考虑行波效应的高墩刚构桥地震易损性分析

基于传统可靠度理论,结合IDA方法和大质量法,将空间效应引入地震易损性分析,提出了实现考虑行波效应的桥梁地震易损性评估方法。以一座墩高不一致的双肢薄壁高墩刚构桥为算例,建立系统近场和远场地震易损性曲线。结果表明:评估桥梁系统地震易损性时,宜考虑行波效应,否则可能高估其抗震性能;与远场地震易损性相比,近场地震易损性受行波效应影响显著;与矮墩易损性相比,高墩易损性对行波效应敏感。     

近场地震作用下多层RC框架的地震易损性分析

随着对近场地震动研究上的深入,将地震近场效应影响纳入到结构的抗震设计的考虑范畴,已成为工程中的必须。为此,文中对近场脉冲地震作用下的多层RC框架结构的抗震问题进行了研究。首先参考我国抗震规范设计出设防烈度为8度、水平地震影响系数最大值α_(max)增大系数分别取1、1.25、1.5、1.75的四榀多层RC框架结构办公楼,并在OpenSees软件中,对4榀框架在近场水平脉冲地震下的抗震性能,进行了基于增量动力分析(IDA)的地震易损性分析与评价。分析结果表明:按照我国现规范、不考虑地震动近场效应设计出来的多层RC框架结构,在近场地震下的抗倒塌性能存在明显的不足;随着地震影响系数最大值增大系数的加大,框架结构的抗震性能有明显的提高,在设防烈度8度区,规范中规定的地震动影响系数最大值的增大系数偏小,将增大系数调整至1.75时所设计框架,能更好地抵御地震动近场脉冲效应;另外,在震中距分别为5～10 km和0～5 km的近场地震作用下,多层RC框架结构的抗震性能无明显的区别,因而,地震影响系数最大值的取值,不必按震中距5～10 km和0～5 km进行区分。     

一种新的拟合地震动衰减关系的分步回归法

提出了拟合地震动衰减关系的一种新的分步回归法.该方法首先确定近场饱和项,再获得距离衰减项,最后确定震级项.作为算例,采用NGA项目美国西部地区的强震观测资料,对基岩场地自由地表加速度反应谱平台高度值衰减关系进行了回归.结果表明,采用此方法对实际资料的拟合不存在系统偏差,结果稳定,能反映强震地震动在近场的距离饱和与震级饱和特性.对远场数据考虑截尾效应,能使回归结果正确反映地震动的远场衰减特征.     

考虑锈蚀的钢结构地震易损性分析

钢材锈蚀会引起结构的抗震性能与刚度的退化。通过已有钢材锈蚀规律并考虑结构的随机性,将IDA、Pushover与蒙特卡洛抽样结合得到结构概率地震需求及概率抗震能力的统计参数并代入本文提出的地震易损性模型,得到结构在不同极限状态的易损性曲面。以15层3跨钢框架为例,利用建立的方法研究了结构易损性随服役年限的变化规律。研究成果可为结构的全寿命设计、既有结构的运营以及地震风险评估等提供理论依据。     

基于IDA法与Pushover法的混凝土核心筒抗震性能对比分析

足够数量地震输入的增量动力分析方法（IDA方法）是目前最为真实和先进的模拟结构抗震性能手段,而静力推覆分析方法（Pushover Analysis方法）操作简单,更为实用,可以较好揭示结构从弹性到屈服直至倒塌过程中构件的工作状态。采用2种方法对钢筋混凝土核心筒算例进行评估,并作对比分析。结果表明,采用IDA方法得到的4个性能水平与Pushover方法得到的指标限值有一定误差,但均在一定范围之内,采用IDA方法得到顶点位移角限值偏大;采用单一侧力模式的Pushover方法无法完全体现高阶振型及地震动等因素的影响,造成Pushover方法分析结果与结构实际弹塑性地震响应有一定差异。     

基于单地震动记录IDA方法的结构倒塌分析

增量动力分析(Incremental Dynamic Analysis, IDA)作为静力Pushover分析的动力拓展,可以全面、准确地分析结构的性能变化,尤其可以很好地分析结构倒塌这一动力失稳问题.本文基于单地震动记录的IDA方法,提出了"折半取中"原则,以确定结构倒塌极限状态点.以一榀五层三跨钢筋混凝土框架结构为例,分别考虑钢筋强化模型、理想弹塑性模型和软化模型,对其进行倒塌分析.结果表明:钢筋的屈服后强化特性对结构抗倒塌能力具有显著的影响.     

