) by an equivalent method, which is verified by a finite element model. The vibration control equations of an equivalent cantilever beam with a NES attachment are established. The Galerkin method is adopted for discretization. The displacement responses of beams with and without a NES attachment under external excitation are analyzed. The vibration suppression effect of NES on the structure is studied by calculating the external excitation response of NES attachments at different positions in the structure. In addition, the external excitation response of NES attachments with different masses at different positions are also investigated. The effect of NES additional mass on the vibration reduction is obtained. The results show that the NES attachments can reduce the response efficiency of the x-truss under transient excitation When the mass of the NES attachments increases, the vibration amplitude of the system declines more rapidly and the energy consumption efficiency of the NES attachments becomes higher. The NES passive vibration reduction effect is compared with the linear stiffness damping damper (TMD). The results show that, in the structure with additional NES, the attenuation of the structure amplitude is appreciable at about 5 seconds after the excitation occurred, and the decline in the amplitude is steeper. This means that the NES passive reduction effect is much better than that of the linear stiffness damping damper (TMD). Additionally, the attenuation effect of the NES attachments with different qualities is verified through experiments, in which the same displacement excitation amplitude (15 mm) is applied to the free end of a beam. The results show that the greater the mass of the NES attachment is, the higher is the attenuation efficiency of the transient response of the cantilever structure. The experimental results are in good agreement with the theoretical calculation results.
SEISMIC PERFORMANCE OF CONCENTRICALLY BRACED FRAMES CONSIDERING THE BRACE FRACTURE AND GUSSET PLATE EFFECT
Yao CUI, Xiao-zhuo XU, Chi LIN
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0648
Abstract:
The concentrically braced frame (CBF), which shows good seismic performance with a low cost, is a popular seismic resistant structural system. Generally, CBFs are designed to meet the ductility requirement to ensure that the braces buckle in compression or yield in tension. As observed in previous major earthquakes, the ultimate failure mode of CBFs is the fracture of the braces. However, CBFs are often idealized as trusses in a frame analysis or design, considering the boundary of braces as pinned or fixed connections and ignoring the fracture behavior of the braces. In this paper, a numerical model using OpenSees considering the brace fracture and gusset plate effect was proposed. A single-brace model, a one-story frame model and a three-story frame model were simulated to verify the reliability of the numerical model. The simulated results showed good agreements with the corresponding experimental results. The calibrated three-story frame model was then adopted for an incremental dynamic analysis. The results indicated that the collapse margin ratio of the frame was overestimated if the brace fracture was not considered. It is strongly recommended that the brace fracture and gusset plate effect should be considered for the design and detailing of CBFs to reasonably evaluate the seismic performance.
THE IMPACTED DAMAGE STUDY OF A SINGLE CLEAVAGE DRILLED COMPRESSION SPECIMEN BASED ON BOND-BASED PERIDYNAMICS
Ning LIU, Meng-fan HU, Fei ZHOU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0076
Abstract:
A dynamic analytical model is built for a single cleavage drilled compression specimen (SCDC) impacted by a split Hopkinson pressure bar based on bond-based peridynamics, in which the Hopkinson bar is simplified as 1D model and the specimen is described as 2D model. The repelling short-range force is used for modeling the impact process. The dynamic failure behaviors of the single cleavage drilled compression specimen are studied using the model. The force analysis indicates that: the stress distribution on the end faces of the specimen is showed as a V-shape pattern and it well solves the limitation of the end face loading way of the traditional experimental-numerical method. Then the crack propagation processes and failure modes are studied under different impact velocities. It shows that: the numerical model accurately predicts the times of the crack initiation, arrest and the secondary crack initiation. Simultaneously, the crack initiation toughness at the crack tip is calculated according to the algorithm of dynamic stress intensity factor in bond-based peridynamics, which provides a new method for the dynamic fracture toughness analysis of materials.
EXPERIMENTAL STUDY ON MECHANICAL BEHAVIOR OF STEEL REINFORCED CONCRETE STOCKY COLUMN WITH MONOSYMMETRIC CROSS-SHAPED STEEL UNDER AXIAL COMPRESSION
Tian-hua ZHOU, Ji-peng YU, Ya-peng LI, Yu ZHANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0050
Abstract:
To investigate the axial compression behavior of the composite column with monosymmetric cross-shaped steel, 9 stocky columns were tested under axial compression. The experimental parameters were the cross-shaped steel eccentricity ratio, concrete strength, steel ratio and volume-stirrup ratio. The failure pattern, the load-deformation curves, the law of strain change of the specimens were obtained by the test. The stress mechanism and the influences of four parameters on axial compression behavior of the composite columns were analyzed. Based on Mander model, a calculation method of axial bearing capacity for the composite column is proposed by partitioning different confined areas of concrete. The experimental results show that the specimen failure was concentrated in the reverse cross-shaped steel eccentric direction. The steel profile, longitudinal bar, stirrup and concrete can work together, and the strength of them can be mobilized. The axial compressive bearing capacity and ductility of the specimen decrease with the increase of eccentricity and stirrup spacing of cross steel. Increasing the concrete strength and the steel ratio can enhance the axial bearing capacity of the specimens. However, increasing the concrete strength reduced the ductility of the specimens. The axial bearing capacities of the specimens calculated by the JGJ138-2016, EC4 and ACI318-14 are relatively conservative. Calculation results from the axial bearing capacity formula proposed for the composite column under axial compression agree well with the test results.
STUDY ON AXIAL COMPRESSION PERFORMANCE OF CONCRETE STUB COLUMN STRENGTHENED BY PRESTRESSED STEEL HOOP
Jian XIE, Li YANG, Fu-quan XU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0020
Abstract:
Both thirty-three concrete stub columns reinforced by prestressed steel hoops (PSHC) and nine unreinforced columns were tested under axial compression. The studied parameters were the hoop ratio (the spacing of hoops and the concrete diameter), the prestressing level and the initial axial compression ratio. The influences of these parameters on the carrying capacity and deformation capacity of PSHC were obtained and discussed. The results show that the bearing capacity and deformation capacity of the PSHC can be improved by 107% and 540%, respectively, compared with the comparison column. The reinforcement effect will become better with the increase of the hoop ratio. When the prestress ratio increases gradually, the carrying capacity of PSHC increases gradually and the peak strain decreases gradually. The initial axial compression ratio has no obvious influence on the reinforcement effect, the PSHC can be used as a non-unloading reinforcement method. Based on the experiment results, a prediction equation was proposed and verified by the comparison of prediction values and test data in this investigation and other references.
NON-LINEAR DEFLECTION PERFORMANCE OF WELDED STAINLESS STEEL I-SECTION BEAMS
Huan-xin YUAN, Xiao-wan CHEN, Ji-sheng CAI, Xin-xi DU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0022
Abstract:
Five welded stainless steel I-section beams were subjected to three-point bending to explore the non-linear deflection behavior of stainless steel beams. Finite element (FE) models were developed by considering the material nonlinearity, initial geometric imperfections and welding residual stresses. The models were validated against the experimental results. Based on the validated numerical models, both the calculation method in the Chinese technical specification for stainless steel structures (CECS 410) and the proposal of Real-Mirambell were evaluated. A simplified calculation formula for the yielding moment M0.2 of stainless steel cross-sections was proposed based on the plane section assumption and the stress–strain relationship of stainless steels. The decrease in the initial flexural stiffness resulted from the welding residual stresses was considered by introducing reduction coefficients for different stainless steel alloys. Revised formulas for the CECS 410 method and the Real-Mirambell proposal were presented, which provided accurate and reasonable deflection predictions for welded stainless steel I-section beams.
COMPLEX MODE SUPERPOSITION METHOD OF HYBRID STRUCTURE SEISMIC RESPONSES BASED ON DYNAMIC CHARACTERISTICS
Pan-xu SUN, Hong YANG, Qing-lin LIU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0723
Abstract:
The damping matrix of a hybrid structure of different material damping characteristics is difficult to determine. By the aid of mathematical simplicity, Rayleigh damping model is widely used in the construction of damping matrix of a hybrid structure. But the calculation precision of Rayleigh damping model is affected by the choice of reference frequencies. Thusly, a calculation method of Rayleigh damping coefficients is proposed based on the characteristics of structural dynamic responses. The corresponding complex mode superposition method is also realized. The damping coefficients are determined based on the natural frequencies of the first two modes when the structural transient responses are calculated. The damping coefficients are determined based on fundamental frequency and certain frequency when the structural steady state responses are calculated. The certain frequency is the natural frequency close to external excitation frequency. According to the spectrum characteristics of seismic wave, a Rayleigh damping model is obtained based on the predominant frequency of seismic wave. Combined with the linear assumption of earthquake acceleration, a complex mode superposition method of hybrid structure is realized. The harmonic frequencies of seismic wave could be obtained by trigonometric series. Another Rayleigh damping model is developed based on the harmonic frequencies, and the corresponding complex mode superposition method is proposed. The cases show that the proposed method could avoid the arbitrariness of selective modes based on traditional methods. The calculation error of the proposed method is small. Compared with the complex mode superposition method based on the predominant frequency of seismic wave, the computational amount of complex mode superposition method based on the harmonic frequencies is larger, but with higher calculation accuracy and wider range of application.
DETERMINATION OF THE CRACKING STRENGTH, TENSILE STRENGTH AND DOUBLE K FRACTURE PARAMETERS OF CONCRETE
Jun-feng GUAN, Ze-peng LIU, Xian-hua YAO, Lie-lie LI, Shuang-hua HE, Min Zhang
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0084
Abstract:
It presents an improved fracture theory and an associated method for determining the independent material parameters of concrete, e.g. cracking strength, initial fracture toughness, tensile strength and fracture toughness for different types of specimens, in which the heterogeneous properties of concrete were considered. Based on the concrete fracture tests of three-point-bending (3-p-b), wedge-splitting (WS) and four-point-bending (4-p-b) specimens, the corresponding cracking strength, initial fracture toughness, tensile strength and fracture toughness were simultaneously determined. The rationality and applicability of the proposed model and the associated method were verified by the experimental concrete strength and the double K fracture parameters determined by the double K model. The whole initial fracture curves and fracture failure curves of concrete were obtained using the determined materials. The theoretical minimum concrete specimen size for determining the initial fracture toughness to meet the condition of linear elastic fracture mechanics was given. Based on the proposed simple analytic expressions between the cracking strength and the initial fracture toughness, the initial loads of all 3-p-b specimens, WS specimens and 4-p-b specimens were successfully predicted. The initial fracture toughness of concrete was also determined using the analytic expressions.
ADAPTIVE MESH REFINEMENT ANALYSIS OF FINITE ELEMENT METHOD FOR ELASTIC BUCKLING OF CIRCULARLY CRACKED CURVED BEAMS
Yong-liang WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0173
Abstract:
In this paper, the scheme for the cross-section damage defects in circularly curved beam is established to simulate the magnitude (depth), location and number of the cracks. The h-version adaptive finite element method for non-uniform Euler-Bernoulli beam is introduced to solve the elastic buckling of circularly curved beam with cracks. Using the proposed method, the final optimized meshes and high-precision buckling loads and modes meeting the preset error tolerance can be obtained. Numerical examples show that the non-uniform mesh refinement can adapt to the change of buckling mode induced by crack damage, which is applied to the elastic buckling analysis for some typical kinds of subtended angles and crack damage distribution conditions of circularly curved beams. Furthermore, the influences of crack damage on the buckling load and mode of circular curved beams is quantitatively analyzed, and the accuracy and reliability of the proposed algorithm are verified.
THEORETICAL ANALYSIS OF THE ELASTIC BUCKLING COEFFICIENT OF RECTANGULAR LONGITUDINALLY PROFILED STEEL PLATES
Dong-dong XU, Yuan-qing WANG, Xiao-ling LIU, Hui-yong BAN, Ming LIU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0628
Abstract:
Longitudinally profiled (LP) steel plates will be widely used in engineering structures due to their adaptation to the needs of modern buildings such as super high-rise and large span buildings. Because of the geometric characteristics, the local buckling deformation of LP steel plates is more likely to occur at positions near the thin end, and the performance of local stability is significantly different from that of the steel plates with a constant thickness under the same load case. As a consequence, the local stability problem of LP steel plates needs to be studied in depth. Based on the energy principle, the Galerkin and Rayleigh-Ritz method (GRM) is used in the theoretical formulae derivation of the elastic buckling coefficient, where the target rectangular LP steel plates are under uniaxial uniform compression and four different boundary conditions. The resultant formulas are verified by using finite element software ANSYS. The relationship curves between the elastic buckling coefficient of rectangular LP plates with different thickness parameters and length-to-width ratios are obtained, which provide a theoretical guidance and design basis for engineering applications of LP steel plates.
DYNAMIC ANALYSIS OF MULTI-LOOP CABLE-STRING DOME DUE TO SUDDEN CABLE FAILURE
Chao ZHANG, Xin-di FU, Xiu-li DU, Xue-yuan YAN, Li XU, Hong-yu JIA
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0781
Abstract:
The multi-loop cable-string dome (MLSD) is a complex suspended-dome structure. Sudden failure of any cables will cause a very significant dynamic impact on MLSD. Based on the AP method, this study proposes a dynamic analysis method to analyze the dynamic response of MLSD due to sudden cable broken. The sensitive analysis of different parameters was conducted, such as failure paths, failure time, damping ratio and initial loadings. The ideal parameters suitable for MLSD are recommended. The dynamic analysis results show that: the displacement and internal force response of the remaining MLSD due to cable sudden broken will be greater than the cable slowly failure. The dynamic amplification factor should be seriously considered when suffered from cable sudden broken. Moreover, the dynamic amplification factor (DAF) of some responses will be larger than 2.0 recommended by current design codes. Finally, the discussion on displacement DAFs due to different cables sudden broken shows that the DAFs due to the sudden failure of any cables of the same loop are the same. The DAFs caused by sudden failure of cables on the outer loop will be significantly greater than that of other loops. Both DAFs due to cable failure of the outer loop and the string are significant, but the DAFs value distribution are quite different. The dynamic response caused by multiple cable breakages is not always greater than that of a single cable.
