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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
Abstract362)      PDF(pc) (482KB)(341)       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
Abstract290)      PDF(pc) (3410KB)(337)       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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A HIGH-EFFICIENCY SIMULATION METHOD FOR ANALYZING THE IMPACT OF EXHAUSTED AIR FROM TEMPORARY HOSPITALS BUILT FOR THE TREATMENT OF NOVEL CORONAVIRUS PNEUMONIA
GU Dong-lian, ZHANG Yin-an, LIU Hua-bin, MA You-cai, CAO Xiao-qing, Lyu Zhong-yi, XIE Lin-lin, XU Zhen, XU Yong-jia, ZHENG Zhe, YANG Can-tian, LU Xin-zheng
Engineering Mechanics    DOI: 10.6052/j.issn.1000-4750.2020.02.0047
Accepted: 10 February 2020

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

Abstract247)      PDF(pc) (3388KB)(212)       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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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
Abstract245)      PDF(pc) (17514KB)(245)       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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INTRODUCTION TO THE HISTORY OF THE THEORY OF STRUCTURES: SEARCHING FOR EQUILIBRIUM
LI Guo-qiang, JI Chang
Engineering Mechanics    2019, 36 (11): 13-26.   DOI: 10.6052/j.issn.1000-4750.2018.12.0665
Accepted: 29 April 2019

Abstract230)      PDF(pc) (2376KB)(288)       Save
Mechanics and structures have developed rapidly in recent decades. Meanwhile, the research of the history of the theory of structures has been highly concerned. As an interdisciplinary field of scientific history, the history of the theory of structures provides a shortcut to understand the development of structural engineering, the masterpiece of which is a Germany book named The History of the Theory of Structures:From Arch Analysis to Computational Mechanics published in 2002. The English version of this book was published in 2008, and republished ten years later as the 2nd edition, renamed as The History of the Theory of Structures:Searching for Equilibrium, in 2018. In this book, the development of the theory of structures is introduced from a historic-logical perspective. It demonstrates the complicated relationship of the theory of mechanics and structural engineering spanning from the ancient Greece to modern computer age in a roughly chronological order, which could be called the encyclopedia of the development of the theory of structures. We are honored to have read the book and write this article to make a brief introduction to this book with emphasizing a series of important controversies in the history of the theory of structures.
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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

Abstract203)      PDF(pc) (631KB)(152)       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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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

Abstract201)      PDF(pc) (3115KB)(172)       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

Abstract192)      PDF(pc) (751KB)(156)       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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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
Abstract174)      PDF(pc) (1919KB)(111)       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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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

Abstract168)      PDF(pc) (701KB)(147)       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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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
Abstract165)      PDF(pc) (11893KB)(115)       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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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

Abstract155)      PDF(pc) (2326KB)(160)       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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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
Abstract146)      PDF(pc) (5460KB)(132)       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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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
Abstract143)      PDF(pc) (771KB)(108)       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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CONCEPT AND DEVELOPMENT OF NOVEL BLADE STRUCTURE OF LARGE HORIZONTAL-AXIS WIND TURBINE
YANG Yang, ZENG Pan, LEI Li-ping
Engineering Mechanics    2019, 36 (10): 1-7.   DOI: 10.6052/j.issn.1000-4750.2018.06.ST04
Accepted: 22 January 2019

Abstract141)      PDF(pc) (918KB)(191)       Save
During the development of large-scale horizontal axis wind turbines, the major problem is the contradiction among the structure reliability and the requirement of light weight and aerodynamics efficiency. The structural characteristics of a traditional cantilever blade has restricted the further development of large wind turbines. The novel form of a blade structure is the effective solution to the problem, such as bionic flexible blades, segmented blades and multi-element blades. This paper reviews the state of the art of novel blade structures in recent years, providing some references for large blade design.
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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
Abstract138)      PDF(pc) (525KB)(88)       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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A MODIFIED CHEBYSHEV QUADRATURE
ZHONG Hong-zhi, SHENG Yun-xin
Engineering Mechanics    2019, 36 (12): 1-6.   DOI: 10.6052/j.issn.1000-4750.2018.12.0712
Accepted: 06 June 2019

