Current Issue

2021, Volume 38,  Issue 2

cover
2021, 38(2)
Abstract:
OVERVIEWS
APPLICATION OF GPU-BASED PARALLEL COMPUTING METHOD FOR DEM IN LARGE ENGINEERING STRUCTURES
Ji-hong YE, Jia WANG
2021, 38(2): 1-7. doi: 10.6052/j.issn.1000-4750.2020.07.ST03
Abstract:
The member DEM (discrete element method) is an effective way for the structural analyses concerning with strong nonlinear issues. However, with the expansion of structural numerical calculation model, the member DEM program has been time-consuming dramatically. It proposes element-level parallel and node-level parallel computing methods to improve the calculation efficiency of the member DEM. A parallel computing framework for the member DEM is first developed based on a CPU-GPU heterogeneous platform. Then, the member DEM program that models structural geometric nonlinearity is compiled and embedded into the framework, and finally the GPU-based multi-thread parallel algorithm for the member DEM is established. The design of this parallel algorithm mainly composed of a data storage mode, a GPU thread computing mode, a node physical quantity integration mode and the way of data transmission optimization. The accuracy of the member DEM parallel algorithm proposed in this study is verified by a large-scale space frame model and a spherical shell structure model, and the performance of the algorithm was further tested. The results show that the speedup of the member DEM parallel algorithm can reach 12.7 times at most.
METHODOLOGIES
ADAPTIVE MESH REFINEMENT ANALYSIS OF FINITE ELEMENT METHOD FOR ELASTIC BUCKLING OF CRACKED CIRCULARLY CURVED BEAMS
Yong-liang WANG
2021, 38(2): 8-15, 35. doi: 10.6052/j.issn.1000-4750.2020.03.0173
Abstract:
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 influence 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.
DYNAMIC BEHAVIORS OF POROUS FGVM BEAMS SUBJECTED TO THERMAL MECHANICAL VISCOELASTIC EFFECTS
Feng-xi ZHOU, Yu PU
2021, 38(2): 16-26. doi: 10.6052/j.issn.1000-4750.2020.04.0235
Abstract:
Based on a three-parameter Winkler-Pasternak viscoelastic foundation model, the free vibration behavior of porous functionally graded viscoelastic material (FGVM) beams in thermal environment subjected to initial axial mechanical force is investigated. Temperature distribution is determined by a one-dimensional steady-state heat conduction equation. The material properties are temperature-dependent and described by using Kelvin-Voigt model according to the modified mixture power-law distribution form with even porosity for FGVM beams. Based on n-th order generalized beam theory, the dynamic governing equations for this system are derived by using Hamiltonian principle. An generalized form for Navier method can be utilized to obtain the exact coupling vibration responses of the FGVM beams with both clamped ends, clamped at one end and hinged at the other end, and hinged at both ends. The effects of different beam theories, boundary conditions, thermal-mechanical loads, viscoelastic foundation parameters, structural damping coefficient, porosity, material graded index, length-to-thickness ratio and mode number on the dynamic behavior of FGVM beams are discussed by several numerical examples.
CIVIL ENGINEERING
A SUBSTRUCTURE MODEL FOR WATER-AXISYMMETRIC CYLINDER INTERACTION DURING EARTHQUAKES
Xiao-jing WANG, Mi ZHAO, Pi-guang WANG, Xiu-li DU, Xing-lei CHENG
2021, 38(2): 27-35. 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.
ENERGY DISSIPATION PERFORMANCE OF OUTRIGGER IN TALL BUILDINGS
Wei ZHEN, Yi-kun QIU, Qing-shun YANG, Wan-kai ZHANG
2021, 38(2): 36-43. doi: 10.6052/j.issn.1000-4750.2020.10.ST08
Abstract:
The outriggers are the key components of super-tall structures. Increasing the energy dissipation capacities of outriggers is of a great significance on improving the structural aseismic performance. The commonly used outriggers include regular outriggers, buckling restrained braces (BRB) outriggers, and outriggers with dampers. Based on a super-tall frame-core-outrigger structure, the energy dissipation and aseismic performance of regular outriggers, buckling restrained braces (BRB) outriggers, and outriggers with dampers are investigated and compared. The results indicate that different outriggers have some impacts on the seismic energy input and energy distribution of the structure. Compared with the ordinary outrigger system, the BRB and damped outrigger systems have better energy consumption performance. In addition, the damped outrigger has a more obvious effect on the damage control of the core cylinder, while the BRB outrigger has the best effect in the displacement response control for the overall structure of a super-tall building.
