汶川地震动弹性和弹塑性反应谱分析

利用汶川地震获得的数字强震记录研究了汶川近场无速度脉冲、近场含速度脉冲和远场(盆地效应)地震动的弹性和弹塑性反应谱,后者包括等延性强度折减系数谱Rμ、等延性位移比谱Cu和等强度折减系数位移比谱CR.与相同场地条件PEER近场无速度脉冲、集集近场含速度脉冲地震动的谱进行了比较.汶川近场含速度脉冲地震动的弹性反应谱在0.2～0.8s周期内明显偏小,而它的弹塑性反应谱在短周期段(0.1 ～0.4 s)与汶川近场无速度脉冲地震动谱差别不大,但等延性强度折减系数谱Ru要大于集集地震含速度脉冲地震动的谱,而等延性位移比谱Cu和等强度折减系数位移比谱CR则小于集集地震动情况,此后随周期增长(至0.6 ～1.Os后)它们都逐渐过渡至与集集地震动的谱相当.汶川远场(盆地效应)地震动的弹性反应谱具有较宽并随周期缓慢增长的平台值和较长的特征周期,可达1.7s及以上.提出了远场(盆地效应)与近场地震动的弹性反应比谱和弹塑性位移比谱的概念.     

序列型地震作用下考虑损伤的强度折减系数

基于性态的结构抗震设计中的强度折减系数是确定结构非弹性反应谱的重要依据。本文研究主余震序列型地震作用下单自由度体系考虑损伤的强度折减系数谱。首先收集主余震实测记录并按中国抗震规范要求进行场地类别划分,对余震峰值进行调幅后进行单自由度结构弹塑性动力时程分析,研究了结构周期、延性系数、损伤指数、余震作用等因素对强度折减系数需求的影响。结果表明余震对强度折减系数的影响显著,考虑累积损伤的强度折减系数(R_D)是基于位移延性的强度折减系数(R_μ)的0.6至0.9倍。最后,经过统计平均和回归分析,建立了平均强度折减系数谱的简化公式。     

基于强度和延性的残余位移比谱及其影响因素分析

结构震后残余位移是抗震性能评估和地震损失评估的重要参数。文中针对理想弹塑性单自由度体系,采用与残余位移相关性最好的归一化参数定义残余位移比,通过动力时程分析建立统计平均的等延性残余位移比谱和等强度残余位移比谱,研究场地条件、延性系数及强度折减系数对等延性残余位移比谱和等强度残余位移比谱的影响,通过回归分析构建了等延性残余位移比谱和等强度残余位移比谱的预测方程。结果表明:残余位移与弹塑性谱位移的相关性较大,与弹性谱位移的相关性较小;软土场地下结构残余位移的评估需考虑场地条件的影响;残余位移比离散性受延性系数和强度折减系数影响显著。     

双向地震动作用的拟等延性系数谱

首先建立了以强度折减系数表述的恢复力特性满足二维屈服面模型的理想弹塑性单质点系统(它在2个相互垂直的主轴方向上分别具有水平平动自由度)在双向地震动作用下的归一化运动方程。然后引入单向地震动作用下等延性系数的强度折减系数谱,给出了双向地震动作用的拟等延性系数谱(定义为系统分别承受双向和单向地震动作用,在同一主轴方向上的最大位移反应之比)最后通过硬土场地10组双向地震动记录拟等延性系数谱的统计平均结果,分析了结构周期、位移延性系数和阻尼等因素对谱值及结构双向地震反应的影响。结果表明,双向地震动作用与单向地震动作用相比主要增加结构较长周期方向的最大位移反应。若在基于位移的抗震设计中降低结构较短周期方向的设计位移延性系数,可在一定程度上降低双向地震动的不利影响。因定义的谱为比值形式,阻尼对其影响不大。     

考虑设计地震分组的强度折减系数的研究

强度折减系数既是基于强度的抗震设计中确定设计地震力的关键因素,又是基于性态的抗震设计理论中确定非弹性反应谱的主要依据. 本文结合我国抗震设计反应谱的形式和特点,应用823条国内外水平向地震动记录（充分利用了我国取得的强震记录）,给出了一种考虑设计地震分组和场地类别的强度折减系数模型,研究了结构周期、延性、场地类别、设计地震分组、震级、震中距等因素对强度折减系数的影响. 结果表明:场地条件对强度折减系数的影响是不可忽略的,特别是对延性较大的短周期结构更应注意场地条件的影响;设计地震分组是影响强度折减系数的一个重要因素,在应用我国规范设计反应谱构造非弹性反应谱所用的强度折减系数必须考虑设计分组的影响;震级对强度折减系数的影响较小;如不考虑近场大脉冲地震动记录的影响,震中距对强度折减系数的影响是可以忽略的.      

