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  • 工程力学
    Engineering Mechanics
    (月刊,1984年创刊)
    主管单位:中国科学技术协会
    主办单位:中国力学学会
    主  编:陆新征
    编辑出版:《工程力学》编辑部
    ISSN 1000-4750 CN 11-2595/O3
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AN EXPLICIT TIME-DOMAIN INTEGRATION SCHEME FOR SOLVING EQUATIONS OF MOTION IN STRUCTURAL DYNAMICS BASED ON A TRUNCATED TAYLOR EXPANSION OF ACCELERATION
WEN Ying, TAO Rui
Engineering Mechanics    2018, 35 (11): 26-34.   DOI: 10.6052/j.issn.1000-4750.2017.08.0661
Abstract234)      PDF(pc) (553KB)(92)       Save
The aim of this paper is to present a novel time integration algorithm with a high level of balance among applicability and reliability and computational efficiency for the dynamic analysis of structures. A formula for approximating acceleration with a forth-order degree of accuracy has been developed, based on the Taylor expansion approach. In applying the Taylor expansion method, a truncation parameter is defined to consider the contributions of high-order terms upon the accuracy of predicted results. Through an integration of the obtained acceleration and considering the dynamic equilibrium condition at the initial state of a typical time step, a single-step equation for computing displacement and velocity at the end state is correspondingly developed. A revised acceleration can be obtained from the calculated displacement and velocity through the equations of motion at the end state. In this regard, as compared with the multiple-step integration scheme, it is not required for the present method to temporarily record the state variables of previous steps. From the results of stability analysis, the maximum step length to period ratio within which the obtained responses remain bounded has been increased by 40% in comparison to the central difference method. By carrying out a series of numerical analyses for the purpose of demonstration, it is generally observed from the natural and forced vibration investigations for linear systems that the computational amplitude decay and period elongation were less than 5% even if the ratio between the time step length and system inherent period/load period mounts to 0.2. However, to reduce the effects of amplitude decay and period distortion for the time integration of nonlinear systems, the magnitude of the above mentioned ratio should generally be restricted below 0.1.
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RESEARCH PROGRESS ON DURABILITY OF STRESSED CONCRETE UNDER ENVIRONMENTAL ACTIONS
LUO Da-ming, NIU Di-tao, SU Li
Engineering Mechanics    2019, 36 (1): 1-14,43.   DOI: 10.6052/j.issn.1000-4750.2018.08.ST11
Abstract172)      PDF(pc) (853KB)(162)       Save
Field concrete structures are often working under the coupling effect of mechanical loads and environmental actions. The loads acting on a structure may cause the change of the physical properties of the concrete, and then influence the durability of a concrete structure. The research results of concrete durability have a certain deviation when neglecting the effect of loading. Recent studies on the durability of stressed concrete under the environmental actions are summarized, and the research results of concrete impermeability, concrete neutralization, ion erosion, and freezing-thawing are emphatically introduced, and the prospect of concrete durability research is put forward.
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APPLICATION OF GRAPHICS PROCESSING UNIT BASED ALGORITHM IN NONLINEAR RESPONSE ANALYSIS TO COMPLEX HIGH-RISE BUILDING STRUCTURES
LI Hong-yu, TENG Jun, LI Zuo-hua, ZHANG Lu
Engineering Mechanics    2018, 35 (11): 79-85,91.   DOI: 10.6052/j.issn.1000-4750.2017.08.0656
Abstract142)      PDF(pc) (1380KB)(57)       Save
Currently, most of the commercial finite element (FE) softwares are based on the CPU architectures, which causes massively time consuming, low efficiency, and rigor of requirements of hardware during analyzing the nonlinear response of high-rise structures. Meanwhile, the emergence of GPU based algorithms presents significantly superior performance in floating-point operation and parallel computation due to its special configuration. Therefore, GPU based algorithms can provide a feasible solution for the perplexing issues of nonlinear computation of high-rise structures. Our work is to develop a parallel FE algorithm by introducing GPU and to construct a corresponding heterogeneous platform, ultimately leading to speed up the computation. Firstly, the mapping between the degrees of freedom (DOFs) of a refined model and the threads of GPU is formed. Then, the implicit integration algorithm for solving the dynamic response will be parallelized in threads; meanwhile, the strategies of storage are optimized in terms of element-by-element scale and the demand of memory was reduced while solving the equations. All of the GPU based algorithms have been validated by comparing with the experimental results of a shaking table. Moreover, the validated algorithms are extended to apply to the analysis of the elastic-plastic seismic response of a practical high-rise reinforced concrete frame tube structure. The results show that the proposed algorithm can not only guarantee the accuracy but also improve efficiency dramatically in the procedure of structural nonlinear response analyses.
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REVIEW ON ASEISMIC BEHAVIOR OF PRECAST PIERS: NEW MATERIAL, NEW CONCEPT, AND NEW APPLICATION
WANG Jing-quan, WANG Zhen, GAO Yu-feng, ZHU Jun-zheng
Engineering Mechanics    2019, 36 (3): 1-23.   DOI: 10.6052/j.issn.1000-4750.2018.10.ST03
Abstract134)      PDF(pc) (17514KB)(163)       Save
With accelerated bridge construction, the precast pier system has been widely applied in non and low seismic zone, but limited in moderate and high seismic zone by lack of knowledge about its aseismic performance. This paper classifies precast pier systems into two types: emulative precast piers and nonemulative precast piers, based on their aseismic performance. On one hand, the emulative precast pier is further categorized into grouted sleeve connection, grouted steel corrugated duct connection, pocket connection, socket connection, and cast-in-place wet joint connection by the type of connection. On the other hand, the nonemulative precast pier is further categorized into two types based on whether special energy dissipation device is used or not. The research about aseismic performance and typical engineering application are systematically reviewed for each of these categories. Three high performance materials, including Ultra high-performance concrete, fiber reinforced polymer and shape memory alloy, are reported for the research status of their application in the precast pier system to improve their aseismic performance. The proper way is pointed out to apply the three high performance materials in the precast pier system. Two methods are summarized to apply the new concept of earthquake resilience in the precast pier system, which are an external replaceable energy dissipation device and an internal energy dissipation bar with mechanical connection. The research review is conduct for the aseismic performance of precast piers using the two-connection ways. Based on the summarization of the aseismic performance of a precast pier system, the precast pier system is proposed to apply in the four types of bridges, including higher aseismic requirement, larger stiffness requirement, longer service life requirement, and stricter environmental protection requirement. The new issues caused by the new application fields are pointed out.