THE SEISMIC PERFORMANCE OF PRECAST BRIDGE PIERS WITH GROUTED SLEEVES
Wen-jing XU, Biao MA, Hong HUANG, Jian SU, Jian-zhong LI, Rui-long WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0667
Abstract:
The grouted sleeves embedded in precast column bodies were taken as the research object. The mechanical behavior of the column-to-footing joint and the influence on the overall seismic performance of this kind of bridge piers were theoretically analyzed. A quasi-static test of precast bridge piers with grouted sleeves was carried out. The difference between the seismic performance of the cast-in-place piers and the precast bridge piers with grouted sleeves was compared by a numerical simulation. The influence of different sleeve diameters and lengths on the seismic performance of the bridge piers was also investigated. The results show that the precast piers with grouted sleeves were easy to form a rigid region in the connecting section due to the large rigidity of the sleeves, and that the redistribution phenomenon of the curvature occurred in the columns, resulting in an increase in the curvature and rebar strain concentration adjacent to the end of the sleeves. In addition, the precast bridge piers with embedded grouted sleeves in the plastic hinge area were found to have a reduced displacement capacity as compared to cast-in-place piers with the same reinforcement. This phenomenon was more serious when a larger sleeve diameter was adopted. The larger the diameter and the longer the length of the sleeves, the more obvious the strain concentration at the joint, which resulted in the transformation of the final failure form of the pier from the traditional concrete failure in the plastic hinge area to steel fracture in the joint at the bottom of the pier.
COMPARATIVE ANALYSIS OF EXPERIMENTS ON PLANE STEEL FRAME AND DAMPED STEEL FRAME WITH DOUBLE FLANGED RIGID CONNECTIONS CONTAINING CORE TUBE
Ai-lin ZHANG, Qing-bo WANG, Yan-xia ZHANG, Guang-hao SHANGGUAN, An-ran LIU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0032
Abstract:
A plane steel frame and its damped frame with double flanged rigid connections containing core tube were proposed in this paper and their substructures were designed to conduct pseudo-dynamic tests. Test results such as hysteretic behavior, strain variation of typical positions, lateral stiffness and energy dissipation capacity of both frames were comparatively analyzed to study their seismic performances. The results show that under the actions of 8-degree frequent earthquake and fortification earthquake, the intermediate column with friction damper can provide certain lateral stiffness, limit story drift response, mitigate and even avoid the plastic damage of the structure. Under the actions of 8-degree rare, 8-degree (0.3 g) rare and 9-degree rare earthquake, the friction damper can provide stable energy dissipation and effectively delay the plastic damage of the structure. The stiffness and energy dissipation capacity of the damped frame are superior to those of the plane steel frame, the double flanged rigid connections of both frames present favorable seismic performance and the seismic performance of double flanged rigid connections of the damped frame is superior to that of the plane steel frame.
EXPERIMENTAL STUDY ON THE MECHANICAL BEHAVIOR OF COMPOSITE BEAMS WITH SUPERPOSED SLABS AFTER FIRE
Jun-li LÜ, Shengnan ZHOU, Jing-jing LÜ, Yong-yuan CAI, Qi-chao CHEN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0186
Abstract:
In order to study the performance of composite beams with superposed slabs after fire, five composite beams with superposed slabs after exposure to fire and one composite beams with superposed slabs at room temperature were statically tested. Influence of factors such as the thickness of post cast slab, the stud spacing, the overlapping length of the precast slab on the upper flange of the steel beam, the joint form of precast slabs and exposure to fire or not on failure mode, bearing capacity and initial flexural stiffness of composite beams with superposed slabs were tested. The results indicate that the ultimate bearing capacity of integral composite beams with superposed plates are 9% higher than that of separated composite beams with laminated slabs after fire. The thickness of post-casting layer and the spacing of stud are the main factors influencing the initial flexural stiffness of integral composite beams with superposed plates after fire. Before and after the fire, the integral composite beams with superposed plates are subjected to bending failure under the action of load, and the failure modes are basically the same. However, after the action of fire with high temperature, the cracking of integral composite beams with superposed plates occurs earlier, and the flexural capacity and ductility decrease to different degrees, In this test, the flexural capacity and ductility of integral composite beams with superposed plates after fire under load are reduced by 23.3% and 55.4%, respectively, compared with those under normal temperature. The existence of the joint of precast base plate in the separated composite beams with laminated slabs damages the continuity of the precast base plate and causes the bond failure of the specimen. However, the cooperative performance of the superposed slabs is good at the place far away from the joint. The proposed calculation method for the residual strength and flexural rigidity of composite beams after fire has high accuracy.
A SUBSTRUCTURE MODEL FOR WATER-AXISYMMETRIC CYLINDER INTERACTION DURING EARTHQUAKES
Xiao-jing WANG, Mi ZHAO, Pi-guang WANG, Xiu-li DU, Xing-lei CHENG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0037
Abstract:
A substructure analysis method for water-axisymmetric cylinder dynamic interaction problems is presented to simulate the seismic response of water-structure interactions. According to the wave equation and boundary conditions for the three-dimensional incompressible water and by applying the method of separation of variables, the model is transformed into a two-dimensional model, which is analytical in the circumferential direction and numerical in the vertical and radial directions. The dynamic stiffness equation of the infinity water at the truncated boundary is derived by using the scaled boundary finite element method, then the hydrodynamic pressure on the structure can be obtained by coupling the finite element equation of the near field water with the hydrodynamic on the truncated boundary. The finite element equation in time domain of a water-axisymmetric cylinder interaction system is developed by coupling the finite element equation of the structure with the hydrodynamic pressure. The numerical examples demonstrated that the proposed method is accurate and efficient. Numerical results show that the effect of the hydrodynamic pressure on the natural frequency and the dynamic response of the axisymmetric structure is increasing with the increase of the water depth in general.
CALCULATION OF ERRORS OF NODAL DISPLACEMENTS IN ONE-DIMENSIONAL FINITE ELEMENT METHODS USING ELEMENT ENERGY PROJECTION TECHNIQUE
Si Yuan, Qin-yan Xing, Quan Yuan
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.07.0446
Abstract:
Using super-convergent solutions calculated by the Element Energy Projection (EEP) method, equivalent nodal load vectors from the residual load term were derived in this paper without changing the finite element (FE) meshes and the global stiffness matrices. The subsequent back-substitutions can generate highly accurate estimates for the errors of nodal displacements and hence greatly improve the nodal accuracy. Taking a general second-order ordinary differential equation as the model problem, the algorithm of the proposed method and associated numerical examples were given to show that the proposed method is simple and effective, and that using elements of degree m≥1, the improved nodal displacements can gain the super-super-convergence orders h2m+2 and h3m+mod(m, 2) for simplified and condensed EEP forms, respectively. A variety of significant further extensions and applications were also discussed.
THE MECHANICAL MODEL AND VIBRATION ISOLATION PROPERTIES OF COLLOIDAL DAMPERS
Mu-chun YU, Peng ZHAO, Zhi-ling NIU, Bing-wei LI, Zi-jun NANGONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0119
Abstract:
The colloidal damper is a new type of vibration isolation material consisting of water and hydrophobic nano-porous particles. To perform modeling and mechanical analysis of the colloidal damper, a colloidal damper isolator was formed by sealing the colloidal damper into a compressible chamber. Quasi-static and dynamic loading experiments were conducted to investigate the hysteresis of colloidal damper isolators. A mechanical model with unknown parameters, including the cubic stiffness, viscous and Coulomb frictional damping, was established. Dynamic loading experiments were utilized to identify the unknown parameters. The vibration isolation performance of the colloidal damper was evaluated. The results show that the colloidal damper exhibited excellent low frequency vibration isolation properties and a strong damping effect. Therefore, it has a favorable application prospect as a damper for vibration reduction.
RESEARCH ON FREEZE-THAW DAMAGE MODEL OF FIBER BEAM-COLUMN CONSIDERING REINFORCEMENT SLIP EFFECT
Yi-xin ZHANG, Shan-suo ZHENG, Xian-liang RONG, Zhuo-han WANG, Li-guo DONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0657
Abstract:
The reinforcement slip in the beam-column joints or column footings can make a significant contribution to the total lateral displacement of reinforced concrete members. In order to accurately evaluate the seismic performance of reinforced concrete (RC) with freeze-thaw damage, the reinforcement slip effect is taken into consideration in this study based on the framework of the fiber model accounting for the uneven distribution of freeze-thaw damage. Firstly, the bond strength degradation model with the consideration of the distribution of freeze-thaw damage is built according to the bar pull-out test data. An analytical procedure is proposed for the prediction of reinforcement slip in the frozen-thawed anchorage area based on the assumption of simplified bond stress distribution along the bar and on the governing equations. The model is validated by comparing the data come from frozen-thawed bar pullout experiments. Then the proposed model is implemented to the zero-length section using the finite element software OpenSEES for formulating the modelling method for RC columns considering the uneven distribution of freeze-thaw damage and reinforcement slip effects. Pseudo-static test data from column specimens subjected to freeze-thaw cycles are used to validate the proposed column model and previous fiber model. The research results show that comparing with the fiber modelling results, the calculated hysteretic curves through using the proposed column model are closer to that of the test results, and that the strength errors, the ultimate displacement errors, and accumulated energy errors indicated that the proposed column model can accurately simulate the seismic response of RC column with freeze-thaw damage.
RESEARCH ON THE SIMILARITY THEORY OF TEMPERATURE FIELD OF LIGHT STEEL MEMBERS (STRUCTURES) UNDER FIRE
Canghu Qiu, Gengyuan Zhang, Baiyu Li, Guangyong Wang, Yu Tong, Qing Liu
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0009
Abstract:
Based on heat transfer theory, the similarity theory of temperature field focusing on light steel members (structures) under fire is researched, and the simplified furnace temperature curves are proposed and proved by numerical and experimental methods. Meanwhile, the factors that influence the similarity theory of temperature field focusing on light steel members (structures) with or without non-bulgy fire retardant coating are compared. The results show that the temperature of experimental models under the simplified furnace temperature curves with time similarity constant "1" is basically the same as that of prototype structures under the standard ISO834 temperature curve. This implies that the similarity theory of temperature field focusing on light steel members (structures) under fire is valid. Furnace temperature curves are negatively correlated with steel density and specific heat, and positively correlated with specific surface area and size similarity constant. For light steel members (structures) with non-bulgy fire retardant coating, they are also negatively correlated with coating thermal resistance, and positively correlated with the coating thickness similarity constant.
A GENERALIZED YIELD FUNCTION FOR THE ULTIMATE STRENGTH OF STEEL FRAMES WITH I-SECTIONS
Lu-Feng YANG, Xia-Yong TAN, Jing-Jing HAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0025
Abstract:
The exact generalized yield function of steel members with I-sections under spatial loading is usually implicit and inconvenient to use, while current approximate explicit generalized yield functions cannot fully consider the geometry of I-sections, leading to inaccuracy and unsuitability for engineering applications. To overcome this problem, a homogeneous generalized yield function is proposed for I-sections with wide applicability and high fitting accuracy that fully considers sectional geometry. An efficient linear elastic iteration method is presented for the ultimate strength of frame structures with I-section members under plane loading and spatial loading. The influence of the cross sectional geometry on the generalized yield function is investigated. Choosing the ratio of web to flange section area γ1 and the ratio of flange width to web thickness γ2 as the sectional geometric parameters, a homogeneous generalized yield function is developed for I-section members under plane loading and spatial loading by regression analysis. By strategically reducing the elastic modulus of the highly stressed elements, an efficient and accurate linear elastic iteration method is presented for the ultimate strength of steel frame structures with I-section members. The comparative investigation shows that the proposed method has a wide range of application with high computation efficiency.
ONE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF WARPING TORSION FOR THIN-WALLED MEMBERS WITH OPEN-CLOSED CROSS SECTIONS BASED ON COMPATIBLE WARPING FIELD
Ying WEN, Ze-lin CHEN
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0639
Abstract:
The warping torsion of thin-walled members with open and closed cross sections was well addressed by the classical theories presented by Timoshenko and Benscoter, respectively. However, the restrained torsional behavior of thin-walled members with open-closed profile cannot be correctly accounted for without considering the distinctive warping properties between open and closed parts of the cross section. The development of warping shear flows within the mid-plane of the cross section needs further elaborations. This work assumes that the torsional warping of open and closed segments correspondingly adheres to the classical assumptions of Vlasov and Umanskii. The warping displacements are required to coincide at the common points of the open and closed segments, leading to a compatible warping field which contains undetermined warping parameter. The warping parameter is explicitly obtained based on the equilibrium requirements. A one-dimensional finite element model is naturally developed for warping torsion analysis of a thin-walled member with open-closed cross section. It is shown by numerical investigations and parametric studies that the type I method based on the Second Umanskii theory can artificially introduce the additional shear flows that reduce the accuracy of shear stresses. As an alternative, the type II method based on the Second Umanskii theory can only obtain the average shear stress of each segment of thin-walled section which fails to provide the correct distribution of shear flows. The Beam-189 element model based on the Vlasov assumption unfortunately neglects the induced warping displacements and shear flows by the constrained effects of the closed contour. Hence, the use of Beam-189 element will reduce the accuracies of both normal and shear stresses. Close agreement can be observed between the Shell-63 element model and the present method for calculating the torsional deformation and stresses, which demonstrates the capability of the one-dimensional finite element model to describe the torsional and warping stiffness of the thin-walled members with open-closed cross section.