考虑场地类别与设计分组的延性需求谱和弹塑性位移反应谱

非线性反应谱是基于性能的抗震设计理论中亟待解决的基础性课题之一。本文将四种场地类别上的641条地震记录,按我国现行抗震规范设计分组的要求分为12组,对大量具有不同屈服强度系数的单自由度体系作了弹塑性时程分析。研究了结构强度水平、周期、场地类别以及设计分组等因素对延性需求的影响。结果表明,在给定屈服强度水平下结构的延性需求强烈地依赖于场地条件、设计分组等因素。对于短周期结构,延性需求随场地土变软而增大,同类场地随设计分组特征周期增大而增大。通过非线性回归分析,建立了与场地类别、设计分组相对应的延性需求谱μ-ξy-T的计算公式。在此公式的基础上,结合现阶段抗震设计规范构建了弹塑性位移反应谱,可用于结构弹塑性位移需求的简化计算,同时讨论了弹塑性位移反应谱的基本特点。     

剪切型结构的抗震强度折减系数研究

为了研究剪切型结构抗震强度需求的变化规律,本文基于单自由度体系的非线性时程分析,研究了不同场地条件下延性折减系数与位移延性系数和结构自振周期的关系;采用修正等效单自由度体系位移延性折减系数的方法,研究了剪切型多自由度体系的延性折减系数;以基于中国建筑抗震规范设计的代表不同抗震能力要求的RC框架结构为分析对象,通过静力弹塑性分析,研究了RC框架结构的体系超强能力。分析结果表明场地类别、位移延性水准和结构振动周期对单自由度体系的延性折减系数有显著的影响;多自由度体系的抗震延性折减系数明显比其相应的等效单自由度体系的抗震延性折减系数小;RC框架结构的超强系数一般随结构楼层数的增加而减小,随抗震设防烈度的增大而减小,内框架的超强系数比边框架的超强系数大。     

考虑我国场地土类型的弹塑性反应谱法在高层混合结构中的应用

弹塑性反应谱法中,强度折减系数、延性系数、周期之间的关系模型（R—μ—T关系）是影响计算结果的一个重要参数。各国学者考虑不同地震动记录、滞回模型、场地土条件、阻尼比等参数,提出了不同的模型,但在场地特征对关系影响上存在不同认识。本文按考虑我国场地土类型的模型,分别进行了某高层混合结构在设防7度、7．5度、8度、8．5度、9度下的弹塑性反应谱计算,得到了一系列结构最大层间位移角,并与增量动力分析（IDA）的结果进行了对比。分析表明,考虑我国场地土类型的高层混合结构弹塑性反应谱计算结果与IDA分析50％均值曲线吻合较好。本文计算结果可为弹塑性反应谱法在复杂高层结构中的应用提供基础。     

SSI效应对自复位结构体系延性需求谱的影响分析

为研究土-结构相互作用(soil-structure-interaction, SSI)对自复位结构体系延性需求谱的影响规律,建立了土-自复位结构的数值分析模型,其中上部结构采用旗帜形单自由度滞回系统模拟,并基于锥模型概念模拟土-基础动力相互作用。选取40条Ⅲ类场地远场地震动记录对SSI系统进行非线性时程分析,讨论了刚性地基结构的周期T、强度折减系数R、结构-土体刚度比a₀、结构高宽比s、屈服后刚度比α和耗能系数β对结构延性需求的影响规律。研究结果表明：忽略SSI效应会低估自复位结构的延性需求;对于考虑SSI效应的单自由度自复位结构,延性系数μ与R、a₀的相关性较强,且μ与R和a₀呈正相关,提高R或a₀会增大结构延性需求;延性系数μ与屈服后刚度比α、耗能系数β及结构高宽比s的相关性较弱,其中μ与α和β呈负相关,提高α或β会减小结构延性需求,且随着a₀的增大,α和β对延性需求谱的影响越大;当a₀=1时,s对延性需求谱基本无影响,而a₀取...     