DISCRETE ELEMENT SIMULATION OF THE SHEAR BEHAVIOR OF CEMENTED METHANE HYDRATE-BEARING SANDS
Xuan WANG, Ming XU
2021, 38(2): 44-51. 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.
THE AXIAL STRENGTH OF CONCRETE-FILLED ALUMINUM ALLOY CIRCULAR TUBULAR STUB COLUMNS
Xiang ZENG, Wan-bo WU, Jing-si HUO, Tao HU
2021, 38(2): 52-60. 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.
STUDY ON AXIAL COMPRESSIVE BEHAVIORS OF NOVEL STEEL-CONCRETE-STEEL COMPOSITE WALL
Jia-bao YAN, An-zhen CHEN, Tao WANG
2021, 38(2): 61-68. 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 standard and the European code, it is found that the load capacity design formula based on European code is safer.
ANALYTICAL SOLUTION FOR NONLINEAR CONSOLIDATION OF SAND-DRAINED GROUND WITH EXPONENTIAL FLOW UNDER VACUUM COMBINED SURCHARGE PRELOADING
Wen-hao JIANG, Liang-tong ZHAN
2021, 38(2): 69-76, 133. 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 flow index m, the faster the consolidation rate of sand-drained ground, but in the later stage of consolidation, the larger m is, the slower the consolidation rate of sand-drained ground 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.
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
2021, 38(2): 77-91. 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 intensively 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.
THEORETICAL SOLUTION OF SLIDING CABLE STRUCTURES CONSIDERING FRICTIONAL EFFECT
Shi-zai CHEN, Meng-gang YANG
2021, 38(2): 92-100. 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 effects of geometrical nonlinearity and friction on sliding need to be taken into account in the analysis simultaneously. 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 respectively established, according to the characteristics of the invariant total unstressed length and balanced tension at the sliding point. The analytical equations of continuous cables are extended to cable-supported trusses. 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 a theoretical basis for the design and analysis of sliding cable structures.
THE TENSILE MECHANICAL PROPERTIES AND CONSTITUTIVE RELATIONSHIP OF IONOMER INTERALYER AT MEDIUM-TO-HIGH STRAIN RATES AND DIFFERENT TEMPERATURES
Yu-jia LU, Su-wen CHEN, Yang ZHANG
2021, 38(2): 101-109. doi: 10.6052/j.issn.1000-4750.2020.04.0204
Abstract:
To systematically study the tensile mechanical properties of ionomer interlayer at medium-to-high strain rates and different temperatures, dynamic tensile tests are performed at 1 s−1~800 s−1 and −40 ℃~60 ℃. Based on the experimental results, key mechanical parameters are identified, and the effects of temperature and strain rate are analyzed. As the strain rate increases or the temperature decreases, the initial elastic modulus, yielding strength and failure strength increase but the failure strain decreases. Based on G’SELL model, the model parameters are calibrated and validated against the test results. Adopting a stress-compensation method, the paper develops a user subroutine to introduce the proposed constitutive equation into the LS-DYNA software. The effectiveness of the user subroutine is validated through the comparison between numerical and test results.
