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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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A PHILOSOPHIC REVIEW OF STRUCTURAL MECHANICS METHODS
LONG Yu-qiu
Engineering Mechanics    2019, 36 (4): 1-7.   DOI: 10.6052/j.issn.1000-4750.2019.01.ST13
Abstract326)      PDF(pc) (482KB)(307)       Save
The methodology of structural mechanics is reviewed. Five problems are discussed:1) the keynote of the methodology of structural mechanics, 2) features of the structural mechanics methods, 3) the dominant features of the virtual work method and the energy method, 4) the equivalent relationship between the virtual work method and the energy method, and 5) the adjoint theorem between the equilibrium matrix and the geometric matrix.
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EARTHQUAKE ENGINEERING: FROM EARTHQUAKE RESISTANCE, ENERGY DISSIPATION, AND ISOLATION, TO RESILIENCE
ZHOU Ying, WU Hao, GU An-qi
Engineering Mechanics    2019, 36 (6): 1-12.   DOI: 10.6052/j.issn.1000-4750.2018.07.ST09
Abstract257)      PDF(pc) (3410KB)(295)       Save
In recent years, the research on earthquake engineering in our country showed a tendency of development from earthquake resistance, energy dissipation, and isolation to resilience. Earthquake resilience can be defined as the capability of restoring the function for a structure, a system or a city after it has been interrupted by an earthquake event. In respect of structures, an earthquake resilient structure should not only protect life safety during a seismic event, but also restore its function quickly enough after the earthquake in order to minimize the influence to immediate occupancy. The fundamental concepts of earthquake resilience are introduced first. After that, the characteristics of an earthquake resilient structure and its uniqueness compared to a conventional structure are addressed over the aspects of seismic fortification objective, design code and standard, structural systems, design methods, performance indexes and project applications. Lastly, the direction of future development for earthquake resilient structures is forecasted.
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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
Abstract214)      PDF(pc) (17514KB)(225)       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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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
Abstract299)      PDF(pc) (853KB)(207)       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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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
Abstract188)      PDF(pc) (563KB)(163)       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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RESEARCH AND APPLICATION OF MODERN BAMBOO STRUCTURES
TIAN Li-min, JIN Bei-bei, HAO Ji-ping
Engineering Mechanics    2019, 36 (5): 1-18,27.   DOI: 10.6052/j.issn.1000-4750.2018.06.ST06
Accepted: 12 February 2019

Abstract172)      PDF(pc) (3115KB)(161)       Save
Bamboo is one of the renewable resources in the world. It is an ideal material for building industry because of its good mechanical properties. With the improvement of social economy, the development of science and technology, and the promotion of national policy, bamboo structures will be one of the development directions in the future. This is mainly because the whole life cycle of bamboo structures can achieve co-existence with an ecological environment. The basic methods for the research of bamboo structures can learn from more mature traditional structural studies. However, bamboo is the foundation of bamboo structures. This special material makes bamboo structures different from traditional structures in terms of members, joints and systems. At present, the research on bamboo structures lacks uniform material constitutive. Not only that, but the research methods are single, and the connection forms of nodes are limited. The above-mentioned problems limit the wide application of bamboo structures in engineering. An overall review is given on mechanical properties of bamboo, bamboo members and joints, as well as common bamboo structural systems based on published literatures and authors' research work. The structural system of sprayed composite mortar-original bamboo has a good mechanical behavior, functionality, adaptability, and efficiency. It can replace traditional brick concrete structures and is applied to township and rural low-rise buildings. The structural system of sprayed composite mortar-original bamboo has high application value.
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EXPERIMENTAL STUDY ON THE DYNAMIC EFFECTS IN PROGRESSIVE COLLAPSE OF BEAM-COLUMN CONCRETE SUBSTRUCTURES
XIAO Yu-zhe, LI Yi, LU Xin-zheng, REN Pei-qi, HE Hao-xiang
Engineering Mechanics    2019, 36 (5): 44-52.   DOI: 10.6052/j.issn.1000-4750.2018.04.0189
Accepted: 01 April 2019

Abstract167)      PDF(pc) (751KB)(147)       Save
Progressive collapse is a nonlinear dynamic behavior of structure systems. The key issue in establishing the simplified method for the practical engineering design is to evaluate the dynamic effect accurately. To investigate the dynamic progressive collapse mechanism and the dynamic effect of reinforced concrete substructures, one static and four dynamic experiments were conducted on four specimens, which had the identical dimensions and material properties. The results indicated that the stress concentration and asymmetric deformation in the dynamic tests were severer than those in the static test due to the high strain rate effect. Thus, the cracks developed intensively at the beam ends and the concrete spalling area caused by compression was relatively small in dynamic tests. The general dynamic resistance, in which the effects of dynamic damage and high strain rate to the structural resistance were inherently considered, was able to accurately predict the resistance demand in the real progressive collapse process. In addition, the dynamic amplification effect was enhanced by the effect of dynamic damage and high strain rate, thus the practical dynamic amplification factors were larger than the predicted values of the conventional theory.
