Study on the Seismic Behavior of Structures

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Multi-point seismic motions based on focal mechanism and considering local site multi-layer soil effect: theory and program implementation Chinese Journal of Computational Mechanics, 2012 Download
Seismic damage simulation for urban buildings based on high-performance GPU computing Proc. 14th Int. Conference on Computing in Civil and Building Engineering, 2012 Download
Evaluation of Modal and Traditional Pushover Analyses in Frame-Shear-Wall Structures Advances in Structural Engineering, 2011  
Spectra of bedrock earthquake motion and improvement of bedrock displacement input calculation model considering SSI effect Chinese Journal of Rock Mechanics and Engineering, 2011 Download
Multi-scale finite element modeling and its application in the analysis of a steel-concrete hybrid frame Chinese Journal of Computational Mechanics, 2010 Download
Evaluating method of element importance of structural system based on generalized structural stiffness Journal of Architectural and Civil Engineering, 2010 Download
Elasto-plastic seismic analysis for the Beijing Automobile Museum Building Structure, 2009 Download
Seismic performance evaluation using nonlinear time history analysis with three-dimensional structural model for a hybrid frame-core tube structure Journal of Building Structures, 2009 Download
Seismic performances and failure mode analysis of hybrid frame-core tube structures Building Structure, 2009 Download
Influence of post-yielding stiffness to seismic response of building structures Journal of Building Structures, 2009 Download
Finite element analysis and engineering application of RC core-tube structures based on the multi-layer shell elements China Civil Engineering journal, 2009 Download
Comparative evaluation of pushover analysis and modal pushover analysis with invariant spatial earthquake load Journal of South China University of Technology (Natural Science Edition), 2008 Download
Nonlinear static analysis for frame-shear-wall structures Earthquake Resistant Engineering and Retrofitting, 2008 Download
Study on ensuring the strong column-weak beam mechanism for RC frames based on the damage analysis in the Wenchuan Earthquake Building Structure, 2008 Download
Multiscale finite element modeling and its application in structural analysis Journal of Huazhong University of Science and Technology (Urban Science Edition), 2008 Download
Study on the influence of post-yielding stiffness to the seismic response of building structures Proc. the 14th World Conference on Earthquake Engineering, October 12-17, 2008 Download
Analysis on Building Seismic Damage in Wenchuan Earthquake Journal of Building Structures, 2008 Download
Influence of the inter-story post-yield stiffness to the variance of seismic response Engineering Mechanics, 2008 Download
Seismic nonlinear analytical models, methods and examples for concrete structures Engineering Mechanics, 2006 Download
Elasto-plastic Analysis for A Steel Frame-Core Wall Structure Sichuan Building Science, 2008 Download
Introduction of Robustness for Seismic Structures Building Structures, 2008 Download
Study on lateral load patterns of pushover analysis using incremental dynamical analysis for RC frame structures Journal of Building Structures, 2008 Download
Analysis of earthquake-resistant behaviors for RC columns under variable axial loads Industrial Construction, 2007 Download
Numerical Simulation for the Hysteresis Behavior of RC Columns under Cyclic Loads Engineering Mechanics, 2007 Download
High Performance Simulation for Building Structures under Disaster Proc. 1st Symp. on High Performance Computing (HPC) Technology in Engineering Design, 2007 Download
Study on the Accuracy and Applicability of the Pushover Analysis Earthquake Resistant Engineering and Retrofitting, 2008 Download
Spatial finite element analysis for the whole-process of RC core tubes based on the layered shell element Proc. 11th Conf. on earthquake resistance technology of high-rise buildings, 2007. Download
Elasto-plastic time-history computational model for steel frame-core wall structures Architecture Technology, 2007 Download
Parametric study of structural stiffness after yielding on inelastic seismic response for multi-degree of freedom structural systems Journal of Disaster Prevention and Mitigation Engineering, 2007 Download
Numerical Simulation for the Hysteresis Behavior of Prestressed Conrete Structures under Cyclic Loads Earthquake Resistant Engineering, 2006 Download
High strength/performance structural materials and the developments of modern engineering structures and the design theory Proc. 1st International Forum on Advances in Structural Engineering, 2006 Download
Nonlinear FE model for RC shear walls based on multi-layer shell element and microplane constitutive model Proc. Computational Methods in Engineering And Science (EPMESC X), 2006 Download
Shear force distribution in RC frame-shearwall structures under static and dynamic loads Proc. 1st National Symposium on the Research Progress for the Safety of Cities and Engineering, 2006 Download

Multi-point seismic motions based on focal mechanism and considering local site multi-layer soil effect: theory and program implementation,
Chinese Journal of Computational Mechanics, 2012, 29(4): 582-588.