FRACTURE BEHAVIOR OF WELDED JOINTS OF SHIP STEEL PLATES AND NUMERICAL ANALYSIS WITH GTN MODEL
Zi-chao ZHUO, Qing-ya ZHANG, Jiang-chao WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0746
Abstract:
Ship steel structures are always fabricated by welding, while mechanical performance and fracture strength of welded joints significantly influence the strength and service life of the whole ship considering the impact of actual working condition and external loading. In this study, base materials of ship steel plate (Q345 and Q690) were examined by uniaxial tension test to establish strain-stress curves, which can be employed for the assessment of fracture performance. Aiming at Gurson-Tvergaard-Needleman (GTN) failure mode, computational code was programmed and a series of numerical analyses were carried out to investigate the fracture behavior of ship steel plate, while constitutive relations of the examined ship steel plates were proposed with optimized parameters of GTN failure mode. In addition, computation results of strain-stress curves have a good agreement with experimental data. Concentrating on the butt welded joints of ship steel plate with high welding quality, uniaxial tension test was also conducted to obtain stress-strain curves of welded joints. In order to consider the influence of micro welding defects and welding residual stress on fracture performance of welded joints, modified initial void volume fraction and plastic hardening parameters were proposed, and good agreement between computation results and measurements was observed for fracture performance of welded joints.
RESEARCH ON SIMPLY SUPPORTED BEAM -TRACK INTERACTION AND REASONABLE GAP POSITION OF RACK RAILWAY
Qian ZHANG, Xiao-pei CAI, Xiang-hui CAI, Min ZHANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0269
Abstract:
The beam-track interaction of rack railway on a simply supported beam bridge has an important impact on vehicle safety and structural stability. Based on the finite element theory, a space-coupling calculation model for the rack (rail) -sleeper-beam-pier is established. The beam-rail interaction of rack railway on a simply supported beam bridge under different loads is analyzed. The results show that the beam-track interaction of rack railway on a simply supported beam bridge is stronger than that of a continuous welded rail(CWR) on bridge. Under the longitudinal train load, the rail force, beam rail relative displacement, longitudinal force and displacement of pier top are 40% larger than those of the CWR on bridge. It is recommended to strengthen the restraint between track foundation and beam to increase the longitudinal resistance and prevent the crawling of the track under longitudinal force. The maximum stress of rack is less than its allowable stress so that the rack strength is not used as a control factor for structural design. It is recommended that the position of rack gap be staggered from the beam gap to effectively prevent the rack gap from changing too much.
MECHANICAL MECHANISM OF INFLUENCE OF INTER-GRANULAR FRICTION ON GRANULAR LUBRICATION
Fan-jing MENG, Hua-bo LIU, Shao-Zhen Hua
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.05.0341
Abstract:
Granular lubrication is a new type of lubrication method which can be used in harsh working conditions. The law and characteristics of the effect of friction between particles on granular lubrication are the key scientific issues to clarify the theory of granular lubrication. On the other hand, it can also provide technical support for the design and parameter selection of granular lubricated bearing under extreme conditions. In order to analyze the influence of the friction between granules on the macro and micro characteristics of the granular lubrication system as well as the friction between the lower friction pair and the granular lubrication medium, a discrete element numerical model of the granular lubrication is constructed, and the above problems are analyzed and studied. The results show that the inter-granular friction has a significant effect on the antifriction lubrication characteristics of a granular lubrication system. The mean friction coefficient between the lower friction pair and the granules increases with the increased inter-granular friction coefficient. The coordination number and the sliding fraction in the granular lubrication system increase with the decrease of the inter-granular friction coefficient. The macroscopic flow behavior of the granular lubrication medium in the friction pair gap has obvious stratification characteristics, and the macroscopic flow velocity of granules decreases with the increase of the inter-granular friction coefficient. Further analysis results show that the fluctuation of granular lubrication medium is the key parameter directly reflecting the macroscopic flow speed of granules.
PARAMETER OPTIMIZATION OF COVARIANCE-DRIVEN STOCHASTIC SUBSPACE IDENTIFICATION METHOD BASED ON SENSITIVITY ANALYSIS
Wei LIU, Na YANG, Fan BAI, Peng CHANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0223
Abstract:
The accurate estimation of the modal properties of civil structures in operational modal analysis is critical in many applications, including structural health monitoring. Based on the sensitivity analysis, the model system order N and the number of block rows of the Toeplitz matrix i are investigated. The rules of their influence on the results of modal identification in Covariance-driven Stochastic Subspace Identification (SSI-Cov) are developed. The parameter optimization of SSI-Cov algorithm is analyzed based on a classical numerical example and the field measured data of the ancient Tibetan wall. The system order is identified through the theory of singular entropy increment. The recommended value of the number of block rows of Toeplitz matrix is proposed. The basis of the recommended value is the condition number of Toeplitz matrix or system matrix and the variation coefficient of the identification result. The research shows that: the smaller the condition number of the Toeplitz matrix or of the system matrix, the higher the accuracy of the calculation result, the smaller the coefficient of variation of the recognition frequency and damping ratio, and the better the quality of the corresponding modal stability diagram. The system order N of the structure can be accurately identified through the singular entropy increment theory. It is equal to the corresponding order when the first-order sensitivity of the singular entropy increment drops to zero. The suggested value of the number of block rows of the Toeplitz matrix i is between \begin{document}$2\beta $\end{document} and \begin{document}${{4}}\beta $\end{document}, in which \begin{document}$\beta $\end{document} is the ratio of the sampling frequency to the fundamental frequency. Based on the parameter optimization method proposed, the dynamic characteristics of the ancient Tibetan wall are effectively identified, including frequency, mode shape and damping ratio.
DEVELOPMENT OF A CRYOGENIC FATIGUE TEST FACILITY FOR HIGH TEMPERATURE SUPERCONDUCTING TAPES
Yuan-zhou PAN, Tian-hu HE, Can-jie XIN, Ming-zhi GUAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0797
Abstract:
Because of the high critical current density in the intense magnetic field, wider temperature margin, resistance irradiation and good mechanical properties, high temperature superconducting tapes (BSCCO and ReBCO taps) have a huge potential application in accelerator magnets, high field magnets and superconducting electric power systems. Some expectable opportunities will be created for modern high-tech electromagnetic equipment. High temperature superconducting tapes with substrate layers usually have high tensile strength. Thus, they can be applied under an intense electromagnetic field. However, in its application process and under the operation conditions, many kinds of inevitable fatigue loads will occur, which have an impact on the current-carrying capacity of the high temperature superconducting tapes and can destroy the high temperature superconducting magnets. A cryogenic fatigue test facility for high temperature superconducting tapes is introduced, the system can be used to measure the mechanical, thermal and strain-field-dependent behaviors of fatigued superconducting wires and tapes under variable cryogenic temperatures. Based on the cryogenic fatigue test facility, the mechanical behaviors and current-carrying characteristics of tension-compression fatigued YBCO tapes were experimentally studied. The preliminary test results show that their mechanical behaviors and current-carrying characteristics showed a nonlinear dependence on the stress ratio during the fatigue test. The successful development of the cryogenic fatigue test facility will provide a basic fatigue test platform for the design and development of accelerator high temperature superconducting magnets.
A GEOMETRIC NONLINEAR PLANE BEAM ELEMENT BASED ON COROTATIONAL FORMULATION AND ON STABILITY FUNCTIONS
Jihua DENG, Jianpin TAN, Pin TAN, Zhong-chu TIAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0012
Abstract:
The establishment of an accurate and efficient geometric nonlinear beam element is significantly important for describing the nonlinear behavior of frame structures. This paper presents a geometric nonlinear plane beam element based on a co-rotational procedure and a stability function. The deformation is separated from the rigid body displacement during the formation of the element, and the stability function is used in the local coordinate system to consider the influence of the element P-δ effect. The co-rotational procedure method and the differential method are used to consider the geometric nonlinearity of the displacement transformation from the local coordinate system to the global one. The total equilibrium equation and tangent stiffness matrix of geometric nonlinear plane beam elements are developed in a global coordinate system. The expression of the element tangent stiffness matrix considering beam ends with hinges is derived according to the characteristics of zero bending moment at the end of the hinged beam. Finally, the accuracy and efficiency of the analytical method are verified by several typical examples.
EXPERIMENTAL STUDY ON TORQUE COEFFICIENT AND on SHEAR PERFORMANCE OF A NOVEL BLIND BOLTED CONNECTION WITH HIGH-STRENGTH BOLTS
Junwei FAN, Lu YANG, Huiyong BAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0111
Abstract:
To further develop connection techniques in prefabricated steel building structures as well as deconstructable steel structures, a novel blind bolted connection with traditional high-strength (HS) bolt is introduced herein, and five slip-critical ones are designed. Based on a shearing test, their torque coefficient, slip coefficient, shear capacity and shear mechanism are investigated, and the test results are compared with design values in accordance with standard for the design of steel structures GB 50017−2017. The finite element model for the HS bolted connection is developed with ABAQUS, and its accuracy and applicability are verified against the test results. Parametric analyses are carried out. It is indicated that this new blind bolted connection with HS bolt is favourable to installation and disassembly. During the shear loading process, the loose of pretension within the bolts is up to 15%~20%, and current national standard is generally still adequate for predicting slip coefficient and shear capacity of such bolted connections. Research outcomes obtained may provide an important basis for the utilization of such novel blind bolted connections in practice.
A HIGH-ORDER PROCEDURE FOR DYNAMICS OF MULTI-DEGREE-OF-FREEDOM DAMPING SYSTEMS
Hong-jing LI, Xiao-peng YANG, Yu-chen MEI
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0162
Abstract:
The lower order schemes are usually adopted in the traditional time-history integration methods, in which time steps must be selected small enough to meet requirements in the accuracy of computational results. We extend the integral differentiation procedure for dynamics of structures to the multi-degree-of-freedom (MDOF) systems. A high-order dynamic method is developed for the MDOF damping systems without more computational efforts. The duration is divided into a few time intervals consisting of ρ equidistant time steps, and the matrix exponential at each time node over the time interval in consideration is obtained by combining precise time-step integration method (PTIM) with the Qin Jiu-shao algorithm, based upon the dynamic solution of Duhamel’s integral for MDOF system. The differential quadrature (DQ) rule is employed in the inverse way to obtain the responses from the matrix exponential solution with convolution form interval by interval. According to this high-order dynamic procedure, only a series of matrix multiplications and their recursions are required in the whole analysis process, without solving the equation and performing extra interpolation. The dynamic responses at ρ discrete time instants can be acquired simultaneously (generally ρ=10~15 may be chosen for dynamic analysis in practice), and it indicates the characteristics of efficient and explicit algorithm. Since it is unnecessary to directly calculate the definite integral term in the integral solution of the dynamic response, the difficulty in special processing of the inhomogeneous term of the dynamic equation would be avoided. Numerical examples further show that: this approach owns better numerical stability, the result can quickly converge to an accurate solution, and high calculation accuracy can be still achieved even in the case of large time steps.
EXPERIMENTRAL STUDY On SEIMEIC PERFORMANCE FOR AN INNOVATIVE SELF-CENTERING SMA BRACE
Shu-jun HU, Qi GU, Guo-qing JIANG, Jin-gang XIONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0087
Abstract:
During rare earthquake, the effective improvement of the ductility and energy dissipation capacity and reduction of residual deformation of a brace is currently in higher demand to ensure the seismic safety and seismic resilience capacity. Based on the ideals of shape memory alloy (SMA) and friction slip, an innovative self-centering brace with low friction and SMA is developed, which has the advantage of good seismic performance, high self-centering capacity and zero damage. Low frequency cyclic tests were carried on five non-SMA brace specimens and six self-centering SMA brace specimens, thusly the hysteresis curves, skeleton curves, secant stiffness, energy dissipation capacity and self-centering ratio of these specimens can be investigated. The test results show that: the self-centering SMA braces proposed have excellent energy dissipation capacity, bearing capacity, ductility and self-centering capacity, while all the steel plates in the specimens remain elastic without any yielding during the test, and the SMA in the specimens can return to the initial state. In addition, hysteretic behavior of the brace can be idealized as a flag-shape with little residual deformation, and the self-centering ratio has reached 93.7%. Therefore, the innovative brace has excellent seismic performance, which can be used as a self-centering damper.