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SELECTION AND SCALING OF REAL ACCELEROGRAMS AS INPUT TO TIME-HISTORY ANALYSIS OF STRUCTURES: A STATE-OF-THE-ART REVIEW
ZHANG Rui, LI Hong-nan, WANG Dong-sheng, CHENG Hu
Engineering Mechanics    2019, 36 (2): 1-16.   DOI: 10.6052/j.issn.1000-4750.2018.01.0037
Abstract128)      PDF(pc) (563KB)(118)       Save
This paper reviews various selection methods of real records for time-history analysis of structures in recent years. The selections of criteria and required numbers of records are summarized and classified. Specific earthquake scenarios, such as the magnitude, distance and site classification, are generally considered in the first step. Then, the target spectrum and other intensity measures (IMs) of the ground motions are taken into consideration. Presently, dozens of IMs have been developed, but there is no agreement on the relationship between IMs and structural responses, as well as the advantages of IMs in the selection of records. The method that selects and scales real ground motion records according to target spectra is the most popular. There are many kinds of target spectra, among which the design spectra in codes are the most popular because of the easy implementation in practice. The Conditional Mean Spectrum (CMS) is more accurate. How to introduce CMS into the Chinese code is worth of further studying. The selection of deviation parameters and scaling methods for estimating the mean responses of a structure should be taken in aspect of getting the optimum selection in real records that can match the spectral shape. With the development of the performance-based seismic design and the gradually perfection of Probabilistic Seismic Hazard Analysis (PSHA), estimations of structural responses have been developed from mean values to probability distributions. The selection criteria and required number of records for estimations of the probability distributions of structural responses need to be further studied.
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A REVIEW OF ADVANCES IN SEISMIC FRAGILITY RESEARCH ON BRIDGE STRUCTURES
LI Hong-nan, CHENG Hu, WANG Dong-sheng
Engineering Mechanics    2018, 35 (9): 1-16.   DOI: 10.6052/j.issn.1000-4750.2017.04.0280
Abstract111)      PDF(pc) (502KB)(110)       Save
In light of the proposed formal probabilistic framework for the Performance-Based Earthquake Engineering (PBEE), it is required to assess the seismic performance of bridge structures on the basis of probability. Seismic fragility analysis, combining the seismic response analysis and structural capacity analysis, has attracted wide attention. To improve the current level of research on seismic fragility analysis for bridge structures in China, firstly, the historic stage and development process of fragility analysis were reviewed, and studies on the seismic fragility analysis for bridge structures were summarized. Subsequently, the basic theory and research approaches of seismic fragility analysis were introduced in detail, i.e., the empirical analysis approach, theoretical analysis approach and the combined empirical-theoretical analysis approach. In addition, the shortcomings of current studies were analyzed. Furthermore, the application prospective and implications for future studies on seismic fragility analysis of bridge structures were suggested. The results indicate that various problems are needed to investigate as vital topics in the area of seismic fragility analysis for bridge structures, i.e., the consideration of uncertainties in environment, ground motions, site conditions and structural parameters, the selection of suitable ground motion intensity measures (IMs) and engineering demand parameters (EDPs), the correlation between components and their contributions to the seismic performance of bridge system, etc. More complicated issues were also identified involving the studies on site liquefaction, special fields and large-span bridges, which are significant for the development of the bridge structural seismic engineering.
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MAIN CONTENTS OF THE STANDARD FOR WIND LOADS ON ROOF STRUCTURES
YANG Qing-shan, TIAN Yu-ji, CHEN Bo, HUANG Guo-qing
Engineering Mechanics    2018, 35 (7): 1-6.   DOI: 10.6052/j.issn.1000-4750.2017.06.ST03
Abstract103)      PDF(pc) (536KB)(60)       Save
This paper comprehensively introduces the main contents of the Standard for Wind Loads on Roof Structures. Regarding the wind-induced response analyses and wind-resisting design for main load-resisting structures of roofs, the nominal values of wind loads on the main structures are expressed by the sum of mean wind pressures and equivalent static wind pressures. The equivalent static wind pressures correspond to extreme responses induced by fluctuating wind loads, which can be obtained by the proposed method for single or multiple targets. On these bases, the design figures and tables of shape factors for the mean wind pressures and equivalent pressure factors for fluctuating wind responses considering multiple targets are presented for different types of roof structures. These include plane truss structures, beam string structures, grid truss structures, spherical/cylindrical shell structures, saddle structures and overhanging structures. The extreme wind pressure coefficients are estimated based on specified methods, which are applicable to different cases of short/long wind pressure samples, to consequently determine the nominal values of wind loads on cladding and components. Furthermore, the design figures and tables of corresponding extreme wind pressure coefficients are proposed for mono-slope, gable, hip roofs of low-rise buildings; roofs of middle-/high-rise buildings; open roofs and overhanging canopies. Generally, in the current Standard for Wind Loads on Roof Structures, the Chinese wind-resisting design specifications for roof structures have been improved by introducing the concepts of equivalent pressure factors for the wind-induced fluctuating responses of main load-resisting structures and the extreme wind pressure coefficients of cladding and components.
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A 4-NODE ISOPARAMETRIC ELEMENT FORMULATED WITH GENERALIZED CONFORMING CONDITIONS
CHEN Xiao-ming, LI Yun-gui
Engineering Mechanics    2018, 35 (12): 1-6,14.   DOI: 10.6052/j.issn.1000-4750.2017.09.0706
Abstract98)      PDF(pc) (409KB)(83)       Save
By using optimized generalized conforming conditions to formulate the plane 4-node element Q4, it is proved that the generalized conforming theory can be expanded to the most fundamental isoparametric elements. Based on the second-order additional displacement field of Q6 and QM6, a new form of additional displacement field was overlaid on Q4 to develop a new element GQM6, which is still second-order and formulated with generalized conforming theory. The numerical results show that the generalized conforming conditions can present more relaxed constraints at element sides than numerical integrals used in QM6, thus the new element GQM6 can exhibit better properties especially on the resistances of mesh distortion. The research shows that it i's still valuable to combine the generalized conforming theory with those traditional finite elements deeply.
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CONTRASTIVE ANALYSIS ON ASEISMIC PERFORMANCES BETWEEN MONOLITHIC PRECAST CONCRETE AND CAST-IN-PLACE SHEAR WALL STRUCTURE
BAI Guo-liang, QIN Chao-gang, XU Ya-zhou, SU Ning-fen, WU Tao, SUN Yu-zhe
Engineering Mechanics    2019, 36 (2): 36-44.   DOI: 10.6052/j.issn.1000-4750.2018.10.ST07
Abstract92)      PDF(pc) (6917KB)(79)       Save
To study the aseismic behavior of a monolithic precast concrete structure (MPCS), two 1:5 scale models of 12-storey monolithic precast concrete and cast-in-place shear wall structures (CIPS) made under the same conditions were tested by a shaking table. The crack pattern, failure mechanism, natural frequency, vibration mode and damping ratio, storey shear, overturning moment, inter-storey drift, maximum interlayer displacement angle, and ductility coefficient were analyzed contrastively. For the initial damage of the connection in a monolithic precast concrete structure, the natural frequency decreased obviously after the first earthquake excitation. While the vibration modes and damping ratios were similar. In the elastic stage, the storey shear, overturning moment, inter-storey drift, and maximum interlayer displacement angle changed along the increasing of the PGA of input seismic waves, and the values were similar too. In the plastic stage, the cracks and the distribution of the two model structures were different. As the differences of damage mechanism and crack distribution, the natural frequency and maximum interlayer displacement angle of cast-in-place structure were greater than that of the monolithic precast concrete structure. The aseismic parameters of the model structures could conform to the 3-level design requirement for the fortification against an earthquake.