Abstract: n this paper, a framework for generating multi-point earthquake motion of target filed in China, basing on focal mechanism and taking account of the spatial variability of soil properties, is given and proposed. The main contents include: (1) the transfer function of site including multiple soil layers is established based on random vibration theory, (2) based on the improved bedrock spectrum applicable to the target site in China, the variability among different site condition is reflected by establishing the transfer function of local site, (3) non-flat factor of site surface is considered on the basis of previous literature, (4) explicit expression phase-angle change by the filtration of multiple soil layers is also given for the convenience of the subsequent program code. Then, according to the theory framework, the visual program MEMS V2011.6 (Multi-support Earthquake Motions Simulation Version 2011.6) is developed and run successfully. The specific functions of the program involves the focal parameters assignment, inputting soil parameters, calculating and displaying transfer function of site soil with multi-layer, adjusting non-stationary parameters and frequency, generating multi-point earthquake motion histories, verifying the coherence of spatial seismic motions, fitting code-specified spectrum for bridge, building and electronic facility. In addition, based on a bridge example, the multi-point seismic motions of the target field are generated using the program MEMS V2011.6, and the sensibility analysis of the generated ground motions to local site effect and epicentral distance is analyzed as well. The content in this paper involve theory and practicability, and can provide directly reference for engineering.
Key words: multi-point earthquake motion; beck-rock spectrum; local soil site; non-stationary; code-specified response spectrum

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Seismic damage simulation for urban buildings based on high-performance GPU computing,
Proc. 14th Int. Conference on Computing in Civil and Building Engineering, 2012.06. Moscow, Russia :368-369

Abstract: Refined models have been an important development trend of urban regional seismic damage prediction. However, the application of refined models has been limited due to their high computational cost if implemented on traditional Central Processing Unit (CPU) platforms. In recent years, Graphics Processing Unit (GPU) technology has been developed and applied rapidly due to its powerful parallel computing capability and low cost. In this paper, a simulation method for urban regional seismic damage is developed based on GPU-CPU cooperative computing technology, which reduces the computing time significantly. The seismic damage simulation is then applied to a medium-sized city using the proposed method to illustrate the unique advantages of GPU technology in large-scale regional seismic damage simulations.
Keywords: urban regional seismic damage simulation, GPU, parallel computing

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Evaluation of Modal and Traditional Pushover Analyses in Frame-Shear-Wall Structures
Advances in Structural Engineering, 2011, 14(5): 815-836.

Abstract: Nonlinear static analysis (or pushover analysis) has been widely used in the last decade as a simplified and approximate method to evaluate the structural seismic performance and to estimate inelastic structural responses under severe ground motions. However most currently used pushover procedures with invariant lateral load patterns cannot fully reflect the effect of higher-order modes on structural dynamic responses. To overcome such a problem, a so-called Modal Pushover Analysis (MPA) was proposed based on the modal decoupling response spectrum method where the effect of higher modes was considered. To date, most research on MPA has been focused on frame structures. In engineering practice, however, most medium-to highrise building structures are in the form of frame-shear-wall. Therefore it is necessary to extend the current research activity to implement the MPA to frame-shear-wall structures. In this study, two reinforced concrete frame-shear-wall structures of 10 and 18 stories are analyzed to evaluate the performance of the MPA method and the pushover procedures with invariant load patterns. The evaluation is based on the exact solutions of a nonlinear dynamic time-history analysis. The results show that the MPA method including higher-order modes is more accurate than the other pushover procedures. This is more evident when estimating structural responses for high-rise structures than the medium-rise counterparts.
Key words: nonlinear static analysis, nonlinear time-history analysis, modal pushover analysis (MPA), frameshear-wall structures, medium-to high-rise structures.

Spectra of bedrock earthquake motion and improvement of bedrock displacement input calculation model considering SSI effect,
Chinese Journal of Rock Mechanics and Engineering, 2011, 30(5): 884-892.

Abstract: In this paper, the applicability of spectra of bedrock earthquake motion and rationality of calculation model considering soil-structure interaction (SSI) for structural seismic response analysis are studied. Firstly, in order to obtain the spectra of bedrock earthquake motion in China, not only the expressions of the current spectra of earthquake bedrock motion are compared and the preferred one is selected, but also the high-cut filter function is modified to fit the recorded earthquake motion of target fields in China. Then, the current SSI calculation model for structural seismic response analysis is expounded essentially and the unnegligible problem inherent in the model is pointed out. To solute the problem, the Massless Rigid Element (MRE) method proposed by the authors to solute the problem inherent in the earthquake ground displacement input model is extended and applied to solute the corresponding problem in the current bedrock displacement input model considering SSI effect. At last, based on the works above, the program for generating bed-rock displacement spectrum is coded and a soil-layers model is analyzed. The analysis results can further indicate that the MRE method is quite applicable to the calculation model considering SSI effect. The works of this paper belong to fundamental study and can provide necessary reference for the relevant study of SSI effect.
Keywords: bedrock earthquake motion; Massless Rigid Element (MRE) method; soil-structure interaction (SSI)

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Multi-scale finite element modeling and its application in the analysis of a steel-concrete hybrid frame,
Chinese Journal of Computational Mechanics, 2010, 27(3): 469-475.

