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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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NONLINEAR STATIC RESPONSES OF FGM BEAMS UNDER NON-UNIFORM THERMAL LOADING
MAO Li-juan, MA Lian-sheng
Engineering Mechanics    2017, 34 (6): 1-8.   DOI: 10.6052/j.issn.1000-4750.2015.10.0868
Abstract225)      PDF(pc) (759KB)(964)       Save
Due to the variation in material properties through the thickness of functionally graded material (FGM) structures, an FGM beam simply supported at both ends exhibits characteristics quite different from those of a FGM beam clamped at both ends. An exact, closed form solution is obtained for nonlinear static responses of FGM beams subjected to non-uniform in-plane thermal loadings. The equations governing the axial and transverse deformations of FGM beams are derived based on the nonlinear classical beam theory and the physical neutral surface concept. The two equations are reduced to a single nonlinear fourth-order integral-differential equation governing the transverse deformation. For an FGM beam clamped at both ends, the equation and the corresponding boundary conditions lead to a differential eigenvalue problem, whereas for an FGM beam simply supported at both ends, an eigenvalue problem does not arise due to the inhomogeneous boundary conditions. This consequently results in quite different behavior between a clamped and a simply supported FGM beams. The nonlinear equation is directly solved without any use of approximation and a closed-form solution for thermal bending deformation is obtained as a function of the applied thermal load. By using the exact solutions, the nonlinear deformation problems for buckling, postbuckling and nonlinear bending of the beam can be investigated. Finally, the numerical analyses are carried out to investigate the effects of material gradient properties and thermal loads on the nonlinear static responses of FGM beams.
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STRONG-COLUMN WEAK-BEAM GLOBAL SEISMIC FAILURE MODE CONTROL-BASED DESIGN OF REINFORCED CONCRETE FRAME STRUCTURES
BAI Jiu-lin, JIN Shuang-shuang, OU Jin-ping
Engineering Mechanics    2017, 34 (8): 51-59.   DOI: 10.6052/j.issn.1000-4750.2016.03.0175
Abstract170)      PDF(pc) (824KB)(828)       Save
A strong-column weak beam global seismic failure mode control-based design approach is developed for reinforced concrete (RC) frame structures. Based on the concept of energy balance and plastic internal force mechanism, a modified energy balance equation and design method for plastic internal forces are proposed to achieve the seismic design of structures with different hysteretic behaviour for multiple different seismic hazard levels. Four RC frame structures with different geometry configurations are designed and the distribution of strong-column weak-beam ratio along the height is investigated. Pushover analyses and nonlinear time history analyses under 22 ground motions for severe seismic hazard level are conducted, and the global capacity curves, yield mechanism, maximum inter-story drift ratio distribution as well as the moment demands of column ends are studied. The analytical results indicate that the proposed method can achieve the desired seismic performance and global failure mode without any iterations, avoiding the shortcoming of conventional seismic design method which employs the trial an error strategy to achieve the required seismic performance.
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FLUTTER BOUNDARY PREDICTION OF TURBULENCE EXCITATION RESPONSE BASED ON RANDOM DECREMENT METHOD
LI Yang, ZHOU Li, YANG Bing-cai
Engineering Mechanics    2017, 34 (6): 9-16.   DOI: 10.6052/j.issn.1000-4750.2016.01.0019
Abstract112)      PDF(pc) (421KB)(796)       Save
A flutter boundary prediction technique is developed upon turbulence excitation response of wind tunnel flutter tests. Firstly the random decrement method is employed to extract the system's free decaying signal from the turbulence excitation response. Then main modal parameters, which are needed to establish the stability criterions, are identified through the matrix pencil method. Eventually, a curve fitting about variation of the criterion with dynamic pressure or velocity is plotted to extrapolate the flutter boundary. The simulated and wind tunnel test results show that: the modal parameters of turbulence excitation response can be identified precisely through the method of random decrement and matrix pencil, and the stability criterions have a clear downward trend so that it will be very helpful for advanced prediction of flutter boundary and the reduction of potential risk during flutter tests.
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DISCUSSION AND DEFINITION ON YIELD POINTS OF MATERIALS, MEMBERS AND STRUCTURES
FENG Peng, QIANG Han-lin, YE Lie-ping
Engineering Mechanics    2017, 34 (3): 36-46.   DOI: 10.6052/j.issn.1000-4750.2016.03.0192
Abstract469)      PDF(pc) (944KB)(506)       Save
The yield point is a very critical characteristic of structural performance in design and research of engineering structures, which is the basis of evaluating properties such as ductility, yield-ultimate ratio and so on. However, there is no unified definition and expression for yield point of structures. With the development of new mechanical behavior of emerging structural materials, the existing graphic method, the equivalent energy method, and the residual plastic deformation method are not suitable for them. In this paper, a unified expression of yield point for the typical materials including steel, concrete and fiber reinforced polymer is given based on the original definition of metal yielding under uniaxial tension. Then, for structural members and structures, the definition of the yield point based on the application conditions and the physical reality is proposed, which provides the basis for design of emerging material structures. As examples, this definition is applicable for reinforced concrete beams and short columns. Furthermore, a simplified method named Farthest Point Method is given, which has a specific physical meaning and a wide applicability. This method is more suitable for the computer programming. Based on existing experimental results of members and structures, the rationality of the farthest point method is verified by comparing the yield points defined by farthest point method and the presented definition. Thus, an explicit and unified definition for yield points of materials, members and structures is given in terms of the fundamentals and determination approach.