EXPERIMENTAL STUDY ON THE SEISMIC BEHAVIOR OF RC BEAMS OF LOW SHEAR-SPAN RATIOS SUBJECTED TO FREEZE-THAW CYCLES
Shan-suo ZHENG, Jin-ming JI, pei PEI, Jin-chuan HE, Yi-xin ZHANG, Li-guo DONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0770
Abstract:
An artificial climate simulation laboratory was used to perform an accelerated freeze-thaw cycle test on six reinforced concrete (RC) beam specimens with a shear-span ratio of 2.6, which were then subjected to quasi-static loading. According to the test results, the effects of the freeze-thaw cycles and concrete strength grades on the seismic performance indicators of RC beam specimens such as the failure mode, hysteretic curve, strength, deformation capacity and energy dissipation were analyzed. The results show that after the freeze-thaw cycles, the compressive strength of the concrete decreased, the internal porosity of the concrete became larger, the micro-cracks were increased, and cracks appeared on the surface of the beam specimens. Six beam specimens exhibited a flexure-shear failure mode after the quasi-static test. With the increase in the number of freeze-thaw cycles, the strength and energy dissipation capacity degraded, and ductility first increased slightly and then decreased greatly. With the increase in the concrete strength grade, the degree of damage caused by the freeze-thaw cycle of the beam specimens was reduced, the yield, peak and ultimate strengths of specimens were increased, the energy dissipation capacity was enhanced, and the ductility was not significantly changed.
A STOCHASTIC MODEL FOR SEQUENTIAL GROUND MOTIONS BASED ON THE COPULA THEORY
Jia-xu SHEN, Jun CHEN, Guo DING
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0128
Abstract:
The existing ground motion physical stochastic model is extended to a stochastic model for sequential ground motions by considering the spatial correlation between the mainshock and aftershock. Considering the physical mechanism of ground motion generation and propagation, the sequential ground motions are represented by the Fourier model of 16 physical random variables. Meanwhile, considering the spatial correlation between the mainshock and aftershock, the model is more accurately represented by six two-dimensional random variables and two one-dimensional random variables based on the Copula theory. To describe the process of the ground motion propagation on local sites, a random field model of sequential ground motions is established. Based on 1038 pairs of measured sequential ground motions and five sets of ground motion array data, the probability distribution of each parameter is given by parameter identification and statistical analyses of physical random variables in the model combined with the Copula function. The comparison between the measured and the simulated ground motions shows that the proposed stochastic model for sequential ground motions can realistically reproduce both the spatial correlation of sequential ground motions and the wave traveling effect of ground motions at local sites.
ANALYTICAL SOLUTIONS FOR FORCED VIBRATIONS OF TIMOSHENKO CURVED BEAM BY MEANS OF GREEN’S FUNCTIONS
Xiang ZHAO, Yang ZHOU, Yong-bo SHAO, Bo LIU, Ren ZHOU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0708
Abstract:
This paper derives analytical solutions for the forced vibrations of Timoshenko curved beams and establishes the vibration equation of Timoshenko curved beams by analyzing the equilibrium equation for the intersection of curved beams. Green’s functions of Timoshenko curved beams are solved for different boundary conditions using the separation of variables and Laplace transform. Two characteristic parameters are introduced to measure damping effects on beam vibrations. Numerical calculations are conducted to validate analytical solutions, and the effects of various related physical parameters are investigated. The results show that by setting the radius R to infinity, it can be simplified to the Timoshenko straight beam vibration model, and on this basis, if the shear correction factor κ is set to infinity, it can be reduced to the Prescott straight beam vibration model. Finally, the moment of inertia γ is set to 0, which can be reduced to the Bernoulli-Euler straight beam vibration model. Numerical calculations are performed to validate the solutions.
NUMERICAL SIMULATION AND FIELD MEASUREMENT OF DYNAMIC RESPONSES OF BRIDGES WITH TWIN CIRCULAR-CYLINDER PIERS SUBJECTED TO WATER FLOW
Xu-gang HUA, Wu-peng DENG, Zheng-qing CHEN, Yu TANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0143
Abstract:
The Dalin Bridge in Tibet is a 7-span concrete beam bridge with a continuous bridge deck, supported with several twin-circular cylinder piers. In July 2018, significant vibration along the bridge direction appeared on the pier and deck of Dalin Bridge under the action of water flow. This paper described the field measurements and numerical simulations of dynamic response of the bridge system subject to water flow. The field measurement showed that: the longitudinal vibration of bridge deck is a beat vibration dominated by its fundamental mode while the lateral vibration is random vibration; the longitudinal maximum acceleration is about 0.08 m/s2, maximum displacement is about 1.56 mm. Based on the first-order longitudinal fundamental mode, the bridge is simplified as a SDOF system, two-dimensional numerical simulation of twin-circular cylinders is carried out for flow velocity U 2~10 m/s (reduced flow velocity Ur=1.69~8.45, Reynolds number Re=2.6×106~1.3×107), and the lift and drag forces, and the dynamic responses of piers under different damping are obtained. After incorporating a correction accounting for the pier vibration mode and velocity profile of water flow, the vortex-induced vibration amplitude at pier top is derived. The results indicate that the interference effect of upstream cylinder will increase the lift force of downstream cylinder. Vortex-induced vibration (VIV) is observed from flow velocity 3~6 m/s. The three-dimensional effect has a significant impact on the displacement of pier top in two-dimensional numerical simulation and the numerical simulation result matches well with the measurement when damping ratio ζ=0.01. The maximum VIV amplitude will decrease with the increase of structural damping, but the velocity regime of VIV remains unchanged.
STUDY ON THE MECHANISM OF TORSION INDUCED BY STEEL BRACE DYNAMIC BUCKLING AND THE MECHANISM OF TORSION REDUCTION SUPPLIED BY BRB
Xiang-yu GAO, Yang-long LI, Jian-qin LI, Ji-min XU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0748
Abstract:
The characteristics of the lateral and torsional seismic responses of steel braced concrete frame structures are studied. It is revealed that the dynamic buckling of steel brace will have an impact on the resistance torque during the repeated loading process, and the plastic hinge state of the structure will change imbalanced, resulting in inelastic torsion. By using D'alembert principle, the mechanism of the steel braced structure causing inertial force, inertial torque and inelastic torsional surge induced by the brace buckling is studied, and the similar performance is verified by shaking table test and finite element nonlinear analysis. The anti-torsion effect of buckling-restrained braces on structures and the working mechanism of preventing inelastic torsional burst of structures are studied. Finally, suggestions are proposed to use the ordinary steel braces as the first seismic defense line of CBF concrete frame structures, and the technical measures of using buckling-restrained braces to reduce of inelastic torsion are given.
STUDY ON AXIAL COMPRESSIVE BEHAVIORS OF NOVEL STEEL-CONCRETE-STEEL COMPOSITE WALL
Jiabao YAN, Anzhen CHEN, Tao WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0188
Abstract:
A type of novel shear connectors for steel-concrete-steel (SCS) composite wall were reported. By using the SCS composite walls with C-channel connectors, the axial compression tests of six specimens were carried, the influences of shear connectors spacing and concrete material on the compressive behaviors were studied. The results show that the arrangement of connectors and material properties of concrete have a great influence on the compressive behaviors of SCS composite walls. The greater spacing of shear connectors reduce the ultimate capacity and the ductility of SCS composite wall, but has little effect on the initial stiffness. Ultrahigh performance concrete (UHPC) can significantly improve their compressive resistance and initial stiffness, but reduce the ductility as well. Meanwhile, by comparing the experimental values with the theoretical values based on the Chinese code and the European code, it is found that the load capacity design formula based on European code is safer.
WHEEL/RAIL DYNAMIC RESPONSES DUE TO THE WHEEL FLAT OF HEAVY-HAUL LOCOMOTIVES
Yi-fan YANG, Liang LING, Yun-fan YANG, Kai-yun WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0033
Abstract:
The wheel flat will cause a severe wheel/rail impact, thus aggravating fatigue damage to vehicle and track components. To reveal the characteristics of the coupled vibration response of heavy-haul locomotives and tracks due to actual wheel flat, a fitting model for wheel flat was established based on the field measured data. Using a heavy-haul locomotive-track coupled dynamic model that considers the interaction between the rail pad and fastening clip in detail, the wheel/rail dynamic response caused by locomotive wheel flat was simulated and analyzed in time and frequency domains. The results show that the geometry of the actual wheel flat was not symmetrical. The P2 force induced by the wheel flat had a great influence on the track components. The wheel flat would cause temporary separation between the rail and the fastening system. This research provided a theoretical reference for identifying locomotive wheel tread damages and maintaining heavy-haul track components.
RESEARCH ON ANTI-COLLAPSE PERFORMANCE OF STEEL FRAME STRUCTURE WITH DIFFERENT FORTIFICATION LEVELS
Yuan-xi WANG, Chen WANG, Xi-kai DU, Jing-hong LIU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0733
Abstract:
Although steel frame structures have excellent seismic performance, they will inevitably collapse under strong earthquakes, resulting in enormous economic losses and casualties. In order to ensure the seismic safety of steel frame structures, the numerical modeling method of steel frame structures based on lumped plastic hinge model is introduced firstly. Then the anti-collapse ability of five-story-three-span steel frame structures with different fortification levels are analyzed using the incremental dynamic analysis (IDA) method. The results show that the lumped plastic hinge model can accurately simulate the damage of steel frame structures and can significantly improve the calculation efficiency. With the improvement of seismic fortification level, the limit value of collapse deformation capacity of steel frame structures with the same plane and elevation layout increases gradually. Therefore, it is unreasonable to evaluate the anti-collapse ability of steel frame structures with the same layout and different fortification levels using the same story drift limit value. The anti-collapse ability of steel frame structures with different fortification levels designed according to the current Chinese code meets the requirements of no collapsing under strong earthquakes, but their collapse margin ratio decreases with the improvement of fortification level.
ANALYSIS OF SINGLE-BOX MULTI-CELL COMPOSITE BOX GIRDER WITH CORRUGATED STEEL WEBS DUE TO TRANSVERSE FORCE
Peng QIAO, Cheng-xing ZHONG, Jin DI, Feng-jiang QIN
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0627
Abstract:
To investigate the characteristics of transverse force in the top slabs of a single-box triple-cell composite box girder with corrugated steel webs (CBGCSW) and the effective distribution width under wheel loads, a finite element model of a single-box CBGCSW with single-cell, double-cell and triple-cell was established. The regulation of transverse stress and effective distribution width of three different box girders were compared. The results of finite element analysis, which had been verified by scaled-models tests, show that the transverse force in a single-box multi-cell CBGCSW can be approximately simplified as that of a single-box single-cell box girder. However, there is a big error in calculating the effective distribution width of CBGCSW according to the current code. Using finite element models, the influences of the transverse location of wheel load, the distance between webs, the length of flange slabs, the thickness of top slabs, the size and type of corrugated steel webs on the effective distribution width of a single-box single-cell CBGCSW were analyzed. It is shown that the transverse location of wheel load and the distance between webs of loading chambers are the most important factors. The practical calculation formulas of the effective distribution width of a single-box single-cell CBGCSW were obtained by the surface fitting according to results of parametric analysis. The formulas of the effective distribution width of a single-box multi-cell CBGCSW were proposed to be 0.9 times of that of a single-cell CBGCSW. Finally, the transverse stress in the top slab of a single-box triple-cell CBGCSW were analyzed as an illustration under transverse single and multiple wheel loads, separately. The transverse stress was calculated by the elastic frame method, using the effective distribution width calculated by formulas proposed and the current code method. The results, compared with the finite element analysis, finding that when transverse multiple wheel loads were imposed the calculated transverse stress may be unsafe, on the condition that the effective distribution width of different chambers were adopted as the same value. Consequently, the stress reduction factor of transverse stress in adjacent chamber which is presented in this paper are proposed to improve accuracy. the formulas presented are more accurate than those of current code, and the errors can be reduced by 20%-40%, comparing with current code method.
POLYGON SCALED BOUNDARY FINITE ELEMENT NONLINEAR EFFICIENT ANALYSIS METHOD
Jia-long LI, Gang LI, Ding-hao YU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0634
Abstract:
The scaled boundary finite element method (SBFEM) is a high-precision semi-analytical numerical solution method, which is especially suitable for solving problems such as unbounded media and stress singularity, and the advantage of the polygon boundary element is more obvious to simulate the crack growth process and local mesh re-segmentation problems than the finite element method. At present, the scaled boundary finite element method is more concerned with the solution of the linear elasticity problem, while the research of the nonlinear scaled boundary element is in its infancy. In this paper, an efficient inelasticity-separated scaled boundary finite element method (IS-SBFEM) is proposed based on the basic theory of the SBFEM and the inelasticity-separated theory. The proposed method considers that the sector sub-element of each boundary line covered domain is independent, and its shape function and strain-displacement matrix can be obtained by the semi-analytical elastic solution. Moreover, the nonlinearity strain field of each sector sub-element is establish by introducing nonlinear strain interpolation points, and the nonlinear constitutive relations can be introduced to achieve efficient nonlinear analysis of polygon scaled boundary element. The stiffness matrix of the polygon scaled boundary element can be obtained by assembling the stiffness of each sector sub-element, the numerical integration of each sector domain can be obtained by using Gaussian integration scheme, and its accuracy remains unchanged. Because more nonlinear strain interpolation points are introduced, the dimension of the Schur complement matrix is larger. The Woodbury approximation approach is used to solve the governing equations of the inelasticity-separated scaled boundary element. This method has efficiency advantages for the calculation of large-scale nonlinear problems. Numerical examples are adopted to verify the correctness and efficiency of the algorithm. Popularize this method that is important to practical engineering analysis.
