考虑退化效应的非弹性体系震后概率残余位移分析

震后残余位移是评价工程结构震后可修复性和可用性的重要指标,而刚度和强度退化对震后残余位移的影响显著。本文采用综合考虑刚度和强度退化效应的非弹性地震动力响应分析的Bouc-Wen模型,结合从NGA强震数据库中所筛选的69条强震记录,定量地分析了刚度和强度退化效应对非弹性体系震后概率残余位移的影响,进而以自振周期、屈服后刚度比以及刚度和强度退化参数作为控制参数,建立了考虑退化效应的非弹性体系震后残余位移的预测模型。分析表明,刚度退化导致非弹性体系的位移时程曲线向平衡点位置方向偏移,从而引起残余位移减小;强度退化使非弹性体系的位移时程曲线向远离平衡点位置方向偏移,从而导致残余位移增大;增大结构的屈服后刚度比可以有效减小非弹性体系的残余位移。     

基于Reinborn-Valle损伤模型的填充墙框架结构地震损伤分析

本文采用Reinborn-Valle损伤模型,并考虑结构构件的刚度、强度退化以及捏拢效应,对都江堰市某拟建的填充墙框架结构,从考虑和不考虑填充墙两个方面进行罕遇地震作用下的损伤分析。     

单自由度结构体系抗地震倒塌能力研究

首先介绍了结构倒塌分析的单自由度模型。然后,基于结构抗倒塌能力谱,研究了结构周期、结构延性、屈服后刚度和软化段刚度、滞回捏拢、承载力和刚度退化以及P-Δ效应对单自由度结构体系抗地震倒塌能力的影响。最后通过远场、近场有速度脉冲和近场无速度脉冲3组地震动输入下抗地震倒塌能力谱的比较,研究了地震动特性对结构抗倒塌能力的影响。结果表明:结构的自振周期、延性和P-Δ效应是抗地震倒塌能力的主要影响因素;自振周期为0.4~1.8 s的单自由度结构在近场有速度脉冲的地震动作用下更易发生倒塌破坏,而自振周期为2.6~5.0 s的单自由度结构在远场地震动作用下更易发生倒塌破坏。     

考虑动力损伤退化的钢筋混凝土柱恢复力模型

基于16根钢筋混凝土柱的静力和动力循环往复加载试验,研究了动力效应对柱抗震性能的影响。依据修正Park-Ang损伤指标建立的静力和动力损伤指标,能够兼顾考虑最大位移与循环加载次数对柱损伤退化指标的影响。分别建立静力和动力加载下性能退化参数与相应位移比、损伤指标之间的关系,并结合建构的动力退化函数,提出能够反映滞回曲线的负刚度段、循环退化效应以及捏缩效应的钢筋混凝土柱动力恢复力模型。与试验数据对比的结果表明,提出的宏观力学模型可以有效模拟静力和动力加载情况下钢筋混凝土柱的滞回特性,且动力恢复力模型相比于静力恢复力模型能够更好地刻画钢筋混凝土柱在地震应变率作用下的力学性能。文中建立的恢复力模型及方法可为钢筋混凝土结构的抗震分析提供理论参考。     

双段消能摇摆结构体系弹性地震反应的简化分析模型及参数分析

双段消能摇摆结构体系是基于单段摇摆结构体系应用于高层建筑的发展,由两段串联的摇摆结构、主体结构、刚性连杆以及位移型阻尼器组成,可以减小高层建筑结构在地震作用下的动力响应,控制主体结构变形更加均匀,并削弱结构高阶振型的影响,提高结构的抗震性能。基于双段消能摇摆结构体系的刚度组成,建立了双自由度简化分析模型,并结合有限元分析模型进行验证。提出了影响双段消能摇摆结构体系弹性地震反应的无量纲控制参数,结合参数分析的结果,给出了无量纲控制参数的建议范围。研究表明,双自由度简化分析模型可以准确模拟双段消能摇摆结构体系的弹性地震反应,并较准确地反映了主体结构刚度、阻尼器刚度对结构弹性动力响应的影响,降低结构的计算成本;相比于单段摇摆结构,双段摇摆结构能够减小高层建筑下段结构的弹性地震反应,提高高层建筑的抗震性能。     