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RESEARCH AND APPLICATIONS OF PREFABRICATED STEEL STRUCTURE BUILDING SYSTEMS
HAO Ji-ping, SUN Xiao-ling, XUE Qiang, FAN Chun-lei
Engineering Mechanics    2017, 34 (1): 1-13.   DOI: 10.6052/j.issn.1000-4750.2016.08.ST14
Abstract400)      PDF(pc) (3080KB)(430)       Save
The development of steel structures can resolve excess capacity of steel industry and promote building greenization, industrialization and informatization. Promoted by the national policy, the assembled steel structures in China have marched from v1.0 towards v2.0 quickly, during which three new types of building systems have been developed, including the improved system based on traditional steel structures, the modular construction system, and industrialized residential building system. Under the new situation, precast concrete components have solved the traditional problems of steel structures, new types of envelope system have been developed due to the application of different walls, and information technology speeded up the development of the construction industry. Fully assembled steel frames and box-type modular building systems are new types of low-rise multi-story construction system which use the design concept of "building elements". They are based on the combination of basic components including structural components and building functional units, which have the advantages of assembly, integrated envelope, industrialized production and so on. The new MCFTS (Multi-Core Concrete Filled Steel Tube System) high-rise steel structure system is suitable for residential and public buildings. The MCFTS consists of multi-core concrete filled steel tube frame-braced residential system and multi-core concrete filled steel shear-wall-concrete filled steel tube frame system for public buildings. The MCFTS takes the combination of multi-core concrete filled steel tube column and the double side plate beam-to-column connection as its core technology. It can be concluded that the system has excellent seismic performance and can be repaired.
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SHELL-SPRING-CONTACT-GROUND MODEL BASED ON SEGMENT JOINT STIFFNESS NONLINEARITY
XU Guo-wen, WANG Shi-min, WANG Dong-bing
Engineering Mechanics    2016, 33 (12): 158-166.   DOI: 10.6052/j.issn.1000-4750.2015.05.0402
Abstract162)      PDF(pc) (1404KB)(359)       Save
The bending stiffness of segment joints, which has nonlinear characteristics, is related to their moment and axial force. The nonlinear characteristics of joints make tunnel's mechanism complicated. The bending stiffness of joints has great influence on internal force of lining through calculation. So, shell-spring-contact-ground model is established, among which the joint bending stiffness is adjusted according to the joint force. The real stress state of lining is obtained by iterative calculation. The model calculation results are verified through large scale laboratory tests. Then the model is used to analyze the force of Shiziyang tunnel lining in composite strata. The results show that the joint bending stiffness of iterative model is closer to the laboratory tests than constant stiffness model. For composite strata, the difference between iterative model and constant stiffness model is big, and it becomes even larger with the increased ratio of the soft layer thickness to the diameter of tunnel. When shield tunnel is set in homogeneous strata, the joint stiffness at each location of the whole-ring has little difference. If the appropriate values of joint stiffness is chosen, the constant stiffness model can also yield accurate results.
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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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ANALYSIS METHODS FOR THE REINFORCEMENT LOADS OF GEOSYNTHETIC-REINFORCED SOIL RETAINING WALLS
LIU Hua-bei, WANG Lei, WANG Chun-hai, ZHANG Ya
Engineering Mechanics    2017, 34 (2): 1-11.   DOI: 10.6052/j.issn.1000-4750.2016.06.ST11
Abstract213)      PDF(pc) (382KB)(298)       Save
Geosynthetic reinforced soil (GRS) retaining wall is a new type of earth retaining structure. It has the advantages of cost-effectiveness, good performance, and high adaptability, but its application is in need of a rational method to analyze the reinforcement load. Several methods for the analysis of the reinforcement load of GRS retaining walls are discussed, focusing on their applicabilities and limitations. These methods include the active earth pressure method, the K stiffness method, the limit equilibrium method based on slope stability analysis, the nonlinear elastic methods, and the incremental method considering soil dilatancy. It is found that the active earth pressure method and the limit equilibrium method may reasonably calculate the reinforcement load at the strength limit state, providing that the soil strength is fully mobilized, which in turn is dependent on the reinforcement stiffness. Under working stress condition, the analytical methods considering soil-reinforcement compatibility may accurately predict the reinforcement load, providing that the long-term reinforcement stiffness and the influence of facing are properly taken into account.
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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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SEISMIC DAMAGE ASSESSMENT OF RC FRAME STRUCTURES BASED ON VULNERABILTY INDEX
YU Xiao-hui, LÜ Da-gang, FAN Feng
Engineering Mechanics    2017, 34 (1): 69-75,100.   DOI: 10.6052/j.issn.1000-4750.2015.09.0731
Abstract161)      PDF(pc) (762KB)(271)       Save
An index in terms of vulnerability index is proposed to assess structural damage due to earthquake based on conventional seismic fragility analysis. The methodology of assessing earthquake consequences at the regional scale using the damage index is adopted and the numerical expectation of the damage index is calculated to quantify the vulnerability index of an individual building, where the damage state probability is derived through analytical seismic fragility analysis. Two groups of RC frames of 8- and 10-story height are considered as study cases, each of which includes frames designed to various seismic fortification levels. Seismic fragility curves, damage state probability curves, vulnerability index curves and vulnerability indices at frequent earthquake (FE), design-based earthquake (DBE) and maximum consider earthquake (MCE) intensities are computed separately. The results show that the RC frames designed according to the current Chinese codes can basically satisfy the performance requirements of "no damage under FE", "no unrepairable damage under DBE" and "no collapse under MCE". At MCE intensities, the reference frames illustrate good performance of controlling the occurrence of severe damages. Structural resistance against earthquake is enhanced due to the increase of seismic fortification level; however the conditional seismic vulnerability indices upon FE, DBE and MCE are increased accordingly.
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PARAMETER IDENTIFICATION OF NONLINEAR VIBRATION SYSTEMS BASED ON THE HILBERT-HUANG TRANSFORM
WANG Li-yan, LI Dong-sheng, LI Hong-nan
Engineering Mechanics    2017, 34 (1): 28-32,44.   DOI: 10.6052/j.issn.1000-4750.2015.06.0498
Abstract165)      PDF(pc) (576KB)(261)       Save
Parameters of time-varying damping systems and nonlinear vibration systems, such as the Duffing and Van der Pol vibration systems, were identified by the Hilbert-Huang transform (HHT) in this study. The nonlinear vibration signal was first decomposed into free vibration and forced vibration components by the empirical mode decomposition. Subsequently, the amplitude envelope and the instantaneous frequency of the decomposed components were computed by the empirical envelop method. Damping ratios and other parameters of the nonlinear vibration systems were finally identified by using the least square method. Compared with the results from the wavelet analysis, the proposed method is proven to be more effective through numerical simulations of three typical nonlinear vibration systems and is featured by a higher level of accuracy.