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SENSITIVITY ANALYSIS OF STRUCTURAL TOPOLOGY DESIGN VARIABLES UNDER HARMONIC EXCITATIONS BASED ON GENERALIZED MODAL TRUNCATION AUGMENTATION METHOD
ZHOU Da-wei, CHEN Biao-song, LI Yun-peng, ZHANG Sheng
Engineering Mechanics    2018, 35 (11): 1-7,16.   DOI: 10.6052/j.issn.1000-4750.2017.08.0618
Abstract91)      PDF(pc) (593KB)(79)       Save
Based on the variable density method for structural topology optimization, the analytical sensitivity formulation of the frequency response displacement amplitude of structures under harmonic excitations is proposed using the adjoint method. The generalized modal truncation augmentation method is introduced to obtain high accuracy without high computational cost in contrast to the poor accuracy of the traditional modal displacement method in sensitivity computation. Numerical examples are presented to compare the proposed method with the global finite difference method and other computation methods. The computational results demonstrate the effectiveness of the proposed method in computing accurate sensitivities with high efficiency under different excitation frequencies and different densities of finite element meshes.
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STRUCTURAL SOLUTIONS OF LARGE-SCALE ENGINEERING PROJECTS BASED ON ENGINEERING MECHANICS
LÜ Hai-shuang, ZHOU Bei-lei, CAO Qian, WANG Yang
Engineering Mechanics    2019, 36 (3): 40-52.   DOI: 10.6052/j.issn.1000-4750.2018.08.ST10
Abstract91)      PDF(pc) (11893KB)(65)       Save
In recent years, lots of large-scale, complex, and “beyond-limit” building structures have been constructed both at home and abroad, most of which are irregular structures. In designing practice, we often encounter the problems out of the scope of regulations or the problems not specified in pertinent codes. The existing standards cannot be applied to these problems, and they are also lack of clear goals, evidence and methods for the problems. Under these circumstances, aiming at a series of large engineering projects of (ARUP) engineering consulting company in China, this paper introduces the solutions of the problems by engineering mechanics.
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FINITE ELEMENT ANALYSIS ON ASEISMIC BEHAVIOR OF HIGH-STRENGTH STEEL BEAM-TO-COLUMN CONNECTIONS IN STEEL FRAMES BASED ON MICROMECHANICS OF FRACTURE
WANG Lei, BAN Hui-yong, SHI Yong-jiu, WANG Yuan-qing
Engineering Mechanics    2018, 35 (11): 68-78.   DOI: 10.6052/j.issn.1000-4750.2017.08.0608
Abstract88)      PDF(pc) (4626KB)(50)       Save
The fracture resistance of beam-to-column connections may affect the overall aseismic performance of steel frames directly, and it is essential for ensuring the design principle in terms of strong connections and weak members. In order to study the fracture behavior of high-strength (HS) steel frame beam-to-column connections subjected to cyclic loading, this paper uses cyclic void growth model (CVGM) to simulate the fracture of the connections. Through the finite element (FE) software ABAQUS, a 3D FE model of beam-to-column connection is developed, with the CVGM being embedded by using the USDFLD program. 21 specimens fabricated from different grades of steel with various configuration details are analyzed through the model and compared with the test results. It is indicated that load-deformation hysteresis curves, bearing capacities, and number of cycles before fracture commencing are in a good agreement with the tests. The results show that:the CVGM has good adequacy for simulating the extremely low-cycle fatigue fracture of the beam-to-column connections under cyclic loading, and it is suitable for different cyclic loading conditions and steel grades. A basic methodology and a valuable reference will be thusly provided for aseismic performance evaluation and anti-fracture design of the HS steel frame beam-to-column connections.
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ADAPTIVE FINITE ELEMENT-DISCRETE ELEMENT ALGORITHM, SOFTWARE ELFEN AND APPLICATION IN STIMULATED RESERVOIR VOLUME OF SHALE
WANG Yong-liang, JU Yang, CHEN Jia-liang, YANG Yong-ming, Li C F
Engineering Mechanics    2018, 35 (9): 17-25,36.   DOI: 10.6052/j.issn.1000-4750.2017.06.0421
Abstract82)      PDF(pc) (18352KB)(42)       Save
The adaptive algorithm of finite element (FE)-discrete element (DE) for fluidic-mechanical-fracture coupling analysis was introduced in this study. The novel computational software ELFEN based on this method was introduced and applied in a three-dimensional mechanism analysis of a staged stimulated reservoir volume of shale. The superconvergent patch recovery (SPR) method was used to obtain the superconvergent FE stress solutions, by which the error of conventional FE stress solutions was estimated. The adaptive local remesh for domains of crack tips was expected to be characterized by efficient analysis strategy and application for more accurate stress solutions and reliable crack propagation path. Numerical examples were given to show the effectivity, reliability and practicability of the numerical algorithm and the software for staged stimulated reservoir volume of single-and multi-horizontal wells with fluidic-mechanical-fracture coupling.
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ELASTIC-PLASTIC BUCKLING BEHAVIOR OF STEEL MATERIAL UNDER COMPLEX CYCLIC LOADING PATHS
WANG Yu-hang, YU Jie, WU Qiang
Engineering Mechanics    2018, 35 (7): 24-38.   DOI: 10.6052/j.issn.1000-4750.2017.07.0525
Abstract81)      PDF(pc) (4888KB)(67)       Save
After compressive yielding, local buckling will occur on steel tubes in concrete-filled steel tubular column under complex seismic loading. In a bar-system finite element model (FE model), the seismic response of steel structure members cannot be effectively simulated by steel constitutive models without considering the influence of buckling. To study the buckling behavior of steel under complex cyclic loading, 30 steel specimens with strength grades Q235 and LYP160 were designed, and various complex cyclic loading paths were adopted to obtain the stress-strain hysteretic relation and elastic-plastic buckling behavior of steel under various complex cyclic loading. On the basis of three steel cyclic constitutive models in the literature:Légeron Model, GA Model and DM Model, the predicting results were compared and analyzed with the test results. It can be seen that Légeron Model fails to stimulate the buckling effect of post-compressive yielding steel, and in GA Model, the stress-strain properties of compressive buckling agree well with the experimental results. The unloading stiffness of tension and compression calculated by the DM Model agrees well with the test results.
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ADVANCES IN RESEARCHES ON STOCHASTIC DAMAGE MODELS OF CONCRETE
YU Zhi-wu, SHAN Zhi
Engineering Mechanics    2018, 35 (8): 1-8,13.   DOI: 10.6052/j.issn.1000-4750.2017.05.ST13
Abstract81)      PDF(pc) (491KB)(72)       Save
The studies on the micro damage mechanism and stochastic damage model are reviewed. Furthermore, the advances in researches on the stochastic damage model of concrete by the team of authors are introduced as well. The micro damage mechanism analysis was obtained by taking into account mode-Ⅱ microcracks, the stochastic damage model (the fiber bundle-irreversible chain model) was proposed and verified by experiments, and an X-ray computed tomography method for the damage quantification of concrete under compression was developed. Additionally, some related conclusions are drawn.