STUDY ON INTERFACIAL FAILURE MECHANISM OF STEEL AND STEEL FIBER REINFORCED CONCRETE COMPOSITE STRUCTURE UNDER DIFFERENT LOADING CONDITIONS
Kai WU, Xiao-yi LIU, Feng CHEN, Shi-qi LIN, Chao XU
2021, 38(2): 110-121. doi: 10.6052/j.issn.1000-4750.2020.04.0206
Abstract:
An innovative method to replace steel reinforcement cage by steel fiber to form the steel and steel fiber reinforced concrete has been proposed to solve the construction problems of steel reinforced concrete structures, such as the position conflict between steel and steel bars, and the difficulty of concrete placement. The push-out tests of 36 specimens and four-point bending tests of 13 specimens were carried out, the interfacial failure of the steel and steel fiber reinforced concrete composite structures was studied under axial force and bending moment, and then the internal force transfer and failure mechanism of the steel and steel fiber reinforced concrete were analyzed under different loading conditions. The bridging effect is formed by the pull-out behavior of steel fibers at concrete cracks, which restrains the crack development and improves the tensile properties of concrete after cracking; as a result, the problem of poor interfacial bond behavior caused by the decrease of cover thickness is solved which occurs between the steel and steel fiber concrete, and the interfacial bonding failure is delayed or even avoided. Under the action of axial force, the interface between the steel and steel fiber reinforced concrete is extruded due to Poisson's ratio effect and the concrete is under tension in two orthogonal directions, which is the main cause of damage and cracking of steel fiber reinforced concrete. The damage degree of steel fiber reinforced concrete is directly related to the interfacial bonding behavior, and is also affected by the Poisson's ratio of steel. In the four-point bending test, the bond cracks concentrate in the mid-span area where only bending moment exists. The internal force transfer between the steel and steel fiber reinforced concrete and the interfacial tensile stress are the main reasons for the large number of bond cracks. Bond crack appears at the tip of steel flange and grows from the tips toward the concrete surface until it reaches the outer surface of the steel fiber reinforced concrete. The trapezoidal failure surface of the steel fiber reinforced concrete cover is finally formed in the mid-span area.
FAILURE IDENTIFICATION METHOD OF FASTENING SYSTEM BASED ON RAIL RESPONSE UNDER PULSE EXCITATION
Bo-wen HOU, Jia-jing LI, Liang GAO, Xiao-pei CAI
2021, 38(2): 122-133. doi: 10.6052/j.issn.1000-4750.2020.04.0210
Abstract:
Focusing on the failure detection of high-speed railway ballastless track fastening system, it proposed a failure identification algorithm based on the rail vibration response under pulse excitation. The failure of the fastening system was simulated by removing the elastic bar manually. The time-domain vibration responses of the rail with both functional and failed fasteners under pulse excitation were measured with the 1∶1 full-scale model in the laboratory. By carrying out the Fast Fourier transform and the octave analysis, the vibration acceleration levels of the rail under functioning and failed fastener conditions were obtained. By adopting the rail acceleration level difference and the characteristic frequency band percentage with and without failed fasteners as the evaluation indicator, the influence of frequency band division, vibration acceleration difference threshold and characteristic frequency band percentage threshold on the identification accuracy were further studied. The fastening system failure identification algorithm was proposed and the sensitive parameters for the failure of fasteners were selected. Together with the laboratory test results and field tests in Beijing-Shenyang high-speed railway, the effectiveness of the algorithm was verified. On this basis, the influence of the fixing position of the measuring accelerometer, the existence of non-target failure fasteners in the near-by span, and the human operation error on the recognition accuracy were further studied. The results show that the accuracy of the fastener failure identification algorithm proposed in this paper can reach 100% under the condition of one-sided failure of the fastener. When fasteners' failures on near-by span exist, the detection accuracy rate of the target fastener failure is also 100%. When the measuring accelerometers are located on the rail web and rail bottom where the target fastener is, the detection accuracy rate is above 95%. By taking the center line of the fastener as the reference, the detection accuracy rate is above 95% when the deviation between the excitation position and the reference position is less than 6 cm, or the deviation between the accelerometer fixing position and the reference position is less than 6 cm along the line operation direction.
EXPERIMENTAL STUDY ON THE PROPERTIES OF A NEW ROTATION-MAGNIFIED VISCOELASTIC DAMPER
Hong-nan LI, Yuan-long LI, Zhou HUANG, Xing FU
2021, 38(2): 134-145. 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.