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FINITE ELEMENT ANALYSIS OF SEEPAGE IN ROCK BASED ON CONTINUUM DAMAGE EVOLUTION
WANG Yong-liang, LIU Zhan-li, LIN San-chun, ZHUANG Zhuo
Engineering Mechanics    2016, 33 (11): 29-37.   DOI: 10.6052/j.issn.1000-4750.2015.03.0229
Abstract267)      PDF(pc) (6723KB)(257)       Save
Based on continuum damage mechanics, a seepage model for damaged rock reservoirs is established in this paper, which can be used to analyze the damage failure process and seepage characteristics of rock reservoirs. Weibull distribution is used effectively to simulate the heterogeneity characteristics of rock. By statistical strength theory, the Drucker-Prager strength criterion and continuous damage theory, the governing equations and definite conditions of continuous damage evolution via the Biot constitutive relation for rock reservoirs are derived, which are then solved by the finite element method (FEM) to obtain reliable results. Numerical examples are given to show that the proposed method is consistent with the experimental results and to demonstrate the effectiveness and reliability to analyze seepage characteristics, volume fracturing and the mechanical properties of laminated rock mass.
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REVIEW OF ADVANCES AND OUTLOOK IN REANALYSIS METHODS
WANG Hu, CHONG Hao, GAO Guo-qiang, HUANG Guan-xin, LI Guang-yao
Engineering Mechanics    2017, 34 (5): 1-16.   DOI: 10.6052/j.issn.1000-4750.2015.11.0944
Abstract234)      PDF(pc) (1662KB)(248)       Save
Reanalysis is a fast computational method to predict the response of a modified structure based on its initial analysis results. Due to its advantages in efficiency, the reanalysis method has made a significant progress in recent several decades. With the increase of requirements for computational performance in numerical methods, the reanalysis method should play a more important role in complex product design. Therefore, this paper investigates and discusses some characteristics of recent developed directions and approximation methods from the view point of static and dynamical problems. Moreover, some suggestions for advancing the reanalysis method have been also given according to the state of the art reanalysis.
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BUCKLING ANALYSIS OF THIN SHELL USING THE FINITE PARTICLE METHOD
ZHANG Peng-fei, LUO Yao-zhi, YANG Chao
Engineering Mechanics    2017, 34 (2): 12-20.   DOI: 10.6052/j.issn.1000-4750.2015.07.0623
Abstract155)      PDF(pc) (2816KB)(242)       Save
In the perspective of Newton mechanics, the finite particle method (FPM) is a new numerical analysis method, discretizing the analytic domain into a group of particles whose motions can be easily determined according to the forces applied on them. It has extraordinary superiority for analyzing structures and mechanisms with nonlinear properties undergoing rigid body motions or large deformations. Based on FPM, the buckling of a thin shell is analyzed in this paper. In order to trace the full equilibrium path, the explicit arc-length method (ALM) is cooperated to solve the snap through phenomena. Also an explicit contact algorithm is modified for contact analysis during buckling or lager deformation. Finally, several numerical examples with behaviors of static, dynamic etc. are presented to demonstrate the performance and applicability of the proposed approach. Compared with other works and experiments, the results of numerical examples solved by a self-designed program reveal that the presented method is feasible for the buckling analysis of a thin shell and can capture the full equilibrium path during buckling.
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DISCUSSION OF SAFETY FACTOR DEFINITIONS AND COMPUTATION METHODS FOR GEOTECHNICAL STRUCTURES
SONG Er-xiang, KONG Yu-fei, YANG Jun
Engineering Mechanics    2016, 33 (11): 1-10.   DOI: 10.6052/j.issn.1000-4750.2016.06.ST12
Abstract193)      PDF(pc) (408KB)(241)       Save
Taking common geotechnical problems, such as the bearing capacity of soil foundations and slope stability, as examples, two different definitions for the safety factor of structures, i.e. the ratio of limit load to allowable load and that of the available strength to required strength, are discussed. It is noted that the first definition is valid only for certain types of structures, whereas the second can be used for any type of structures. When both definitions can be employed, the proper choice depends on the characteristics as well as the loading environment of a specific structure, and different values for the required safety factor should be specified to reach the same level of reliability when a different safety factor definition is adopted. Moreover, the available methods for the computation of safety factors are reviewed, including the classical methods such as the slip line method, the limit analysis method, and the limit equilibrium method; as well as the modern methods such as the ordinary elasto-plastic finite element method, the strength reduction finite element method, and the finite element limit analysis method. The advantages and disadvantages of each method are discussed, and some suggestions are also presented with regard to their applications.
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INFLUENCE OF SEISMIC ACTION ADJUSTMENTS ON SEISMIC DESIGN AND SAFETY OF RC FRAMES
LU Xiao, LU Xin-zheng, LI Meng-ke, GU Dong-lian, XIE Lin-lin
Engineering Mechanics    2017, 34 (4): 22-31.   DOI: 10.6052/j.issn.1000-4750.2016.11.0871
Abstract301)      PDF(pc) (1072KB)(237)       Save
The experience of Wenchuan earthquake and Lushan earthquake shows that the actual seismic intensity suffered by buildings was often much greater than the code-specified seismic design intensity, which caused very serious damage to buildings. Although the seismic safety margin of buildings in China is in continuous improvement with the updating of seismic design code and seismic hazard map, many experts still believe that to date the seismic safety level of buildings in China is not sufficient yet. Hence, how to determine the reasonable seismic action is important and meaningful to ensure the seismic safety. Based on a series of reinforced concrete frames designed according to the Code for Seismic Design of Buildings (GB 50011-2010), these frames are redesigned with the adjustments of seismic design parameters, including dynamic amplification factor (bmax), seismic action, and dead and live load combination factors. The earthquake-induced collapse analysis is conducted for these frames. Consequently, the influence of the adjustments on the seismic forces, material consumption and seismic safety is discussed. The results indicate that the parameters adjustments make the axial compression ratio for columns increase by about 8%, and the reinforcement ratio for beams and slabs increase by about 6%. For frames whose collapse starts from the bottom story, the parameters adjustments can obviously improve the seismic safety of the frames. However, with the increasing of seismic design intensity, the increased amplitude of seismic safety will decrease slightly.