基于OpenSEES的RC梁柱组合件低周反复试验数值模拟

梁柱节点是框架结构的关键部位,在地震作用下节点核心区的非弹性变形将导致节点失效甚至结构倒塌。基于某钢筋混凝土框架中间层中节点拟静力试验,利用OpenSEES分析平台,建立了宏观单元分析模型。基于节点区的三种失效机制,采用核心区剪切块、钢筋滑移和交界面剪切三分量组合的方法来模拟节点的二维非弹性性能。用修正压力场理论对核心区剪切块的骨架曲线进行标定。数值模型采用多点位移同步控制的加载模式,用罚刚度法施加位移边界条件。结果表明:经参数标定的数值模型较好地模拟了捏拢效应、加卸载路径和强度退化;但由于节点模型中未考虑楼板,导致梁端底部钢筋较早屈服,反向加载骨架较试验值低。     

钢框架结构在地震作用下累积损伤分析及试验研究

钢框架结构在强地震作用下将进入非线性状态,结构的刚度和强度等力学性能随之降低,从而影响到结构以后的抗震性能。因此,如何确定结构在一次或多次地震作用后的力学性能,是结构在多次地震作用下动力分析的重要内容,为了达到这个目的,首先需要确定结构在每次地震作用后各层的累积损伤指数,再通过损伤指数来定量确定结构的剩余刚度和剩余强度。本文通过钢框架结构的多次振动台模拟试验,应用损伤力学理论,建立钢框架结构在地震作用下考虑损伤累积效应的双线性恢复力模型,结构在地震作用下的动力分析采用层间模型,并运用Wilson-θ法进行计算分析,通过试验和计算的对比,在多次地震作用后,由于框架结构的层间模型产生了强度和刚度的退化,考虑损伤累积效应后的计算结果更符合试验结果,最终为地震作用后的结构的修复和抗震能力的评估提供分析基础。     

两层预制板砖砌体结构房屋模型双向拟动力试验研究

对一栋缩尺为1∶2的两层单开间预制板砖砌体结构房屋模型进行不同强度地震作用下的双向拟动力试验和非线性地震响应分析,研究该结构在地震作用下的破坏机制、变形、滞回特性及耗能能力等。结果表明：构造柱与圈梁的存在,使得预制板砌体结构具有较好的延性,地震破坏主要集中在底层,即使墙体严重开裂,也不至于整体结构垮塌;双向地震作用下一个方向的承载力与刚度退化会加剧另一个方向承载力与刚度的退化,从而导致砌体结构整体抗震能力的下降;滞回曲线由弓形最后发展到反S形,具有明显的捏缩和滑移效应;建立的砌体结构非线性空间有限元模型,能够反映预制板砌体结构的弹塑性地震响应,计算结果与实测结果基本吻合;两层砌体结构房屋能够满足设计规范的抗震要求。     

薄钢板剪力墙结构滞回行为研究

为研究薄钢板剪力墙结构的滞回行为,采用通用有限元分析软件ABAQUS建立其非线性有限元分析模型,并对计算平台、单元选取、网格划分、初始缺陷施加及材料循环本构模型等予以介绍。结合国内外已有的钢板剪力墙拟静力试验,验证了提出的分析模型能够准确地模拟由于平面外变形、局部屈曲、塑性应变累积等因素造成的承载力和刚度退化、曲线捏拢等,并预测了结构的破坏形态。在此基础上,结合试验结果以及有限元分析结果对钢板剪力墙的滞回性能、承载性能、耗能行为、损伤退化特征以及断裂性能进行分析。试验和有限元分析结果均表明:不同的钢板剪力墙局部构造会影响结构的滞回性能、耗能能力、损伤退化行为以及承载性能;开竖缝钢板剪力墙能够显著提高结构的耗能能力,改善曲线捏拢情况,但其承载力有较大降低;加劲钢板剪力墙承载性能有所提高,但其荷载-位移滞回曲线仍然存在明显的捏拢现象,因此在实际工程中需要对加劲肋的尺寸进行优化,使其能够提供足够的约束,有效提高结构抗震性能。     