Abstract136)      PDF(pc) (306KB)(146)       Save
Numerical integration is of great importance in a numerical analysis. With the reference to Chebyshev's equal weight quadrature, a modified Chebyshev quadrature is proposed after incorporating the end points of an interval. The practical application of Chebyshev's equal weight quadrature is restrictive since the order of quadrature with mere real abscissas cannot exceed nine. The modified Chebyshev quadrature alleviates the restriction considerably and renders it applicable in a weak-form quadrature element analysis. It is applied to the evaluation of integrals and linear and non-linear weak form quadrature element analysis of rods and beams. Results are compared with analytical solutions and those obtained using Lobatto quadrature, verifying the accuracy and the effectiveness of the proposed quadrature.
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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

Abstract134)      PDF(pc) (693KB)(137)       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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ARTIFICIAL BEE COLONY ALGORITHM FOR FLUTTER DERIVATIVES IDENTIFICATION OF BRIDGE DECKS USING FREE VIBRATION RECORDS
LIN Yang, FENG Zhou-quan, HUA Xu-gang, CHEN Zheng-qing
Engineering Mechanics    2020, 37 (2): 192-200.   DOI: 10.6052/j.issn.1000-4750.2019.03.0143
Accepted: 19 July 2019

Abstract133)      PDF(pc) (952KB)(90)       Save
Based on the coupled free vibration records of bridge deck sectional model testing, a flutter derivatives identification method based on the artificial bee colony (ABC) algorithm is proposed. The objective function is constructed as the ensemble residual quadratic sum of the vertical and torsional vibration time histories in the sense of least squares. The ABC algorithm is used to search the optimal parameters so that the value of the objective function is minimized. Compared with other iteration methods, the ABC algorithm can facilitate the identification process with no need for initial values. In order to investigate the effectiveness of the ABC algorithm in the flutter derivatives identification, an ideal thin-plate model simulation and a real bridge sectional model testing are carried out. The results show that the ABC algorithm for the flutter derivatives identification of bridge decks is robust and reliable.
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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
Abstract131)      PDF(pc) (4943KB)(133)       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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STUDY ON SEISMIC PERFORMANCE AND COLLAPSE-RESISTANT CAPACITY OF TYPICAL FRAME-CORE TUBE STRUCTURES WITH SINGLE AND DUAL LATERAL-FORCE RESISTING SYSTEM
CHEA Cheav Por, XIE Lin-lin, LIN Yuan-qing, LU Xin-zheng
Engineering Mechanics    2019, 36 (10): 40-49.   DOI: 10.6052/j.issn.1000-4750.2018.11.0635
Accepted: 25 March 2019

Abstract131)      PDF(pc) (3435KB)(111)       Save
In the design code system of China, frame-core tube structure should be designed as a dual lateral-force resisting system, and there are strict requirements for the secondary lateral-force resisting system of such structure. In other words, the outer frame of the frame-core tube structure should have sufficient lateral stiffness and strength. However, in the design codes of other countries (e.g., ASCE-7 of the United States), the outer frame of the frame-core tube structure is permitted to only carry the vertical load. Therefore, to compare the seismic performances of the single and dual lateral-force resisting systems of the frame-core tube structure, a dual lateral-force resisting system model was firstly designed following the design codes of China. Subsequently, under the same gravity load (and the same concrete consumption), the single lateral-force resisting system model of the frame-core tube structure was design according to the following procedures:1) the secondary lateral-force resisting system was removed from the dual system, and the shear force adjustment of the frame was ignored; 2) the seismic detailing requirement of the frame was lowered to reduce the sectional size. As a result, the tube beared most of the seismic load, and the frame only resisted the vertical load. The structural responses and component damage of these two systems under SLE (Service Level Earthquake) and MCE (Maximal considered earthquake) were analyzed. Furthermore, the collapse mechanisms of two structures and their collapse-resistances were investigated. Finally, the variation of the shear force and shear distribution of the frame under different levels of earthquake and the corresponding damage of key components were discussed. The research shows that the response of the dual system structure was slightly greater than that of the single system, and their collapse resistant capacities were similar. However, the steel consumption of the single system was less than that of the dual system.
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ROLLING TECHNOLOGY OF LONGITUDINALLY PROFILED STEEL PLATE (LP STEEL PLATE) AND BEARING CAPACITY OF LP FLEXURAL MEMBERS
WANG Yuan-qing, LIU Xiao-ling, LIU Ming, BAN Hui-yong, LI Jing-nian
Engineering Mechanics    2019, 36 (11): 1-12.   DOI: 10.6052/j.issn.1000-4750.2018.06.ST02
Accepted: 22 January 2019