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A SIMPLIFIED METHOD FOR COLLAPSE-RESISTANT PERFORMANCE EVALUATION OF RC FRAME STRUCTURES
LIANG Dan, LIANG Xing-wen
Engineering Mechanics    2017, 34 (2): 102-110.   DOI: 10.6052/j.issn.1000-4750.2015.06.0492
Abstract145)      PDF(pc) (520KB)(235)       Save
Quantitative evaluation of collapse-resistant performance of structures has attracted widespread attention in the past few years, urging a set of evaluation indexes with practicality and feasibility to be proposed. In this study, based on the requirement for ductility design in national codes for seismic design of buildings in China, the influence of the ratio of column-to-beam moment strength on the collapse-resistant performance of structure was considered. The effect of the ratio of column plastic shear demand-to-shear capacity was also taken into account. In addition, the correlation of the impact caused by the above two structural parameters on the collapse-resistant performance of structures was analyzed. The results indicate that the ratio of column-to-beam moment strength has a significant impact on the collapse-resistant performance of the structure, and so does the ratio of column plastic shear demand-to-shear capacity. The above two structural parameters also exhibit a strong correlation with collapse performance evaluation. At the same time, by adjusting and combining the above two structural parameters, the collapse-resistant performance of structures was investigated, and a simplified evaluation index of the collapse-resistant performance was established, offering a reference to the quantitative evaluation of collapse-resistant performance of structures.
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AN IMPROVED YEOH CONSTITUTIVE MODEL FOR HYPERELASTIC MATERIAL
LI Xue-bing, WEI Yin-tao
Engineering Mechanics    2016, 33 (12): 38-43.   DOI: 10.6052/j.issn.1000-4750.2015.05.0388
Abstract263)      PDF(pc) (484KB)(229)       Save
Rubber is generally regarded as incompressible, isotropic, and hyperelastic material whose constitutive model is usually described in terms of strain energy density functions. An improved Yeoh model for hyperelastic material is proposed in this paper to improve the ‘soft’ property of the Yeoh model. The strain-stress relations of three special deformation modes for the proposed model are presented based on the large deformation theory of continuum mechanics, and compared with those obtained by the original Yeoh model and by the experiment data. It is found that:the improved Yeoh model represents an inversed "S" shape of the strain-stress relation, and effectively overcomes the ‘soft’ property of Yeoh model when predicting the strain-stress curve of equibiaxial extension at the same time. The proposed model precisely predicts the strain-stress relations of uniaxial, planar and equibiaxial tension-compression in a large strain range and has great values in engineering application.
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RESEARCH PROGRESS OF COMPOUND SECTION COLD-FORMED THIN-WALL STEEL STRUCTURES
CHEN Ming, HUANG Ji-hui, ZHAO Gen-tian
Engineering Mechanics    2016, 33 (12): 1-11.   DOI: 10.6052/j.issn.1000-4750.2016.05.ST03
Abstract202)      PDF(pc) (3128KB)(226)       Save
Cold-formed thin-walled steel buildings are characterized by superior seismic behavior and suitable for industrialized construction. These features make it have a place in the construction industry at home and abroad. Meanwhile, it meets the new requirements of China's ‘The thirteenth Five-Year Plan’ for the development of building construction. Researches and design codes on the mechanical performance of cold-formed thin-walled steel buildings were comprehensively reviewed in this paper. Some deficiencies are found in traditional cold-formed thin-walled steel buildings in load-transfer mechanism and member section type. The ‘non-box’ type frame system using cold-formed thin-walled steel compound section was put forward. Summarizing the research progress in mechanical performance of the member, joint, and the overall frame, this paper present formulas of the composite column stability capacity, joint ultimate moment and joint initial stiffness. Finally, some future researches on the compound section cold-formed thin-walled steel frame system are proposed.
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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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A STUDY OF THERMAL-MECHANICAL COUPLED METHOD OF ANALYZING STEEL STRUCTURES' THERMAL RESPONSE IN FIRE BASED ON FDS-ABAQUS
DUAN Jin-tao, SHI Dan-da, WANG Jin-hui, JIAO Yu, HE Pei-shan
Engineering Mechanics    2017, 34 (2): 197-206.   DOI: 10.6052/j.issn.1000-4750.2016.01.0061
Abstract179)      PDF(pc) (7211KB)(223)       Save
To perform thermal-mechanical coupling analysis of steel structures, International Standard ISO834 is commonly employed to describe the temperature-time curve induced by a fire. However, previous studies demonstrated that the ISO834 cannot accurately describe the temperature profile in a real fire. Taking the overall structure as a research object, this paper developed a fire-thermal-structural coupled analysis method based on FDS and ABAQUS, which can be used to simulate the steel structures' thermal response according to the real temperature curve resulting from a fire. The dynamic temperature fields are transmitted from FDS to ABAQUS models through an FDS-ABAQUS coupling interface, which was developed in this study. Meanwhile the mechanical performance of the overall structure under fire is numerically analyzed using ABAQUS. The results of case study demonstrated that the proposed method can effectively transmit temperature fields from FDS to ABAQUS with an error of less than 2.18%. The results of simulation are more accurate when internal forces due to uneven thermal expansion are taken into account.