Abstract: As an effective process to obtain appropriate balance between accuracy requirements and calculation workloads, multi-scale calculation has been introduced into many research fields as well as different engineering practices. In the field of structural multi-scale finite element analysis, an important research question is how to make the local microscopic model and structural macroscopic model work together. To accomplish a reliable interface between microscopic model and macroscopic model, a methodology was proposed and its constraint equations of deformations including axial deformation, transverse deformation and rotation were presented. With a user-defined subroutine, the multi-scale modeling was realized in commercial finite element software and a simple tube was calculated to verify the methodology. Based on an accurate microscopic column-to-beam connection model validated by test, elasto-plastic multi-scale analysis of a steel-concrete hybrid frame was carried out and the results show that multi-scale calculation can simulated the complex boundary condition of this connection well. The proposed methodology meets the deformation compatibility well at the interface between different-scale models and is applicable in engineering application.
Keywords: multi-scale; interfacial connection; finite element; engineering application; elasto-plastic time history analysis

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Evaluating method of element importance of structural system based on generalized structural stiffness
Journal of Architectural and Civil Engineering, 2010, 27(1): 1-6.

Abstract: A summary of existing researches and engineering experience on element importance in the structural systems were presented. Based on the consensus that elements transferring more loads in the load path were generally more important in the structural systems, the element importance index was defined as the change in generalized structural stiffness under a certain load pattern after removing the element from the system. Then, the generalized structural stiffness taking into account the load pattern was proposed as a basis for evaluating the element importance. This index was further expressed in terms of the rate of structural strain energy change. The element importance of a series of frame structures under gravity and horizontal seismic load were then evaluated by the proposed method. The results show that the method is rational, convenient for calculating, and applicable to most structures.
Keywords: Structural safety, element importance index, generalized structural stiffness, loading path, structural strain energy

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Elasto-plastic seismic analysis for the Beijing Automobile Museum,
Building Structure, 2009, 39(12): 118-120.

Abstract: The Beijing Automobile Museum is a stadium structure with complex shape, which also has some complicated steel-reinforced concrete joints to carry the columns that sit on beams. This work uses macro-scale nonlinear finite element model with fiber-beam-element and multi-layer-shell-element to study the elasto-plastic static and transient seismic response of the whole structure, and micro-scale model with continuum elements to study the elasto-plastic behavior of the complicated joints. The loading capacities of the joints from the micro-scale model are compared with the internal forces from the global structural analysis. The results show that the Beijing Automobile Museum can satisfy the seismic requirement of design fortification VIII, and the joints have enough strength. This work provides examples for the elasto-plastic seismic analysis of similar stadium structures.
Keywords: Beijing Automobile Museum, seismic resistance, elasto-plastic analysis, joint loading capacity

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Seismic performance evaluation using nonlinear time history analysis with three-dimensional structural model for a hybrid frame-core tube structure,
Journal of Building Structures, 2009, 30(4): 119-129

Abstract: Accurate prediction for the structural nonlinear behaviors is important to the structural safety assessment against earthquakes. Some new models, which are used to establish three-dimensional structural model for nonlinear time history analysis under strong earthquakes, are presented. In these models, the material stress-strain relationship can be connected directly with the force-displacement behavior of the structural elements, such as beams, columns, shear walls and core tubes, so that the complicated coupled axial force-bending moment-shear force behaviors, as well as the corresponding cycle behaviors, can be properly simulated. With the secondary development user subroutines, convenient p re and post process functions and extinct nonlinear capacity of general purpose FEA software of MSC. MARC, the spatial seismic responds of structures can be simulated in detail. A practical hybrid frame-core tube structure was analyzed with dynamic time-history analysis based on these models and the complicated seismic behaviors of the structure were simulated. According to the analytical results under ground motions with different intensities, the exterior frame and the core tube made up of four sub-tubes in this structure can form effective dual seismic resistant system which has three seismic fortification lines: coup ling beam, sub-tubes and exterior frame.
Keywords: hybrid frame-core tube structure; fiber model; multi-layer shell element; nonlinear analysis; seismic performance

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Seismic performances and failure mode analysis of hybrid frame-core tube structures,
Building Structure, 2009, 39(04): 1-6.