土与一般刚度偏心结构地震动力相互作用的研究

采用极坐标表示楼层任意刚度偏心位置,能更加详细地分析结构各层刚度中心在任意位置的偏心对结构平移-扭转耦合地震响应的影响,另外考虑实际边界条件,即并入土与结构相互作用（SSI）以达到结构整体性能,因而提出了分析土与一般刚度偏心结构地震动力相互作用的基本框架.首先,采用极坐标建立双向地震作用下两层一般刚度偏心结构（GSES）的动力方程（6个自由度）;接着,使用5个自由度土阻抗函数来表征土与一般刚度偏心结构相互作用;最后,建立土与一般刚度偏心结构相互作用（SGSESI）的动力方程,使用SGSESI系统的标准化均方根位移和加速度来分析其地震动力相互作用.通过设置不同的刚度偏心位置,数值研究了在双向地震作用下,考虑SSI的同轴、非同轴刚度偏心对结构平-扭耦合地震响应的影响.     

Physical Parameter Identification of Structural Systems with Hysteretic Pinching

This research investigates the physical parameter identification of a nonlinear hysteretic structure with pinching behavior for real‐time or rapid structural health monitoring (SHM) after a major seismic event. The identification procedure is based on the overall least squares linear regression and hypothesis testing. It is applied to a general, nonlinear slip‐lock (SL) pinching model. In particular, the hysteresis loop is reconstructed using data available from current sensor technologies. The path dependent hysteresis response is first divided into different loading and unloading subhalf cycles with a single valued function. These subhalf cycles are then assumed to be piecewise linear, and the number of segments for each subhalf cycle is identified using the sup F type test. The overall least squares linear regression is finally applied to the identified subhalf cycles to compute the regression coefficients and breakpoints that yield the elastic stiffness, plastic stiffness, and cumulative plastic deformation. The performance and robustness of the proposed method is illustrated using a single degree of freedom shear‐type reinforced concrete structure with 10% added root mean square noise and variable pinching behavior. The proposed method is shown to be computationally efficient and accurate in identifying the damage parameters within 10% of true values. These results indicate that the system is able to capture nonlinear behavior and structural parameters, such as preyielding stiffness, postyielding stiffness and cumulative plastic deformation, directly relevant to damage and performance using a computationally efficient and simple method. Finally, the method requires no user input and could thus be automated and performed in real time for each half cycle, with results available effectively immediately after an event, as well as during an event, if required.     

Effects of connection deformation softening on behavior of steel moment frames subjected to earthquakes

In the years since the 1994 Northridge earthquake, the profession has paid significant attention to the potential effects of various forms of deterioration in connection strength and stiffness that steel moment-resisting frames can experience during severe seismic excitations. The brittle connection fractures that a number of welded steel moment-resisting frame structures experienced during recent earthquakes have been the most extensively studied to date. However, cyclic testing of post-Northridge beam-column connections demonstrates that ductile connections may suffer other forms of deterioration. Negative post-yield tangent stiffness or capping, hereafter referred to as deformation softening, is a behavior of particular interest because it may have significant adverse effects on frame system behavior. The effects of deformation softening on frames subjected to pulse excitations were examined as part of an integrated experimental and analytical investigation of the effect of various forms of hysteretic deterioration on the overall system behavior of moment resisting steel frames. Pulse excitations, and the near-field ground motions they represent, can be highly damaging to structures and are therefore the primary focus of the results presented in this paper. The experimental portion of this study consisted of a series of thirty-two shaking table tests, which were performed on a one-third scale, two-story, one bay, steel moment frame with idealized, mechanical connections. These tests and subsequent analytical studies show that, in general, significant loss of connection strength capacity, whether from deformation softening or other types of deterioration, leads to large residual drifts and, for large pulse excitations with durations longer than the fundamental period of the structure, to collapse. In particular, frames with connections exhibiting negative post-yield stiffness tend to have substantially increased peak and residual displacements when subjected to pulse excitations.     

