Elastic-plastic steel damper(EPSD) is a new device controlling seismic responses.The mechanical principle of EPSD was presented and a comparison was conducted between the theoretical formulas and finite element(FE) si...Elastic-plastic steel damper(EPSD) is a new device controlling seismic responses.The mechanical principle of EPSD was presented and a comparison was conducted between the theoretical formulas and finite element(FE) simulation of damper units.The verified force-displacement hysteretic curve of the damper system was obtained with reference to tests.The Nanjing Jiangxinzhou Bridge(NJB) was subsequently taken as the case to investigate the seismic response control effect of EPSDs on single-tower self-anchored suspension bridges.A 3-dimensional FE model of the bridge was established in ANSYS and the dynamic and static analyses of the bridge were conducted,the control effect of EPSDs under different seismic waves was further investigated through nonlinear time-history analysis based on the validated model.Results showed that both the simplified theoretical and FE simulation methods can preferable reflect the mechanical performance of EPSD,and that seismic responses of NJB with EPSDs are better than those with elastic connection device or fluid viscous damper.However,the control effect of EPSDs is influenced by seismic wave characteristics.展开更多
A new method of robust damper design is presented for elastic-plastic multi-degree-of-freedom(MDOF)building structures under multi-level ground motions(GMs).This method realizes a design that is effective for various ...A new method of robust damper design is presented for elastic-plastic multi-degree-of-freedom(MDOF)building structures under multi-level ground motions(GMs).This method realizes a design that is effective for various levels of GMs.The robustness of a design is measured by an incremental dynamic analysis(IDA)curve and an ideal drift response curve(IDRC).The IDRC is a plot of the optimized maximum deformation under a constraint on the total damper quantity vs.the design level of the GMs.The total damper quantity corresponds to the total cost of the added dampers.First,a problem of generation of IDRCs is stated.Then,its solution algorithm,which consists of the sensitivity-based algorithm(SBA)and a local search method,is proposed.In the application of the SBA,the passive added dampers are removed sequentially under the specified-level GMs.On the other hand,the proposed local search method can search the optimal solutions for a constant total damper quantity under GMs’increased levels.In this way,combining these two algorithms enables the comprehensive search of the optimal solutions for various conditions of the status of the GMs and the total damper quantity.The influence of selecting the type of added dampers(oil,hysteretic,and so on)and the selection of the input GMs on the IDRCs are investigated.Finally,a robust optimal design problem is formulated,and a simple local search-based algorithm is proposed.A simple index using the IDRC and the IDA curve of the model is used as the objective function.It is demonstrated that the proposed algorithm works well in spite of its simplicity.展开更多
Isolation bearings and dampers are often installed between piers and superstructures to reduce the seismic responses of bridges under large earthquakes. This paper presents a novel steel damper for bridges. The damper...Isolation bearings and dampers are often installed between piers and superstructures to reduce the seismic responses of bridges under large earthquakes. This paper presents a novel steel damper for bridges. The damper employs steel plates as energy dissipation components, and adopts a vertical free mechanism to achieve a large deformation capacity. Quasi-static tests using displacement-controlled cyclic loading and numerical analyses using a finite element program called ABAQUS are conducted to investigate the behavior of the damper, and a design methodology is proposed based on the tests and numerical analyses. Major conclusions obtained from this study are as follows： （1） the new dampers have stable hysteresis behavior under large displacements; （2） finite element analyses are able to simulate the behavior of the damper with satisfactory accuracy; and （3） simplified design methodology of the damper is effective.展开更多
This study proposes a novel mild steel damper with non-uniform vertical slits. The influence of different shapes of vertical slits of the core energy plate on the energy dissipation and buckling resistance capacities ...This study proposes a novel mild steel damper with non-uniform vertical slits. The influence of different shapes of vertical slits of the core energy plate on the energy dissipation and buckling resistance capacities is analyzed. Based on the theoretical analysis, formulas of key parameters of the dampers, including the elastic lateral stiffness, shear bearing capacity and yield displacement, are derived. The effectiveness of the proposed damper is demonstrated through pseudo static tests on four 0.25-scale specimens. Performance of these dampers, i.e. cyclic deformation, stress distribution, energy dissipation capacity, etc., are presented and discussed. Using the numerical models of dampers calibrated through test data, earthquake time-history analyses were conducted, and it is observed that the dampers significantly reduce the seismic responses of the prototype frame and have a desirable energy dissipation capacity.展开更多
The crack tip stress-strain fields of the elastic-plastic cracked specimens have been analyzed using finite element calculations.The crack initiation and steady propagation behaviours have also been investigated by me...The crack tip stress-strain fields of the elastic-plastic cracked specimens have been analyzed using finite element calculations.The crack initiation and steady propagation behaviours have also been investigated by means of slip line pattern etching technique and mechanical tests. The results show that there are HRR near field and distant field in the crack tip region,and the later depends on the specimen configuration.The crack initiation behaviour is controlled by a single parameter J.In contrast,the steady crack propagation is affected by the distant strain field and can not be described by single parameter only.展开更多
This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation met...This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.展开更多
Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase ...Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase transformations on the plastic behaviour of a low-alloy steel. It is now well known that the plastic strain rate can then be decomposed as the sum of two terms. The first one corresponds to classical plasticity while the second one is due to the evolution of the transformation and is usually referred to as corresponding to transformation induced plasticity. A theoretical approach of the problem has been achieved ([1][2][3]] and a macroscopic model has been proposed in the case of ideal-plastic phases. The theoretical approach has been assessed and completed using micromechanical numerical simulations but these were based on rather coarse 3D meshes due to limited computer capabilities in the 80’s. This paper presents new finite element micromechanical calculations using refined meshes to analyse the classical plastic behaviour and transformation induced plasticity. The results of the computations are discussed and compared with the calculations initially performed. Finally improvements of the macroscopic model are proposed.展开更多
A new combined steel lead damper (NCSLD) was presented. Construction and working mechanism of NCSLD were introduced,pseudo-static tests of the small size dampers which would be used in the subsequent shaking table tes...A new combined steel lead damper (NCSLD) was presented. Construction and working mechanism of NCSLD were introduced,pseudo-static tests of the small size dampers which would be used in the subsequent shaking table tests were carried out for the study of mechanical properties of NCSLD using electro-hydraulic servo press-shear machine. Processing technology of the damper was improved. Shaking table tests under two-dimensional excitation on structural aseismic control of a one-story structure model were carried out using the small size NCSLD; parameters of the structure and shaking table were also introduced. Results indicate that process improvement is beneficial to the implementation of working mechanism of the damper,NCSLD has full hysteresis loop which takes on bilinearity,NCSLD has obvious energy dissipation effect and it can control structural seismic response effectively.展开更多
The principle of increasing structural loading abillity by the using of elastic-plastic con- trolling design, which can make steel reach a highcr yield slrength through controlling undue strains produced in loaded box...The principle of increasing structural loading abillity by the using of elastic-plastic con- trolling design, which can make steel reach a highcr yield slrength through controlling undue strains produced in loaded box steel structures and no damager to the static mechanical properties of the used materials, is dealt with under the guarantee of strength, rigidity, and stability. A new idea of elastic--plastic controlling design, which is mainly based on the elastic-plastic theory and experi- mental results and is different from the current design which is mainly based handbooks and design- er' s experience, is established. That is: the loading time and its effect on loaded structures are con- sidered, and the potential strength in used matcrials is fully utilized through the controlling of struc- tural strains in design. By the using of this design method, the weight and cost of box structures will be reduced in large amount.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 50908046)the Teaching & Scientific Research Fund for Excellent Young Teachers of Southeast University,the Basic Scientific &Research Fund of Southeast University (Grant Nos. 3205001101,Seucx201106)the Priority Academic Program Development Foundation of Jiangsu Higher Education Institutions are gratefully acknowledged
文摘Elastic-plastic steel damper(EPSD) is a new device controlling seismic responses.The mechanical principle of EPSD was presented and a comparison was conducted between the theoretical formulas and finite element(FE) simulation of damper units.The verified force-displacement hysteretic curve of the damper system was obtained with reference to tests.The Nanjing Jiangxinzhou Bridge(NJB) was subsequently taken as the case to investigate the seismic response control effect of EPSDs on single-tower self-anchored suspension bridges.A 3-dimensional FE model of the bridge was established in ANSYS and the dynamic and static analyses of the bridge were conducted,the control effect of EPSDs under different seismic waves was further investigated through nonlinear time-history analysis based on the validated model.Results showed that both the simplified theoretical and FE simulation methods can preferable reflect the mechanical performance of EPSD,and that seismic responses of NJB with EPSDs are better than those with elastic connection device or fluid viscous damper.However,the control effect of EPSDs is influenced by seismic wave characteristics.
基金Part of the present work is supported by the Grant-in-Aid for Scientific Research(KAKENHI)of the Japan Society for the Promotion of Science(Nos.18H01584,JP20J20811)This support is greatly appreciated.
文摘A new method of robust damper design is presented for elastic-plastic multi-degree-of-freedom(MDOF)building structures under multi-level ground motions(GMs).This method realizes a design that is effective for various levels of GMs.The robustness of a design is measured by an incremental dynamic analysis(IDA)curve and an ideal drift response curve(IDRC).The IDRC is a plot of the optimized maximum deformation under a constraint on the total damper quantity vs.the design level of the GMs.The total damper quantity corresponds to the total cost of the added dampers.First,a problem of generation of IDRCs is stated.Then,its solution algorithm,which consists of the sensitivity-based algorithm(SBA)and a local search method,is proposed.In the application of the SBA,the passive added dampers are removed sequentially under the specified-level GMs.On the other hand,the proposed local search method can search the optimal solutions for a constant total damper quantity under GMs’increased levels.In this way,combining these two algorithms enables the comprehensive search of the optimal solutions for various conditions of the status of the GMs and the total damper quantity.The influence of selecting the type of added dampers(oil,hysteretic,and so on)and the selection of the input GMs on the IDRCs are investigated.Finally,a robust optimal design problem is formulated,and a simple local search-based algorithm is proposed.A simple index using the IDRC and the IDA curve of the model is used as the objective function.It is demonstrated that the proposed algorithm works well in spite of its simplicity.