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COMPARISON STUDY ON CONSTITUTIVE RELATIONSHIP OF LOW YIELD POINT STEELS, Q345B STEEL AND Q460D STEEL
WANG Meng, QIAN Feng-xia, YANG Wei-guo, YANG Lu
Engineering Mechanics    2017, 34 (2): 60-68.   DOI: 10.6052/j.issn.1000-4750.2016.01.0051
Abstract213)      PDF(pc) (1633KB)(221)       Save
In order to investigate the effect of constitutive behaviors on mechanical performance of members and structures, the constitutive relationship tests of LYP100 low yield point steel were carried out firstly. The monotonic behavior, ductility, hysteretic behavior, energy-dissipation capacity and cyclic constitutive model were analyzed. Based on these results, the constitutive relationship of low yield point steel, normal strength steel (Q345B) and high strength steel (Q460D) were fully compared. Finally, the predicted hysteretic behaviors of different steels with both cyclic constitutive model and ideal elastic-plastic model were compared to further discuss the significant effect of constitutive relationship on members and structures. The results show that the monotonic and cyclic tensile-to-yield ratios of low yield point steels are more than 2.0~3.0, 2.0~3.0 times of normal strength steel and high strength steel. Meanwhile, low yield point steels have better ductility and energy dissipation capacity. Because low yield point steels have obvious isotropic behaviors, significant difference is observed between the calculated results using cyclic constitutive model and ideal elastic plastic model. Therefore, for structural analysis, an appropriate constitutive relationship should be adopted according to different steels.
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FATIGUE RELIABILITY EVALUATION OF STEEL BRIDGES BASED ON COUPLING RANDOM VIBRATION ANALYSIS OF TRAIN AND BRIDGE
LI Hui-le, XIA He
Engineering Mechanics    2017, 34 (2): 69-77.   DOI: 10.6052/j.issn.1000-4750.2015.04.0334
Abstract155)      PDF(pc) (710KB)(216)       Save
Based on the random vibration analysis of a coupled train-bridge system, an approach for fatigue reliability assessment of railway steel bridges is presented. A coupled train-bridge system model is established. Train speed and track irregularities are selected as the basic random variables to perform the random vibration analysis and to identify probabilistic models of the equivalent fatigue stress range and its cyclic number of bridge components. On this basis, a fatigue limit state function is constructed to conduct fatigue reliability analysis by using the S-N curve approach. As an illustrative example, the fatigue reliability assessment is performed for a through steel truss bridge on railroad. The effects of train speed and track irregularities on the fatigue reliability of components are discussed. The results show that the presented approach can be utilized to effectively assess the fatigue reliability of railway steel bridges. Because of the randomness in train speed and track irregularities, both the train-induced equivalent fatigue stress range and its number of cycles of bridge components are indeterminate, which should be considered as random variables and can be represented by a lognormal distribution. Train speed and track irregularities can significantly affect the fatigue reliability of bridge members. The reliability indexes of fatigue-critical members increase with the enhancement in track smoothness.
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AEROELASTIC WIND TUNNEL TEST MODEL DESIGN AND EXPERIMENT ON VERY FLEXIBLE HIGH-ASPECT-RATIO WINGS
XIE Chang-chuan, HU Rui, WANG Fei, LIU Yi, CHANG Nan
Engineering Mechanics    2016, 33 (11): 249-256.   DOI: 10.6052/j.issn.1000-4750.2015.04.0254
Abstract194)      PDF(pc) (4985KB)(213)       Save
The aeroelastic characteristics for a very flexible aircraft is the focus of present theoretical research, and the wind tunnel experiment is the necessary way to view the mechanism of large aeroelastic motion and to validate the theoretic method. In order to study the influence for geometric nonlinearity of high-aspect-ratio wings, a wind tunnel model is designed and constructed. With the combination of the theoretic analysis of geometric nonlinear aeroelasticity and the vibration test of the model, the aeroelastic wind tunnel test is performed on the base of consistency between the analysis model and the test model. The experiment results show that the large deformation of a high aspect ratio wing will affect the aeroelastic property to some extent. The large deformation causes the instability of the horizontal bending mode and decreases the flutter speed, which are coincident with the predictions by the nonlinear aeroelastic theoretic method. The flutter speed and the flutter mode are all in a good agreement with those of the theoretic method. Thusly, the availability and accuracy for the geometric nonlinear aeroelastic analysis method is verified.
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AN IMPLICIT DIRECT FORCE IMMERSED BOUNDARY METHOD FOR SIMULATING COMPLEX FLOW
WANG Wen-quan, ZHANG Guo-wei, YAN Yan
Engineering Mechanics    2017, 34 (2): 28-33,93.   DOI: 10.6052/j.issn.1000-4750.2015.07.0600
Abstract123)      PDF(pc) (2415KB)(211)       Save
To avoid the traditional body-fitted numerical methods and extend the application of immersed boundary method to complex flow, a new numerical method for simulating complex flow based on the implicit direct force immersed boundary method is presented. A mathematical model described the interaction between an immersed rigid body and fluid is established and whose governing equation is solved using the projection step method similar to the fractional step method for solving the incompressible Navier-Stokes equation. The moment source is not pre-calculated, but determined implicitly in such a way that velocity at the immersed boundary interpolated from the corrected velocity field accurately satisfies the no-slip boundary condition. Also, the second velocity near the solid wall updated is implemented using a δ smooth function. The QUICK upwind scheme and the second central scheme are applied to solve convection and diffusion terms respectively. The second explicit Adams-Bashforth method is used to the time discretization. The present immersed boundary method(IBM) is validated by the basic numerical example of flowing over one cylinder at Reynolds number 25,40 and 300.
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STUDY ON CONSTITUTIVE MODEL OF HIGH-STRENGTH STRUCTURAL STEEL UNDER MONOTONIC LOADING
SHI Gang, ZHU Xi
Engineering Mechanics    2017, 34 (2): 50-59.   DOI: 10.6052/j.issn.1000-4750.2015.09.0799
Abstract136)      PDF(pc) (422KB)(209)       Save
The constitutive model of steel under monotonic loading is the basis for structure analysis. In order to calculate the response of high-strength steel structures and to analyze the member behaviour more accurately and to give some references to engineers when applying high-strength steel, this paper updated the parameters of the multi-linear constitutive model of high-strength steel and presented a nonlinear constitutive model based on the Ramberg-Osgood model by means of summarizing the experiment results and by carrying out lots of tensile tests. It has been proved that a nonlinear constitutive model could simulate the stress-strain relationship of high-strength steel under monotonic loading well by comparison with the experiment data. Moreover, to give a consideration to both accuracy and efficiency, a revised multi-linear constitutive model is proposed, which could present the nonlinear material property of high-strength steel and show the similarity in the meantime.