框架-核心筒结构整体抗震性能评价指标研究与应用

在已有的动力弹塑性时程分析和模型振动台试验中发现,受损伤程度和损伤部位的影响,结构各阶振型对应的周期变化(刚度退化)不同。为此,基于动力作用下结构刚度退化,提出了框架-核心筒结构整体抗震性能的评价指标——刚度退化系数及其计算方法,并通过已完成的两个实际工程缩尺模型振动台试验进行验证。试验和计算结果吻合较好,所得的刚度退化系数变化规律一致。利用刚度退化系数指标对5个框架-核心筒模型进行抗震性能评价和比较,结果表明：框架-核心筒结构模型的刚度退化系数随着峰值加速度的增加而增大;在设防烈度及超设防烈度的罕遇地震作用下,单重体系模型的刚度退化系数明显高于双重体系模型,且相同峰值加速度下框剪比越大的模型刚度退化系数越低;双重体系的抗震性能优于单重体系,且框剪比越大的模型,其整体延性和抗震韧性更好。刚度退化系数指标概念明确、计算简便,评价结论与倒塌概率、倒塌储备系数等指标一致,可作为框架-核心筒结构整体抗震性能的评价指标。     

Research and application on overall seismic performance evaluation index of frame-core tube structure

在已有的动力弹塑性时程分析和模型振动台试验中发现，受损伤程度和损伤部位的影响，结构各阶振型对应的周期变化(刚度退化)不同。为此，基于动力作用下结构刚度退化，提出了框架-核心筒结构整体抗震性能的评价指标——刚度退化系数及其计算方法，并通过已完成的两个实际工程缩尺模型振动台试验进行验证。试验和计算结果吻合较好，所得的刚度退化系数变化规律一致。利用刚度退化系数指标对5个框架-核心筒模型进行抗震性能评价和比较，结果表明：框架-核心筒结构模型的刚度退化系数随着峰值加速度的增加而增大；在设防烈度及超设防烈度的罕遇地震作用下，单重体系模型的刚度退化系数明显高于双重体系模型，且相同峰值加速度下框剪比越大的模型刚度退化系数越低；双重体系的抗震性能优于单重体系，且框剪比越大的模型，其整体延性和抗震韧性更好。刚度退化系数指标概念明确、计算简便，评价结论与倒塌概率、倒塌储备系数等指标一致，可作为框架-核心筒结构整体抗震性能的评价指标。     

Efficient Modeling Scheme for Transient Analysis of Inelastic RC Structures

Abstract: Simple modeling schemes for efficient and reliable analysis of reinforced concrete structures in the inelastic range are presented. The objective of the modeling techniques is to represent overall behavior in terms of macromodels. A reinforced concrete structure is discretized into a series of macroelements: beam columns, shear walls, and general-purpose inelastic springs. Each element macro-model is developed from distributed flexibility concepts in which the effects of spread plasticity are implicitly included. Nonlinear material behavior is specified by means of hysteretic force-deformation models that incorporate stiffness degradation, strength deterioration, and pinching or bondslip effects. The models are incorporated into a microcomputer program that is capable of analyzing two-dimensional or entire three-dimensional wall-frame systems that can be discretized into a series of interconnected parallel frames. Solution modules for nonlinear static, monotonic, quasistatic cyclic, and transient seismic loads are developed. The efficiency and reliability of the modeling are demonstrated in terms of its effectiveness in reproducing experimentally observed behavior.     

