主余震序列作用对剪力墙结构动力响应影响分析

为了研究主余震序列作用对高层剪力墙结构动力响应的影响,以某超高层作为研究基础建立了其动力弹塑性分析模型,开展了相关研究工作。选取10个真实主余震序列作用事件,构造了14条主余震序列作用作为输入的地震荷载;以PGA、PGV、PGA/PGV等作为表征地震动强度的指标,计算了结构在主余震序列作用及仅主震作用下的结构塑性耗能、最大残余层间位移角的增量损伤比及Karl Pearson相关系数;分析了主余震序列作用下结构塑性耗能及最大残余层间位移角的特点和地震动强度指标与增量损伤比的相关性。结果表明,主余震序列作用加剧了结构损伤,其塑性耗能增量平均达24%～28%;主余震序列作用下结构最大残余层间位移角有可能增大,也有可能减少。基于塑性耗能的结构主余震增量损伤比与PGV、SED、S_I等速度相关的地震动强度表征指标均表现出了较强的相关性,可考虑作为选择和调整主余震序列作用地震波的指标;基于最大残余层间位移角的结构主余震增量损伤比则与地震动强度指标相关性较弱。     

钢筋混凝土框架结构的损伤状态相关余震易损性分析

一次主震过后通常伴有多次余震发生,由于主、余震间隔时间较短,主震损伤结构通常要遭受进一步的余震作用.为了评估震损结构的余震安全,提出了一种损伤状态相关的余震易损性分析方法.该方法采用有限次整体调幅的主余震序列作为输入,利用Park-Ang指数描述结构在主余震序列作用下的主震损伤和累积损伤,基于logistic回归方法生...     

基于分步调幅法的钢筋混凝土结构主余震易损性曲面分析

传统主余震易损性分析多采用仅考虑主震强度或余震强度的标量式易损性函数，所获得的易损性曲线无法全面反映主、余震强度对结构抗震性能的综合影响。为解决这一问题，提出了一种同时包含主、余震强度的主余震易损性曲面分析方法。通过对主余震序列进行主、余震分步调幅，获得包含不同主、余震强度组合的主余震序列输入。通过分步拟合，构建同时包含主、余震强度的主余震需求模型，生成主余震易损性曲面，并进一步计算获得具有不同危险性水平的主、余震强度所对应的主余震易损性指数。以一栋按我国规范设计的钢筋混凝土框架结构为例，采用所提出方法进行了主余震易损性曲面分析。分析结果表明：所提出方法可以有效地生成结构的主余震易损性曲面，给定主震危险性水平而提升余震危险性水平或给定余震危险性水平而提升主震危险性水平，均可带来结构主余震易损性指数的提高，且后者引起的主余震易损性指数提高幅度更为显著，证明了主震作用在主余震易损性分析中的主导地位。     

主余震序列作用下结构损伤性能研究现状综述

一次地震中包含大量余震,研究余震造成的损伤对结构抗震性能的合理安全评估具有重大意义。文章总结目前研究结论,从输入地震序列、结构增量损伤、地震易损性分析和不利主余震序列四个角度出发,对主余震序列作用下结构的损伤量化分析与性能状态变化研究现状展开综述,简述了分析过程使用的方法和发展过程,对该研究中可进一步完善之处进行讨论,为主余震序列研究工作提供参考。     

主余震序列作用下屈曲约束支撑框架易损性分析

主震引发的多次强余震可能导致屈曲约束支撑(BRB)在地震作用下发生疲劳破坏。BRB突然失效可能使主震引起的微小损伤加剧,引发结构倒塌。因此,有必要考虑余震对BRB构件和BRBF结构的影响。通过增量动力方法,对考虑BRB疲劳性能的屈曲约束支撑框架(BRBF)进行易损性分析,对比了在单独主震和主余震序列作用下BRBF结构的地震易损性差异。结果表明,在高强度主余震序列作用下,BRBF结构的失效概率显著增加,对其性能要求更高。此外,分别以峰值层间位移角和残余峰值层间位移角作为需求参数指标,对比分析了BRBF结构在主余震序列作用下的易损性差别。结果表明,以残余峰值层间位移角为参数指标时,对结构性能要求更严格。     