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NUMERICAL SIMULATION ON DYNAMIC COMPRESSIVE BEHAVIOR OF ULTRA-HIGH TOUGHNESS CEMENTITIOUS-COMPOSITES
XU Shi-lang, CHEN Chao, LI Qing-hua, ZHAO Xin
Engineering Mechanics    2019, 36 (9): 50-59.   DOI: 10.6052/j.issn.1000-4750.2018.03.0147
Accepted: 12 July 2019

Abstract125)      PDF(pc) (2326KB)(142)       Save
Investigates the dynamic compressive behavior of PVA fiber reinforced ultra-high toughness cementitious-composites (PVA-UHTCC) using Split Hopkinson Pressure Bar (SHPB) test based on HJC constitutive model. Firstly, 21 parameters of HJC model are determined and the numerical simulation is verified. Then dynamic compressive stress-strain curves under 5 different strain rates are obtained for analyzing the strain-rate effects on Dynamic Increase Factor (DIF). The failure modes of specimens under different strain rates are also researched. The results show that with the increase of strain rate, DIF increases and the strain-hardening dominated behavior will transform into a strain-softening dominated behavior. Besides, PVA-UHTCC shows an obvious different strain-rate sensitivity in the different range of strain rates. Thusly, a functional expression between DIF and lgε is proposed. Compared with Steel Fiber Reinforced Cementitious Composites (SFRCC) and normal concrete, PVA-UHTCC has a lower strain-rate sensitivity. Finally, the crack propagation mechanism and failure modes are observed at LS-DYNA software to furtherly understand the dynamic compressive behavior of PVA-UHTCC.
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SEISMIC FRAGILITY MODELS AND FORWARD-BACKWARD PROBABILISTIC RISK ANALYSIS IN SECOND-GENERATION PERFORMANCE-BASED EARTHQUAKE ENGINEERING
Lü Da-gang, LIU Yang, YU Xiao-hui
Engineering Mechanics    2019, 36 (9): 1-11,24.   DOI: 10.6052/j.issn.1000-4750.2018.07.ST08
Accepted: 22 January 2019

Abstract168)      PDF(pc) (631KB)(135)       Save
The seismic fragility in 2nd-generation performance-based earthquake engineering (PBEE) generally refers to the seismic capacities of both structural components and non-structural components. However, this concept is different from the definition and the content of seismic fragility in traditional seismic risk theory. To clarify the differences between the two fragility definitions, the definition and its probabilistic model for seismic fragility in traditional seismic risk theory are firstly introduced. And then, five seismic fragility models in 2nd-generation PBEE are identified:seismic demand fragility model, seismic capacity fragility model, seismic damage fragility model, seismic loss fragility model, and seismic decision fragility model. The differences and their relationships of the five seismic fragility models are pointed out. The analytical formulations for the probability models and their distribution parameters in a seismic demand fragility model and a seismic damage fragility model are derived. On the basis of the above theoretical deduce, the concepts of forward PBEE and backward PBEE are put forward according to the directions of uncertainty propagation. Through this new concept, the risk integration equation in 2nd-generation PBEE can be solved by different methods. By integrating the approximate formulation of seismic hazard and the analytical formulations of fragility probability models and their distribution parameters, the three probabilistic seismic risk formulations with the same formats for EDP, DM and DV levels are obtained via the methods of forward PBEE and backward PBEE. Through the study of this paper, the traditional seismic risk theory and the 2nd-generation PBEE are unified into a consistent theoretical framework.