STUDY ON THE MECHANICAL PROPERTIES OF COLD-FORMED STEEL FRAMED SHEAR WALL WITH SLITS
Lu YE, Yu-hang WANG, Yu SHI, Wei LUO, Wei-bo KONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0005
Abstract:
In order to study the mechanical behavior of the cold-formed steel framed shear wall with slits (CFS-WS) which is suitable for low-rise and multi-story cold-formed thin-walled steel buildings, pseudo-static tests of 1 ordinary CFS-WS and 3 buckling-restrained CFS-WS were conducted to gain the mechanical properties of CFS-WS, including the failure modes, load-displacement hysteresis curves, skeleton curves and energy dissipation capacities, and the design value of shear capacity was put forward. The test results indicates that the CFS-WS relies on the "torsion-recovery-reverse torsion" of steel plate between vertical slits and the deformation of the steel frame to resist horizontal loads and dissipate energy. The steel plate tears and the end of the hat column buckles when the CFS-WS is broken. The CFS-WS has good bearing capacity, plasticity, ductility and energy dissipation capacity; however, the rheostriction of its load-displacement hysteresis curve is rather severe. Compared with ordinary CFS-WS, the buckling-restrained CFS-WS has higher shear stiffness, bearing capacity and energy dissipation capacity, and the rheostriction of its load-displacement hysteresis curve is mitigated. Furthermore, the stiffeners and the cold-formed steel beams and columns are connected to form a steel frame through the stiffener connectors, which can effectively enhance the early shear stiffness, bearing capacity and energy dissipation capacity of CFS-WS, and greatly improve the seismic performance of the structure.
3D NONLINEAR RESPONSE CHARACTERISTICS OF THE PILE-RAFT-SUPPORTED AP1000 NUCLEAR ISLAND BUILDING IN SOFT DEPOSITS SUBJECTED TO STRONG GROUND MOTIONS
Sheng-dong ZHU, Guo-xing CHEN, Peng-cheng JIANG, Wei-yun CHEN, Wen-sheng GAO
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0121
Abstract:
The seismic safety of nuclear islands constructed in loose and soft deposits subjected to strong earthquake motions is becoming a major engineering challenge. An example of such nuclear islands is the AP1000 nuclear islands located in the coastal deposits, China. Using the three-dimensional (3D) finite element method, we conducted a nonlinear seismic response analysis of a pile-raft-supported AP1000 nuclear island building. In the proposed response analysis, the engineering geology characteristics and nonlinear dynamic behavior of the soils, the artificial boundary conditions and the simulation model were considered in detail. A special emphasis was given to the 3D model for the pile-raft-supported AP1000 nuclear island building and the input bedrock motions from the near-field, middle-far-field, and far-field strong earthquakes. The spectral accelerations (SAs) of the nuclear island building were more intense to the bedrock motion frequency components close to the fundamental frequency of the main structure of the nuclear island. The SA predominant periods were almost the same as those of the bedrock motions. The influence of the seismic responses of the sloshing water in the water storage tank (cooling system) on the nuclear island building was similar to the whipping effect. The peak acceleration amplification factors (PAAFs) increased with the increasing nuclear island heights. The PAAFs were mainly dependent on the nuclear island itself and the seismic wave propagating from bedrock to nuclear island base through soft deposits for the near-field and far-field strong earthquake motions, respectively. The peak relative displacements (PRDs) between the various nuclear island heights and its base increased with the increasing heights, and the PRDs to the far-field strong earthquake motion ware more intense. With the increasing peak bedrock accelerations, the PAAFs of the nuclear island building were decreased while the PRDs were increased. The flexible ground and the soil-pile-raft-nuclear island building interaction had an effect on the high-frequency de-amplification and the low-frequency amplification for the bedrock motions. It significantly increased the peak acceleration at the lower part and decreased it at the middle-upper part of nuclear island building.
CONSTITUTIVE MODEL FOR ENGINEERED CEMENTITIOUS COMPOSITES UNDER BIAXIAL COMPRESSION
Shan-fu CHEN, Jing-fen CHEN, Feng-xiang YANG, Zhi-ming LIU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0018
Abstract:
Based on the Darwin-Pecknold method considering the biaxial behavior of concrete, a two-dimensional constitutive model for engineered cementitious composites (ECC) is developed, taking into account the nonlinear mechanical behavior and the variation of compressive strength under biaxial compression. A nonlinear stress-equivalent uniaxial strain relationship is established after introducing the equivalent uniaxial strain in two orthotropic directions caused by biaxial loading to account for the biaxial nonlinear behavior of ECC. A biaxial strength envelope is used to determine the compressive strengths of the two directions. An explicit numerical algorithm of the model is derived, and user-defined material subroutine UMAT containing the numerical algorithm is coded and implemented in finite element procedure ABAQUS v6.14. The efficiency of the proposed model is validated through numerical simulations of two sets of ECC specimens with different mix proportions under biaxial compression loading at various biaxial stress ratios. The stress-strain curves and the compressive strengths in the major compressive stress direction obtained by numerical simulations are in a good agreement with the experimental results. It is shown that the proposed constitutive model can effectively predict the biaxial nonlinear mechanical behavior and the failure strengths of ECC under biaxial compression.
NUMERICAL SIMULATION ON SELF-CENTERING BEAM-COLUMN JOINTS REINFORCED WITH SUPERELASTIC SMA BARS
Hui QIAN, Zong-ao LI, Jin-zhao PEI, Li-ping KANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0791
Abstract:
In order to improve the energy dissipation capacity and self-centering capacity of the frame structure, an earthquake resilient beam-column joint based on super-elastic SMA bar was proposed. The numerical model of self-centering SMA reinforced concrete beam-column joints was established based on OpenSees finite element software platform, by using SMA material self-centering double-flag constitutive model, and nonlinear simulation under low-cycle reciprocating load was carried out to obtain the hysteretic curves and skeleton curves of the joints. The validity of the numerical model was verified by comparing the analysis data with the experimental results. The parameter analysis was carried out, considering the amount, length and yielding strength of SMA material, while the influences of SMA material parameters on the hysteretic performance and self-centering ability of the joints were analyzed. The results show that the concrete beam-column joints reinforced with super-elastic SMA bars have high energy dissipation and self-centering capacity. The numerical analysis model can well simulate the hysteretic behavior of self-centering SMA joints under low cyclic reciprocating loads. The mechanical parameters of SMA bars have a great influence on the seismic performance of joints. Under the condition of proper reinforcement, a larger SMA bars area leads to smaller residual displacement and stronger the self-centering capacity. Under the same condition, when the SMA bar exceeds the plastic hinge length, the length has little influence on the joint performance. Under the condition of proper reinforcement, increasing the yield strength of SMA can improve the bearing and self-centering capacity of the joint.
BEARING CAPACITY FORMULAS OF MULTI-PLANAR DKT-JOINT CONTAINING INTERNAL STIFFENERS UNDER AXIAL COMPRESSION
Ai-lin ZHANG, Wen-chao CAI, Yan-xia ZHANG, Di-nan SHAO
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0591
Abstract:
For the construction of steel structures of Beijing Daxing International Airport Terminal, and based on the completed full-scale multi-planar DKT-joint tests, 192 groups of finite element models with different parameters are simulated and analyzed to further study the mechanical mechanism of the DKT-joint. The influences of opening size, thickness and quantity of stiffeners on mechanical properties of the multi-planar DKT-joint are investigated. Multiple nonlinear regression towards the design and ultimate bearing capacity of the multi-planar DKT-joint containing various stiffener arrangements under axial compression is conducted, and the magnification coefficient η for design value and ultimate capacity of the DKT-joint is obtained. The formulas of design value and ultimate capacity of the multi-planar DKT-joint containing internal stiffeners are derived based on current Standard for design of steel structures. Experiments and finite element analysis (FEA) results indicate that the formulas of design value and ultimate capacity of the multi-planar DKT joint containing internal stiffeners meet the precision requirements well, and can provide reliable reference for the design of similar joints in practical engineering.
EXPERIMENTAL STUDY ON THE VIBRATION CHARACTERISTICS OF UNTOPPED PRECAST RC FLOORS UNDER BOUNCEAND JUMPING LOADS
Rui PANG, Wen-kang WANG, Tian-peng ZHANG, Ke XU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0192
Abstract:
To study the dynamic characteristics and vibration responses of discretely connected precast RC diaphragms (DCPCD) under human-induced excitation, six full-scale DCPCD specimens and one cast-in-place specimen were tested by hammer modal test and human-induced excitation test under bounce and jumping loads. The effects of plate seam and connector layout on DCPCD vibration characteristics were examined. The results show that the low-order vibration mode of DCPCD and cast-in-situ floor was basically the same, but the natural frequency of DCPCD was slightly lower. The DCPCD had the same vibration transmission mechanism as the cast-in-situ floor. The vibration response of DCPCD was slightly larger than that of the cast-in-situ floor under the same excitation. The peak acceleration value of the cast-in-situ floor appeared at the edge of the mid-span, and the peak acceleration of DCPCD appeared at the edge of the slab joint near the mid-span. The natural frequency of DCPCD increased with the increase of the slab joint connectors and with the decrease of the slab joint connections, where the effect of the connector on the frequency was greater than that of the slab joint connection. Methods for calculating the vertical natural frequency and acceleration of the DCPCD in the orthogonal slab laying directions with two pairs of sides simply supported were proposed. The accuracy of the proposed methods was verified by the experimental results.
CRACKING LOAD CALCULATION FOR STEEL-UHPC COMPOSITE SLABS BASED ON THE SECTION-STRESS METHOD
Yi-zhi BU, Xin-yi LIU, Qing-hua ZHANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0738
Abstract:
The local cracking problem of steel-UHPC (ultra-high-performance concrete) composite structures under negative bending moments is the basis of the application and development. Based on the UHPC tensile bilinear constitutive model and plane cross-section assumption, a section stress method is set up to describe the stress distribution of the steel-UHPC composite slabs and calculate the cracking load under a pure bending condition. The proposed method is verified by 4 specimens of 2 groups and the test results in the literature. The results indicate that the section-stress method can accurately describe the cracking behavior of steel-UHPC composite plates under pure bending and the average ratio of calculated to measured values is 0.95. The UHPC cracking strength is an intrinsic property dependent on the nature of the material itself and is not influenced by the steel-UHPC composite slab. The height of the UHPC strain hardening zone represents the combination effect and reinforcement constraint when visible cracks appear. By reducing the cover thickness or increasing the reinforcement ratio, the UHPC strain hardening height can be increased and the flexural behavior of the steel-UHPC composite slab can be improved.
CALCULATION METHOD FOR MOMENT-CURVATURE OF HIGH-STRENGTH CONCRETE SHEAR WALL CONFINED WITH HIGN-STRENGTH RECTANGLE SPIRAL REINFORCEMENTS
Hua-jing ZHAO, Qing-ning LI, Jun ZHAO, Shu-feng LI, Yu ZHENG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.08.0603
Abstract:
In order to improve the seismic performance of high-strength concrete shear walls, the high-strength rectangular spiral reinforcements (HRSRs) are applied to the constrained edge members and wall body of high-strength concrete shear wall. Through the seismic performance investigations of 10 high-strength concrete shear walls confined with HRSR, and considering the strong constraint of HRSR, the bending moment curvature calculation method of high-strength concrete shear walls confined with HRSR is proposed corresponding to the cracking, yielding, peak and ultimate states. The study shows that the bending moment curvature formula of the bending member can describe the load-deformation relation of the shear wall more accurately, and the calculated values are in good agreement with the experimental values. Compared with the form of common stirrup, the continuous closed HRSR can significantly improve the sectional bearing capacity and deformation capacity of high-strength concrete shear walls.
THE LOAD CHARACTERISTICS OF THE BOGIEFRAME OF HIGH-SPEED EMUS
Zun-song REN, Jie CAO, Yu-yi LI, Bin-jie WANG, Xue WEI
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0181
Abstract:
The bogieframe of the bogie of a high-speed electric multi-unit (EMU) carries not only forces from the primary and secondary suspensions, but also loads caused by the vibrations of the components of the vehicle. The components include the motors, gear boxes, traction devices, brake equipment and so on. Consequently, the structural strength of the bogieframe is important to the operation safety and reliability of the high-speed EMU. However, there are few studies related to the load characteristics of the bogieframe of EMUs. The decoupling and dimension reduction method for load identification is presented. The identification loads of the bogieframe include the axlebox spring force, lateral force of the trailing arm knot, motor vertical and lateral forces, gearbox force and anti-roll bar force. The bogieframe of a Chinese standard high-speed EMU was manufactured and calibrated for the force measurement. All forces were measured in a field experiment on a high-speed railway in China. The measured peak speed of the high-speed EMU was 368 km/h. After dealing with the sampled data, the time history of the forces was obtained. The dynamic characteristics of the forces were analyzed in the time and the frequency domains. The rain flow count method was implemented to count the loads. The maximum loads and load spectra were presented with different operation speeds of the train. The equivalent loads of the measured forces of the bogieframe for two-million-time fatigue tests were presented according to the load spectrum and the service life of the high-speed train. The results show that the operation speed of the train and track excitations had a great effect on the axlebox spring forces, trailing arm knot forces, motor forces and gearbox forces. The operation speed of the train and curve radius of the track had great influences on the forces of the anti-roll bar devices. Large impact loads of the bogieframe occurred because of the field welding joints of the rails. The frequency of the impact loads of the axlebox springs ranged from 49 Hz to 51 Hz. The maximum dynamic load factor of the axlebox force was 0.23. When the train operated on the main section of the railway, the maximum vertical and roll load coefficients of the bogieframe were 0.14 and 0.1, respectively. The peak loads of the motor and gearbox were close to the dynamic values presented by JIS E4028. The amplitude ratio is helpful to reveal the changing characteristics of the amplitude in the frequency domain. The investigation is useful to disclose the dynamic characteristics of the loads and to study the structural damages and fatigue test of the bogieframes of high-speed EMUs.