考虑余震影响的RC框架结构抗震设计方法

历史地震表明强余震会进一步增大结构的破坏程度甚至使其倒塌，但是我国乃至世界上的所有抗震设计规范均只考虑主震作用而没有直接考虑余震影响。为提出能有效考虑余震影响的抗震设计方法，文章基于主余震设计谱和主震设计谱共设计了12个钢筋混凝土(RC)框架结构。选取50条实际主余震地震动对所有结构进行增量动力分析进而得到结构倒塌易损性，对比分析了主余震、主震影响区域结构的倒塌储备系数CMR，发现仅采用设计谱进行弹性设计会使得主余震影响区域结构的CMR会小于主震影响区域结构。为实现主余震、主震影响区域结构的倒塌储备等效，首先给出了以基本周期T1为变量的Sa, 50% collapse预测公式，然后推导了结构倒塌储备等效方程，并结合设计谱进行数值求解，最后给出了倒塌储备等效条件下以主震影响区域结构基本周期T1,M为变量的主余震影响区域结构基本周期T1,A预测公式，综合使用该预测公式和主余震设计谱可以实现主余震、主震影响区域结构的倒塌储备等效。     

多塔斜拉桥在主震-余震序列波下地震位移研究北大核心

桥梁等结构在遭受地震时,总是会历经前震、主震与余震等一系列地震波动。余震的存在可能会使结构的地震需求超过主震时期,可以说余震对于结构安全有着不可忽略的影响。建立有限元模型,对常规摩擦支座的减隔振体系桥梁结构输入主震-余震序列波,得到墩梁相对位移时程,通过对比分析结构在主震作用下、在余震单独作用下以及在主震-余震序列波作用下支座位移之间的差别,来研究强余震对结构位移峰值以及残余位移的影响。分析研究表明:强余震在很大程度上影响了结构的位移峰值以及残余位移,在抗震设计中余震的作用是不可忽视的,在地震波输入时,应当考虑主震余震序列波。     

多塔斜拉桥在主震-余震序列波下地震位移研究

桥梁等结构在遭受地震时,总是会历经前震、主震与余震等一系列地震波动。余震的存在可能会使结构的地震需求超过主震时期,可以说余震对于结构安全有着不可忽略的影响。建立有限元模型,对常规摩擦支座的减隔振体系桥梁结构输入主震-余震序列波,得到墩梁相对位移时程,通过对比分析结构在主震作用下、在余震单独作用下以及在主震-余震序列波作用下支座位移之间的差别,来研究强余震对结构位移峰值以及残余位移的影响。分析研究表明:强余震在很大程度上影响了结构的位移峰值以及残余位移,在抗震设计中余震的作用是不可忽视的,在地震波输入时,应当考虑主震余震序列波。     

主余震序列地震作用下一级抗震预应力型钢混凝土空腹桁架转换层框架结构抗震性能研究

基于"三道防线抗震设防"的设计方法,以2榀8度(0.2g)设防区的上抬层数不同的一级抗震预应力型钢混凝土(PSRC)空腹桁架转换层框架结构为研究对象,完成了罕遇烈度水准下不同余震主震强度比■的系列弹塑性时程分析。然后,通过层间位移角、转动能力需求比和损伤指数等多个性能指标,对构件、防线以及结构整体等不同层次的抗震性能和损伤状况进行研究。结果表明:在主震及主余震序列地震作用下,结构均未发生整体破坏,当余震较强时,以损伤指数计算的个别上抬框架梁出现局部破坏;结构后续两道防线的损伤明显小于第一道防线,形成主要以第一道防线内梁铰耗能的"梁柱混合出铰机制","三道防线抗震设防"的设计原则得以实现;余震作用下,结构的整体损伤指数显著增加,且"二次损伤"明显;较大余震下,转换柱出铰普遍,甚至出现"层侧移机制",应加强转换柱柱端弯矩增大措施。     

基于能量及损伤的主余震地震动对超限高层结构抗震性能影响研究

以第一周期为8.57s的某超限高层框架-核心筒建筑结构为研究对象,选取7条实际长周期主余震序列型地震动,并与单主震地震动一起作为输入样本,通过有限元软件PERFORM-3D对结构进行非线性动力时程分析;着重从结构整体、楼层滞回耗能情况及构件材料损伤等反应量角度来研究主余震地震动对超限高层建筑结构抗震性能的影响。研究结果表明,相对单主震地震动,结构在主余震地震动作用下整体滞回耗能增幅最大达到31.34%,楼层滞回耗能增幅最大可达到45.71%;同时余震地震动作用会使结构中构件损伤逐步累积过渡,导致部分构件转变为严重损伤状态。因此,对于超限高层建筑结构,仅根据现行规范或超限高层建筑专项审查研究超限高层在单次主震地震动作用下的抗震能力并不能很好地评估结构的抗震性能,建议对超限高层建筑结构进行非线性动力时程分析时补充余震地震动作用的影响,从而全面、安全可靠地评估超限高层建筑结构的抗震性能。     