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LITERATURE REVIEW OF RESEARCHES ON RIGID BODY MODEL OF ROCKING STRUCTURE
ZHAO Zi-xiang, SU Xiao-zu
Engineering Mechanics    2019, 36 (9): 12-24.   DOI: 10.6052/j.issn.1000-4750.2018.08.0454
Accepted: 29 April 2019

Abstract133)      PDF(pc) (701KB)(125)       Save
A rational theoretical model is essential for structure analysis. The most widely used model in theoretical research for rocking structure is rocking rigid body model, which is systematically reviewed in this paper. The research origin and research status of rocking rigid body model are introduced. The classical rocking rigid body model, and other typical rocking rigid body model, as well as related experimental research, finite element simulation and application in structure system, are discussed. The advantages and limitations of existing rocking rigid body models are discussed and key issues in future study of rocking rigid body model are highlighted, which provides reference for the establishment of a more complete and practical rigid body model for rocking structure and its application to the analysis of rocking structure.
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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
Abstract127)      PDF(pc) (5460KB)(124)       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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COLLAPSE CAPACITY ASSESSMENT OF RC FRAME STRUCTURES USING EXPLICIT ALGORITHM
ZHAO Peng-ju, YU Xiao-hui, LU Xing-zheng
Engineering Mechanics    0, (): 0-.   DOI: 10.6052/j.issn.1000-4750.2019.04.0165
Accepted: 19 July 2019

Abstract105)      PDF(pc) (693KB)(114)       Save
Explicit algorithms have better performance with regarding convergence than implicit algorithms widely used in the conventional dynamic analysis. Explicit algorithms are more suitable for simulating the strong nonlinear behaviors of the structures close to the collapse state. This paper adopts an explicit algorithm based on a modified leapfrog format to evaluate the seismic collapse resistance of the reinforced concrete (RC) frames designed according to the current Chinese codes. OpenSees is used as the software platform. The seismic collapse fragility curves and the collapse margin ratios are obtained for the RC frames. Four criteria to describe collapse limit states are used and their effects on the collapse resistance of structures are investigated. The first two collapse criteria are corresponding to the inelastic inter-story drift ratio of 1/50 and 4% recommended by Chinese and US codes. The third collapse criterion is defined from the IDA curve with the tangent slope equal to 20% of the initial elastic slope. The fourth collapse criterion is determined by the vertical displacement equaling to 1m. The results show that explicit algorithms have better nonlinear simulation performance than implicit algorithms and can well approach to the collapse limit state. The first three criteria for the definition of collapse states are suitable for seismic design to avoid the occurrence of structural collapse due to earthquake excitations. The fourth collapse criterion is derived based on the physical meaning of the structural collapse, whose evaluation result is closer to the actual structural collapse resistance.
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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
Abstract287)      PDF(pc) (553KB)(109)       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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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
Abstract145)      PDF(pc) (11893KB)(106)       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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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
Abstract153)      PDF(pc) (6917KB)(101)       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
Abstract141)      PDF(pc) (593KB)(98)       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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INERTER SYSTEM AND ITS STATE-OF-THE-ART
ZHANG Rui-fu, CAO Yan-ru, PAN Chao
Engineering Mechanics    2019, 36 (10): 8-27.   DOI: 10.6052/j.issn.1000-4750.2018.09.0496
Accepted: 12 April 2019

Abstract124)      PDF(pc) (3418KB)(98)       Save
An inerter is a two-terminal acceleration-dependent mechanical element for structure control systems. The inerter system is an integrated system for the structural vibration control with inerters. A large number of studies and research projects on the inerter systems have been comprehensively reviewed in this paper. The state-of-the-art of inerter systems in the field of structural vibration control system were discussed from the following three aspects:realization of the inerter mechanism; performance of the inerter system and design of the structures with inerter system. Compared with traditional vibration control systems, the inerter system has its advantages including:the inertia of the structure can be adjusted and the tuning can be achieved flexibly; additional physical mass is negligible when the inertia of the structure changes obviously; the efficiency of energy dissipation is enhanced. This review paper is intended to provide theoretical evidence and practical guidance for the design, application and further development of inerter systems.