Abstract129)      PDF(pc) (1706KB)(109)       Save
Longitudinally profiled steel plate (LP steel plate) is a new type of green-saving steel product which could be widely used in industrial and civil buildings, bridges and other special structures. Its research and development have a great significance for structural optimization design and energy conservation in construction. The unusual rolling and straightening technology of LP steel plate is briefly introduced. The recent researches of Tsinghua University on material performance and component bearing capacity are comprehensively reviewed, which were studied by theoretical analysis, experimental and numerical simulation. The variation of material mechanical properties is concluded. The design methods of I-section beam with longitudinally variable thickness flanges for bearing capacity design value and deformation behavior at serviceability limit state are proposed.
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ESTIMATION OF STRAIN RATES FOR WHEEL-RAIL SURFACE MATERIALS UNDER HIGH-SPEED ROLLING-SLIDING CONTACT
KOU Jun-yu, ZHAO Xin, ZHANG Peng, WEN Ze-feng, JIN Xue-song, WANG Ping
Engineering Mechanics    2019, 36 (4): 239-247.   DOI: 10.6052/j.issn.1000-4750.2018.02.0099
Abstract127)      PDF(pc) (852KB)(46)       Save
A 3D wheel-rail transient rolling contact model has been developed using the explicit finite element method to calculate the average strain rates of rail surface material of 0.25 mm~0.5 mm deep at 300 km/h, for which smooth rail, rail corrugation (wavelength of 30 mm~170 mm) and macro-roughness (wavelength of 4 mm~30 mm) are considered. Obtained results have shown:1) the highest strain rate occurs on the surface layer spatially, and during the loading or unloading processes of a material particle passing the contact patch; the rate of the normal strain is the largest among all strain components, being 1.50~1.86 times of Von Mises (V-M) strain rate; 2) element size and time step have important effects on strain rate results; 3) the V-M strain rate of smooth surfaces reaches the maximum of 64.1 s-1 when the element size is 0.5 mm and the time step is 0.32 μs, the material elasto-plasticity has no effects, the rail corrugation and macro-roughness result in the maximum V-M strain rate of 92.5 s-1 and 79.4 s-1 in elasticity respectively; the results are 1.65~1.88 times higher when an element size of 0.25 mm and a time step of 0.042 μs are used; 4) the maximum strain rate increases linearly with speed, monotonically with increasing friction coefficient, while the influence of traction coefficient is negligible.
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STUDY ON THE MECHANICAL PROPERTIES OF CFRP CIRCUMFERENTIALLY CONFINED CONCRETE FILLED STEEL TUBE COLUMN OF MARINE STRUCTURE UNDER COMPRESSION-BENDING-TORSION COMBINED LOAD
WANG Yu-hang, WANG Yu-yan, HU Shao-wei
Engineering Mechanics    2019, 36 (8): 96-105.   DOI: 10.6052/j.issn.1000-4750.2018.07.0377
Abstract127)      PDF(pc) (3372KB)(73)       Save
In order to study the mechanical properties of CFRP circumferentially confined concrete filled steel tube column under combined compression-bending-torsion load, pseudo-static tests were conducted, including 4 CFRP circumferentially confined concrete filled steel tube columns and 2 concrete filled steel tube columns. The number of CFRP layers and axial load ratio were studied. The failure modes and the load-deformation hysteretic curves under bending-torsion and compression-bending-torsion load were obtained. The experimental results showed that the failure mode of CFRP circumferentially confined concrete filled steel tube column was bending failure and the process could be summarized as:the local buckling of steel tube initialed in plastic hinge area and circumferential cracks of CFRP appeared, then CFRP ruptured and was peeled off steel tube, and the steel tube finally cracked in the buckling region. The existence of axial force made the failure mode of steel tube more likely to be the "elephant leg" type. CFRP confinement had little effect on the bearing capacity and ductility of concrete filled steel tube under bending-torsion load. For CFRP circumferentially confined concrete filled steel tube columns subjected to compression-bending-torsion load, CFRP confinement can improve the ductility and energy dissipation capacity of concrete filled steel tube effectively, and it can delay stiffness degradation despite of little improvement of the bearing capacity. Furthermore, the energy dissipation capacity of members increased with the increasing CFRP layers as the local buckling of the steel tube was restricted effectively.
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COMPUTATIONAL INVESTIGATIONS FOR AERODYNAMIC CHARACTERISTIC ANALYSIS OF LOW REYNOLDS NUMBER DOUBLY-TANDEM WING CONFIGURATIONS
ZHANG Qing, YE Zheng-yin
Engineering Mechanics    2019, 36 (10): 244-256.   DOI: 10.6052/j.issn.1000-4750.2018.09.0514
Accepted: 25 June 2019