THE HYSTERETIC BEHAVIOR AND WORKING MECHANISM OF SELF-CENTERING STEEL BUCKLING-RESTRAINED BRACES
Long-he XU, Peng CHEN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0034
Abstract:
A novel self-centering steel buckling-restrained brace (SC-SBRB) is proposed, which is mainly comprised of a buckling-restrained energy-dissipation system and a self-centering system of pre-pressed disc springs in parallel. The fundamental configuration and working mechanism of the SC-BRB are introduced. A restoring force model that accurately describes the unique hysteretic behavior of the SC-SBRB is established. Four solid numerical models of SC-SBRBs with different design parameters are built using ABAQUS finite element software. The hysteretic behavior and self-centering performance of the SC-SBRB under cyclic loading are studied and compared with the calculation results of the restoring force model. The results demonstrate that the SC-SBRB exhibits a stable and full flag-shaped hysteretic response under cyclic loadings, and that the proposed restoring force model is capable of accurately predicting the mechanical properties at different stages. The self-centering performance of the SC-SBRB is gradually exerted as the initial pre-pressed force of disc springs increases, while the residual deformation is reduced simultaneously. The maximum residual deformation ratio of the brace is decreased to 0.039% when the self-centering ratio is 1.0, indicating a good coordination of the self-centering and energy-dissipation performance.
RUNNING SAFETY AND SEISMIC DESIGN OPTIMIZATION OF FAULT-CROSSING SIMPLY-SUPPORTED GIRDER BRIDGE OF HIGH-SPEED RAILWAY UNDER EARTHQUAKES WITH DIFFERENT INTENSITIES
Hui JIANG, Min WANG, Cong ZENG, Lei HUANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0599
Abstract:
An eight-span simply-supported girder bridge of high-speed railway was taken as a research object, which crosses a strike-slip fault. By means of OpenSEES platform, an integrated non-linear model was established by considering bridge-track interaction. The fault-crossing horizontal ground motions were synthesized and inputted. The damage characteristics of bridge and CRTS II slab ballastless track structures were discussed under different earthquake intensities, and the seismic safety of structural components was evaluated quantitatively. With code control criteria of horizontal deformation, the running safety of track was assessed under different speeds, and the optimal design of track structure was discussed. The results show that the seismic responses of the fault-crossing span and its adjacent spans are the largest, and these bridge spans face great risk of damage. The horizontal deformation of track is obvious and the positions imposing potential threats to running safety are mainly the two ends of the fault-crossing span and its adjacent spans. By increasing the number of lateral rail block, the horizontal deformation of track can be effectively reduced. For the case of 6 pairs of rail block per span and line, the deformation can still meet the safety limit with speed of 100 km/h, except for the parallel turning angles of the fault-crossing span under rare earthquakes.
EXPERIMENTAL STUDY ON INFLUENCE OF COVERED KARSTIC FREE SURFACE ON FIXED END BEARING CAPACITY OF LATERALLY LOADED PILE
Tian-yu LI, Qiu-yan FAN, Wei HAN, Jiang-hui LIANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0704
Abstract:
Bedrock surface in karst region is undulating. When laterally loaded piles are fixed nearby covered karstic free surface, the destabilization of the pile may occur and result in the loss of fixed-end bearing capacity. An interior fixed-end model with combined geological conditions of a covered karstic free surface and a weak structural plane is designed, and two working conditions are considered: the free surface is absence of the pile and the free surface is inserted the pile. A lateral loading test was conducted and proved that the existence of the free surface and the structural plane reduces the fixed-end bearing capacity, and that the impact of the free surface before pile is more significant. Based on this result and the limit equilibrium method, a method for calculating the fixed-end bearing capacity of rock mass containing covered karstic free surface and structural plane is proposed. Calculation and test results were compared to validate the assumptions and the method.
ANALYSIS OF SEISMIC RESPONSE AND OVERTURNING RESISTANCE OF ROCKING DOUBLE-DECK BRIDGE SYSTEM
Jing-yi CHEN, Xiu-li DU, Qiang HAN, Yu-long ZHOU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0647
Abstract:
Double-deck viaducts based on traditional ductility design are vulnerable to earthquake-induced damage. To control the seismic damage, a double-deck bridge is developed with the lower floor designed as a rocking structure. To investigate the dynamic response of the rocking bridge, an analytical model of rigid bodies is derived through the Lagrange method and momentum conservation law. The seismic response analysis and parametric analysis adopted structural parameters such as the size and dimension parameter of columns are performed using this model. The overturning resistance of the rocking double-deck bridge is estimated qualitatively and quantitatively with a mathematical model of Ricker wavelets. The results show that the rocking double-deck bridge with dimension in practice can satisfy the seismic design demand of the E2 earthquake according to the seismic design code of bridges in China. However, the rocking bridge is more prone to overturn under near-fault ground motions with a high amplitude velocity pulse. The overturning acceleration spectra and overturning modes of a rocking double-deck bridge system were obtained due to Ricker wavelets. The rocking bridge is more stable with the larger slenderness and size of columns.
THE RESEARCH OF NEW TESTING METHOD FOR OBTAINING THE J (δ) RESISTANCE CURVES OF DUCTILE MATERIALS BASED ON EQUIVALENT ENERGY PRINCIPLE
Yun-qiang PENG, Li-xun CAI, Li-ming WEI
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0706
Abstract:
Based on the elasto-plastic semi-analytical expressions of load-displacement relation and J integral-load relation for mode I cracks deduced from the equivalent energy principle, the J resistance curves of different components are successfully determined using the semi-analytical method. Furthermore, the J resistance curve of small C-shaped outside edge-notched compression (COEC) specimen at high temperature can also be obtained by the same method. According to the growing crack size of sharp cracked specimen determined by the semi-analytical equation, the crack tip opening displacement (CTOD, δ) resistance curves of ductile materials can also be determined.
ANALYSIS ON THE FIRE RESISTANCE OF SQUARE CONCRETE-FILLED STEEL TUBULAR COLUMN TO COMPOSITE BEAM WITH OUTER RING PLATE CONNECTIONS AFTER EARTHQUAKE DAMAGE
Wen-da WANG, Run-ting CHEN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0259
Abstract:
To study the fire resistance of the square concrete-filled steel tubular column to composite beam with outer ring plate connections after earthquake damage, finite element numerical models were established and verified by experimental data of other researchers. The finite element models for the fire resistance of composite beam joints under three fire conditions after earthquakes were established. The impact of the shedding position and degree of the fire protection layer of the column in hysteretic loading and three fire conditions on the fire resistance and failure modes was analyzed. The results indicate that the stress value and deformation degree of the steel tube increased obviously with the increase of the damage degree of the joint under the hysteretic loading at the column end. When the joint was exposed to fire in the area below the RC slab, the temperature gradient of the stud from the bottom to the top was obvious with the increase of the fire time. The temperature field distribution of the RC slab was wavy due to the influence of the stud. Different damage degrees and different fire conditions had significant effects on the failure modes. However, there was no significant difference on the failure modes with or without the fire protection layer falling off under the three fire conditions. Under the two fire conditions in the area below the RC slab and the area above the RC slab, the shedding fire layer had a significant influence on the fire resistance of severely damaged joints. Under the condition that both the upper and lower areas of the RC slab were under fire, the shedding fire layer had no significant influence on the fire resistance of the joints.
DOUBLE-K FRACTURE PARAMETERS OF CONCRETE IN THREE-POINT BENDING BEAMS WITH SMALL SPAN-DEPTH RATIOS
Yang-yang YIN, Shao-wei HU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0031
Abstract:
Three-point bending (TPB) beams with small span-depth ratios were utilized to research the fracture properties of concrete. An approach for determining the fracture parameters of TPB beams with small span-depth ratios was provided, which was based on linear interpolation between the calculation formulas of TPB beams with the span-depth ratios of 2.5 and 4. The experimental results of TPB specimens with three small span-depth ratios and the available results in the literature were used to verify the present formulae. The results indicate that when the specimen depth was increased from 100 mm to 200 mm, the obtained initial fracture toughness remained constant, while the unstable fracture toughness increased gradually but the growth was small. The obtained double-K fracture parameters by the presented method were in good agreement with the results determined by the method proposed in the literature. The initial fracture toughness obtained by the analysis method agreed well with those obtained by the experimental method. The applicability of the presented method to TPB beams with small span-depth ratios was further verified by the experimental data in the literature.
A UNIFIED RDA FOR THE SEISMIC RELIABILITY ESTIMATION OF DEPENDENT FAILURE LIFELINE ENGINEERING SYSTEMS
Qian GU, Heng XIA, Jun HE
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0697
Abstract:
Based on the recursive decomposition algorithm (RDA) of network connectivity reliability analysis, a unified RDA is developed by integrating the three parts of the original RDA for different network weighting forms. To estimate the seismic reliability of dependent failure lifeline engineering systems, the sequential compounding method (SCM) and Gumbel Copula function are used to calculate the joint failure probability of a disjoint minimum path and a disjoint minimum cut event in RDA, respectively. The unified RDA for the seismic reliability estimation of dependent failure lifeline engineering systems is developed. The calculation results of the reliability of a 36-node grid network show that the method can be used for dynamic seismic reliability estimation of dependent failure network systems with high accuracy.
DEFORMATION OF FRICTION PAIRS OF STATIC AND DYNAMIC PRESSURE HYBRID BEARING WITH TILTING OIL PAD
Xiao-dong YU, Shi-wei ZHAN, Fei HAN, Fa-kun WANG, Fan SUN, Dian-bin HUANG, Jian-hua JIAO
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0157
Abstract:
During the operation of the hydrostatic bearing under high-speed and heavy-load conditions, due to the combined effects of strong extrusion and high-speed shear, the temperature and pressure distribution of micro-gap oil film are not uniform, resulting in fluid-heat-solid coupling deformation of the hydrostatic bearing friction pairs. In order to solve this problem, a new type of hydrostatic bearing structure with tilting oil pad is proposed, which can realize micro-swing in any direction during operation, generate additional dynamic pressure and form a static and dynamic hybrid bearing to achieve high-speed and heavy-load working conditions. Based on the fluid-thermo-solid coupling theory, ANSYS Workbench is used to analyze the deformation of the hydrostatic bearing friction pairs, and the fluid-thermo-solid coupling deformation law of the rotational worktable, tilting oil pad and base under the extreme operating conditions of 0 t ~ 32 t is discussed. The deformation data is extracted and then the deformation relationship of the friction pair is obtained by using Matlab program. It is found that the deformation at the corner of the outer sealing oil side of the oil cavity is the largest, where the gap oil film is the thinnest and the tribological failure is most likely to occur, and the results provide a new method for further control of friction pairs deformation and tribological failure mechanism.
TRACKING AND QUANTITATIVE EVALUATION OF EARTHQUAKE-INDUCED STRUCTURAL DAMAGE USING HEALTH MONITORING DATA
Jia-zeng SHAN, Han-qing ZHANG, Nan GONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0138
Abstract:
Structural nonlinear behavior is allowed during strong earthquakes according to the ductility-based structural design, which relates to the earthquake-induced structural damages. From the viewpoint of physics and mechanics, the peak effect and cumulative effect of seismic damage are comprehensively considered in numerical modeling and performance assessment of structural behaviors. However, the application of classical Park-Ang damage model for large-scale existing structures, which is mostly used in seismic studies, may be relatively limited due to the lack of prior knowledge (such as the hysteretic energy dissipation, the yielding force and the ultimate displacement capacity). Inspired by the model reference concept in the field of control study, a data-driven damage evaluation model is proposed in this paper to quantify both the peak and cumulative damage effects, which may be used for different deformation modes. A full-scale reinforced concrete (RC) column subjected to shake table test from the NEES Database is utilized to investigate the correlation between the development of damage and the proposed damage model and the tracking performance in the time-domain. The new damage evaluation index is proved to be able to distinguish the difference in damage development between the shear and flexural deformation of RC column. Generally, the proposed damage index, adopting the model reference concept, may not require structural hysteresis characteristics and the calculation of dissipated energy, and can be applied to practical seismic evaluation.
COMPRESSIVE CONSTITUTIVE RELATION OF ALKALI SLAG CERAMSITE CONCRETE MASONRY BUILT BY ALKALI SLAG POTTERY MORTAR
Wenzhong ZHENG, Rigele AO, Ying WANG, Wenxuan HUANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.12.0739
Abstract:
In order to investigate the compressive constitutive relation and basic mechanical properties of alkali slag ceramsite concrete block masonry, the axial center resistance tests of 126 alkali slag ceramsite concrete block masonry specimens built with alkali slag pottery mortar were conducted. The results show that when the compressive strength of the block and the compressive strength of the mortar are the same, the peak compressive strain and ultimate compressive strain of the masonry are lower than those of the ordinary concrete block masonry because the shrinkage of alkali slag pottery mortar is large. Based on experimental results, the calculation formulas of peak compressive strain, ultimate compressive strain and elastic modulus of masonry are established with masonry compressive strength, block compressive strength and mortar compressive strength as independent variables.