THREE-DIMENSIONAL SEISMIC RESILIENCE QUANTIFICATION FRAMEWORK FOR THE URBAN GAS NETWORK
Cheng-cai ZONG, Kun JI, Rui-zhi WEN, Xi-rong BI, Xiao-rui ZHANG
2021, 38(2): 146-156. doi: 10.6052/j.issn.1000-4750.2020.04.0219
Abstract:
In order to comprehensively evaluate the seismic resilience of the urban gas network, this paper proposes a quantitative assessment framework in three dimensions: technical, organizational and social dimensions, which accounts for the uncertainties in ground motion input and includes network connectivity performance assessment and repair process. The connectivity of the gas network is calculated based on Monte Carlo simulation which uses the ground motion prediction equation (GMPE) as input. Then the real-time repair process of the gas network is obtained by randomly allocating the repair resource under each simulated damage condition. The performance recovery curve in three dimensions is given, and the corresponding indices such as post-earthquake performance, repair rate and resilience are calculated. Repeating the above steps N times, the expectation of the above indicators and the probability distribution of the recovery time for different performance levels are obtained. Taking a northern city of China as an example, the whole procedure is applied to assess the seismic resilience of a gas network system. The results show that the post-earthquake performance of the gas network in three dimensions roughly follows the normal distribution, and the performance recovery time for 75%, 90%, and 100% original performance levels in organizational and social dimensions roughly follows log-normal distribution. Neglecting the connectivity of the pipe network, the resilience results in technical dimension underestimate the actual damage level, and the recovery curve is close to linear-type. On the other hand, the results in organizational and social dimensions are close to the reality, and are greatly affected by repair order and resource allocation. The proposed seismic resilience quantification procedure comprehensively considers the uncertainty of various aspects after the earthquake, which can provide a reference framework for probabilistic resilience assessment of gas networks, and could be expanded to other lifeline network systems.
PARAMETER OPTIMIZATION OF COVARIANCE-DRIVEN STOCHASTIC SUBSPACE IDENTIFICATION METHOD BASED ON SENSITIVITY ANALYSIS
Wei LIU, Na YANG, Fan BAI, Peng CHANG
2021, 38(2): 157-167, 178. 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.
STRESS-STRAIN RELATIONSHIP OF SHORT CIRCULAR TIMBER COLUMNS STRENGTHENED BY A COMPOSITE METHOD IN AXIAL COMPRESSION
Si-ha A, Chang-dong ZHOU, Li-gan YANG
2021, 38(2): 168-178. doi: 10.6052/j.issn.1000-4750.2020.04.0231
Abstract:
The composite reinforcement method with near surface mounted steel bars and wrapped CFRP (carbon fiber reinforced polymer) strips can effectively improve the strength and deformation capacity of historical timber columns. To establish the stress-strain model of strengthened timber columns, 42 timber columns strengthened by the composite reinforcement method were tested under axial compression, taking the number of wrapped CFRP strips and near surface mounted steel bars as the experimental factors. The test results indicated that the composite reinforcement method can improve the ductility and compressive strength of the timber columns. Because of the inevitable initial defects of timber, the failure of timber columns mainly occurred in the area where the initial defects concentrated. The load-strain curves of timber, CFRP strips and steel bars were consistent at the same measurement point, which showed that there were good bond properties between the timber and CFRP strips or steel bars, so that they can deform and work together. According to the existing researches, the formulas of peak stress and peak strain of the strengthened timber columns were given by fitting the experimental data. Trilinear and polynomial constitutive models of strengthened timber columns under axial compression were proposed. Considering the discreteness of timber material, the theoretical model curves were consistent with the test curves. It verified the reliability of the obtained stress-strain models.
INVESTIGATION ON THE INFLUENCE OF WELDING PROCESSESON MECHANICAL PROPERTIES OF STAINLESS STEELFILLET WELD CONNECTIONS
Zhi-lin LI, Lu YANG, Yao CUI, Fei YIN, Yao-hua LIANG
2021, 38(2): 179-186, 210. doi: 10.6052/j.issn.1000-4750.2020.04.0232
Abstract:
In order to study the effect of different welding processes on mechanical properties of stainless steel fillet weld connections, the monotonic tensile tests of 12 austenitic and 12 duplex stainless steel specimens were carried out. The results show that the failure surface of specimens made by TIG (Tungsten Inert Gas Welding) is quite different from that of specimens made by SMAW (Shielded Metal Arc Welding), and the latter is much smoother. Besides, the true failure angle of the transverse fillet weld connections is not the theoretical value of 45° due to the influence of the complex stress. For austenitic stainless steel, the strength ratios of specimens made by TIG to SMAW are 1.03 (for transverse fillet weld connections) and 1.13 (for longitudinal fillet weld connections), and the ratios of relative deformation are 1.46 and 1.11. For duplex stainless steel, the strength ratios are 1.12 and 1.04, meanwhile the relative deformation ratios are 1.66 and 1.45. The connections made by TIG show better mechanical properties. For the two stainless steel, the strengths of transverse fillet weld connections are much better than those of the longitudinal fillet weld connections, so it is suggested that the influence of the increase of the strength of transverse fillet weld connections be taken into account in the compilation or revision of the related specifications.