Strength reduction factor for MDOF soil–structure systems

In most of the seismic design provision, the concept of strength reduction factor has been developed to account for inelastic behavior of structures under seismic excitations. Most recent studies considered soil–structure interaction (SSI) in inelastic response analysis are mainly based on idealized structural models of single degree‐of‐freedom (SDOF) systems. However, an SDOF system might not be able to well capture the SSI and structural response characteristics of real multiple degrees‐of‐freedom (MDOF) systems. In this paper, through a comprehensive parametric study of 21600 MDOF and its equivalent SDOF (E‐SDOF) systems subjected to an ensemble of 30 earthquake ground motions recorded on alluvium and soft soils, effects of SSI on strength reduction factor of MDOF systems have been intensively investigated. It is concluded that generally, SSI reduces the strength reduction factor of both MDOF and more intensively SDOF systems. However, depending on the number of stories, soil flexibility, aspect ratio and inelastic range of vibration, the strength reduction factor of MDOF systems could be significantly different from that of E‐SDOF systems. A new simplified equation, which is a function of fixed‐base fundamental period, ductility ratio, the number of stories, structure slenderness ratio and dimensionless frequency, is proposed to estimate strength reduction factors for MDOF soil–structure systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of support flexibility on seismic responses of a reticulated dome under spatially correlated and coherent excitations

Reticulated domes with substructure system are affected by multiple-support seismic excitations that are spatially correlated and coherent. The influence of the coherency on the seismic responses of such a structure has been investigated but the effect of the spatial correlation and coherency on the responses for the system with different flexibility of the substructure has not been studied. A parametric investigation is carried out to address this issue for a single-layer reticulated dome. For the analysis, sets of records for multiple-support are simulated and used for time history analysis. The statistics of the responses of the dome with substructures of varying degree of flexibility are extracted from analysis, and compared with those obtained under uniform excitations. The results show the importance of considering spatially correlated and coherent excitations, especially as the stiffness of the substructure system increases. They also show that a flexible substructure system for the dome acts as a “base isolation” system for the dome under spatially correlated and coherent multiple-support excitations, and reduces the potential yielding and damage of the structure under large earthquakes. As the stiffness of the substructure system increases the consideration of uniform excitations instead of spatially correlated and coherent excitations can underestimate the seismic load effect by more than 25% for structural members in the reticulated dome and by more than 100% for the columns.     

Statistical evaluation of the damage potential of earthquake ground motions

This study focuses on the damage potential of earthquake ground motions based on the inelastic dynamic response of equivalent single degree of freedom structures. Their yield resistances are selected in accordance with seismic design codes. An index accounting for the accumulation of damage due to inelastic excursions is used to represent structural damage. A set of 94 ground motions are employed for this analysis, which are all scaled to the same peak ground acceleration of 0.4 g. Earthquake ground motions are classified with respect to both the ratio of peak velocity to peak acceleration (V/A ratio) and their effective excitation duration. The effect of these parameters on damage potential is investigated by using sensitivity analysis and probabilistic techniques. It is concluded that both V/A ratio and effective duration significantly influence the damage potential of earthquake ground motions, although they are not represented appropriately by the spectral definitions of earthquake excitations in seismic design codes.     

Modelling criteria for r/c elements constructed with ultra‐high‐strength concrete and subjected to cyclic loading

High‐strength concrete (HSC) has several benefits in high‐rise concrete buildings; however, its structural use in active seismic regions may be questioned due to the lower ductility of such concretes. In addition, seismic macro‐models being used currently are based on R/C elements constructed with normal‐strength concretes (f ≤ 40 MPa (5.8 ksi)). In this paper, the performance of plastic hinges in flexural elements constructed with a concrete strength up to 175 MPa (25.4 ksi) is investigated. In addition, other variables were studied such as the sectional reinforcement asymmetry, hinge shear strength and hinge shear demand. The seismic performance is presented in terms of stiffness deterioration, strength degradation, pinching phenomenon and displacement ductility. The requirements to implement the use of HSC in current macro‐models are examined. Current hysteretic models may be used to evaluate structural components constructed with higher concrete strength; however, the influence of concrete strength is controlled by the other test variables. Copyright © 2009 John Wiley & Sons, Ltd.