Vulnerability assessment of a high‐rise building subjected to mainshock–aftershock sequences

Strong aftershocks have the potential to further aggravate the damage state of structures, and much less attention has been given to the seismic vulnerability of high‐rise buildings than that of low‐ to medium‐rise buildings. This study assesses the seismic vulnerability of a 32‐storey frame–core tube building by performing the incremental dynamic analysis on the material‐based three‐dimensional numerical model. A storey damage model based on the material damage is developed using the weighted average method. Eighteen recorded mainshock–aftershock sequences, whose mainshock records match the target spectrum, are selected. The results indicate that the developed stroey damage model can effectively reflect the additional damage induced by aftershocks. Strong aftershocks have high potential to change the location of weak storeys. Notably, shifts of weak storeys are observed in more than 30% of aftershocks with relative spectral acceleration of 0.8. As the mainshock‐induced damage state becomes more severe, the mainshock‐damaged building becomes increasingly fragile to the aftershock excitation and more sensitive to aftershock intensities. The probability of exceeding severe damage state increases from 35.3% to 62.1% due to the effects of strong aftershocks. The results in this study can provide supports to the seismic resilience assessment of this high‐rise building.     

Seismic design requirements for reinforced concrete piers considering aftershock-induced seismic hazard

The main purpose of this study is to develop an estimation procedure of seismic design level setting for reinforced concrete (RC) piers considering aftershock-induced seismic hazards. This work develops an assessment method of the seismic hazards induced by aftershocks and takes an example of the Chi–Chi Earthquake in Taiwan. The number of aftershocks is assumed to follow the modified Gutenberg–Richter law with lower and upper bounds when analysing the cumulative density function of the magnitude of the aftershock within a specified post-mainshock period for the earthquake. Additionally, this work considers the spatial uncertainty in the hypocentres of aftershocks to assess the aftershock-induced seismic hazards. Fragility curves and residual factors of damaged RC piers are used in the transition probability matrix of Markov Chain model for considering the cumulative damage induced by aftershocks by incorporating uncertainty into aftershock events, as well as into structural capacity and residual factors corresponding to a specified damage state, the exceedance probabilities for various damage states can be estimated using Markov Chain model and Monte Carlo Simulation. Finally, in the case study, the proposed procedure is used to determine the important factor in the preliminary seismic design of typical RC piers for the Chi–Chi Earthquake in Taiwan.     

Evaluation of drift demands in existing steel frames under as-recorded far-field and near-fault mainshock-aftershock seismic sequences

This paper presents results of a study aimed at evaluating the effect of aftershocks in steel framed buildings. For that purpose, three frame models representing existing steel moment-resisting frames were subjected to a set of as-recorded mainshock-aftershock seismic sequences. For this purpose, 64 as-recorded seismic sequences registered as a consequence of the 1994 Northridge and 1980 Mammoth Lakes earthquakes were considered in this study. In particular, this investigation employed 14 seismic sequences recorded in 7 accelerographic stations in the near-fault region. An examination of the as-recorded seismic sequences shows that the frequency content of the mainshock and the main aftershock is weakly correlated. The response of the frame models was measured in terms of the peak and residual (permanent) drift demands at the end of the earthquake’s excitation. From the results of this investigation, unlike previous results based on artificial seismic sequences, it was found that as-recorded aftershocks do not significantly increase peak and residual drift demands since the predominant period of the aftershocks (i.e. frequency content) is very different from the period of vibration of the frame models. In addition, it was shown that artificial seismic sequences could significantly overestimate median peak and residual drift demands as well as the record-to-record variability.     

Seismic capacity assessment of postmainshock damaged containment structures using nonlinear incremental dynamic analysis

This paper investigates the structural performance and seismic capacity of the postmainshock damaged containment structure through the incremental dynamic analysis (IDA). To evaluate the seismic capacity with minimum uncertainty, the damage measure (DM) and intensity measure (IM) for IDA curves are selected in term of the coefficient of variation. The IDA using mainshock records is implemented to examine the seismic damage process of a containment structure and determine key damage states. The static cyclic loading analysis and aftershock IDA are also conducted on mainshock‐damaged containment structures to investigate the effect of initial damage states on the dynamic characteristics of structures. Finally, based on IDA results, limit states of a containment structure are defined using a generalized multidimensional limit‐state function that allows considering the dependence between the mainshock‐damaged level and residual seismic capacity. These proposed bidimensional limit‐state functions can be used in the fragility analysis and risk assessment of containment structures under mainshock–aftershock, which can improve the accuracy of seismic assessment.     