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INTENSITY MEASURES FOR SEISMICALLY ISOLATED TALL BUILDINGS
YANG Can-tian, XIE Lin-lin, LI Ai-qun, ZENG De-min, LIU Li-de
Engineering Mechanics    2018, 35 (8): 21-29.   DOI: 10.6052/j.issn.1000-4750.2017.07.0531
Abstract81)      PDF(pc) (702KB)(44)       Save
Research on the seismic resilient structures has become a critical issue in earthquake engineering recently. The seismic isolation technology is an important method to achieve seismic resilience for tall buildings located in high seismic regions. Critical engineering demand parameters (EDPs), including maximum inter-story drift ratio (MIDR), maximum roof displacement (MRD), maximum floor acceleration (MFA) and maximum bearing displacement (MBD), are the essential indexes for the resilience assessment of seismically isolated tall buildings. To predict the abovementioned seismic responses and evaluate the seismic resilience of a seismically isolated tall building, an impartial intensity measure (IM) is required. Various factors, including the structural systems, structural heights, seismically isolated schemes, yield ratio of the isolation system and types of ground motions, are considered to yield impartial intensity measures for seismically isolated tall buildings based on 4 real engineering practices. The correlation between 25 IMs and the critical EDPs are evaluated. The IMs that has the best correlation with each EDP are identified. The IM which achieves the balance between the correlations with 4 EDPs is further identified. In addition, the influences of various factors are investigated. The research outcome will assist in providing a useful reference for resilience-based seismic design and evaluation methods of seismically isolated tall buildings.
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SPARSE PARTIAL LEAST SQUARES REGRESSION-POLYNOMIAL CHAOS EXPANSION METAMODELING METHOD
ZHAO Wei, BU Ling-ze, WANG Wei
Engineering Mechanics    2018, 35 (9): 44-53.   DOI: 10.6052/j.issn.1000-4750.2017.08.0644
Abstract77)      PDF(pc) (407KB)(52)       Save
To circumvent the curse of dimensionality and multicollinearity problems of traditional polynomial chaos expansion approach when analyzing global sensitivity and structural reliability of high-dimensional models, this paper proposes a sparse partial least squares regression-polynomial chaos expansion metamodeling method. Firstly, an initial estimation of polynomial chaos expansion coefficients is obtained with the partial least squares regression. Secondly, according to the principle of maximum sparsity under the allowance of regression error threshold, polynomials which have strong correlation with the structural response are adaptively retained with the penalized matrix decomposition scheme. Next, an updated estimation of the polynomial chaos expansion coefficients is obtained with the partial least squares regression. Sobol sensitivity indices are obtained with a simple post-processing of the expansion coefficients. Finally, the metamodel is greatly simplified by regressing with important inputs, leading to accurate estimations of the failure probability without additional computational cost. The results show that with acceptable accuracies, the new method overperforms the traditional counterpart in terms of computational efficiency when solving high-dimensional global sensitivity and structural reliability analysis problems.
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MESO-SCALE SIMULATIONS ON FLEXURAL FAILURE AND SIZE EFFECT OF REINFORCED CONCRETE BEAMS
JIN Liu, SU Xiao, DU Xiu-li
Engineering Mechanics    2018, 35 (10): 27-36.   DOI: 10.6052/j.issn.1000-4750.2017.06.0436
Abstract77)      PDF(pc) (1663KB)(81)       Save
The sources of size effect on RC members are the heterogeneity of concrete material and the interaction between steel and concrete. From the view of microcosmic, a three-dimensional micromechanical model for reinforced concrete beams was set up. In the model, the concrete heterogeneity was considered, and the interactions between steel and concrete was described by a nonlinear spring element. Base on the well agreement between simulation results and experimental results, the failure behavior of large beams was studied, meanwhile, the change of failure pattern and flexural strength of different size beams under monotonic and cyclic loading were analyzed. The simulation results show that:1) in the working condition of this article, the flexural of RC cantilever beams have the size effect, and the flexural strength decreases with the increase of depth of the beam; 2) under cyclic loading, the bending beam is brittle because of the fatigue of the bonding performance between concrete and steel; 3) compared to monotonic loading, the cantilever beam damage is more brittle and the size effect of nominal flexural strength is more obvious under a cyclic loading condition.
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RESEARCH ON ASEISMIC PERFORMANCE OF PRC COUPLING BEAM-HYBRID COUPLED SHEAR WALL SYSTEM
TIAN Jian-bo, SHI Qing-xuan, LIU Yun-he, LI Shen, MA Hui
Engineering Mechanics    2018, 35 (11): 53-67.   DOI: 10.6052/j.issn.1000-4750.2017.07.0575
Abstract76)      PDF(pc) (1873KB)(64)       Save
PRC coupling beam-hybrid coupled shear wall system is a new structural system formed by replacing the concrete coupling beam with the plate-reinforced composite (PRC) coupling beam in traditional reinforced concrete coupled shear walls. It is still lack of systematic research on its aseismic behavior. Therefore, based on the aseismic performance study of the PRC coupling beam with a small span-to-depth ratio, the BS basic model specimen of the PRC coupling beam-hybrid coupled shear wall system is designed. The aseismic behavior of the PRC coupling beam-hybrid coupled shear wall system is analyzed by using the finite element software. The stress distribution of steel plates, reinforcing bars in coupling beams and concrete is investigated. Meanwhile, the plastic hinges developing law of this hybrid coupled shear wall system is also studied. Further, the influence of a coupling ratio, the section size of a coupling beam, the height-width ratio of a single side wall, the total height of a structure, and the role of a slab on the aseismic behavior of the new structural system is studied. It is recommended that the reasonable coupling ratio for the PRC coupling beam-hybrid coupled shear wall system in a high intensity seismic fortification area is from 40% to 60%.
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EXPERIMENTAL STUDY ON ASEISMIC BEHAVIOR OF REINFORCED CONCRETE COLUMNS WITH GRADE 600 MPa STEEL BARS
LI Yi-zhu, CAO Shuang-yin, XU Peng-jie, NI Xiang-yong
Engineering Mechanics    2018, 35 (11): 181-189.   DOI: 10.6052/j.issn.1000-4750.2017.08.0659
Abstract76)      PDF(pc) (1358KB)(60)       Save
To investigate the aseismic behavior of RC columns with grade 600 MPa steel bars, five RC columns with grade 600 MPa steel bars and one RC column with conventional steel for comparison were tested under cyclic loading. The effects of steel bar strength, stirrup spacing and axial compression ratio on failure model, hysteretic behavior, bearing capacity and ductility, dissipation capacity, and degradation of stiffness and strength were analyzed. The test results showed that:the failure pattern of specimens is the bending failure, and the bond failure between the grade 600 MPa longitudinal bars and concrete and the fracture of longitudinal bars were observed. The bearing capacity and energy dissipation of specimens increased significantly with the improvement of steel bar strength, while the ductility and energy dissipation capacity of specimens decreased. Increasing the stirrup spacing decreased the ductility and energy dissipation capacity and accelerated the strength degradation of specimens in late loading, but there was little effect on bearing capacity of specimens. It is concluded that the RC columns with grade 600 MPa steel bars has a good aseismic behavior and can be used in aseismic structures by reasonable design.