Abstract123)      PDF(pc) (17547KB)(45)       Save
As a configuration with high aerodynamic efficiency, a tandem wing is an innovative kind of aerodynamic configuration for flight vehicles with inflatable aerodynamic structures such as stratosphere airships or inflatable wings at low Reynolds number flow regimes. However, its aerodynamic characteristics are limited understanding because of complicated interferences of the two wings. Therefore, based on conducted wind tunnel experiments, computational simulations have been carried out. Then the effects of airfoil thickness, surface wavelet and hindwing deflection angle on general aerodynamic characteristics were compared and presented quantitatively. The computational results demonstrate that at the computational range of attack angle, tandem wing configuration could delay, or even suppress the trailing edge separation and then increase the aerodynamic efficiency significantly, thus it is concluded that the aerodynamic configuration is attractive and promising for UAVs or airships with flexible structures in the near future.
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FREE VIBRATION ANALYSIS OF RIBBED SKEW PLATES WITH A MESHFREE METHOD
QIN Xia, LIU Shan-shan, WU Yu, PENG Lin-xin
Engineering Mechanics    2019, 36 (3): 24-32,39.   DOI: 10.6052/j.issn.1000-4750.2018.01.0006
Abstract121)      PDF(pc) (1909KB)(70)       Save
Based on the first-order shear deformation theory (FSDT), a meshfree method for solving the free vibration problem of ribbed skew plates is proposed. The plates and ribs are discretized with a series of points to obtain a meshfree model of the stiffened plate. The FSDT and the moving least-squares approximation are used to establish the displacement field. The total dynamic energy and total potential energy of the stiffened plate are obtained by simulating the ribs as beams. The governing equation for the free vibration of the stiffened plate is derived by the Hamilton principle. The boundary condition is introduced by the full transformation method, and the free vibration frequencies are solved. Several examples are calculated, and the results given by the proposed method are compared with those from other researches or ABAQUS. The results show that the method can effectively analyze the free vibration problem of ribbed skew plates and can avoid the redistribution of plate nodes when the rib position changes.
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SEISMIC EXPERIMENT AND THEORETICAL ANALYSIS ON SELF-INSULATING STRUCTURAL WALLS WITH INNER SKELETON
SHI Feng-kai, LIU Fu-sheng, WANG Shao-jie, YUE Yi-bo, LIU Kang, HUANG Xing-huai
Engineering Mechanics    2019, 36 (4): 158-166,187.   DOI: 10.6052/j.issn.1000-4750.2018.02.0093
Abstract120)      PDF(pc) (2308KB)(70)       Save
A self-insulating structural wall with inner skeleton and its structural system were designed for realizing the integration of anti-seismic and energy-saving performance. A horizontal low-cyclic load test was conducted to investigate the wall's seismic performance, and it revealed the transformation process of the wall's failure mechanisms. Accordingly, the failure process was divided into three stages, including common working stage, transition stage and weak frame working stage. This study proposed cracking load and ultimate capacity formulas based on the wall's final failure mode and theoretical analysis of the test results. The two formulas were respectively established on the basis of the elastic equivalent model and the modified softened strut-and-tie model. The relative errors between theoretical analysis and test results were 3.2% and 3.3%, respectively, indicating the theoretical formulas have a clear physical significance and an adequate level of accuracy. Additionally, the experiment results verified the wall's superiorities, including seismic behavior, construction convenience and economic performance. The wall is well-suitable for application in multi-story residential buildings such as villages and towns.
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ENERGY-CONSERVING TIME INTEGRATION METHOD FOR TIMOSHENKO BEAMS
YANG Hao-wen, WU Bin, PAN Tian-lin, XIE Jin-zhe
Engineering Mechanics    2019, 36 (6): 21-28.   DOI: 10.6052/j.issn.1000-4750.2018.01.0033
Abstract117)      PDF(pc) (460KB)(63)       Save
An energy-conserving time integration method is proposed for the nonlinear dynamic analysis of Timoshenko beams. Co-rotational techniques are used to consider its structural geometric nonlinearity, and a linked interpolation form is adopted in the spatial discretization to avoid shear-locking phenomenon of a beam. The multi-parameter correction method is used to modify the equivalent nodal dynamic equations in the time discretization, which results in the energy conservation of the discrete system under conservative loading. The method has second-order local accuracy and shows better numerical stability, compared to the average acceleration method and the implicit midpoint method. The proposed method is compared to the Simo's method in two-dimensional cases and it is found that the Simo's method does not conserve system energy under a conservative external moment. Finally, the excellent performance and energy-conserving characteristic of the algorithm are verified by three numerical simulations.
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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
Abstract116)      PDF(pc) (581KB)(107)       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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COMPARISON ON THE SEISMIC DEISGN OF BASE-ISOLATED RC FRAMES USING TWO CHINESE CODES
YIN Chuan-yin, XIE Lin-lin, LI Ai-qun, ZENG De-min, CHEN Xi, GE Dong-dong, YANG Can-tian
Engineering Mechanics    2019, 36 (9): 197-204,212.   DOI: 10.6052/j.issn.1000-4750.2019.02.0044
Accepted: 23 May 2019