A MODIFIED P-Y CURVE MODEL OF LARGE-MONOPILES OF OFFSHORE WIND POWER PLANTS
Yi-long SUN, Cheng-shun XU, Xiao-ling ZHANG, Xiu-li DU, Ren-qiang XI
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0051
Abstract:
The monopile is one of the most common solutions for the foundation of offshore wind power plants. The p-y curve recommended by API is commonly used to obtain the horizontal displacement of a monopile. For piles of a more than 2 m diameter, the p-y curve model overestimates the initial stiffness of subgrade reaction and yields inaccurate horizontal displacement. An evaluation of the current p-y method was made to obtain the key factors responsible for overestimating the initial stiffness of subgrade reaction. These key factors were amended. A modified p-y curve model was proposed in which the nonlinear impact of the dimeter and depth on the initial stiffness K was considered based on the calculation results of FLAC3D. The developed p-y curve model was compared with test data and the results of the current p-y curve and the previous modified model. The results show that the good agreement between the calculated results of the developed modified p-y model and test values verified the rationality of the modified p-y model.
THE AXIAL STRENGTH OF CONCRETE-FILLED ALUMINUM ALLOY CIRCULAR TUBULAR STUB COLUMNS
Xiang ZENG, Wan-bo WU, Jing-si HUO, Tao HU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0178
Abstract:
To investigate the axial strength of concrete-filled aluminum alloy circular tubular (CFACT) stub columns, six specimens with confinement coefficients of 0.57 to 1.26 were tested under concentric compression. The failure patterns, axial load versus axial strain curves, lateral deformation coefficient, peak load, and ductility were analyzed. The failure patterns included drum-shaped failure and oblique shear failure. The test results show that the columns exhibited a good composite effect between the aluminum tube and core concrete, and had high strength and ductility. An equivalent stress-strain relationship for the core concrete confined by the aluminum tube was proposed for the concrete plastic damage model, and a nonlinear finite element analysis (NFEA) model for CFACT columns was developed using the software ABAQUS. The NFEA model was verified by the test results. To reasonably design the CFACT columns, the axial strength of the CFACT stub columns was discussed and defined. Based on the NFEA model, the axial strengths of twenty-seven columns with different parameters including the confinement coefficient, diameter-thickness ratio, aluminum ratio, and material strength were obtained. Using the acquired axial strengths of thirty-three test and simulated columns, the cross-section composite strength was calculated. The ratio of composite strength to the concrete compressive strength was linearly related to the confinement coefficient. A formula for the composite strength was established by regression analysis.
A HIGH-EFFICIENCY SIMULATION METHOD FOR ANALYZING THE IMPACT OF EXHAUSTED AIR FROM TEMPORARY HOSPITALS BUILT FOR THE TREATMENT OF NOVEL CORONAVIRUS PNEUMONIA
Dong-lian GU, Yin-an ZHANG, Hua-bin LIU, You-cai MA, Xiao-qing CAO, Zhong-yi Lyu, Lin-lin XIE, Zhen XU, Yong-jia XU, Zhe ZHENG, Can-tian YANG, Xin-zheng LU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0047
Abstract:
The outbreak of the novel coronavirus pneumonia at the end of 2019 imposed severe pressure on the medical system of China. Several Chinese cities began to build temporary hospitals for the centralized treatment of the pneumonia patients. Because the design and construction of the temporary hospital must be completed in 6 to 10 days, only a few hours are allowed for the analysis of the impact of exhausted air on the surrounding environment. To overcome this difficulty, a high-efficiency simulation method for analyzing the impact of exhausted air is proposed in this study. Based on the open-source computational-fluid-dynamics (CFD) software FDS, the proposed method realizes the fast modeling of temporary hospitals, the cloud computing-based CFD computation, and the monitoring and visualization of harmful air. The proposed method provides an efficient tool for the rapid analysis in the design stage of new-built temporary hospitals. A case study of Wuhan Leishenshan Hospital was conducted to demonstrate the application value of the proposed method in the epidemic prevention of the pneumonia.
EXPERIMENTAL RESEARCH ON SEISMIC PERFORMANCE OFWCFT COLUMN-STEEL BEAM JOINTS
Yu-qi HUANG, Ji-ping HAO, Chun-lei FAN, Qiang XUE, Li-jun WANG, Xiao-ling SUN, Han-chao LIU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0092
Abstract:
Side-plate joints for walled concrete-filled steel tubular column and steel beam are proposed. In order to study the seismic performance of the joint, the quasi-static tests of three full-size side-plate joint specimens were carried out. The failure pattern, hysteretic curve, skeleton curve, ductility, energy dissipation capacity, stiffness degradation and strain of the joint panel were analyzed. The results are as follows. The joint panels of three specimens remain elastic; the plastic hinge failure occurs at the beam end of side-plate joint specimens meeting the horizontal and vertical strength ratio requirements; the joint specimens with plastic hinge occurring at beam ends have good deformation performance and energy dissipation capacity, while the side-plate joints whose horizontal or vertical strength ratios are less than 100% undergo brittle failure. Based on the experimental study and the internal force transmission mechanism at beam ends, three failure modes of side-plate joint outside the joint panel and corresponding discriminant formulas were put forward, which were basically consistent with the experimental results and could be used as reference for engineering design.
NONLINEAR TORSIONAL ANALYSIS OF A SINGLE PILE IN AN EXPANSIVE SOIL FOUNDATION
Jie JIANG, Shun-wei WANG, Xiao-duo OU, Zhi WANG, Di YANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.04.0243
Abstract:
The pile-soil interaction in an expansive soil foundation is complicated, and the influence of the inundation swelling deformation on the torsional bearing characteristics of the pile foundation remains unknown. In this paper, the displacement governing equations for the pile shaft were proposed considering the load transfer method. The distribution of the vertical resistance of the shaft was calculated by the finite difference method considering the influence of the swelling deformation of the expansive soil on the shaft resistance and the boundary condition of the pile tip. A new nonlinear analytical method for the torsion of a single pile due to the inundation swelling deformation was proposed incorporating the boundary element method. The distribution law of the circumferential frictional resistance of piles was revealed and the effectiveness of the proposed method was verified by model tests. It was shown that the ground heave induced by the swelling of the expansive soil foundation would significantly reduce the torsional bearing capacity of the single pile. In addition, the safety is threatened because the conventional calculation method overestimates the ultimate torque of the pile and the loading stiffness of the pile-soil system. The torque of a single pile approximately decreases linearly along the pile shaft prior to the inundation swelling deformation. However, the torque of the pile shaft is close to that of the pile top and the torque of the pile shaft decreases rapidly in the “unslip section”. The length of the interface “slap section” increases and torsional force capacity of the single pile decreases with the increase of the swelling ratio.
THE INFLUENCE OF FAST FILLING ON THE RESIDUAL STRESS OF COMPOSITE OVERWRAPPED PRESSURE VESSEL FOR HYDROGEN
Yong JIANG, Ming XU, Shu-tao WEI
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0146
Abstract:
Temperature rise is an important issue during the fast filling of a composite overwrapped pressure vessel (COPV) for hydrogen storage. There exists a thermal-mechanical coupling effect due to the non-uniform temperature distribution and different thermal expansion coefficients. In this study, a fluid-thermal-solid coupling analysis method is proposed for the thermal-mechanical behavior of COPV during fast filling. In this method, a computational fluid dynamics (CFD) model is set up first to obtain the temperature field, which is input into a thermal-mechanical model as boundary condition. By this method, the influences of filling rate, inlet location and geometry of the COPV on the temperature and stress fields are studied. The results of this work will provide a guidance for the design of COPV and the optimization of filling processes.
COMPARATIVE STUDY ON FATIGUE STRENGTH OF 8 KINDS OF VENA CAVA FILTERS UNDER TWO WORKING CONDITIONS
Yue-tong WANG, Hai-quan FENG, Xiao-tian WANG, Yong-gang WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0590
Abstract:
In order to explore the reasons of fatigue failure of vena cava filters, it is necessary to study the fatigue strength of the filter under cyclic variable loads. SolidWorks software was used to build models of 8 filters, ABAQUS software was used to analyze the fatigue strength of 8 filters under circumferential pulsating cyclic load and radial compression cyclic load, and the safety of one filter was verified by experiments. In the circumferential fatigue analysis, all the alternating strain points of 8 filters are below the fatigue limit curve, and the safety factors are greater than 1, which meet the fatigue life requirements. In the radial fatigue analysis, some alternating strain points of the new filter and the TrapEase filter are above the fatigue limit curve, and the safety factors are less than 1. The other 6 filters meet the fatigue life requirements. The recyclable filter may not meet the requirement of fatigue life of 10 years and can be used as a temporary filter. Through 14 days, 21 days and 28 days of animal experiments, three small sweetgum pigs were implanted with Aegisy filter. The safety of Aegisy filter is comprehensively evaluated. The results show a good reference for the design, development and clinical application of vena cava filters.
A BOUNDARY FORCED RESPONSE DISPLACEMENT METHOD FOR SEISMIC ANALYSIS OF SYMMETRICAL UNDERGROUND STRUCTURES
Run-bo HAN, Cheng-shun XU, Zi-gang XU, Jia-wei JIANG, Xiu-li DU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0075
Abstract:
A boundary forced response displacement method is proposed for the seismic analysis of symmetrical underground structures based on the requirement of quasi-static pushover test of soil-underground structure systems. The implementation procedure and special features of the method are introduced in detail. We took the Daikai subway station which was damaged during the Kobe earthquake in Japan as an example for the analysis, and compared the results of boundary forced response displacement method, the FEM seismic deformation method and the dynamic time-history analysis method. The results show that the accuracy of the new method was much higher than the FEM seismic deformation method when the width of the model was reasonable. The errors of the internal forces and the story drift were less than 15%. The new method is an effective simplified method for seismic response analysis of symmetrical underground structures. The attenuation law of lateral boundary forced displacement was analyzed. It provides references for the quasi-static pushover test of soil-underground structure system.
POINT ESTIMATION FOR STATISTICAL MOMENTS BASED ON THE BIVARIATE DIMENSION-REDUCTION MODEL AND KRIGING APPROXIMATION
Wenliang Fan, Man Yuan, Runyu Liu, Xiaoyang Yang, Zhengliang Li
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0096
Abstract:
When estimating statistical moments for complex random systems, the bivariate dimension-reduction method can alleviate the curse of dimension to some extent. However, there are many bivariate component functions for high-dimension random systems. It makes the estimation unfeasible. An efficient point estimation for moments is proposed in this paper, in which the dimension-reduction model is modified by the Kriging approximation model. Considering the characteristics of function approximation and the abscissas of numerical integration, a “star” shape point-selection strategy is proposed. Based on this point-selection strategy, a Kriging approximation model of the bivariate component function is developed. By replacing each bivariate component function in the bivariate dimension-reduction model for the original function or its moment function with their corresponding Kriging approximations, two modified methods for the moment estimation are presented. The efficiency and accuracy of the proposed methods are verified by several examples. The results show that the Kriging approximation of the bivariate component function based on the "star" shape point-selection strategy has higher accuracy. Correspondingly, the statistical moment estimation of the proposed methods has comparable accuracy with the existing methods, while fewer function evaluations are required.
SEISMIC DAMAGE ANALYSIS ON STEEL REINFORCED CONCRETE FRAMES WITH SPECIAL-SHAPED COLUMNS
Zu-qiang LIU, Bengyou REN, Jian-yang XUE, Chao-feng ZHOU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0123
Abstract:
To realize the seismic damage analysis of steel reinforced concrete (SRC) frames with special-shaped columns, a damage model which can reflect the migration and evolution of the member damage, the floor damage and the whole frame damage was established by using the weighted coefficient method. Seismic damage tests and finite element simulation were carried out on two SRC frames with special-shaped columns. The moment-rotation hysteresis curves of the beams and the horizontal load-displacement hysteresis curves of the columns were obtained. The seismic damage index of specimens was calculated and analyzed. The results show that the change law of the damage index of members, floors and the whole frame were in good agreement with the failure development processes of the specimens, indicating that the seismic damage model of the SRC frame with special-shaped columns is reasonable. Based on the failure states of the specimens and the seismic damage analysis results, the range of the damage index of SRC frames with special-shaped columns corresponding to five performance levels was proposed. It provides the basis for the post-earthquake damage assessment of this type of structure.
DISCRETE ELEMENT SIMULATION OF THE SHEAR BEHAVIOR OF CEMENTED METHANE HYDRATE-BEARING SANDS
Xuan WANG, Ming XU
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0174
Abstract:
The methane hydrate is a new type of clean energy, and is widely distributed in deep sea sediments and permafrost. It is necessary to study the mechanical properties of the methane hydrate-bearing sands. In this paper, a method of generating the discrete element model of cemented methane hydrate-bearing sands is proposed. The model is used to simulate a drained biaxial test. The accuracy of the discrete element model is verified by comparing it with previous experimental data. The macro and micro characteristics of the methane hydrate-bearing sands are then analyzed using the model. The results show that the shear strength, strain softening characteristics and dilatancy of the sand increase with the increase of methane saturation, that the evolution of the hydrate fracture number is closely related to the deviator stress, that the hydrate fracture number increases most rapidly when the deviator stress reaches the peak value, and that the hydrate fracture, particle movement and the porosity change inside and outside the shear band during the test are obviously different. Through the analysis of some micro indexes such as the bond breaking ratio and local porosity inside and outside the shear band, the mechanism of the macro behavior such as the deviator stress and volume change of the methane hydrate-bearing sand is further explained.