NUMERICAL INVESTIGATION ON RANDOM TRAFFIC-BRIDGE COUPLED VIBRATION USING CELLULAR AUTOMATON-BASED MICROSCOPIC SIMULATION
Jun-yong ZHOU, Jian-xu SU, Sa QI
2021, 38(2): 187-197. doi: 10.6052/j.issn.1000-4750.2020.04.0239
Abstract:
A numerical delicacy method for random traffic-bridge coupled vibration analysis is proposed. Incorporating the classical vehicle-bridge interaction theory, it is a newly established multi-axle single-cell cellular automaton (MSCA)-based microscopic traffic load simulation approach. The utilized equations and models in the classical vehicle-bridge interaction theory are introduced. The concepts and routes of the realization of MSCA for vehicle-bridge coupled dynamic analysis are proposed, and the relevant code program is developed. An engineering example with measured time-history dynamic deflections is utilized to verify the accuracy of the vehicle-bridge interaction analysis by MSCA. MSCA is used to analyze the dynamic load effects of a cable-stayed bridge under the excitation of random traffic loads, to demonstrate the reliability of the proposed approach. The results indicate that MSCA has good accuracy in vehicle-bridge coupling analysis. The maximum error in the engineering example is 11.6%. The static and dynamic time-history deflections of the cable-stayed bridge under random traffic loads show that they have good consistency, and the difference between them becomes more significant along with the increase in the pavement roughness grade. These prove the reliability of the proposed model and method in the random traffic-bridge coupled vibration analysis. This study forwards MSCA's ability to analyze various types of dynamic load effects of bridges under the excitation of random traffic flow, which provides more applications of MSCA in monitoring and evaluation of real bridges.
TIME-DEPENDENT BEHAVIOR OF MULTI-SPAN CONTINUOUS STEEL-RAC COMPOSITE SLABS CONSIDERING THE LOADING DISTRIBUTION EFFECTS
Qing-he WANG, Yong-ze LIANG, Huan ZHANG, Yi-chao ZHANG, Qing-xin REN
2021, 38(2): 198-210. doi: 10.6052/j.issn.1000-4750.2020.04.0242
Abstract:
To quantify the impact of recycled coarse aggregate (RCA) incorporation on the time-dependent behavior of multi-span continuous steel-RAC composite slabs, nonlinear thermal-mechanical finite element (FE) models were proposed based on ABAQUS, considering the combined effects of non-uniform shrinkage, non-uniform creep and concrete cracking. The proposed models were benchmarked against the long-term data from 18 full-scale composite slabs. The feasibility of current design procedures was also evaluated. Using the verified FE models, the influence of the RCA replacement ratio (r) on the time-dependent distributions was quantified. The results show that by specifying the temperature variation to simulate the non-uniform shrinkage and creep, the proposed FE models could well predict the time-dependent behavior of steel-RAC composite slabs based on the age-adjusted effective modulus method. The maximum error between the measured and calculated mid-span deflections was 20.3%. The time-dependent behavior of the composite slabs was remarkably influenced by the RAC incorporation. The influence magnitudes were similar for the composite slabs under different loading distributions. Under uniformly distributed loading, 22.1% and 45.0% increments in the mid-span deflection and 5.3% and 10.8% increments in the hogging moment were obtained for r ratios of 50% and 100%, respectively. The influence of the loading distribution on the mid-span deflection and hogging moment was within 10%.