Abstract114)      PDF(pc) (651KB)(86)       Save
There will be two seismic design codes for the base-isolated structures in the near future in China, including Code for Seismic Design of Buildings and Code of Design for Seismic Isolated Buildings. It is notable that significant differences exist in terms of design methods and critical design indexes between these two codes. However, comparisons on the seismic design of base-isolated structures using these two codes are rarely reported. The seismically isolated reinforced concrete (RC) frame structure is herein selected as the study subject. Using three pairs of structure cases with different heights which were designed according to the two codes, the controlling factor for the seismic design of such structures using Code of Design for Seismic Isolated Buildings was identified. In addition, the seismic responses and economic investment of such structures designed according to the two codes were compared and analyzed. The results indicate that the abovementioned controlling factor is base shear ratio. For the superstructure, a smaller stiffness is selected if Code of Design for Seismic Isolated Buildings is adopted, and the corresponding seismic load reduces by approximately 15%~20% in comparison with that designed following Code for Seismic Design of Buildings. However, because the degree of stiffness reduction of superstructure is greater than that of seismic load reduction, a significant increase of maximum inter-story drift ratio (i.e., θmax) of superstructure is observed. Furthermore, the increment of θmax basically increases with the increase of total height of structure. As for the material consumption, the concrete consumption is reduced by 7.7%~12.1% while the reinforcement consumption is increases by 11.02%~26.29% if Code of Design for Seismic Isolated Buildings is adopted. With the increase of total height of structure, the reduction of concrete consumption increases, while the increment in reinforcement consumption decreases. The research outcome will assist in providing a useful reference for seismic design of base-isolated RC frame structures.
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DUCTILE FRACTURE LOCUS VALIDATION METHOD OF THIN STEEL PLATES CONSIDERING THE LODE ANGLE PARAMETER
WANG Jun-jie, WANG Wei
Engineering Mechanics    2019, 36 (5): 37-43.   DOI: 10.6052/j.issn.1000-4750.2018.03.0150
Accepted: 28 March 2019