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Development and key issues of reticulated shells with semi-rigid joints
FAN Feng, MA Hui-huan, MA Yue-yang
Engineering Mechanics    2019, 36 (7): 1-7,29.   DOI: 10.6052/j.issn.1000-4750.2018.06.ST05
Abstract123)      PDF(pc) (771KB)(98)       Save
The assemble joints which are usually connected with members by one or several bolts are named semi-rigid joints. Due to the limit study of assemble joints, they are assumed as pin joints during the analysis and design of structures. However, the study results show that assemble joints are typical semi-rigid joints, and some new assemble joints have the merits of being stiffer and more efficient, which can be used in a larger span single-layer reticulated shell. The reticulated shells with semi-rigid joints have a wide application prospect, and the semi-rigid joint systems and semi-rigidly jointed reticulated shells have become a new research hotspot in the field of engineering structures. A state-of-the-art review of research on the semi-rigid joints and semi-rigidly jointed reticulated shells are thusly present. The research findings are presented and some key issues for further study are suggested. The research on the semi-rigid joints and semi-rigidly jointed reticulated shells has already obtained certain positive results. However, more experimental and theoretical study should be carried out on the joints under complex load combinations, the new joint design for larger span structures, the static and dynamic stability of single-layer reticulated shells with semi-rigid joints. The results should be analyzed and summarized in detail to promote the practical application of single-layer reticulated shells with semi-rigid joints.
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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
Abstract139)      PDF(pc) (409KB)(97)       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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RESEARCH PROGRESS AND APPLICATION OF FLAPPING WING AERODYNAMICS
XIANG Jin-wu, SUN Yi, SHEN Tong, LI Dao-chun
Engineering Mechanics    2019, 36 (4): 8-23.   DOI: 10.6052/j.issn.1000-4750.2018.03.0175
Abstract94)      PDF(pc) (4943KB)(95)       Save
Insects, birds and bats have superb flying ability. They are the main imitators of a flapping-wing aircraft. In recent years, a great progress has been made in the field of flapping-wing aerodynamics. This paper summarized the main research results, and focus on the recent advances in flapping-wing aerodynamics, including the flapping-wings lift mechanism of insects, birds and bats, the effects of wing morphological parameters and microstructures, wing flexibility, dynamic deformation, wing-wing interference, wing-body interference, inter-individual interference, and ground effect on the flapping wing aerodynamics. We also introduced the research progress of aerodynamic research on bionic flapping-wing aircraft design. At the end, the main problems and challenges faced by flapping-wing aerodynamics are presented.
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EXPERIMENT ANALYSIS OF MECHANICAL PROPERTIES OF O-SHAPED STEEL PLATES AND HIGH DAMPING VISCOELASTIC COMPOSITE ENERGY DISSIPATORS
CHEN Yun, CHEN Chao, JIANG Huan-jun, WAN Zhi-wei, LIU Tao
Engineering Mechanics    2019, 36 (1): 119-128.   DOI: 10.6052/j.issn.1000-4750.2017.11.0805
Abstract93)      PDF(pc) (4439KB)(94)       Save
A new composite energy dissipator made of two O-shaped steel plate metal dampers and one high damping viscoelastic damper was developed. The construction details and working mechanisms were introduced. Cyclic loading tests on the dissipator were carried out. The test results show that the composite energy dissipator possesses a large deformation capability and a full hysteresis curve. The mechanical properties of the dissipator are stable and insensitive to loading frequencies. It has the advantages of the velocity-dependent damper and displacement-dependent damper. When the deformation is small, the viscoelastic damper plays the major role in energy dissipation, and the O-shaped steel plate metal dampers contribute to stiffness. When the deformation is large, two types of dampers dissipate the seismic energy together. Compared with the dampers of a single type, the composite energy dissipator offers a much larger damping force and seismic safety margin. The calculation model for the composite dissipator was established by using the Bouc-Wen model. The calculation results were in good agreement with experimental results.
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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
Abstract117)      PDF(pc) (959KB)(93)       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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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
Abstract85)      PDF(pc) (4464KB)(93)       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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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
Abstract95)      PDF(pc) (1698KB)(93)       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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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
Abstract140)      PDF(pc) (1564KB)(87)       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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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
Abstract105)      PDF(pc) (1845KB)(87)       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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ROBUST OPTIMIZATION DESIGN METHODS OF STRUCTURAL DYNAMICS: A REVIEW
XU Ben-sheng, ZANG Chao-ping, MIAO Hui, ZHANG Gen-bei
Engineering Mechanics    2019, 36 (4): 24-36.   DOI: 10.6052/j.issn.1000-4750.2018.09.0484
Abstract120)      PDF(pc) (525KB)(85)       Save
How to improve the robustness of structural dynamic performance, and how to minimize the influence of various uncertainties on mean design are one of the hot issues both in academic and engineering fields. In this paper, the basic concept of structural dynamic robust optimization design is described. The robust optimization design methods of structural dynamics are reviewed from three aspects that are based on Taguchi method, multi-objective optimization and response surface methods. Taking a dual-rotor as an example, the dynamic robust optimization design is carried out by using the response surface modeling and multi-objective optimization methods. The results show that multiple robust optimization design schemes can be obtained based on response surface modeling and multi-objective optimization, and robust design methods have great potential for application in structural dynamics to deal with uncertain problems. Finally, the current research methods and future work are briefly summarized and prospected.