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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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ADVANCES IN SHAPE-FREE FINITE ELEMENT METHODS: A REVIEW
CEN Song, SHANG Yan, ZHOU Pei-lei, ZHOU Ming-jue, BAO Yi, HUANG Jun-bin, WU Cheng-jin, LI Zhi
Engineering Mechanics    2017, 34 (3): 1-14.   DOI: 10.6052/j.issn.1000-4750.2016.10.0763
Abstract213)      PDF(pc) (1039KB)(204)       Save
As the most important tool for simulation and computation, the finite element method has been widely applied in engineering and scientific problems. However, this powerful method still suffers from some inherent deficiencies, such as the sensitivity problem to mesh distortion and so on, which have not been completely solved yet. This paper systematacially introduces some research developments on new finite element methods, i.e., the shape-free finite element methods, including the hybrid stress-function elements for plane and 2D fracture problems, the hybrid displacement-function elements for Reissner-Mindlin plate bending problem, and new unsymmetric finite element for plane and 3D elasticity. Based on the existing hybrid stress and unsymmetric finite element methods, some advanced techniques, including the analytical trial function method, new natural coordinate method, generalized conforming technique, etc., were adopted in the aforementioned new approaches. The resulting new finite element models possess high precision and good robustness. In particular, they can keep their level of performance even in extremely distorted meshes. Furthermore, some historical challenges in the finite element method, such as the limitation defined by the MacNeal's theorem, the edge effect problem of the Resissner-Mindlin plate, were also successfully solved. At the end of this paper, some features of the new methods and further development are discussed.
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MODELS FOR DETERMINISTIC AND STOCHASTIC DAMAGE CONSTITUTIONS OF CONCRETE-A SHORT REVIEW
YU Zhi-wu, WU Ling-yu, SHAN Zhi
Engineering Mechanics    2017, 34 (9): 1-12.   DOI: 10.6052/j.issn.1000-4750.2016.04.0291
Abstract121)      PDF(pc) (458KB)(203)       Save
The establishment of a concrete-damage-constitutive model is of great importance to characterize the behavior of concrete and understand the essence of concrete. The research history and the latest progress of concrete damage constitutive models in worldwide were summarized from deterministic and random aspects. The different definition methods, the evolution laws, and the physical mechanism of damage in the literatures are discussed. In addition, by comparing main characteristics such as nonlinearity, stochasticity and strain rate related, some critical issues need to be resolved for the accurate prediction of the concrete behavior are proposed, which provides a reference for establishing a more-reasonable and convenient concrete-damage-constitutive model.
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NUMERICAL INVESTIGATION ON DYNAMIC STALL OF WIND TURBINE AIRFOIL UNDERGOING COMPLEX MOTION
LIU Xiong, LIANG Shi
Engineering Mechanics    2016, 33 (12): 248-256.   DOI: 10.6052/j.issn.1000-4750.2015.04.0364
Abstract228)      PDF(pc) (978KB)(201)       Save
The blade of large-scale wind turbine undergoes significant deflection and vibration during operation, which will impact the dynamic flow field around the blade and consequently alter the aerodynamic forces. Therefore, it is important to develop a deep understanding of the dynamic stall characteristics of airfoil undergoing complex motion, so that the operational loading of large-scale wind turbines can be accurately predicted. Applying computational fluid dynamics (CFD) techniques, this paper presents 2-dimensional numerical simulations of the dynamic stall characteristics of S809 airfoil undergoing different forms of motion. Firstly the dynamic stall behavior of the airfoil undergoing pitching motion in stall-development and deep-stall regimes is simulated using S-A, SST k-ω and RSM turbulence models. Comparisons with the experimental measurements indicate that all the three turbulence models can effectively predict the unsteady aerodynamic forces of the airfoil. Subsequently, the dynamic stall characteristics of the airfoil undergoing flapwise motion and combined pitching edgewise motion are simulated using SST k-ω model. The results are compared with those obtained by considering only pitching motion in the same condition. The dynamic stall of airfoil undergoing flapwise motion is weaker than that of airfoil undergoing pitching motion, but it is considerable and cannot be neglected. The dynamic stall of airfoil undergoing combined pitching edgewise motion is much stronger than that of airfoil undergoing pitching motion. The results suggest that in the design stage of a wind turbine, in order to obtain a conservative aerodynamic loading prediction, it is necessary to translate the motion of the blade cross-section in flapwise and edgewise directions into an equivalent angle of attack, and superimpose it on the main angle of attack to perform the dynamic stall calculation.
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RESEARCH ON LAYOUT PRINCIPLE OF BRACES FOR BUCKLING-RESTRAINED BRACED FRAMES
FENG Yu-long, WU Jing, MENG Shao-ping
Engineering Mechanics    2016, 33 (12): 104-111.   DOI: 10.6052/j.issn.1000-4750.2015.04.0289
Abstract185)      PDF(pc) (589KB)(200)       Save
The layout principle of the buckling-restrained braces (BRBs) for buckling-restrained braced frames (BRBFs) significantly affects the mitigating effect and the structural aseismic performance. To test the mitigating effect, 6-story and 16-story steel moment resisting frames are built as benchmark models. Taking the displacement and the drift concentration factor (DCF) respectively as the indices to measure the structural seismic damage degree and the damage concentration effect, the optimal, economic and practical brace layout principle are studied between the braces and the frames as well as those among different stories. The ruselts show that the mitigating effect is weakened with the increase of the BRB area, and the fundamental period of structures shoud reduce no more than 1.5~2.0 times after installing the BRBs to the main frames. When the linear distribution proportional coefficient of the BRB area among different stories is 0.5~1.0, the DCF of the BRBF is insignificant. Using the performance target that the yielding of the upper BRBs should occur before the adjacent lower frame yielding, a theoretical formula determining the upper limit value of the BRB-area-ratio among different stories is deduced. A numerical example is used to verify the formula, showing that when the stiffness or the yield displacement of the main frames is small, the BRB-area-ratio should be limited rigorously to prevent the serious phenomenon of damage concentration that the BRBs yield only at one or a few stories. Based on the above layout principle, the design process of the BRBF is obtained.