Abstract113)      PDF(pc) (3388KB)(86)       Save
It was observed that shear fracture dominates in the fracture of steel beam webs. For this reason, the lode angle parameter should be taken into account along with the stress triaxiality. A new ductile fracture calibration method applicable to thin steel plates is proposed in this paper. Five groups of specimens were designed in this paper. They are flat plates, holed flat plates, flat grooved plates, 90° shear plates and 45° shear plates. The true stress-ture strain (σ-ε) curves were obtained through flat plate, halted flat plate specimens and relevant finite element (FE) method iterations. The FE models of other specimens were computed with this σ-ε relationship and compared with related experimental results to obtain the corresponding equivalent fracture strain, average stress triaxiality and average lode angle parameter. With the help of the Matlab Optimization Toolbox, the optimal parameters of the fracture model can be determined.
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Influence of self-weight on the fracture properties of three-point bending concrete beams
YIN Yang-yang, HU Shao-wei, WANG Yu-hang
Engineering Mechanics    2019, 36 (7): 48-56,108.   DOI: 10.6052/j.issn.1000-4750.2018.08.0458
Abstract111)      PDF(pc) (583KB)(71)       Save
Self-weight has a significant influence on the fracture properties of beams under three-point bending (TPB). However, the influence of initial crack mouth opening displacement (CMODini) caused by self-weight was rarely considered in previous research on concrete fracture properties based on TPB beams. To investigate the influence of CMODini on the fracture properties of TPB beams, a calculation formula of CMODini, effective crack length (ac) and unstable fracture toughness (KICun)considering the influence of CMODini are presented. The calculated results of the formula were compared with the experimental data of specimens of different sizes and initial crack-depth ratios. The results indicate that CMODini is slightly influenced by the specimen sizes. The influence of the self-weight on CMODini, ac and KICun is less than 5% even if the specimen size is 2200 mm×550 mm×240 mm and the initial crack-depth ratio is 0.4. CMODini is greatly influenced by the initial crack-depth ratio. The influence increases with the increase of the initial crack-depth ratio. Moreover, the influences of the self-weight on CMODini, ac and KICun are 24.26%, 1.73% and 17.31%, respectively, when the specimen size is 1143 mm×305 mm×76 mm and the initial crack-depth ratio is 0.818. Therefore, the influence of CMODini caused by the self-weight of TPB beams should be taken into account when both the specimen size and the initial crack-depth ratio are large.
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THEORETICAL INVESTIGATION ON NORMAL SECTION FLEXURAL CAPACITY OF UHPC BEAMS
XU Ming-xue, LIANG Xing-wen, WANG Ping, WANG Zhao-yao
Engineering Mechanics    2019, 36 (8): 70-78.   DOI: 10.6052/j.issn.1000-4750.2018.06.0307
Abstract110)      PDF(pc) (309KB)(59)       Save
The relationships among peak compressive strain, cube compressive strength, elastic modulus, and axial compressive strength were established respectively based on 64 groups of Ultra High Performance Concrete (UHPC) compressive test data. The equivalent tensile strength of UHPC in the tensile zone was deduced through the mechanics of composite materials. Based on the plane section assumption, the formula for calculating normal-section flexural capacity of UHPC beams and the parameters of an equivalent rectangular stress block of UHPC in the compressive zone were deduced and the equivalent rectangular strength was calculated with the UHPC compressive constitutive relationship. Based on the data of 28 test beams, the feasibility of calculating the flexural capacity and the parameters of equivalent rectangular stress block was verified. The results show that the parameters of an equivalent rectangular stress block are reasonable and the calculated results of the normal-section flexural capacity of UHPC beams are in a good agreement with the experimental ones.
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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
Abstract109)      PDF(pc) (8377KB)(82)       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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STABILITY AND VIBRATION BEHAVIOR OF FGM BEAMS UNDER HYGRO-THERMAL-MECHANICAL-ELASTIC LOADS
PU Yu, ZHOU Feng-xi
Engineering Mechanics    2019, 36 (9): 32-39.   DOI: 10.6052/j.issn.1000-4750.2018.08.0443
Accepted: 17 May 2019