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STUDY ON HYSTERETIC MODEL AND SEISMIC PERFORMANCE OF DAMPING ENERGY DISSPATION BRACE WITH SELF-CENTERING CAPABILITY
XU Long-he, WANG Kun-peng, XIE Xing-si, LI Zhong-xian
Engineering Mechanics    2018, 35 (7): 39-46.   DOI: 10.6052/j.issn.1000-4750.2017.03.0204
Abstract75)      PDF(pc) (881KB)(63)       Save
On the basis of a traditional magnetorheological (MR) damper, a novel damping energy dissipation brace with self-centering capability is developed. A restoring force calculation model, the improved double Bouc-Wen model, is established to portray the hysteretic behaviors of the damping energy dissipation brace by improving the traditional Bouc-Wen model, which is simulated in Simulink environment, and the simulation results are compared with the finite element analysis results. The secondary development program of the improved double Bouc-Wen model is carried out based on OpenSees platform, and using a 9-story benchmark steel frame structure as a numerical example, the comparisons of the seismic performances between a structure with the damping energy dissipation braces and a structure with buckling restrained braces (BRBs) are conducted. The hysteretic curves obtained from the double Bouc-Wen model agree well with those obtained from the finite element simulation, and the flag-shaped hysteretic behaviors of the brace can be accurately portrayed by the proposed improved double Bouc-Wen model. The maximum interstory drift and residual deformation of a steel frame structure after earthquakes are effectively reduced, so that the structure with damping energy dissipation brace exhibits a good recovery performance.
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SIMULATION OF FLUCTUATING WIND VELOCITY CONTINUOUS STOCHASTIC FIELD BY DIMENSION REDUCTION APPROACH
LIU Zhang-jun, YE Yong-you, LIU Zeng-hui
Engineering Mechanics    2018, 35 (11): 8-16.   DOI: 10.6052/j.issn.1000-4750.2017.07.0570
Abstract75)      PDF(pc) (446KB)(59)       Save
Based on the frequency-wavenumber spectrum representation correlating with the standard orthogonal random variables, a hybrid approach of frequency-wavenumber spectrum and a random function for simulating the continuous spatio-temporal stochastic field is proposed by introducing the random function of standard orthogonal random variable sets. Meanwhile, the simulation efficiency of the proposed approach is greatly enhanced by employing Fast Fourier Transform (FFT) algorithm technique. Benefiting from the proposed approach, the probability characteristics of the spatio-temporal stochastic field can be described on the probability density level with only two elementary random variables. Therefore, the complete representative point sets with assigned probabilities of the elementary random variables can be obtained through the number-theoretical method. As a result, the dimension reduction representation of the continuous spatio-temporal stochastic field can be realized. Numerical examples indicate that when using the same number of samples and taking the efficiency and accuracy into consideration at the same time, the proposed approach have a similar simulation result to the conventional frequency-wavenumber spectrum representation. However, the smallest number of the elementary random variables is needed in the proposed approach, which leads to a smaller number of representative samples with a complete probability set. Consequently, it could naturally be combined with the probability density evolutionary method (PDEM) to carry out the accurate analysis of stochastic dynamic response and dynamic reliability assessment of engineering structures. Finally, combining the Kaimal fluctuating wind velocity spectrum with Davenport spatial coherence function, a numerical example of simulation for horizontal-fluctuating-wind velocity continuous stochastic field is presented to verify the accuracy and superiority of the proposed approach.
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INFLUENCE OF CHANGING SHEAR ADJUSTMENT STRATEGY ON ASEISMIC PERFORMANCE OF FRAME-CORE TUBE STRUCTURE
LU Xin-zheng, GU Dong-lian, ZHOU Jian-long, BAO Lian-jin, QIAN Peng, LU Xiao, LIN Yuan-qing
Engineering Mechanics    2019, 36 (1): 183-191,215.   DOI: 10.6052/j.issn.1000-4750.2017.11.0853
Abstract71)      PDF(pc) (1845KB)(71)       Save
The frame-core-tube structural system is one of the common structural systems used in supertall buildings. While a shear adjustment regulation for the frame of a frame-core tube structure has been specified in related Chinese codes, its applicability in supertall buildings needs to be further studied. Similar regulations in the codes of China and the United States are compared in this work. Furthermore, based on an actual supertall building, a new design is proposed by changing the shear adjustment strategy. Then the refined finite element (FE) models of both original design and new one are established. And both nonlinear time history analysis (THA) under the maximum considered earthquake (MCE) and earthquake-induced collapse analysis are performed for these two models. The results indicate that:compared with the original design, the new one, whose shear adjustment strategy is different, has a lower design difficulty, a similar aseismic performance under MCE, and a higher anti-collapse resistance. The results can provide a reference for the design of supertall frame-core tube structures.
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REAL-TIME SEPERATION OF TEMPERATURE EFFECT ON DYNAMIC STRAIN MONITORING AND MOVING LOAD IDENTIFICATION OF BRIDGE STRUCTURE
SUN Ya-qiong, ZHAO Zuo-zhou
Engineering Mechanics    2019, 36 (2): 186-194.   DOI: 10.6052/j.issn.1000-4750.2017.12.0954
Abstract70)      PDF(pc) (671KB)(20)       Save
Strain monitoring is an important content of health monitoring and condition assessment for a bridge structure. However, in practical engineering application, the value of strain monitoring is usually affected greatly by temperature, so that it is not able to distinguish the strain monitoring value caused by a moving load from the total measured strain, which lead to the loss of efficacy of a pre-established early-warning index. Based on the monitoring results of strain and temperature of a cable-stayed bridge in Hefei, an engineering method for the real-time separating temperature effect from strain monitoring is derived. First, the temperature distribution in the girder of the bridge has been analyzed, and a suggestion for temperature sensors distribution is put forward. Then, according to the analysis of the monitoring value of strain, the temperature effect value is obtained by the time-varying average value method. The simple and efficient method can be applied to the real-time temperature correction of monitoring data and the setting of dynamic early-warning index in an online bridge structure health monitoring system. The residual strains of different locations can be used to identify the moving load of a bridge structure.