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WIND TUNNEL TEST STUDY ON COMPLEX WIND FIELD AND VEHICLE AERODYNAMIC EFFECTS IN EMBANKMENT-CUTTING TRANSITION ZONE IN HIGH-SPEED RAILWAY
ZHANG Jing-yu, ZHANG Ming-jin, LI Yong-le, FANG Chen, XIANG Huo-yue
Engineering Mechanics    2019, 36 (1): 80-87.   DOI: 10.6052/j.issn.1000-4750.2017.09.0749
Abstract80)      PDF(pc) (493KB)(83)       Save
The topography and geomorphology are complex and changeable in China, and the railway transition zones are indispensable. In order to investigate the vehicle aerodynamic effects and complex wind field in embankment-cutting transition zone, a large-scale model was established to measure the wind speed profiles above the track and the train aerodynamic forces at different locations along the track by using wind tunnel test. The test results show that the influence height of embankment-cutting transition zone on air flow is less than 250 mm above the track. The wind velocity profile at the lower height of the railway junction is dominated by the cutting while the higher height is dominated by the embankment. Wind speed has little influence on the changing trend of train aerodynamic forces along the track. In the transition zone, the most unfavorable area for traffic safety exists near the junction of the railway, especially at the sides of embankment. The aerodynamic coefficients decrease while the wind speed increases due to the Reynolds number effect.
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MODIFICATION OF DIF-STRAIN RATE CURVE OF CONCRETE-LIKE MATERIALS IN NUMERICAL SIMULATION OF SHPB EXPERIMENTS
LI Xiao, FANG Qin, KONG Xiang-zhen, WU Hao
Engineering Mechanics    2018, 35 (12): 46-53.   DOI: 10.6052/j.issn.1000-4750.2017.10.0764
Abstract86)      PDF(pc) (640KB)(82)       Save
Numerical simulation is an effective technique to study the response of concrete-like materials to dynamic loads. For predicting the concrete-like materials structure response to dynamic loads, it's important to input the DIF-strain rate curve exactly in numerical simulation. The data in dynamic compressive experiments of concrete-like materials since 1990 was collected, and the inertia-induced effect on dynamic strength of material was stripped out to obtain DIFε-logε curve. It is discovered that DIFs and DIFi increase with specimen size. At the same time, DIFi of concrete-like materials increase less with the strain rate when the quasi-static strength of the materials increases. New curve and semi-empirical formula curve were compared, which show that the new curve was coincided with DIFε of experiments better than the semi-empirical formula at high strain rate. Furthermore, the superiorities of new curve are validated by comparing the DIF recommended by CEB with the new curve as the numerical inputs.
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A DISCUSSION ON BIG DATA IN STRUCTURAL ENGINEERING: PARADIGM, TECHNOLOGY AND EXAMPLE
CHEN Jun
Engineering Mechanics    2019, 36 (6): 175-182.   DOI: 10.6052/j.issn.1000-4750.2018.05.0279
Abstract88)      PDF(pc) (581KB)(82)       Save
Big data is no doubt the most popular topic currently in science and technology field. Application of big data has already reached the level as high as a national strategy. It brings new historical development opportunities to various interdisciplinary fields including structural engineering. This paper discusses, from the point of view of research paradigm shift, the impacts, problems and challenges along with the introduction of big data concepts and technologies to structural engineering. Potential applications of big data in structural engineering are then discussed according to the development trend of the third generation of structural design theory. Finally, an example is given which shows the application of big data idea for investigating live loads in a building.