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EXPERIMENTAL STUDY ON AXIAL BEHAVIOR OF CIRCULAR CFRP-STEEL COMPOSITE TUBE CONFINED CONCRETE STUB COLUMNS
GUO Ying, LIU Jie-peng, MIAO Ya-jun, WANG Yu-hang, XU Tian-xiang
Engineering Mechanics    2017, 34 (6): 41-50.   DOI: 10.6052/j.issn.1000-4750.2016.06.0442
Abstract97)      PDF(pc) (3522KB)(199)       Save
CFRP material has many advantages such as high strength, light weight, good durability and corrosion resistance, but the construction procedure of concrete columns confined by CFRP tube is rather complicated, leading to relatively high cost. Instead, CFRP can be utilized to strengthen steel tube confined concrete columns, in which steel tubes serve as the formwork for the construction of CFRP. Therefore, CFRP-steel tube confined concrete columns are very suitable for concrete structures because of their excellent mechanical properties and convenient construction. In this paper, the behavior of circular CFRP-steel tube confined concrete stub columns subjected to axial compression was investigated through experimental study. Associated methods for calculating the ultimate loading capacity of circular CFRP-steel tube confined concrete stub column were compared and recommended for practical design.
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RESEARCH ON MECHANICAL PROPERTIES OF AXIALLY LOADED STEEL COLUMNS REINFORCED BY OUTSOURCING REINFORCED CONCRETE WHILE UNDER LOAD
ZHOU Le, WANG Xiao-chu, BAI Yun-hao, JIA Lian-guang, TAN Xiang-pei
Engineering Mechanics    2017, 34 (1): 192-203.   DOI: 10.6052/j.issn.1000-4750.2015.05.0542
Abstract140)      PDF(pc) (1698KB)(198)       Save
The mechanical properties and methods for calculating the bearing capacity of axially loaded steel columns reinforced by encasing them in reinforced concrete while already under load were researched through the integration of an experimental study, finite element simulation, and theoretical analysis in this paper. Through experimental study and finite element simulation analysis, the mechanical performance of axially loaded steel structure members reinforced by encasing in reinforced concrete while under load was studied. The influence of the initial loads, concrete strength, and steel strength on the ultimate bearing capacity of reinforced members was researched. The results showed that the bearing capacity and the rigidity of the steel members could be significantly improved using this method of reinforcement. The ultimate bearing capacity of reinforced members decreased with the increase of the initial loads, and increased with the increase of the steel strength. The concrete strength was the most important factor that affected the ultimate bearing capacity of reinforced members. The ultimate bearing capacity of reinforced members increased significantly with the increase of the concrete strength. From analysis of the experimental data and the finite element analysis results, the quantitative results of the influences of concrete strength on the ultimate bearing capacity of reinforced members were obtained. Meanwhile, based on the analysis of the stress and strain state of the various parts of the reinforced members at the time of reinforcement and the time of failure, the bearing capacity calculation formulas were derived for axially loaded steel columns reinforced by outsourcing reinforced concrete while under load, and the results thereof are in good agreement with the test results.
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MODEL TESTS ON THERMAL MECHANICAL BEHAVIOR OF ENERGY PILES INFLUENCED WITH HEAT EXCHANGERS TYPES
WANG Cheng-long, LIU Han-long, KONG Gang-qiang, WU Di
Engineering Mechanics    2017, 34 (1): 85-91.   DOI: 10.6052/j.issn.1000-4750.2015.05.0455
Abstract150)      PDF(pc) (797KB)(198)       Save
Pile geothermal heat pump system (also called energy pile) is a new heat pump system that can save underground space and construction cost, which to date has been used at home and abroad. However, the studies focusing on the heat transfer efficiency and mechanical characteristics of piles in dry sand are still limited. Based on the model test, the heat transfer performance and mechanical characteristics of different heat exchange concrete piles in dry sand are investigated. The temperature of pile and soil around pile, the thermal strain and thermal stress of the piles induced by temperature variation are measured. Moreover, the ultimate bearing capacity of the piles associated with different temperatures is analyzed. The results show that, for different types of heat exchangers under the same power of pump, the strain variation and pile head settlement of the W-shaped and S-shaped piles are more significant than that of the single U-shaped pile.
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SOFTWARE DEVELOPMENT AND EXPERIMENTAL VERIFICATION ON REINFORCED CONCRETE FRAME AFTER FIRE BASED ON FIBER ELEMENT
XIA Min, YU Jiang-tao, LU Zhou-dao
Engineering Mechanics    2016, 33 (11): 163-173.   DOI: 10.6052/j.issn.1000-4750.2015.04.0264
Abstract127)      PDF(pc) (9534KB)(197)       Save
Based on the principle of a fiber element model and a layered shell element model, the secondary development is executed with the scripting language of Python on the platform of ABAQUS software and the Analytical System of a Fire-damaged Concrete Frame (hereafter referred to as the system of ASFCF) is established for the purpose of accurately simulating the residual mechanical properties of the reinforced concrete frame after fire. In order to validate the system of ASFCF, two identical size, single-story and single-span spatial reinforced concrete frames with the floor are designed, one will be burned in fire and the other will not be fired. Then, the test of the beams and slabs of these two frames will be conducted under monotonic loading in order. Nonlinear finite element analyses for the two test specimens are carried out by the system of ASFCF. The results show that the simulation agrees well with the test. It indicates that the fiber element model and the layered shell element model can be used to simulate the beams (columns) and slabs of the reinforced concrete frame after fire, respectively. The thermo-mechanical coupled analysis results of the reinforced concrete frame after fire by use of the system of ASFCF are precise and reliable, and the system of ASFCF can be well utilized to calculate and evaluate the residual bearing capacity of the reinforced concrete frame after fire.