SUPERCONVERGENT PATCH RECOVERY SOLUTIONS AND ADAPTIVE MESH REFINEMENT ANALYSIS OF FINITE ELEMENT METHOD FOR THE VIBRATION MODES OF NON-UNIFORM AND VARIABLE CURVATURE BEAMS
Yong-liang WANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.02.0065
Abstract:
It presents a superconvergent patch recovery method for the superconvergent solutions of modes in the finite element (FE) post-processing stage of non-uniform and variable curvature curved beams. An adaptive method for the in-plane and out-of-plane free vibration of curved beams with variable cross-section is also proposed. In the post-processing stage of the displacement-based finite element method, the superconvergent patch recovery method and the high-order shape function interpolation technique are introduced to obtain the superconvergent solution of mode (displacement). Using the superconvergent solution of mode to estimate the error of the FE solution of mode in the energy form under the current mesh, an adaptive mesh refinement is proposed by mesh subdivision to derive the optimized mesh and accurate FE solution to meet the preset error tolerance. Numerical examples show that the proposed algorithm is suitable for solving the continuous orders for frequencies and modes in the in-plane and out-of-plane free vibration of different kinds of curve shapes, boundary conditions, non-uniform cross-section, and variable curvature forms of the non-uniform curved beams. The computation procedure can provide accurate solutions. The analysis process is efficient and reliable.
THEORETICAL MODEL FOR HFR-LWC BEAM UNDER BLAST LOADING ACCOMPANYING MEMBRANE ACTION AND ITS EXPERIMENTAL VALIDATION
Wan-xiang CHEN, Zhi-kun GUO, Li-sheng LUO, Peng YUAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0200
Abstract:
Membrane effect is regarded as a potential safety factor in current blast-resistance design codes, but the membrane behavior and its contribution to structural resistance are not completely investigated as yet. Based on the equivalent Single-Degree-of-Freedom (SDOF) method, a theoretical model for beam-like member under close-range blast loading accompanying membrane action is proposed. A special loading device of membrane action is manufactured in this paper, and the blast-resistant tests on 8 Hybrid Fiber Reinforced-Lightweight Aggregate Concrete (HFR-LWC) beams are performed. The overpressure history of shock wave, mid-span displacement and failure pattern of HFR-LWC beam are obtained. The influences of constraint stiffness, scaled distance of explosion and reinforcement ratio on load-carrying capacities and failure modes of HFR-LWC beam are discussed, and then the reliabilities of presented model are validated by blast-resistant tests. It is indicated that the analytical results based on the improved SDOF model are in good agreement with the experimental data, which provides a reliable tool for quantitatively estimating the membrane contribution to structural resistance and predicting the dynamic behaviors of HFR-LWC beam under blast loading accompanying membrane action. The blast-resistances of HFR-LWC beam would be significantly enhanced by membrane effect, and the ultimate resistances of beam-like member might be greatly underestimated if the membrane action is neglected.
IDENTIFICATION OF THE MECHANICAL PROPERTIES OF PARTICLEBOARD BY DIGITAL IMAGE CORRELATION TECHNOLOGY
Zhou CHEN, Xinxi DU, Shen ZHANG, Huanxin YUAN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0014
Abstract:
As a kind of artificial material, the surface porosity of particleboard makes the sticking process of strain gauge very difficult, and the measurement accuracy is affected directly by the amount of glue. Digital image correlation technology based on image analysis before and after the specimen deformation is used to identifier the mechanical parameters of particleboard. Compared with the traditional method of sticking strain gauge, this technique has the advantages of high accuracy, non-contact and full field measurement. The “transverse isotropic” model is considered to simulate the mechanical behavior of particleboard. Therefore, the elastic tensor characterizing the mechanical properties of materials depends on five independent elastic parameters: Young’s modulus (EL, ET) and Poisson’s ration (νL, νT), respectively, in the longitudinal and transversal directions, and shear modulus GL in all planes around the symmetry axis. In order to achieve this measurement process, a sheet of particleboard was cut into a batch of beam samples which were then applied to the three-point bending test. By comparing the measured displacement of grid nodes with the analytical solution based on Timoshenko’s beam theory in the region of interest, and through the application of the finite element model updating method, 4 elastic parameters ET, GL, EL and νL were successfully measured. The measured material parameters are very close to reported values in literatures. The measurement method proposed is simple and easy to perform, which can be extended to the measurement of elastic parameter of anisotropic materials.
INVESTIGATION ON THE SEISMIC BEHAVIOR OF STEEL-PLATE AND HIGH DUCTILE CONCRETE COMPOSITE LOW-RISE SHEAR WALLS
Ming-ke DENG, Jun-chao LIU, Hai-bo LIU, Wu-bin JING
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.07.0414
Abstract:
To improve the seismic behavior of low-rise shear walls, the double steel plates and high ductile concrete (HDC) composite low-rise shear wall (DHW) was proposed. One HDC low-rise shear wall (HW), two single steel plate reinforced HDC low-rise shear walls (SHW) and two DHWs were designed. The influence of the axial load ratios and steel distribution form on the failure modes, hysteretic performance, shear capacity, deformation capacity, energy dissipation capacity and stiffness degradation of the specimens were studied by quasi-static tests. The experimental results indicate that the failure modes of the HW, SHW and DHW are the shear failure, the flexural-shear failure and the flexural failure, respectively. The deformability and strength capacity of the steel-plate and HDC composite low-rise shear walls are significantly improved compared with those of the HWs. The axial load ratio has little impact on the peak load and stiffness of the steel-plate and HDC composite low-rise shear walls. With an axial load ratio ranging from 0.5 to 0.7, the deformation capability of the SHW decreases, whereas the deformation capability of the DHW does not decrease. Formulas for the bending capacity of the steel-plate and HDC composite low-rise shear walls are suggested, and the calculation results agree well with the test results.
THEORETICAL SOLUTION OF SLIDING CABLE STRUCTURES CONSIDERING FRICTIONAL EFFECT
Shi-zai CHEN, Meng-gang YANG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0201
Abstract:
Sliding cable structures are widely used in engineering practice. The analyses of such structures are still mainly based on numerical methods at present, which is a lack of theoretical methods. The effect of geometrical nonlinearity and friction on sliding need to be taken into account in the analysis simultaneously. Firstly, based on the catenary theory, the one-dimensional analytical expression of the unstressed length for a single cable is deduced. After the introduction of Euler equation, the analytical equations of multi-span continuous cables under self weight and concentrated loads are established, respectively, according to the characteristics of the invariant total unstressed length and balanced tension at the sliding point. Thereafter, the analytical equations of continuous cables are extended to a cable-supported truss. The Newton-Raphson scheme with controllable accuracy is used to solve the equations, and four examples are analyzed by the program. The results show that the theoretical solution is accurate with high adaptability in engineering, which can provide theoretical basis for the design and analysis of sliding cable structures.
STUDY ON BENDING BEHAVIOR OF CIRCULAR UHPC FILLED HIGH STRENGTH STEEL TUBE BEAMS
Jian-gang WEI, Xia LUO, bao-chun CHEN, Jian-yuan LV
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0158
Abstract:
Taking the steel content and hoop coefficient as parameters, the pure bending tests of 5 circular high strength steel tube ultra-high performance concrete (UHPC) beams and 2 circular ordinary steel tube UHPC beams were carried out to investigate their bending behaviors. The steel ratio and hoop coefficient were employed as test parameters. The experimental results show that UFHST beams failed in ductile. The composite section satisfied the assumption of plane cross-section. The hoop action of the high strength steel tube on UHPC should be considered in the compression zone. Compared with the normal strength steel tube, high strength steel tube can restrain the transverse expansion of UHPC more effectively. The finite element model verified by test results was used to conduct parameter analysis of the hoop coefficient. When the concrete-filled steel tube beam reaches its bending bearing capacity, the corresponding neutral axis and the stresses of steel and concrete are related to the hoop coefficient. With the increase of the hoop coefficient, the neutral axis keeps moving toward the section centerline; there is a decrease in the steel stress in the tensile zone, and an increase in the steel stress and concrete stress in the compressive zone. It was inaccurate and discrete to use Chinese code GB50936-2014 for predicting the bending bearing capacity of UFHST beams. Consequently, a new calculation method was proposed.
RESEARCH ON CONTACT MECHANICAL MODEL OF ROLLING MILL BEARING UNDER MISLIGNED LOADS
Shuilin LIN, Jianliang SUN, Yan PENG
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.03.0139
Abstract:
The paper analyzes the rolling bearing contact mechanical model under the misaligned loads in the strip rolling process, and establishes the Hertz ideal contact model of four-row cylindrical roller bearings for back-up roller and the bearing mechanical model under the misaligned loads using flexibility matrix method. The numerical simulations under different loads between the rolls are conducted, and the ideal contact process and the misaligned load contact process are simulated. The results show that the misaligned loads affect the bearing loads distribution of each row; the rolling body at 15°~30° position angles bears the maximum force where the maximum contact stress exhibits an "M" shape distribution. The simulation results are consistent with the numerical simulation results, but the later is bigger than the former by 15% or less, which is within the error scope of engineering application. As the rolling load increases, the total radial force on the rollers of the same row of bearings increases, and the misaligning of loads become more significant. The research provides theoretical basis for prolonging the life of bearings and ensuring the stable operation of rolling mills.
EXPERIMENTAL STUDY ON THE MECHANICAL PERFORMANCE OF ANGLE SHEAR CONNECTORS WITH AND WITHOUT CONCRETE GAPS
Liang TANG, Jian-sheng FAN, Jian-guo NIE, Sheng-yuan QIU, Guo-ping XU, Shen-you SONG
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.10.0621
Abstract:
Because it is difficult for the flow, vibration and gas exhaust of concrete, gaps may exist near the welded regions of angle shear connectors. Based on the engineering practice and standard provisions, a test on nine groups of full-scale push-out specimens of three different gap depths (0, 10 mm and 20 mm) was conducted. To reduce the discreteness, there were three duplicate specimens in each group. All specimens failed in concrete crushing in the test. Compared with the specimens without a gap, the crushing area was smaller and the deformation of the angle steel was larger in the specimens with a gap. The concrete gap had a significant influence on the strength and stiffness of the angle shear connectors. Compared with that of the specimens without a gap, the strength was decreased by 16.5% and 37.5% and the stiffness was decreased by 48.4% and 70.6% for the specimens with a gap of 10 mm and 20 mm, respectively. Different formulas in the literature were verified based on 62 groups of specimens in other papers and 3 groups of specimens in the current test. The formula proposed by Kiyomiya and Kimura was found to have good accuracy and small discreteness, while the formula proposed by 《Design Code for Steel-Concrete Sandwich Structures》in Japan was conservative. A new shear strength empirical formula was proposed based on the existing experimental data, which showed better accuracy and applicability. Based on the new shear strength formula and a mechanical model considering the concrete gap, a shear strength corrected formula for angle shear connectors with concrete gaps was proposed. The proposed corrected formula was verified based on 3 groups of specimens in other papers and 6 groups of specimens in the current test and was found to have good accuracy and small discreteness.
EXPERIMENTAL STUDY ON DEGRADATION OF MECHANICAL PROPERTIES OF CORRODED HIGH STRENGTH STEEL WIRE
Fan GONG, Sheng-ke QI, Yi-qing ZOU, Cai-kui LIN, Chen WANG, Hai-jun ZHOU
, Available online  , doi: 10.6052/j.issn.1000-4750.2019.11.0669
Abstract:
The morphology, product and degradation of corroded high strength steel wire were tested, which was essential for inspection and mechanical evaluation. The corrosion products were analyzed by high resolution X-ray diffractometer and environmental scanning electron microscope. Three-dimensional scanning was applied to determine the change of the cross section of corroded wire along the axial direction. Static tensile and fatigue loading tests were also carried out. The corrosion morphology of high strength steel wire is determined by the analysis of 3D scanning data. The degradation of the constitutive model parameters of corroded high strength wires are derived by the regression analysis of the test mechanical parameters and corresponding corrosion ratios. The test results show that: the variability of sectional area along wire axis increases with the increase of corrosion degree, the ultimate strength of corroded wire is less than the standard strength of 1770 MPa when corrosion ratio is more than 1.25%; the elongation is less than the specification limit of 4% when the corrosion ratio is greater than 5.05%; the fatigue life is less than 2 million cycles when the corrosion ratio is more than 4.16%; while corrosion has little effects on the elastic modulus. The index for evaluation of corroded wire is refined for the specification based on the above results.
PROBABILITY MODELLING OF PGA AMPLIFICATION FACTORS CORRECTED BY SITE CONDITIONS
Chuan TANG, Long-wei CHEN
, Available online  , doi: 10.6052/j.issn.1000-4750.2020.01.0023
Abstract:
Peak ground-motion acceleration (PGA) is a fundamental parameter in seismic design codes and in earthquake early warning systems. We collected the seismic data recorded by 40 strong-motion stations of the KiK-net seismic station array in Japan, and studied the statistic distribution of PGA amplification factor fPGA. It was demonstrated that the fPGA under a given seismic intensity input was basically log-normally distributed with its mean and standard deviation depending on the site conditions. Any individual site characteristic parameter, such as Vs30, Vs20 or soil thickness D, was poorly correlated with the statistic parameters, i.e., the mean and standard deviation, while a satisfactory correlation was obtained with respect to linear combinations of Vs30, Vs20 and D. By the regression of the data, the statistic parameters of fPGA were calculated according to a linear combination of site characteristic parameters to build the probability density function of the log-normal distribution model of fPGA. Following the fPGA probability model, the ground surface PGA corrected by specific site characteristic parameters could be predicted under different probability levels, and testified by seismic data. The probabilistic predictions of PGA meet the demands of risk analysis in engineering practice, paving the way for site-corrected surface PGA prediction in earthquake early warning and fast seismic intensity estimation.