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REVIEW OF THE RESEARCH ON STEEL STORAGE RACK STRUCTURES
ZHAO Xian-zhong, DAI Liu-si, HUANG Zhao-qi, REN Chong
Engineering Mechanics    2019, 36 (8): 1-15.   DOI: 10.6052/j.issn.1000-4750.2018.10.ST12
Abstract142)      PDF(pc) (1919KB)(81)       Save
With the rapid growth of logistics industry, steel storage racks are not just industrial products. They are commonly used in high-rise warehouses and clad racks. Therefore, the structural safety of storage racks is of vital importance. Steel storage racks are distinct from traditional moment resisting frames in the following aspects. Firstly, storage racks may carry extremely high live loads with comparatively light weight and reach up to 40 meters in height. Secondly, the uprights have open singly- or non-symmetric cross-sections and are continuously perforated along the length, the behavior of which is significantly influenced by local, distortional, global buckling and their interactions. Thirdly, the mechanical beam-to-upright connections and column bases are commonly utilized for their convenience in assembly and adjustment. Their nonlinear moment-rotation behavior and severely pinching characterization requires comprehensive investigations. Fourthly, the influences of the asymmetry configuration of the bracing system on the stability of the overall rack structure need to be carefully studied. Moreover, as for the aseismic behavior of rack structures, further investigations are required for the hysteretic behavior of beam-to-upright connections, the collapse mechanisms of the overall rack structures, and the sliding behavior between pallets and beams. It should be noted that besides usual local and global collapse mechanisms, the falling of pallets should also be considered as an additional serviceability limit state of rack structures. This paper reviews researches on the behavior of steel storage racks. A brief introduction of rack structures is provided, as well as the main research methodologies. The main research results on the static and dynamic behavior are then presented respectively. Finally, the key issues in studies of steel storage racks and the related research topics are proposed.
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Application of adaptive finite element method of lines in 2D unbounded domain problems
DONG Yi-yi, XING Qin-yan, FANG Nan, YUAN Si
Engineering Mechanics    2019, 36 (7): 8-17.   DOI: 10.6052/j.issn.1000-4750.2018.06.0351
Abstract87)      PDF(pc) (938KB)(80)       Save
Unbounded domain problems are frequently encountered in engineering. As a semi-analytical and semi-discretized numerical method, Finite Element Method of Lines (FEMOL) has shown good performance on this type of problems. Based on the proposed theory of infinite elements with mapping technique, the adaptive FEMOL with Element Energy Projection (EEP) super-convergent method is applied to the solution of 2D unbounded domain problems, in which users are only required to pre-specify an error tolerance and a rough initial mesh, and then an adaptive FEMOL mesh is automatically produced by the algorithm, on which the accuracy of FEMOL solution with both regular elements and infinite elements satisfies the specified error tolerance in maximum norm. An introduction of the theory of FEMOL and the infinite elements are given firstly, and then the strategy of adaptive FEMOL based on EEP method is presented. The feasibility of applying the adaptive FEMOL to unbounded domain problems is analyzed. Then three unbounded domain problems are adaptively solved, including the Poisson equation of flow around a circular cylinder, the plane problem of uniaxial tension of infinite plate with a circle hole in elasticity, and the semi-infinite half space body under uniformly distributed circular load. Finally the displacements (function solutions) satisfying the error tolerance can be obtained and the stresses (derivative solutions) with superior accuracy can be calculated. Therefore the adaptive FEMOL can be taken as a new approach for solution of unbounded domain problems.
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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
Abstract160)      PDF(pc) (1358KB)(80)       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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STOCHASTIC SEISMIC RESPONSE AND DESIGN OF STRUCTURAL SYSTEM WITH SERIES-PARALLEL-II INERTER SYSTEM
PAN Chao, ZHANG Rui-fu, WANG Chao, LU Jing-zhou
Engineering Mechanics    2019, 36 (1): 129-137,145.   DOI: 10.6052/j.issn.1000-4750.2017.11.0809
Abstract92)      PDF(pc) (1114KB)(78)       Save
In order to comprehend the response mitigation mechanism of a specified inerter system named series-parallel-Ⅱ inerter system (SPIS-Ⅱ), the response variation trends for a single-degree-of-freedom (SDOF) system with SPIS-Ⅱ are studied and the parametric optimal design method is proposed. The mathematical expressions of frequency-domain response transfer functions and root-mean-square random responses of a SDOF system with SPIS-Ⅱ are derived based on the equations of motion and theories in random vibration. Then the response variation trends of a SDOF system with SPIS-Ⅱ are investigated by adopting Kanai-Tajimi's spectrum as a seismic input model along with the change of key parameters of seismic ground motion and SPIS-Ⅱ. Based on parametric studies, a practical optimal design method of a SDOF system with SPIS-Ⅱ is proposed. For this method, seismic performance demand is taken as the design target and response control, cost minimization, and spectral properties of seismic excitations are all considered during design. Finally, a computer program is developed according to the proposed method to conduct design examples, and dynamic time-history analyses are also carried out. The results of example design and analysis prove the effectiveness of the proposed design method.