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ANALYTICAL MODEL OF ROCKING ELEMENTS BEFORE ROCKING
CUI Hao-ran, WU Gang, FENG De-cheng
Engineering Mechanics    2018, 35 (12): 34-45.   DOI: 10.6052/j.issn.1000-4750.2017.09.0695
Abstract69)      PDF(pc) (560KB)(50)       Save
A new analytical model is developed to calculate the deformation of damaged rocking elements before rocking, which refers to an existing analogous spread plasticity model of rocking elements. With a new effective stiffness ratio accounting for the plastic deformation in calculation, a damage influence coefficient is proposed to consider the effects of damaged corners on the entire rocking elements. The analytical model is verified by the finite element model simulation and the results of existing experiments. The results indicate that the analytical model proposed in this paper could accurately predict the deformation of rocking elements before and after being damaged. The effective stiffness ratio related to the normal stress distribution at the contact surface is proved to be applicable in the analysis of rocking elements before rocking. By adjusting the damage influence coefficient, the effects of different damage degrees of corners on the stiffness of rocking elements can be explicated.
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STUDY ON BENDING STATE NONLINEARITY OF SHIELD-TUNNEL RING JOINTS
ZHANG Jing, HE Chuan, GENG Ping, CHEN Ping-liang, LU Zhi-kai
Engineering Mechanics    2018, 35 (11): 35-44.   DOI: 10.6052/j.issn.1000-4750.2017.08.0624
Abstract67)      PDF(pc) (1373KB)(52)       Save
In order to investigate the bending state nonlinearity of shield-tunnel ring joints under the composite action of longitudinal internal forces, the mechanical behavior of ring joints were classified to 7 deformation modes and 3 internal force states. The analytical expressions involved ring joints rotation angle and longitudinal internal forces for each deformation mode were derived. At the same time, the critical moment expression of the ring joints between different deformation modes was developed. FEM method was employed to verify the results obtained by an analytic derivation. The results showed that bending state nonlinearity was one inherent feature of ring joints because of the discontinuous structure of a shield tunnel. The deformation mode and bending stiffness of shield-tunnel ring joints changed under different internal force combinations. In a pure bending state, the ring joints' bending stiffness had a constant value, and it could be enlarged several times under a compression-bending state, even be enlarged to infinity. The bending stiffness of ring joints under a tension-bending state would be limited to two constant values which were both smaller than that under a pure bending state, and it would be decreased several times when ring joint surface was completely opened.
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LOCKING-FREE ISOGEOMETRIC ANALYSIS OF COMPLEX THREE-DIMENSIONAL BEAM STRUCTURES
XIA Yang, LIAO Ke
Engineering Mechanics    2018, 35 (11): 17-25.   DOI: 10.6052/j.issn.1000-4750.2017.08.0602
Abstract65)      PDF(pc) (1564KB)(75)       Save
The beam structure is widely used in engineering. The numerical simulation of beam structures is an important topic in computational mechanics. In this paper, the locking-free isogeometric analysis of complex three-dimensional beam structures is investigated. The technique of multiple sets of approximation functions originated from quasi-conforming finite element method is first applied to the isogeometric analysis of three-dimensional beam structures to solve the locking problem. Order-reduced approximation functions are applied to simulate the strains of beams. Global formulation of beam strains is applied, and the stiffness matrices of beam elements and patches can be combined without transformation between local and global coordinate systems. The beam structure is described by multi-patch non-uniform rational B-spline functions. The geometry is exactly described, and the geometrical error introduced by finite element mesh can be avoided. The numerical experiments prove that the proposed algorithm can effectively avoid the locking problem in Timoshenko beam formulation, and is suitable for the analysis of complex three-dimensional beam structures.
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FRAGILITY ANALYSIS AND SAFETY EVALUATION OF REINFORCED CONCRETE FRAME STRUCTURES SUBJECTED TO MAINSHOCK-AFTERSHOCK EARTHQUAKE SEQUENCES
ZHOU Zhou, YU Xiao-hui, LU Da-gang
Engineering Mechanics    2018, 35 (11): 134-145.   DOI: 10.6052/j.issn.1000-4750.2017.07.0588
Abstract65)      PDF(pc) (1093KB)(57)       Save
Aftershocks can cause additional damage to mainshock-damaged structures and threaten structural safety under earthquakes. In the light of this, this study extends the conventional seismic fragility theory and conducts the fragility analysis for a five-story RC frame structure designed according to the current Chinese design codes using the earthquake inputs of real and artificial mainshock-aftershock earthquake sequences. Based on the obtained fragility results for earthquake sequences, the limit state failure probabilities, damage state failure probabilities, and the vulnerability index corresponding to the earthquake sequences of different hazard levels are calculated for evaluating the structural safety under sequential earthquakes. The results show that the structural fragility due to mainshock-aftershock earthquake sequences is higher than that due to mainshock earthquakes alone. The artificial earthquake sequences may cause larger structural fragility than the real earthquake sequences. The artificial earthquake sequences based on the repeated method shows the largest damage potential for the structure among the used real and artificial earthquake sequences. The artificial earthquake sequences based on the attenuation method has a similar damage potential to real earthquake sequences.
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AN ENERGY CONSISTENT INTEGRATION METHOD FOR TRUSS ELEMENTS
PAN Tian-lin, WU Bin
Engineering Mechanics    2018, 35 (10): 1-9,36.   DOI: 10.6052/j.issn.1000-4750.2017.06.0434
Abstract64)      PDF(pc) (607KB)(64)       Save
Based on the energy equilibrium theory, an energy consistent integration method for truss elements is proposed in this paper. The method is unconditionally stable in nonlinear systems, and its accuracy is second order. The existence of algorithm parameters is proved by mean value theorem, and the solution form of the parameters is also provided. The discrete dynamic equations are linearized to obtain the equivalent stiffness matrices for iteration. The new algorithm is embedded in a nonlinear finite element program. On the basis of this program, the nonlinear dynamic analysis of a single pendulum and a transmission tower structure is completed. The numerical results show that the classic average acceleration method and implicit midpoint method are both energy inconsistent and may even produce divergent results. In contrast, the proposed method has good stability within different time steps.
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SCATTER AND DIFFRACTION OF ARBITRARY NUMBER OF HILLS FOR INCIDENT PLANE P-WAVES
BA Zhen-ning, PENG Lin, LIANG Jian-wen, HUANG Di-yang
Engineering Mechanics    2018, 35 (7): 7-17,23.   DOI: 10.6052/j.issn.1000-4750.2017.03.0181
Abstract63)      PDF(pc) (2708KB)(42)       Save
The diffraction of plane P waves on multiple hills of an arbitrary number is studied using an indirect boundary element method (IBEM), combined with the technology of ‘conjunction’. The model is divided into an open layered half-space region and multiple independent closed regions. Wave fields are classified as free fields and scattered fields. The free field response can be solved by the direct stiffness method, and the diffraction response of the open layered half-space region and closed regions can be simulated by the Green's function of fictitious distributed loads acting on corresponding boundaries. And the densities of the distributed loads are determined by solving the algebraic system based on boundary conditions. The validity of the method is confirmed by the comparison with published results. Then numerical analyses are performed by multiple hills topography in the cases of different heights, different distances and different numbers. The results show that the surface displacement of multiple hills is significantly bigger than those of a single hill because of the dynamic interaction among hills, making the surface displacement and spectrum amplification of multiple hills obviously different from those of a single hill. The variation of heights and distances of hills on both sides would lead to the changes in the dynamic interaction mechanism within hills, which alter the peak and peak-period amplification of spectrum furthermore. Increases in heights and numbers of hills on both sides, as well as decreases in distances from each other will result in a more intensive dynamic interaction, a bigger displacement and a more complex spatial distribution.