Building life-cycle cost analysis due to mainshock and aftershock occurrences

The objective of this paper is to develop formal stochastic expected financial loss estimation models over the lifetime of the building due to mainshocks and their subsequent aftershock sequences. Mainshocks are typically modeled as a homogeneous Poisson process with constant mean rate of occurrence, while the resulting aftershocks are modeled as a nonhomogeneous Poisson process with random magnitudes which has parameters (mainshock magnitude, m_m, and location) that are conditional on the random mainshock. The initial model to compute expected losses is the simplified homogeneous Poisson mainshock process and nonhomogeneous Poisson aftershock process with “immediate” repair of the building to the initial building state. We then develop a more general Markov and semi-Markov framework where we consider both Poisson and renewal processes for modeling mainshock occurrences with various building damage progression scenarios. Finally, we will incorporate the random aftershock losses into pre-mainshock financial loss estimation. The ability to compute the expected building life-cycle cost due to both mainshocks and aftershocks will be useful as an input to seismic decision making (both post- and pre-mainshock).     

RC框架基于典型相关分析的地震动多元破坏势评估

为了更加全面地评估地震动对结构的潜在破坏势,考虑多个地震动强度参数和多个结构损伤参数对地震动破坏势的影响,提出一种基于典型相关分析的地震动多元破坏势评估方法。为说明所提方法,以具有不同高度和不同抗震设防水平的16个钢筋混凝土框架结构为研究对象,采用100条真实地震动记录作为地震输入。将与地震动加速度、速度和位移相关的8个地震动强度参数进行对数线性组合,构造成地震动多元强度参数的典型变量。将结构最大层间位移角、整体损伤指数、最大楼层加速度进行对数线性组合,构造成结构多元损伤参数的典型变量。通过使地震动强度参数的典型变量和结构损伤参数的典型变量的相关系数达到最大,获得可以较好评估地震动破坏势的复合地震动参数。研究结果表明：相比于单一地震动参数,复合地震动参数可以更好地评估地震动的破坏势,其与结构损伤的相关性也更强。     

Response of nonlinear single-degree-of-freedom structures to random acceleration sequences

Current seismic codes specify design earthquake loads as single events. The structure, however, may experience multiple ground accelerations in a short period of time. The evidence from recent earthquakes confirms this scenario. For instance, the 2004 Niigata earthquake consisted of two acceleration sequences. An earthquake of repeated sequences can cause more damage to the structure than a single ordinary event, due to the accumulation of inelastic deformations. However, information on repeated acceleration sequences is currently limited. This paper proposes a simple stochastic model for representing repeated acceleration sequences. Subsequently, the model is used in investigating the response of nonlinear single-degree-of-freedom (SDOF) structures to random earthquakes of repeated sequences. The ground acceleration is represented as a stationary Gaussian random process modulated by an envelope function of repeated character. The structural response is quantified in terms of the input and hysteretic energies, ductility demand, damage indices and failure probability. Numerical demonstrations of the response of nonlinear SDOF systems to acceleration sequences are provided.     

Spatial coherency of shear waves from the Lotung, taiwan large-scale seismic test

Four events recorded by the very dense Lotung, Taiwan Lsst array are analyzed for spatial coherency. The four events compromise two mainshock-aftershock pairs: one near-field pair and one far-field pair. These events were selected to evaluate the effects of the source dimension and travel path of coherency estimates. The coherencies from these events are compared and the differences are interpreted in terms of a coherency model proposed by Somerville et al. (1988).The far-field mainshock and aftershock coherencies are not significantly different, indicating that the far-field incoherence is dominated by wave scattering along the path. In contrast, the near-field mainshock and aftershock coherencies show some significant differences, particularly at moderate frequencies were the aftershock coherency is lower than the mainshock coherency. While this result is contrary to the Somerville et al. model, the discrepancy may be partly due to nonlinear soil response during the mainshock. Additional deviations from the model may be attributed to source-dependent radiation effects that are particularly evident in the near-source data.The near-field/far-field mainshock coherencies show that at low frequencies the far-field coherency is larger than the near-field coherency; the reverse is true at high frequencies. Coherency studies of additional events are needed to verify and quantify these trends.