Abstract: Frame-core tube system is a type of structure which is widely used in the high-rise buildings. In this paper, the seismic behaviors are analyzed and the rational failure mode of this structure system is discussed. And it is proposed that by controlling the yielding mechanism and failure mode of the core tube based on the idea of the capacity design method and making sure the outer frame has sufficient loading carrying capacity and ductility at the same time, the seismic performance of the frame-core tube structure will be improved and multiple seismic fortification lines can be established. A practical frame-core tube hybrid structure is analyzed with pushover method and dynamic time-history analysis respectively as an example. The analytical results show that the reasonably designed frame-core tube structure can form effective dual seismic resistant system which has three seismic fortification lines: coupling beam, sub-tubes and outer frame. Besides, the structure system has adequate energy dissipation ability and can achieve the rational failure mode.
Keywords: frame-core tube structure, failure mode, seismic performance, seismic fortification lines

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Influence of post-yielding stiffness to seismic response of building structures,
Journal of Building Structures, 2009, 30(2): 17-29.

Abstract: The accurate prediction of elasto-plastic structural response is necessary for establishing the performance based seismic design method of building structures. The influence of post-yield stiffness of structures on the dispersion of elasto-plastic structural response is studied based on a large number of elasto-plastic time-history analysis of single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) systems. The analytical results show that: for SDOF systems with moderate or long vibration periods, the maximal elasto-plastic displacements and the corresponding dispersions will not obviously change with larger post-yield structural stiffness. On the contrary, the maximal elasto-plastic displacements and the corresponding dispersions will obviously reduce by larger post-yield stiffness for SDOF systems with short vibration periods. And for MDOF systems with larger post-yield stillness, the ductility factors and energy dissipations will trend to be evenly distributed, together with obvious smaller dispersions of maximal elasto-plastic inter-story drift. At the end of this paper the engineer measures to increase the structural post-yield stiffness is discussed and three typical examples are demonstrated to illustrate the methods of building up a hardening-type structure from the structural systematic level consideration.
Keyword: earthquake, inelastic response, inelastic system, post-yielding stiffness, discreteness, performance based design

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Finite element analysis and engineering application of RC core-tube structures based on the multi-layer shell elements
China Civil Engineering journal, 2009, 42(3): 51-56.

Abstract£ºAs one of the most widely used lateral resistant structures, reinforced concrete (RC) core tube consists of diverse members and appears spatial mechanical behaviors. Therefore, how to accurately simulate the RC tubes for the whole process of nonlinear behaviors is an important problem in seismic analysis of structures. Based on the multi-layer shell element, the whole process simulation of a pseudo-static testing on RC core tubes is presented in the paper. By correct modeling of the key parts (such as walls, coupling beams, reinforcement), the numerical model is able to simulate the spatial behavior of the tube as well as the complicated nonlinear behaviors such as the yielding and shear failure of coupling beams, cracking of the tube and so on. Results from the simulation match well with those from the tests. Using the proposed core-tube model, an elastoplastic analysis for a practical framed core-tube structure is conducted, to illustrate the implementation of proposed model in real structures. The tube model based on multi-layer shell is helpful in the elasto-plastic analysis of high-rise building under severe earthquakes.
Keywords£ºCore tube, Finite element, Multi-layer shell, Elastoplastic calculation, Seismic Analysis

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Comparative evaluation of pushover analysis and modal pushover analysis with invariant spatial earthquake load
Journal of South China University of Technology (Natural Science Edition), 2008, 36(11): 121-128.

Abstract: Nonlinear static analysis procedure is now widely used as a simplified effective method for estimating the inelastic responses of structures under severe ground motions. Based on structural dynamics theory, the modal pushover analysis (MPA) procedure is proposed to consider effect of the higher structural response modes, which is equivalent to standard response spectrum analysis for elastic systems. Although the MPA procedure is common in structural engineering practice, there are few researches on comparative evaluation of pushover analysis and MPA procedure with invariant spatial earthquake load. Herein, MPA and pushover procedures are estimated to compare with incremental nonlinear dynamic time history analysis with invariant spatial earthquake load for a six-story and a ten-story. It is indicated that the both pushover and MPA procedures give good prediction for inelastic roof displacements, especially the MPA procedure. Whereas, the estimation of the maximum story drift of structure needs to be improved and requires further more investigation.
Key words: nonlinear static analysis, nonlinear time history analysis, modal pushover analysis, RC frame, fiber model

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Nonlinear static analysis for frame-shear-wall structures
Earthquake Resistant Engineering and Retrofitting, 2008, 30(6): 41-48.