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STUDY ON THE SEISMIC BEHAVIOR OF GRADED YIELDING METAL DAMPERS
CHEN Yun, JIANG Huan-jun, LIU Tao, WAN Zhi-wei, LU Zheng
Engineering Mechanics    2019, 36 (3): 53-62.   DOI: 10.6052/j.issn.1000-4750.2018.01.0036
Abstract63)      PDF(pc) (5460KB)(67)       Save
In this paper a new type of graded yielding metal damper composed of two annular metal dampers with different sizes was proposed. The seismic performance of the new damper was studied by cyclic loading tests. The failure mechanism and energy-dissipation mechanism of the damper were revealed. The hysteretic energy-dissipation behavior, strength and stiffness degradation, and fatigue resistance of the damper were analyzed. The experimental results show that the damper not only achieves graded yielding function effectively, but also possesses large deformation capability, full hysteretic loops and excellent anti-fatigue performance. The modification coefficient of the initial stiffness of the damper was obtained by parametric finite element analysis and regression analysis. The formulas to determine the performance points in the load-deformation skeleton curve were proposed. The calculated skeleton curves agree well with the experimental results. Accordingly, the geometry of the damper can be determined by the performance requirement. The research results of this study can provide technical support for the engineering application of the new metal damper.
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LARGE-EDDY-SIMULATION ON COMPLEX TERRAIN BASED ON SPECTRAL ELEMENT METHOD
HU Wei-cheng, YANG Qing-shan, YAN Bo-wen, ZHANG Jian
Engineering Mechanics    2018, 35 (12): 7-14.   DOI: 10.6052/j.issn.1000-4750.2017.08.0663
Abstract62)      PDF(pc) (959KB)(57)       Save
Based on open-source Nek5000, a grid generation method of SEM (Spectral Element Method) for complex terrain was put forward, and the wind field of Askervein hill was numerically simulated by LES (Large-eddy-simulation). The result of numerical simulation was compared with the field observation and another numerical result. The comparisons show that the wind speed acceleration factor on line-A obtained by LES simulation is in good agreement with the results from the field observation. SEM combined with LES turbulence model can be used to predict wind energy resource distribution on complex terrain.
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NEW METHOD FOR CALCULATION OF TIME-DEPENDENT RELIABILITY OF RC BRIDGES
YE Xin-yi, WANG Cao, LI Quan-wang
Engineering Mechanics    2018, 35 (11): 86-91.   DOI: 10.6052/j.issn.1000-4750.2017.09.0667
Abstract60)      PDF(pc) (416KB)(57)       Save
A new method was proposed to improve the calculation efficiency of time-dependent reliability analysis for bridges. Based on the basic theory of structural reliability, the proposed method utilizes the Taylor expansion to simplify the traditional formula in an integration expression as a new formula in an algebraic expression, which essentially improves the calculation efficiency. In order to consider the uncertainties associated with the initial resistance and the degradation process, an explicit formula for time-dependent reliability analysis was also presented using a total probabilistic theorem. The proposed method was applied to the time-dependent reliability analysis of an RC bridge, and the results were compared with that associated with Monte Carlo simulation method to demonstrate the accuracy and high efficiency of the new method.
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RESEARCH ON BASIC SHEAR PERFORMANCE OF CONCRETE FILLED RECTANGULAR STEEL TUBULAR MEMBERS WITHOUT END-PLATE
SHI Yan-li, ZHOU Xu-hong, XIAN Wei, WANG Wen-da
Engineering Mechanics    2018, 35 (12): 25-33.   DOI: 10.6052/j.issn.1000-4750.2017.10.0782
Abstract60)      PDF(pc) (4464KB)(63)       Save
The shear performance of 8 concrete filled rectangular steel tubular members without end-plate was tested. The influences of the section size and shear-span ratio (0.3-0.8) on shear capacity and slip behavior were studied. The result indicates that the specimens experience shear failure when the shear-span ratio is 0.3. With the increasing of shear-span ratio, the failure pattern of the specimens changes from shear failure to bending failure, the shear capacity decreases, and the slip of core concrete decreases. The numerical simulation was carried out using ABAQUS, and the calculating results agree well with the test results in general. The model was verified by the tested results. The influences of parameters such as friction and bonding, with or without end-plate and different axial loading were investigated on the shear performance of the specimens. The results show that calculating results agree well with the test results when the friction coefficient is 0.25 in finite element model. The end-plate has a small effect on the yield platform of load-displacement curves, but it has a great effect on the strength of load-displacement curves. The axial load affects the shear capacity significantly.
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EXPERIMENTAL RESEARCH AND FINITE ELEMENT ANALYSIS ON THE SEISMIC BEHAVIOR OF CORRODED PLANE STEEL FRAMES UNDER OFFSHORE ATMOSPHERIC ENVIRONMENT
ZHENG Shan-suo, ZHANG Xiao-hui, HUANG Wei-zeng, ZHAO Xu-ran
Engineering Mechanics    2018, 35 (7): 62-73,82.   DOI: 10.6052/j.issn.1000-4750.2017.02.0127
Abstract59)      PDF(pc) (4801KB)(57)       Save
In order to study the seismic behavior of corroded steel frames under offshore atmospheric environment, accelerated corrosion tests on 42 tensile coupons and 4 plane steel frames were implemented by the technique of artificial climate accelerated corrosion. Tensile tests were then performed to obtain the functional relationships between mechanical properties (including yield strength, ultimate strength, elongation and elastic modulus) and weight loss rate for Q235B steel subjected to corrosion. 4 plane steel frames were tested under lateral low cyclic loading. The effects of corrosion degrees on the failure mechanism, hysteretic behavior, skeleton curves, stiffness degradation, ductility and energy dissipation capacity of the specimens were analyzed. The test results show that all specimens exhibit ductile failure with a hybrid yield dissipation mechanism. While the corrosion degree increases, the load bearing capacity and energy dissipation capacity decrease significantly, the strength and stiffness degrade obviously, and the ductility is reduced. Based on the experimental study, nonlinear finite element analyses were conducted on the test plane steel frames using ABAQUS. The influence of axial compression ratio on the mechanical properties of specimens were analyzed. The results indicate that with the increase of the axial compression ratio, the bearing capacity and ductility decrease monotonically.