不同类型地震动作用下自复位摇摆桥梁延性需求谱研究

自复位摇摆桥梁的损伤和残余位移小,具有良好的震后可恢复性。文中以自复位摇摆桥梁为研究对象,对不同类型地震动作用下的结构的延性需求谱及其影响因素进行研究。选用FEMA P695推荐的100条典型地震动作为输入,并划分为远场地震动、近场脉冲地震动以及近场无脉冲地震动。研究结果表明,近场脉冲地震动作用下的结构的延性需求最大,设计时需考虑近场脉冲地震动的影响;随着强度折减系数R的增大,结构的延性需求显著增加,设计时不宜采用较高的强度折减系数;增加刚度比α和耗能系数β能在一定周期范围内减小结构的延性需求;阻尼比ξ在0.01～0.05范围内对延性需求的影响基本可以忽略。     

Effect of site amplification on inelastic seismic response

The available models for eff ective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The eff ect of seismic intensity and ductility demand, on the eff ective periods, is investigated, and inelastic site amplifi cation is shown to be strongly correlated to the normalized eff ective period. Two non-dimensional parameters, analogous to the conventional site amplifi cation factors in codes, are defi ned to quantify the inelastic site amplifi cation. It is shown that the inelastic site amplifi cation factor (i.e. ratio of constant ductility spectral ordinates at soil site to those at rock outcrop) is able to represent the site eff ects more clearly, as compared to the inelastic site amplifi cation ratio (i.e. ratio of inelastic spectral ordinates at soil site to the corresponding elastic spectral ordinates at rock outcrop). Further, the peak in the amplifi cation factor corresponding to the eff ective site period diminishes rapidly with increasing ductility demand.     

Capacity spectrum method based on inelastic demand spectra

By means of a graphical procedure, the capacity spectrum method compares the capacity of a structure with the demands of earthquake ground motion on it. In the present version of the method, highly damped elastic spectra have been used to determine seismic demand. A more straightforward approach for the determination of seismic demand is based on the use of the inelastic strength and displacement spectra which can be obtained directly by time-history analyses of inelastic SDOF systems, or indirectly from elastic spectra. The advantages of the two approaches (i.e. the visual representation of the capacity spectrum method and the superior physical basis of inelastic demand spectra) can be combined. In this paper, the idea of using inelastic demand spectra within the capacity spectrum method has been elaborated and is presented in an easy to use format. The approach represents the so-called N2 method formulated in the format of the capacity spectrum method. By reversing the procedure, a direct displacement-based design can be performed. The application of the modified capacity spectrum method is illustrated by means of two examples. Copyright © 1999 John Wiley & Sons, Ltd.     

延性需求谱在基于性能的抗震设计中的应用

基于性能的抗震设计理论涉及如何简便而合理地确定结构在指定强度地震下的弹塑性位移需求。本文给出了利用延性需求谱求解结构位移需求的一般步骤:借助模态Pushover分析将多自由度体系分解为几个非线性单自由度体系,以考虑各阶振型的影响;利用延性需求谱计算对应模态的等效单自由度体系的延性及位移需求,并以一定方式组合转化为多自由度体系位移需求。最后,通过算例分析表明:利用延性需求谱求解结构位移需求是一种具有一定精度可为工程接受的简便方法,在基于性能的抗震设计中具有较好的应用前景。     

Probabilistic estimation of maximum inelastic displacement demands for performance‐based design

A probabilistic approach to estimate maximum inelastic displacement demands of single‐degree‐of‐freedom (SDOF) systems is presented. By making use of the probability of exceedance of maximum inelastic displacement demands for given maximum elastic spectral displacement and the mean annual frequency of exceedance of elastic spectral ordinates, a simplified procedure is proposed to estimate mean annual frequencies of exceedance of maximum inelastic displacement demands. Simplifying assumptions are thoroughly examined and discussed. Using readily available elastic seismic hazard curves the procedure can be used to compute maximum inelastic displacement seismic hazard curves and uniform hazard spectra of maximum inelastic displacement demands. The resulting maximum inelastic displacement demand spectra provide a more rational way of establishing seismic demands for new and existing structures when performance‐based approaches are used. The proposed procedure is illustrated for elastoplastic SDOF systems having known‐lateral strength located in a region of high seismicity in California. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation of ‘equal displacement’ rule for bridges subjected to differential support motions