Abstract: Nonlinear static analysis (or pushover analysis) has been widely used recently as a simplified method to evaluate the structural seismic performance and estimate inelastic structural responses under severe ground motions. But most traditional pushover procedures, which have fixed lateral load patterns that are major based on first structural modal, can not reflect the effect of the higher modal on the structural dynamic response. To overcome this problem, Chopra et al. has proposed a new pushover procedure which is referred as modal pushover analysis (MPA) based on the modal decoupling response spectrum method to consider the effect of the higher mode. Currently, most MPA research is focused on frame structures. In this paper, the problem of MPA when it is implemented in frame-shear-wall structures is high lighted together with proposed solution method. An eighteen story reinforced concrete frame-shear-wall structure is used as an example to benchmark the accuracy of traditional pushover method and MPA method. The structural responses with MPA method and traditional pushover methods are compared with the results of incremental nonlinear dynamic time history analysis, which shows that MPA procedure gives better prediction for inelastic responses of the structure.
Keywords: nonlinear static analysis, nonlinear time history analysis, modal pushover analysis, RC frame-shear-wall structure

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Study on ensuring the strong column-weak beam mechanism for RC frames based on the damage analysis in the Wenchuan Earthquake
Building Structure, 2008, 38(11): 52-59.

Abstract: Typical earthquake damages of RC frames in the Wenchuan earthquake are reviewed with some brief analyses. Special attentions are given to the absence of the preferable damage mode of RC frames known as the ¡°strong column-weak beam¡± mechanism. Analysis is conducted in depth in order to discover the underlying reasons for this adverse phenomenon in the following aspects: influence of the partitions and floor slabs, possible reasons for under-estimating the strength and stiffness of frame beams, reasons for the over-reinforcement of frame beams, factors that may weaken frame columns, structural model changing under stronger earthquake, the difference of reliability of columns and beams under different load stages and so on. Suggestions of ensuring the ¡°strong column-weak beam¡± mechanism for RC frames are proposed for the reference of future design practice and code revision.

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Multiscale finite element modeling and its application in structural analysis
Journal of Huazhong University of Science and Technology (Urban Science Edition), 2008, 25(4): 76-80.

Abstract: A methodology to connect microscopic finite element model to macro model is proposed, which is important to carry out multiscale finite element analysis (FEA) of stuctures. Both the theory and the verifying example show that the methodology meets the deformation compatibility well at the interface between different-scale models. Based on the methodology, a precise microscopic finite element model is implanted into a macro frame structure model to form a multiscale model. In the end, a further example of application is given.
Keywords: multiscale calculation, interface connection, finite element, engineering application£¬elasto-plastic time history analysis

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Study on the influence of post-yielding stiffness to the seismic response of building structures
Proc. the 14th World Conference on Earthquake Engineering, October 12-17, 2008, Beijing, China, CDROM.

ABSTRACT: The response dispersion of structures under strong earthquakes significantly restricts the implementation of performance based seismic design. Besides the variation of earthquake inputs, the inelastic characteristics of structures themselves are also the influence factors on the seismic response dispersion of structures, in which the post-yielding stiffness is key parameters. In this paper the inelastic time-history analysis of numbers of SDOF and MDOF systems are studied to investigate the influence of post-yielding stiffness on the inelastic seismic response and the dispersion. The analytical results show that, (1) for SDOF system, the larger positive post-yielding stiffness will result in smaller the maximum displacement and especially the residual displacement, (2) for the MDOF system, the larger positive post-yielding stiffness results in more uniform distribution of hysteresis energy dissipation and the smaller variation of the maximum inelastic story drift. Hence, the larger of the positive post-yielding stiffness will result in a better control of structural performance under earthquake, so that the performance based design can be easier implementation. The methods to increase the post-yielding stiffness and some practical examples are finally presented in this paper.
KEYWORDS: inelastic seismic response, post-yielding stiffness, dispersion, performance based design

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Analysis on Building Seismic Damage in Wenchuan Earthquake
Journal of Building Structures, 2008, 29(4): 1-9.

Abstract: On May, 12, 2008, an earthquake with a magnitude of 8.0 happened in Wenchuan, Sichuan Province. The earthquake resulted in a large number of collapses and damages of buildings, and brought huge loss to the people's lives and properties. This paper gathers the building seismic damage data in major disaster area from the investigation work of the civil and structural groups of Tsinghua University, Xinan Jiaotong University and Beijing Jiaotong University. The data are classified according to structural type, construction time, earthquake intensity and function of usage. The characters of building seismic damage in this earthquake is analyzed with typical building damage cases, and the lessons are concluded on structural type selection, structural design and construction management and so on.
Keywords: Wenchuan earthquake, Seismic damage analysis, seismic damage cases

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Influence of the inter-story post-yield stiffness to the variance of seismic response,
Engineering Mechanics, 2008, 25(7): 133-141.