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EXPERIMENTAL STUDY ON BEARING CAPACITY OF BOLTED STEEL-PSB-STEEL CONNECTIONS
CUI Zhao-yan, XU Ming, CHEN Zhong-fan, WANG Fei
Engineering Mechanics    2019, 36 (1): 96-103,118.   DOI: 10.6052/j.issn.1000-4750.2017.11.0792
Abstract109)      PDF(pc) (2494KB)(78)       Save
Because of the advantage of the simple fabrication, high security and construction convenience, the bolted connection is widely applied in modern engineered bamboo and wood structures. In order to investigate the mechanical behavior of the bolted steel-Parallel strand bamboo-steel connections, twelve groups of specimens were tested under uniaxial tensile load. The effects of thickness to diameter ratio, fastener spacing and the end distance on the failure modes and the bearing capacity were reported in the paper. The results indicate that the failure mode of single and multi-bolted connections is the occurrence of one plastic hinge when the thickness to diameter ration is 5.0-5.7, and the occurrence of two plastic hinges when the thickness to diameter ration is 8.0-10.0. As the fastener diameter, spacing or the end distance increases, the bearing capacity gradually increases. The bolted connections with one column show good ductility, which gets worse as the number of columns increases. Comparing the experimental results with the calculations using the domestic code for wood structure, wood structure design manual and Eurocode 5, it was found that the domestic code is conservative and the Eurocode 5 has better applicability.
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SEISMIC BEHAVIOR OF STEEL FRAME CONNECTIONS WITH REPLACEABLE HIGH DUCTILITY AND ENERGY DISSIPATION COMPONENTS
WANG Meng, KE Xiao-gang, WU Zhao-zhang
Engineering Mechanics    2018, 35 (12): 151-163.   DOI: 10.6052/j.issn.1000-4750.2017.09.0743
Abstract129)      PDF(pc) (4803KB)(77)       Save
In order to satisfy the urgent requirement of assembled steel structures with high ductility and energy dissipation capacity for the areas with high seismic intensity and population density, high performance low yield point steel is used for the connecting components of steel frame connections instead of ordinary steel. Then, the combination of prefabricated assembly function, ‘ductile energy dissipation fuse’ function and post-earthquake replaceable function is achieved with utilizing high-strength bolts. The non-linear finite element model of ABAQUS proves to be correct in simulating local buckling and bolt slipping phenomena based on published steel frame bolted connection tests at home and abroad. Based on this method, three types of bolted steel frame connections with connecting components using three different materials LYP100, LYP160 and Q235 were established. Their load-carrying capacity, hysteretic behaviour, cumulative plastic strain and energy dissipation capacity were compared, and the mechanism of connections with low yield point steel components was discussed. The results showed that using low yield point steel connecting components could change the failure mode of connections, make the plastic cumulative deformation mainly concentrate in connecting components, dissipate most of energy (around 90%), avoid the main frame encountering plasticity too early and effectively play a role of "ductile and energy dissipation fuse". The energy dissipation capacity of connections with low yield point steel components was higher than that of connections with ordinary steel components. When the rotation of connections reached 0.045 rad, the maximum elongation of low yield point steel components was much smaller than limit value, indicating that the components still had deformation capacity without premature fracture damage, which effectively improved the ductility of connections.
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STRENGTH CALCULATION AND ECCENTRIC COMPRESSIVE TEST OF STEEL TUBE-REINFORCED CONCRETE COMPOSITE COLUMNS
KE Xiao-jun, SU Yi-sheng, SHANG Xiao-yu, SUN Hai-yang
Engineering Mechanics    2018, 35 (12): 134-142.   DOI: 10.6052/j.issn.1000-4750.2017.09.0717
Abstract84)      PDF(pc) (980KB)(77)       Save
According to Technical Specification for Steel Tube-Reinforced Concrete Column Structure, the compression-bending capacity of a steel tube-reinforced concrete composite column without considering the steel tube is not fully utilized. Therefore, the failure pattern and confinement mechanism through eccentric compressive test was performed to complement the existing calculation theory in this paper. The test results show that failure patterns of all specimens are divided into two types, namely the large and the small eccentric failures, whose demarcation failure criterion is that the tensile reinforcements reach the yield strength and the concrete compressive edge reaches the ultimate compressive strain. Furthermore, the cross-section strain obeys the plane section assumption, and the transverse strain of steel tube increases with the decreasing of eccentricity, which fails to yield at the peak loading and is not negligible. Finally, a formula is proposed to calculate the compression-bearing capacity considering the influence of steel tube and its restraining action. Based on 40 groups of test data from this paper and other references, this calculated formula proves to be reasonable, and can be used to guide the design for steel tube-reinforced concrete composite column.