The ‘equal displacement’ rule is employed in seismic design practice to predict inelastic displacements from analyses of the corresponding linear elastic structural models. The accuracy and limitations of this rule have been investigated for ordinary structures but not for bridges subjected to spatially varying ground motions. The present study investigates this rule for moderate levels of inelastic behavior for four highway bridges in California accounting for the effects of spatial variability of the support motions due to incoherence, wave passage and differential site response. The bridge models vary significantly as to their fundamental periods and their overall configurations. Statistical analyses of pier‐drift responses are performed using as input simulated arrays of nonstationary ground motions in accordance with prescribed coherency models. It is found that the ‘equal displacement’ rule is fairly accurate for cases when the fundamental period of the bridge is longer than the transition period between the acceleration‐controlled and velocity‐controlled ranges of the response spectrum. Otherwise, the rule is non‐conservative for cases with large ductility factors and conservative for cases with small ductility factors. Wave passage and incoherence tend to reduce ratios of mean peak inelastic to elastic pier drifts, whereas incorporation of the differential site‐response effect by locating piers on softer soils tends to increase the same ratios. Mild or moderate positive correlation between these ratios and ductility demands is observed in most cases. Effects of spatial variability are more pronounced for longer and stiffer bridges. Copyright © 2013 John Wiley & Sons, Ltd.     

平面不对称结构非弹性地震反应分析的平扭耦联Bouc-Wen模型

综合考虑强度退化、刚度退化、捏拢效应等典型滞回特性的影响,建立了双向地震作用下平面不对称结构非弹性地震动力响应分析的平扭耦联Bouc-Wen模型.该模型采用圆形屈服面来描述双向抗侧恢复力之间的耦合效应,而采用锥体或球体屈服面来描述双向抗侧和抗扭恢复力之间的耦合效应,并结合69条强震记录,定量地分析了平扭耦联效应对平面不...     

Seismic reliability‐based ductility demand evaluation for inelastic base‐isolated structures with friction pendulum devices

The aim of this work is to propose seismic reliability‐based relationships between the strength reduction factors and the displacement ductility demand of nonlinear structural systems equipped with friction pendulum isolators (FPS) depending on the structural properties. The isolated structures are described by employing an equivalent 2dof model characterized by a perfectly elastoplastic rule to account for the inelastic response of the superstructure, whereas, the FPS behavior is described by a velocity‐dependent model. An extensive parametric study is carried out encompassing a wide range of elastic and inelastic building properties, different seismic intensity levels and considering the friction coefficient as a random variable. Defined a set of natural seismic records and scaled to the seismic intensity corresponding to life safety limit state for L'Aquila site (Italy) according to NTC08, the inelastic characteristics of the superstructures are designed as the ratio between the average elastic responses and increasing strength reduction factors. Incremental dynamic analyses (IDAs) are developed to evaluate the seismic fragility curves of both the inelastic superstructure and the isolation level assuming different values of the corresponding limit states. Integrating the fragility curves with the seismic hazard curves related to L'Aquila site (Italy), the reliability curves of the equivalent inelastic base‐isolated structural systems, with a design life of 50 years, are derived proposing seismic reliability‐based regression expressions between the displacement ductility demand and the strength reduction factors for the superstructure as well as seismic reliability‐based design (SRBD) abacuses useful to define the FPS properties. Copyright © 2016 John Wiley & Sons, Ltd.     

Scaling of strength reduction factors for degrading elasto‐plastic oscillators

The inelastic (design) spectra characterizing a seismic hazard are generally obtained by the scaling‐down of the elastic (design) spectra via a set of response modification factors. The component of these factors, which accounts for the ductility demand ratio, is known as the strength reduction factor (SRF), and the variation of this factor with initial period of the oscillator is called an SRF spectrum. This study considers scaling of the SRF spectrum in the case of an elasto‐plastic oscillator with strength and stiffness degradation characteristics. Two models are considered: one depending directly on the characterization of source and site parameters and the other depending on the normalized design spectrum characterization of the seismic hazard. The first model is the same as that proposed earlier by the second author, and is given in terms of earthquake magnitude, strong‐motion duration, predominant period, geological site conditions, ductility demand ratio, and ductility supply‐related parameter. The second model is a new model proposed here in terms of the normalized pseudo‐spectral acceleration values (to unit peak ground acceleration), ductility demand ratio and ductility supply‐related parameter. For each of these models, least‐square estimates of the coefficients are obtained through regression analyses of the data for 956 recorded accelerograms in western U.S.A. Parametric studies carried out with the help of these models confirm the dependence of SRFs on strong‐motion duration and earthquake magnitude besides predominant period and site conditions. It is also seen that degradation characteristics make a slight difference for high ductility demands and may lead to lower values of SRFs, unless the oscillators are very flexible. Copyright © 2004 John Wiley & Sons, Ltd.