基金Natural Science Foundation of China under Grant Nos.51178250 and 51261120377Tsinghua University of China under Grant No.2010Z01001
文摘Isolation bearings and dampers are often installed between piers and superstructures to reduce the seismic responses of bridges under large earthquakes. This paper presents a novel steel damper for bridges. The damper employs steel plates as energy dissipation components, and adopts a vertical free mechanism to achieve a large deformation capacity. Quasi-static tests using displacement-controlled cyclic loading and numerical analyses using a finite element program called ABAQUS are conducted to investigate the behavior of the damper, and a design methodology is proposed based on the tests and numerical analyses. Major conclusions obtained from this study are as follows： （1） the new dampers have stable hysteresis behavior under large displacements; （2） finite element analyses are able to simulate the behavior of the damper with satisfactory accuracy; and （3） simplified design methodology of the damper is effective.
基金Natural Science Foundation of China under Grant No.51278104
文摘This study proposes a novel mild steel damper with non-uniform vertical slits. The influence of different shapes of vertical slits of the core energy plate on the energy dissipation and buckling resistance capacities is analyzed. Based on the theoretical analysis, formulas of key parameters of the dampers, including the elastic lateral stiffness, shear bearing capacity and yield displacement, are derived. The effectiveness of the proposed damper is demonstrated through pseudo static tests on four 0.25-scale specimens. Performance of these dampers, i.e. cyclic deformation, stress distribution, energy dissipation capacity, etc., are presented and discussed. Using the numerical models of dampers calibrated through test data, earthquake time-history analyses were conducted, and it is observed that the dampers significantly reduce the seismic responses of the prototype frame and have a desirable energy dissipation capacity.
文摘The crack tip stress-strain fields of the elastic-plastic cracked specimens have been analyzed using finite element calculations.The crack initiation and steady propagation behaviours have also been investigated by means of slip line pattern etching technique and mechanical tests. The results show that there are HRR near field and distant field in the crack tip region,and the later depends on the specimen configuration.The crack initiation behaviour is controlled by a single parameter J.In contrast,the steady crack propagation is affected by the distant strain field and can not be described by single parameter only.
文摘This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing（CCB） and cylindrical friction damper（CFD） were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses（decision variables） using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures.
文摘Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase transformations on the plastic behaviour of a low-alloy steel. It is now well known that the plastic strain rate can then be decomposed as the sum of two terms. The first one corresponds to classical plasticity while the second one is due to the evolution of the transformation and is usually referred to as corresponding to transformation induced plasticity. A theoretical approach of the problem has been achieved ([1][2][3]] and a macroscopic model has been proposed in the case of ideal-plastic phases. The theoretical approach has been assessed and completed using micromechanical numerical simulations but these were based on rather coarse 3D meshes due to limited computer capabilities in the 80’s. This paper presents new finite element micromechanical calculations using refined meshes to analyse the classical plastic behaviour and transformation induced plasticity. The results of the computations are discussed and compared with the calculations initially performed. Finally improvements of the macroscopic model are proposed.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50508012)Science &Technology Plan Project of Guangdong Province(Grant No. 20055190030)+1 种基金Key Basic Research Project of Science and Technology Ministry (Grant No. 2004CCA03300)Science &Technology Project of Guangzhou Education Bureau(Grant No.08C05)
文摘A new combined steel lead damper (NCSLD) was presented. Construction and working mechanism of NCSLD were introduced,pseudo-static tests of the small size dampers which would be used in the subsequent shaking table tests were carried out for the study of mechanical properties of NCSLD using electro-hydraulic servo press-shear machine. Processing technology of the damper was improved. Shaking table tests under two-dimensional excitation on structural aseismic control of a one-story structure model were carried out using the small size NCSLD; parameters of the structure and shaking table were also introduced. Results indicate that process improvement is beneficial to the implementation of working mechanism of the damper,NCSLD has full hysteresis loop which takes on bilinearity,NCSLD has obvious energy dissipation effect and it can control structural seismic response effectively.
文摘The principle of increasing structural loading abillity by the using of elastic-plastic con- trolling design, which can make steel reach a highcr yield slrength through controlling undue strains produced in loaded box steel structures and no damager to the static mechanical properties of the used materials, is dealt with under the guarantee of strength, rigidity, and stability. A new idea of elastic--plastic controlling design, which is mainly based on the elastic-plastic theory and experi- mental results and is different from the current design which is mainly based handbooks and design- er' s experience, is established. That is: the loading time and its effect on loaded structures are con- sidered, and the potential strength in used matcrials is fully utilized through the controlling of struc- tural strains in design. By the using of this design method, the weight and cost of box structures will be reduced in large amount.