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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
Abstract107)      PDF(pc) (1093KB)(77)       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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A SHEAR DESIGN MODEL FOR RC DEEP FLEXURAL MEMBERS CONSIDERING THE SIZE EFFECT
WEI Hui, WU Tao, LIU Yang, LIU Xi
Engineering Mechanics    2019, 36 (5): 130-136.   DOI: 10.6052/j.issn.1000-4750.2018.03.0169
Accepted: 28 March 2019

Abstract63)      PDF(pc) (405KB)(77)       Save
There is a lack of accurate and reasonable shear design models for reinforced concrete deep flexural members such as typical D-region shear components with complicated force mechanism and significant size effect. In combination with the advantages of the Tan-Cheng model that fully considers the softening effect of concrete and the size effect of struts, and on the basis of the deep understanding of the effect of diagonal strut angle α and composite tensile stress ft on the shear strength of deep flexural members, the relationship between the top node height lc and α was simplified and a modified Tan-Cheng model was proposed by reconsidering the effective action region of web reinforcement. The predictions of 308 deep flexural members from either foreign or domestic source indicate that the proposed model has a comparable accuracy with the Tan-Cheng model, and it can accurately consider the size effect of concrete struts through a concise calculation process. The comparison between the proposed model and current code provisions shows that the predictions by the proposed model has a better agreement with the test results. It further indicates that the proposed model can reasonably predict the shear strength of deep flexural members.
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STUDY ON WIND TUNNEL WALL INTERFERENCE IN DYNAMIC AIRFOIL TEST
LI Guo-qiang, ZHANG Wei-guo, HUANG Xia, WANG Xun-nian
Engineering Mechanics    2019, 36 (8): 235-247.   DOI: 10.6052/j.issn.1000-4750.2018.07.0380
Abstract89)      PDF(pc) (8377KB)(77)       Save
The aerodynamic nonlinear characteristics of airfoil caused by dynamic stall are prominent, and the coupling effect with wall interference brings great uncertainty to wind tunnel test data. In view of this, the mechanism and influence law of the wall effect in the airfoil dynamic test are revealed by means of experiment and numerical method. The results show that:compared to the static test, due to the existence of the wall interference, both the total pressure and the static pressure distribution of the wake zone during the dynamic test of airfoil are even more inhomogeneous. The wind tunnel wall interference of dynamic airfoil test is more serious. The differences of the velocity and pressure distribution on the middle section and the end section of airfoil are more obvious. Compared with the pressure surface, the two-dimensional flow of the suction surface becomes worse. The side wall interference suppresses the flow separation near the middle section of airfoil, and induces a spanwise separation flow near the end. The unsteady pressure coefficient of the upper and lower wall versus real-time attack angle also shows a hysteresis effect, the direction of the hysteresis loop is opposite, and the main characteristic frequency of the wall pressure fluctuation equals to the oscillation frequency of airfoil pitching. Influenced by the wind tunnel wall interference, the three-dimensional dynamic stall vortex structure of the airfoil is "Omega" type. In the positive stroke, the lift coefficient and the lift line slope are increased by the upper and lower wall of the wind tunnel, and the airfoil is induced to be stalled in advance. In the negative stroke, the lift coefficient of airfoil is reduced. The sidewall interference induces a spanwise flow on airfoil surface, reduces the chord-orientation flow velocity of airfoil, causes the reduction of lift coefficient in the negative stroke, but the interference effect is less in the positive stroke, besides the dynamic stall is delayed. The upper and lower wall interference of the dynamic airfoil test in the FL-11 wind tunnel should be a dominant factor. However, the sidewall interference cannot be ignored, especially at the high angle of attack and negative stroke during the oscillation period of airfoil.
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