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RESEARCH ON BOND-ANCHORAGE BEHAVIOR BETWEEN DEFORMED BARS AND HPP FIBER REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE
NIU Jian-gang, HAO Ji, SUN Li-bin, LI Bo-xiao
Engineering Mechanics    2017, 34 (2): 42-49.   DOI: 10.6052/j.issn.1000-4750.2016.05.ST05
Abstract164)      PDF(pc) (397KB)(194)       Save
Through pull-out test of steel bars with strain gauges attached inside, the effect of bar diameter, la/d and c/d on the bond performance between steel bars and HPP fiber reinforced lightweight aggregate concrete was analyzed. The results of the pull-out test with different influential parameters showed that the bond stiffness between the bar and concrete was enhanced with the increase of steel bar diameter, and the ultimate bond strength was increased firstly and then decreased as the diameter was increased. The ultimate bond strength and corresponding free end displacement was reduced as the anchorage length was increased. The bond toughness declined as la/d was increased. The ultimate bond strength was increased firstly and then tended to become stable with the increase of the relative thickness of concrete cover. By comparing the bar anchorage length formula according to the test results with that given in the code, it was shown that the bar anchorage length formula in the code is conservative in terms of ultimate bond strength.
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IMPACT FAILURE SIMULATION OF A SINGLE-EDGED NOTCHED CONCRETE BEAM BASED ON PERIDYNAMICS
YÜ Yang-tian, ZHANG Qing, GU Xin
Engineering Mechanics    2016, 33 (12): 80-85.   DOI: 10.6052/j.issn.1000-4750.2015.05.0396
Abstract242)      PDF(pc) (2335KB)(192)       Save
An improved method for deriving micromodulus in the prototype microelastic brittle (PMB) material of peridynamics (PD) is proposed to remove the "skin effect" of the original PMB model, and then the failure process of a single-edged notched concrete beam subjected to impact loading is simulated by the improved PMB model. The crack propagation angle, trajectory and the maximum crack growth speed in the mixed-mode fracture can be achieved from PD simulation. The results predicted by PD are compared with those of experiments and other numerical methods to verify the accurateness of the improved model. As an effective method in solving impact problems of structures, PD does not have the element size sensitivity when used to simulate the failure process and contains the description of fracture and damage in its constitutive models.
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A URBAN SEISMIC DAMAGE ANALYSIS MODEL FOR TALL BUILDING GROUPS
XIONG Chen, XU Zhen, LU Xin-zheng, YE Lie-ping
Engineering Mechanics    2016, 33 (11): 49-58.   DOI: 10.6052/j.issn.1000-4750.2015.08.0713
Abstract189)      PDF(pc) (4382KB)(191)       Save
Tall buildings are very important parts of urban building groups and current building computational models are not able to meet the requirements of urban seismic analysis for tall buildings. In this work, a nonlinear multiple degree-of-freedom (MDOF) flexural-shear (NMFS) model and its corresponding parameter determination method are proposed. The model has the following advantages:1) Appropriate consideration of nonlinear flexural-shear deformation mode of tall buildings. Compared with traditional nonlinear MDOF shear (NMS) model, the accuracy is significantly improved and the response result agrees well with the refined finite element (FE) model; 2) High computational performance, which is more than 60000 times faster than the refined FE model; 3) Very convenient parameter determination. The nonlinear parameters of the model can be determined using limited building data (i.e., structural height, year of construction, site condition and structural type) of each building; 4) The ability to output time-history responses and inter-story drifts, which may facilitate the future engineering demand parameter (EDP) based loss estimation for tall building in urban area. In this study, a representative tall building is selected to demonstrate the modelling and parameter determination processes of the proposed NMFS model. Verifications are made by comparing with the refined FE model. Finally the method is used to perform the urban seismic analysis for the Central Business District (CBD) of Beijing, which proves the applicability of the method for tall buildings in urban area. Outcomes of this work are expected to provide a useful reference for future works on urban seismic loss estimation of tall buildings.
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INCREMENTAL DAMAGE SPECTRA OF MAINSHOCK-AFTERSHOCK SEQUENCE-TYPE GROUND MOTIONS
YU Xiao-hui, LÜ Da-gang, XIAO Han
Engineering Mechanics    2017, 34 (3): 47-53,114.   DOI: 10.6052/j.issn.1000-4750.2016.03.0206
Abstract175)      PDF(pc) (1112KB)(191)       Save
To quantitatively assess the secondary damage caused by aftershocks on a mainshock-damaged structure, this study focuses on the incremental damage spectra of mainshock-aftershock sequence-type ground motions. A set of 533 real mainshock-aftershock sequences were selected as the input. The index proposed by Park and Ang (1985) was used to define structural damage due to earthquake. The incremental damages induced by aftershocks were quantified by the difference between the structural damages caused by mainshocks and mainshock-aftershock sequences. Results show that the incremental structural damages due to aftershocks show a large degree of variability. Some mainshock-aftershock sequences cause significant incremental damages as oppose to others. In comparison to the structures with short natural periods, the ones with medium-to-large natural periods show larger incremental damages under mainshock-aftershock sequences. If the predominant period of the mainshock is greater than that of the corresponding aftershock, this mainshock-aftershock sequence can be viewed as the unfavourable one, which probably causes significant incremental structural damages.
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EXPERIMENTAL RESEARCH ON SEISMIC PEFORMANCE OF FRAME PIERS OF DOUBLE-DECK VIADUCTS
ZHANG Jie, GUAN Zhong-guo, LI Jian-zhong
Engineering Mechanics    2017, 34 (2): 120-128.   DOI: 10.6052/j.issn.1000-4750.2015.07.0557
Abstract123)      PDF(pc) (1512KB)(188)       Save
Based on a double-deck viaduct, two double-deck viaduct piers with different column longitudinal reinforcement ratios are designed and the influence of the longitudinal reinforcement ratio on the seismic performance of double-deck viaducts is investigated with pseudo-static test and numerical analysis. The experiment results show that the beam and lower-level beam-column joints of the high reinforced pier suffer severe damage. When the reinforcement ratio is reduced, damage mainly appears on the column, and the level of damage on the beam and the joint is mitigated effectively. Based on the experiment results, a finite element model of the pier is built and used for parametric analysis. The analysis results indicate that when the column longitudinal reinforcement ratio increases, the ductility capacity of double-deck viaducts decreases and the beam would collapse before the column, which disobeys the performance objective of strong beam and weak column.
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