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STUDY OF COMPREHENSIVE MONITORING TECHNOLOGY OF THE CONSTRUCTION PROCESS OF COMPLEX LARGE-SPAN SPATIAL STEEL STRUCTURES
LEI Su-su, LIU Yu-fei, DUAN Xian-jun, GUO Xiao-hua, LI Xue-fei, LI Jian-hua, HOU Jin-feng, LI Hai-bing, YANG Jian-ping, XING Kun-tao, CUI Zheng-tao, GUAN Jian, BI Deng-shan, NIE Xin
Engineering Mechanics    2018, 35 (12): 203-211.   DOI: 10.6052/j.issn.1000-4750.2018.09.0836
Abstract59)      PDF(pc) (3823KB)(28)       Save
Construction process monitoring is of great significance to the construction of complex large-span spatial steel structures. The targeted monitoring indicators should be chosen according to different construction methods specifically. The commonly-used monitoring indicators and the corresponding monitoring methods and devices during the process of the construction monitoring of large-span spatial steel structures, and new monitoring technologies are discussed in detail. Based on the construction process of the steel roof of the Beijing New Airport terminal building, the monitoring indicators including the stress and strain of key components, structural displacement and deformation by using 3D laser scanning and UAV monitoring of priority areas are selected comprehensively to inspect the mechanical behavior, deformation feature and partial construction quality problems of the structure. This comprehensive monitoring technology provides a comprehensive and reliable solution to the construction monitoring of complex large-span spatial steel structures.
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SEMI ACTIVE NONLINEAR ROBUST DECENTRALIZED CONTROL BASED ON GUARANTEED PERFORMANCE ADAPTIVE RBF NEURAL NETWORK
PAN Zhao-dong, TAN Ping, ZHOU Fu-lin
Engineering Mechanics    2018, 35 (10): 47-55.   DOI: 10.6052/j.issn.1000-4750.2017.06.0453
Abstract58)      PDF(pc) (510KB)(20)       Save
The semi active decentralized control of nonlinear structures with uncertain parameters is studied. Firstly, the degenerated Bouc-Wen hysteretic model is utilized to simulate the restoring forces, and the error state equation of a sub-control system is established by considering the uncertainty of the model parameters (mass, stiffness and damping) and the coupling between subsystems. Secondly, a sub-controller is designed which composes of a guaranteed cost control term and an adaptive approximation control term. The guaranteed cost control term is obtained by solving the guaranteed cost control problem which is transformed into a linear matrix inequality. The approximation control term is determined by the adaptive control law of RBF neural network, and its stability and boundedness of the weights are proved by Lyapunov stability theory. And then a guaranteed cost adaptive RBF neural network robust decentralized control (GCARBF) algorithm for nonlinear vibration control of uncertain structures is established. A nonlinear 8-story building is selected as a numerical example to evaluate the control performances of the proposed algorithm. The MR semi active decentralized control design and the simulation analysis of 0.3 g~0.8 g intensity are carried out. Numerical simulation results indicate the effectiveness and superiority of the proposed algorithm.
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EXPERIMENTAL STUDY ON FLEXURAL BEHAVIORS OF STEEL-UHPC COMPOSITE GIRDER AND STEEL-CONVENTIONAL CONCRETE COMPOSITE GIRDER
LIU Jun-ping, XU Shuai, CHEN Bao-chun
Engineering Mechanics    2018, 35 (11): 92-98,145.   DOI: 10.6052/j.issn.1000-4750.2017.06.0454
Abstract58)      PDF(pc) (1124KB)(56)       Save
The steel-ultra-high performance concrete (UHPC) composite girder, which is composed of UHPC slab and steel girder, has the advantages of light self-weight, high cracking resistance and durability, and it is of great significance for the development of steel-concrete composite girders. To investigate the difference of mechanical performance of a steel-UHPC composite girder and steel-conventional concrete under bending, in this paper, a trial-design of steel-UHPC composite girder bridge was carried out based on the prototype structure of a practical steel-concrete simply supported composite girder bridge, according to the trial-design results, the experimental study on flexural behaviors of steel-UHPC composite girder and steel-conventional concrete composite girder were carried out. Test results show that flexural behaviors of two kinds of composite girder were similar. Both of their failure modes were that the bottom flange of steel girder was yielded first, and then the upper concrete of slab was crushed. Compared with a steel-conventional concrete composite girder, under the condition of equal ultimate flexural capacity, the slab thickness of steel-UHPC composite girder can be reduced by 28%, and the ductility is better. The shear lag effect and the relative slip between steel girder and concrete slab of steel-UHPC composite girder are much smaller than those of a steel-conventional concrete composite girder. Moreover, the flexural stiffness of the two kinds of composite girder are close in an elastic range. However, due to the decrease of total depth of a steel-UHPC composite girder, its flexural stiffness is some smaller in an elastic-plastic range. The research findings of this paper can provide a reference for further study and engineering practice.
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THEORETICAL STUDY AND EXPERIMENTAL VERIFICATION OF THE MECHANICAL MECHANISM OF SHEAR LINK DEVICES
LI Zong-jing, SHU Gan-ping
Engineering Mechanics    2018, 35 (12): 63-70,80.   DOI: 10.6052/j.issn.1000-4750.2017.09.0679
Abstract57)      PDF(pc) (1698KB)(63)       Save
Based on the classical construction details of shear link devices (SLDs), a mechanical model was built. The semi-inverse method in elastic mechanics was adopted to study its stress distribution pattern. The initial stiffness K, post-yield stiffness K', yield force Fy and yield displacement uy were also studied theoretically. Due to deficiencies of conventional methods for identifying the yield point, a new method based on the Bouc-Wen model and simulated annealing was proposed to identify the equivalent yield point of shear link devices. Finally, a quasi-static monotonic loading test was carried out for verification. The results demonstrate that the stress distribution in the web plate and the mechanical performance parameters calculated by the analytical solution comply with the finite element analysis results and the test results. The proposed method can effectively identify the equivalent yield point and corresponding mechanical performance parameters of the shear link device, and the simulated force-displacement curve fits well with the monotonic test curve. The results of the study may provide effective reference for the design, evaluation and further research of shear link devices.
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NON-LINEAR BURGERS' SEA-ICE MODEL CONGSIDERING DAMAGE EFFECTS AND ITS NUMERICAL APPLICATION
SHI Chu, LUO Yu, HU Zhi-qiang
Engineering Mechanics    2018, 35 (7): 249-256.   DOI: 10.6052/j.issn.1000-4750.2017.03.0217
Abstract56)      PDF(pc) (791KB)(20)       Save
Based on the published creep experiments of sea ice, a non-linear Burgers' sea-ice model, considering damage effects, is proposed. This model improves the sea-ice model presented by Jordaan through considering transition strain rate effects, which make it applicable in high strain rate conditions. The influence of strain rate and confining pressure on the damage process of sea ice is reflected by the experimental failure criteria proposed in this model. The iceberg model is implemented using an implicit integration mid-point (Crank-Nicolson) method and is incorporated into the code LS-DYNA by a user-defined material subroutine. Laboratory-scale experiments (creep experiments) and reality-scale experiment (iceberg-rigid steel plate collisions) are simulated. The curves of strain relations in time series, and area-pressure curves and contact force-penetration relations in time series in iceberg-rigid plate collisions are studied. The simulation results show that the proposed iceberg material model yields reasonably good results.
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