Abstract: The remarkable discreteness of seismic response of structures under strong earthquakes significantly restricts the implementation of performance based seismic design. Response variation may be caused by the variant ground motions and the seismic capabilities of structures. Based on numerical simulations, the influence of structural stiffness after yielding on the inelastic seismic response for multi-degree of freedom (MDOF) structural systems is discussed. By avoiding degradation of structural stiffness after yielding, damage concentration in structures may be prevented which would also reduce the discreteness of inelastic seismic responses. Moreover, it is studied that structures with higher stiffness after yielding are more effective to control the seismic performance of structures, that will achieve the aims of performance based seismic design.
Key words: earthquake response; inelastic MDOF system; stiffness after yielding; discreteness; performance based design

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Seismic nonlinear analytical models, methods and examples for concrete structures
Engineering Mechanics, 2006, 23(sup. II). 131-140.

Abstract: Structures will enter nonlinear stage in strong earthquake, precisely prediction for the nonlinear behavior of reinforced concrete (RC) structures in earthquake is important to assess the aseismic safety of the structures. This paper presents the programs recently developed by the Civil Engineering Department of Tsinghua University, which include the fiber model based the program THUFIBER for RC frames, the program NAT-PPC for prestressed concrete (PC) frames, and multi-layer shell element based shear wall program. These programs can connect the nonlinear nodal force/nodal displacement relationship of elements directly with the nonlinear stress/strain relationship of materials. So complicated cycle behaviors and coupled axial force-biaixal bending-shear behaviors of the RC structures can be correctly simulated. And furthermore, with the convenient pre/post process and nonlinear capacity of common finite element software, these programs not only can precisely simulate the spatial structural nonlinear seismic response, but also can simulate some extreme nonlinear problems such as blast or collapse. The precision and the capacity of the programs are illustrated in this paper with a series of researches and applications.
Keywords: reinforced concrete, seismic, nonlinear, fiber model, shear wall, multi-layer shell

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Elasto-plastic Analysis for A Steel Frame-Core Wall Structure
Sichuan Building Science, 2008, 34(3): 5-10.

Abstract: Structures will enter nonlinear stage during strong earthquakes. Hence accurate prediction for the structural nonlinear behaviors is important to the safety and loss assessment during earthquakes. This paper reviews the existed nonlinear analytic models for structures and presents some novel models for structural nonlinear analysis that recently developed by the Tsinghua University. With these models, the material stress-strain relationship can be connected directly with the force-displacement behavior of the structural elements. So that the complicated coupled axial force-bending moment-shear force behaviors can be properly simulated, as well as the corresponding cycle behaviors. With the secondary development user subroutines, convenient pre and post process functions and extinct nonlinear capacity of general purpose FE software of MSC.MARC, the spatial seismic responds of structures can be precisely simulated. A steel frame-core wall structure with an eccentric tube is analyzed with static pushover and dynamic time-history analysis to demonstrate the applications of the new models.
Keywords: nonlinear analysis, structure, seismic, fiber model, shear wall, multi-layer shell

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Introduction of Robustness for Seismic Structures
Building Structures, 2008, 38(6): 11-15
.

Abstract:The concept of robustness of structures is firstly introduced in this paper. And importance with enough robustness for seismic structures in preventing collapse of the structures under strong intensity earthquake attack is discussed. Then the approaches to increase the robustness of seismic structures, including structural systems, strength and ductility of structure, failure modes and redundancy, are suggested.
Keywords: seismic structure; robustness; structural systems; integrity; failure mode; strength; ductility; redundancy elements.

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Study on lateral load patterns of pushover analysis using incremental dynamical analysis for RC frame structures
Journal of Building Structures, 2008, 29(2): 132-140.

Abstract: In this research, the nonlinear static p rocedures with different lateral load patterns were compared by using incremental dynamical analysismethod based on a six2storey and a ten2storey RC frame fibermodel. For each story of different frames, the inter2story shear force vs. drift curves computed by pushover analysis by using different lateral load patterns and time history analysis with a series of earthquake records on the design site have been compared to give a rational lateral load pattern of pushover analysis. Finally, for a whole frame structure, the lateral load pattern choice was suggested, that is,
uniform load pattern was better for the stories near foundation; load pattern with the story heights taken into consideration was suitable for the mid stories and the SRSS pattern or Chinese Code pattern was suitable for upper stories. It is also shown that the nonlinear static p rocedure gives a safe estimation of the inelastic seismic response statistically for regular RC frames with good numerical stability.
Keywords: RC frame; fiber model; pushover analysis; incremental dynamic analysis; inter-storey shear force and drift relation

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Analysis of earthquake-resistant behaviors for RC columns under variable axial loads
Industrial Construction, 2007. 37(12): 71-75.