DYNAMIC RESPONSE ANALYSIS OF SUBMERGED FLOATING TUNNELS TO COUPLED WAVE-SEISMIC ACTION
Gang LUO, Yu-long ZHANG, Shao-kang PAN, Yi REN
2021, 38(2): 211-220, 231. doi: 10.6052/j.issn.1000-4750.2020.05.0268
Abstract:
To investigate the dynamic response of submerged floating tunnels (SFT) subject to the coupled action of earthquakes and waves, the wave load and seismic load were calculated by the Stokes wave theory and trigonometric series method, and the tube-tether model of SFT under the wave-seismic action was established based on the D’ Alembert principle. Combined with a planned SFT project, the load parameters and the response of the SFT system were analyzed. The results show that the tube-tether model was in good agreement with the tether vibration model under the coupled action of earthquakes and waves. However, the latter could not consider the parameter vibration of the system. The earthquake direction had a significant influence on the response of the SFT system. Under the same peak ground acceleration (PGA), the response of the system to the horizontal earthquake action was greater than that to the vertical earthquake action, and the response of the tethers was greater than that of the tube. There was a certain relationship between the PGA and the response of the system. The maximum displacement of the system increased linearly with the increase of the PGA. Based on the seismic load, the response of the system was increased by considering the wave load. With the increase of the wave height and wavelength, the response of the system increased linearly. Waves of small periods (less than 10 s) were easy to cause resonance of the system.
HYBRID TESTS ON THE SEISMIC BEHAVIOR OF HIGH-STRENGTH STEEL COMPOSITE Y-ECCENTRICALLY BRACED FRAMES
Teng-fei LI, Ming-zhou SU, Yan SUI, Kun ZHAO, Qi ZHANG, Lu-lu WANG
2021, 38(2): 221-231. doi: 10.6052/j.issn.1000-4750.2020.05.0271
Abstract:
As a novel structural system, the high-strength steel composite Y-eccentrically braced frame (Y-HSS-EBF) combines the advantages of the high strength of high-strength steel and the large energy dissipation capacity of the eccentrically braced frame. To investigate the seismic performance of Y-HSS-EBF structures, a series of substructure hybrid tests were conducted with a three-story three-span Y-HSS-EBF as the prototype. The bottom-story steel frame with Y-eccentric brace of the prototype was taken as the experimental substructure, and the rest of the prototype was taken as the numerical substructure in OpenSees to establish the substructure hybrid test model. According to the hybrid test results, the validity of the hybrid test model was verified, and the main seismic performance indexes of the hybrid test model were analyzed. The results show that during different earthquakes, the test results of the hybrid test model were in good agreement with the numerical simulation results of the global structure. During a seldom earthquake, the plastic deformation of the experimental substructure mainly occurred at the web of the link, whereas the beam-columns and braces of the experimental substructure remained in the elastic domain, which conformed to the concept of multi-aspect seismic fortification.
AN ANALYSIS METHOD FOR THE HORIZONTAL BEARING CAPACITY OF PILE FOUNDATION BASED ON THE CAVITY EXPANSION THEORY
Xiao-ling ZHANG, Jing-jiu ZHAO, Yi-long SUN, Cheng-shun XU
2021, 38(2): 232-241, 256. doi: 10.6052/j.issn.1000-4750.2020.04.0278
Abstract:
In recent years, the urban infrastructure construction in China has been constantly developing. The pile foundation is a common form of foundation in infrastructure construction. The calculation of the capacity of a pile foundation is an important subject in the foundation design. Based on the Vesic expansion theory, the actual stress state of the soil on the pile side under horizontal loading is presented. A calculation method of the soil resistance on the pile side in the form of stress increment is derived, and the mechanical method of the horizontal capacity of the pile foundation considering the pile-soil interaction is proposed. The corresponding analysis program was compiled based on MATLAB software and the validity of the proposed calculation method was verified by a comparison with experimental results. The effects of the load and the pile diameter on the mechanical behavior of the pile-soil interaction system was analyzed based on the proposed mechanical model for the horizontal bearing capacity of pile foundation.
MECHANICAL ENGINEERING
THE LOAD CHARACTERISTICS OF THE BOGIEFRAME OF HIGH-SPEED EMUS
Zun-song REN, Jie CAO, Yu-yi LI, Bin-jie WANG, Xue WEI
2021, 38(2): 242-256. 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.