Abstract101)      PDF(pc) (427KB)(91)       Save
The stability and vibration behavior of functionally graded material (FGM) beams resting on a Winkler-Pasternak elastic foundation under the action of initial axial mechanical load considering the hygro-thermal environment is investigated. Three hygro-thermal distributions through the thickness of the beams are assumed. The material properties are temperature-dependent and are distributed according to the Voigt mixture power law model. An n-th order generalized beam theory is proposed. The governing equations of buckling and free vibration are derived from the Hamilton's principle, in which the fundamental unknown functions are the axial displacement, bending and shear components of the transverse displacement. Applying the Navier method, the analytical solutions of the buckling and free vibration responses of FGM simply supported beams are obtained. The availability and accuracy of the n-th order generalized beam theory are tested and discussed through several numerical examples. The results show that it refines the beam theories and can be used as a benchmark to verify or modify other shear deformation beam theories. The effects of three types of hygro-thermal distribution, moisture and temperature rise, initial axial mechanical load, length-to-thickness ratio, elastic foundation stiffness and material graded index on the stability and vibration behavior of FGM beams are analyzed.
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EXPERIMENTAL RESEARCH ON SHRINKAGE OF ULTRA-HIGH PERFORMANCE CONCRETE UNDER RESTRAINED RINGS
LI Cong, CHEN Bao-chun, HUANG Qing-wei
Engineering Mechanics    2019, 36 (8): 49-58.   DOI: 10.6052/j.issn.1000-4750.2018.10.0552
Abstract100)      PDF(pc) (1100KB)(54)       Save
Shrinkage of ultra-high performance concrete (UHPC) was investigated by restrained ring tests taking the restraint degree, sealed or dry circumferential condition and steel fiber as the main parameters. The development of steel ring strain with age was studied. The influences of various parameters on the residual stress under the restrained ring and the mechanical property at key age were analyzed. The tensile stress level and the relaxation rate were used to evaluate the cracking performance of UHPC. Free shrinkage and mechanical properties were also investigated to match the restrained ring test. The results showed a high early cracking risk of UHPC without steel fiber. All specimens cracked with an average width of more than 0.25 mm before 14 d, while the specimens with steel fiber did not crack. Various restraint degrees all have significant effects on both the tensile stress level and stress relaxation rate, indicating that decreasing the restraint degree can reduce the cracking risk effectively. Different from the free shrinkage test results, UHPC under ring restraint showed higher cracking risk at the late stage in a sealed condition than in a dry circumferential condition. The crack resistance at 14 d under a sealed condition is recommended as a control index to evaluate the cracking performance of UHPC under restrained ring.
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TIME DOMAIN CALCULATION METHOD BASED ON HYSTERETIC DAMPING MODEL
SUN Pan-xu, YANG Hong, ZHAO Wen-tong, WANG Zhi-jun
Engineering Mechanics    2019, 36 (6): 13-20.   DOI: 10.6052/j.issn.1000-4750.2018.05.0299
Abstract99)      PDF(pc) (551KB)(69)       Save
The free vibration solution of a complex damping time domain motion equation contains divergent items which make the numerical results of the time domain divergent. Based on the frequency domain motion equation of a complex damping model, the hysteretic damping time domain motion equation can be obtained. According to the characteristics of a hysteretic damping model, the time domain theoretical calculation method of the hysteretic damping model is proposed based on the complex plane method and trigonometric series expression of earthquake acceleration records. It is assumed that the structural vibration response is a harmonic vibration response in a short time step. Based on the average acceleration method, the time domain numerical calculation method of the hysteretic damping model is proposed. The analysis results show that:compared with the time domain numerical method of a complex damping model, the two proposed methods can avoid the time domain divergence phenomena effectively. The time domain calculation results of the two proposed methods are approximately equal to the frequency domain calculation results of a complex damping model. The correctness of the two proposed methods is verified.
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INVERSE ANALYSIS OF INTERNAL DEFECTS IN STRUCTURES USING EXTENDED FINITE ELEMENT METHOD AND IMPROVED ARTIFICIAL BEE COLONY ALGORITHM
WANG Jia-ping, DU Cheng-bin, WANG Xiang, JIANG Shou-yan
Engineering Mechanics    2019, 36 (9): 25-31.   DOI: 10.6052/j.issn.1000-4750.2017.11.0874
Accepted: 26 July 2019

Abstract98)      PDF(pc) (506KB)(71)       Save
The information of defect in a structure is determined using the extended finite element method combined with a kind of improved artificial bee colony algorithm, based on real structural response. As searching optimal value may appear in an arbitrary direction in traditional artificial bee colony (ABC) algorithm, weighted average mutation and a cross operator are introduced to avoid the local optimum in the optimizing. The presented inverse method is also used to determine the location of a single-circular-like defect and an elliptical-like defeat and two irregular defects, and the robustness of the algorithm under the condition of measuring error is also studied. The numerical results indicate that the adapting artificial bee colony (AABC) algorithm proposed can present the real information of defects accurately. The convergence speed of AABC is faster than that of traditional ABC, and it is unlikely that the local optimum will appear in the optimizing. The presented method can locate the defects accurately and show a high robustness.
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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
Abstract96)      PDF(pc) (938KB)(82)       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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