Abstract: Precise prediction for the hysteretic behaviors of reinforced concrete (RC) column under seismic load is important to assess the safety of RC structures under earthquake. Due to the overturning moment in the earthquakes, besides being subjected to seismic lateral forces, RC columns also experience variable axial loads. Therefore the influence of variable axial forces must be taken into account when to study the hysteretic behaviors of RC columns under cyclic loads. In this paper, a numerical analysis model based on a fiber model program have been validated firstly through the rational hysteretic simulations of two RC columns under various patterns of axial loads, Then a frame column has been simulated under various patterns of variable axial loads by numerical method. The analytical results indicate that the variety of axial loads has considerable effect on the hysteretic behaviors of RC columns. Because of the randomness of axial loads and to facilitate carrying on experimental researches and analyzing earthquake-resistant behaviors for RC structures, a equivalent fixed axial load method is put forward to determine the seismic behaviors of RC column in structures under earthquake.
Keywords: fiber model; variable axial load; concrete column; earthquake-resistant behavior; hysteretic analysis

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Numerical Simulation for the Hysteresis Behavior of RC Columns under Cyclic Loads
Engineering Mechanics, 2007, 24(12): 76-81

Abstract£ºPrecise prediction for the hysteresis behaviors of reinforced concrete (RC) columns under seismic loads is important to assess the safety of RC frames and bridges during sever earthquake. Due to the complicated material behavior and complex external force during the earthquake, an accurate simulation of the behaviors under seismic loads currently mainly depends on numerical method, and more precisions are demanded for the hysteresis constitutive laws of concrete and steel reinforcement. In this paper, a fiber model program is developed with more precise hysteresis constitutive laws of concrete and steel reinforcement. Two columns, which are under cyclic compressive-bending loads, with different axial load ratios and reinforcement ratios are analyzed and the simulation results are found agreed well with test results.
Key words: fiber model; cyclic load; concrete column; hysteretic relation; numerical analysis

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High Performance Simulation for Building Structures under Disaster
Proc. 1st Symp. on High Performance Computing (HPC) Technology in Engineering Design, 2007. Dec. 11-12, Shanghai: 93-101.

Abstract: Buildings and building clusters could be destroyed by disaster load, such as earthquake and blast. Accurate prediction for the behavior of building structures in various disasters provided by high-performance numerical computing is important to structural design. The Department of Civil Engineering in Tsinghua University developed a series of advanced numerical models including material laws and element models. Therefore, base on parallel computing and nonlinear methods, analyses about some extreme problems of building structures such as collapse, overturning and the loss of earthquake damage of urban building clusters are successfully processed. Hence, the analyses provide important advice for disaster prevention and mitigation.
Keywords: building structure, high-performance simulating analysis, finite element model, progressive collapse, blast wave, urban building clusters

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Study on the Accuracy and Applicability of the Pushover Analysis
Earthquake Resistant Engineering and Retrofitting, 30(1), 2008, 55-59.

Abstract: The nonlinear static pushover analysis procedure is now widely used as a simple method to estimate the inelastic seismic response for building structures. However, the accuracy of the method still needs to be validated because of the inherent limitation in the theory of the method. Besides, there are some confines on the application of this method. In this paper, a 6-storey RC frame and an 18-storey RC frame-wall structure are analyzed with both pushover method and the incremental dynamical analysis method respectively. The comparison between the results of the two methods shows that the pushover method can be used only for low structures which are controlled by the first modal shape. It is also shown that for the structures which are influenced by the higher modal shape evidently, pushover analysis always gives the much lower capacity result.
Keywords: pushover analysis, RC frame, frame-wall structure, IDA

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Spatial finite element analysis for the whole-process of RC core tubes based on the layered shell element
Proc. 11th Conf. on earthquake resistance technology of high-rise buildings, Nov. 2007. Kunming, China, 184-189.

Abstract£ºAs the most widely used lateral resistant structures, RC core tubes consist of various members and perform spatial mechanical behaviors. Therefore, how to accurately simulate the RC tubes for the whole process of nonlinear behaviors is a significant subject in seismic analysis of structures. Based on the layered shell element the whole process simulation of a pseudo-dynamic testing on RC core tubes is presented in the paper. By correct modeling of the key structural elements (such as walls, coupling beams, reinforcements), the model is able to reflect the spatial behavior of the tube as well as the complicated nonlinear behaviors of the yielding and shear failure of coupling beams, cracking of the tube and so on. Furthermore, results from the simulation match well with those from the tests, which show the finite element model is of some help on elasto-plastic calculation of high-rise RC tubes in severe earthquakes.
Keywords£ºCore tube, Finite element, Layered shell, Elasto-plastic calculation, Seismic Analysis

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Elasto-plastic time-history computational model for steel frame-core wall structures
Architecture Technology, 2007, 38(sup.), 242-244.

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Parametric study of structural stiffness after yielding on inelastic seismic response for multi-degree of freedom structural systems
Journal of Disaster Prevention and Mitigation Engineering, 27(sup.), 2007, 158-162.

Abstract: The remarkable discreteness of seismic response of structures under strong earthquakes significantly restricts the implementation of performance based seismic design. Response variation may be caused by the variant ground motions and the seismic capabilities of structures. Based on numerical simulations, the influence of structural stiffness after yielding on the inelastic seismic response for multi-degree of freedom structural systems is discussed. By avoiding degradation of structural stiffness after yielding, damage concentration in structures may be prevented which would also reduce the discreteness of inelastic seismic responses. Moreover, it is studied that structures with higher stiffness after yielding are more effective in controlling the seismic performance of structures, that will achieve the aims of performance based seismic design.
Keywords: earthquake response; inelastic MDOF system; stiffness after yielding; discreteness; performance based design, cumulative hysteretic energy dissipation

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Numerical Simulation for the Hysteresis Behavior of Prestressed Conrete Structures under Cyclic Loads
Earthquake Resistant Engineering, 28(6), 2006, 25-29.

Abstract: Due to progressively using in practical construction of prestressed concrete structures, the researches for seismatic performance of prestressed concrete (PC) structures has remarkable significance in engineering practice. Because of the complicated behavior of material and loads, the precise simulation of PC structures or members under cyclic loads has to depend on numerical model. In this paper, a numerical analysis model for the simulation of PC member structures has been developed on the basis of a fiber model program. A PC frame, an unbonded PC frame and an unbonded PC column under cyclic loads are simulated with the developed program. The comparison of the results between simulations and tests indicates that, for the reason of using rational hysteretic material model and exactly considering the influence of prestressing, the numerical analysis model based on fiber models developed in this study can accurately predict the hysteretic properties of PC structures and can be used in the parametric analysis and mechanism study.
Keywords: fiber model; cyclic load; prestressed concrete; analysis method

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High strength/performance structural materials and the developments of modern engineering structures and the design theory
Proc. 1st International Forum on Advances in Structural Engineering, Beijing: China Building Industry Press, Beijing, 2006, 208-250.

Abstract: This paper firstly presents the latest development of high strength/performance structural materials in recent years. The rational applications and examples of high strength/ performance structural materials in the structural systems to obtain high performance are discussed and presented. The positive functions of high strength reinforcement used in reinforced concrete frame structures, that can enhance the structural performance against earthquake and reduce the structural seismic damage, are investigated in detail with nonlinear pushover analysis and dynamic analysis. The results show that the high seismic performance of the reinforced concrete frames, including a delayed appearance of plastic hinges at the bottom story columns feet, to form a rational failure mechanism under strong earthquake, and a small residual displacement after earthquake that cause an easy retrofitting after earthquake, can be obtained by replacing normal strength reinforcement with high strength reinforcement in the columns. Finally, the development of the safety and design theory for the structures using high strength/performance materials are discussed.
Keywords: High strength/performance concrete; High strength/performance steel; Engineering Structures; Structure safety; Design theory; Accidental event; Earthquake resistance.

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Nonlinear FE model for RC shear walls based on multi-layer shell element and microplane constitutive model
Proc.
Computational Methods in Engineering And Science (EPMESC X), Tsinghua University Press & Springer-Verlag, Aug. 2006, Sanya, Hainan,China, 2006, CDROM.

Abstract: Nonlinear simulations for structures under disasters have been widely focused on in recent years. However, precise modeling for the nonlinear behavior of reinforced concrete (RC) shear walls, which are the major lateral-force-resistant structural member in high-rise buildings, still has not been successfully solved. In this paper, based on the principles of composite material mechanics, a multi-layer shell element model is proposed to simulate the coupled in-plane/out-plane bending and the coupled in-plane bending-shear nonlinear behaviors of RC shear wall. The multi-layer shell element is made up of many layers with different thickness. And different material models (concrete or rebar) are assigned to various layers so that the structural performance of the shear wall can be directly connected with the material constitutive law. And besides the traditional elasto-plastic-fracture constitutive model for concrete, which is efficient but does not give satisfying performance for concrete under complicated stress condition, a novel concrete constitutive model, referred as microplane model, which is originally proposed by Bazant et al., is developed to provide a better simulation for concrete in shear wall under complicated stress conditions and stress histories. Three walls under static push-over load and cyclic load were analyzed with the proposed shear wall model for demonstration. The simulation results show that the multi-layer shell elements can correctly simulate the coupled in-plane/out-plane bending failure for tall walls and the coupled in-plane bending-shear failure for short walls. And with microplane concrete constitutive law, the cycle behavior and the damage accumulation of shear wall can be precisely modeled, which is very important for the performance-based design of structures under disaster loads.
Keywords: shear wall, nonlinear analysis, microplane, finite element, multi-layer shell element

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