钢筋混凝土建筑结构的抗地震破坏倒塌能力评估研究

在地震作用下钢筋混凝土建筑结构出现破坏倒塌为地震灾害中的关键,有效评估建筑结构抗地震破坏倒塌能力是建筑结构设计的前提,也是当前建筑结构提高抗震性能与加固的依据。提出变形指标极值、失效判断标准以及钢筋混凝土建筑结构倒塌极限状态判断标准,据此获取倒塌储备系数、倒塌易损性、结构整体超强系数、结构整体延性系数等评估标准。采用Pushover分析法选择相应地震波。依据梁柱线刚比对建筑结构抗倒塌能力的影响,以及柱端弯矩增加系数对建筑结构抗地震破坏倒塌能力的影响,对建筑结构易损性进行分析。结果表明:等跨建筑结构抗地震破坏倒塌能力更强;建筑结构底层是薄弱层,COF值越高,结构越容易倒塌。     

设计近场地震和远场地震的确定方法

在建筑抗震设计规范(GBJ11-89)中，明确规定了要按近震或远震考虑场地的地震环境；并针对1977年版的地震烈度区划图，提出了确定近场地震和远场地震的方法．由于新颁布的中国地震烈度区划图(1990)，是采用地震危险性概率分析方法编制的，原有的确定近震和远震的方法已经不适宜．本文考虑到近场地震和远场地震的实质，根据地震危险性概率分析的基本思路，推荐了一种新的确定方法．该方法可以较为妥切地解决GBJ11-89规范与1990年版地震区划图之间的衔接问题．      

基于传力路径的平面不规则RC框架结构减震设计

针对平面不规则RC框架结构,从构件安全层次出发提出基于传力路径的减震设计方法。首先根据广义结构刚度法的基本原理计算结构中所有构件的重要性系数,再假定消能支撑的截面参数,取每层最重要的构件位置布置支撑,经支撑在最不利地震组合下的轴力验算后确定支撑的最终设计参数和数量,然后考虑远场、近场有脉冲以及近场无脉冲地震动从双向输入对结构响应的影响,对减震前、后结构分别进行动力时程分析。分析结果表明,利用此方法优化布置支撑能为结构中重要构件提供有效保护,且在小、中、大震下消能支撑均能运作良好,使整体结构响应得到很好地控制。     

基于FE-IBE耦合方法的地铁车站抗震分析

提出了地下结构非线性地震响应分析的一个FE-IBE耦合方法,通过等效线性化分析考虑土体非线性特性。该耦合方法的特点之一是有限元子域和间接边界元子域相互独立,非常适合并行计算,提高计算效率;特点之二是能够同时考虑近场区域(有限元子域)和远场区域(间接边界元子域)的土体非线性。通过与FLUSH和ANSYS的计算结果相比较,验证了本文耦合方法的正确性和计算精度。以天津某深厚软土场地中双层地铁车站为例,比较分析了土体线性和非线性两种工况下车站结构的地震内力和层间变形。本文算例中,非线性情况下车站结构最大弯矩和层间变形较线性情况均增大近50%。     

Pushover分析中抗力曲线的概率研究

本文在已有的研究基础上,结合我国现行的抗震规范（GB50011—2001）和地震作用统计参数,提出了pushover分析中结构体系抗力曲线的保证率计算方法。以pushover分析所得的塑性铰出现次序和最终数量作为结构主要失效模式,同时考虑了结构抗力以及地震作用的随机性对结构体系抗力曲线的影响,借助于主要随机变量的灵敏度分析,得到了确定性pushover分析曲线的保证率。框架结构算例给出了本文方法的计算结果,并用重要抽样法进行了检验。     

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of concrete gravity dams

As the forward directivity and fling effect characteristics of the near-fault ground motions, seismic response of structures in the near field of a rupturing fault can be significantly different from those observed in the far field. The unique characteristics of the near-fault ground motions can cause considerable damage during an earthquake. This paper presents results of a study aimed at evaluating the near-fault and far-fault ground motion effects on nonlinear dynamic response and seismic damage of concrete gravity dams including dam-reservoir-foundation interaction. For this purpose, 10 as-recorded earthquake records which display ground motions with an apparent velocity pulse are selected to represent the near-fault ground motion characteristics. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The Koyna gravity dam, which is selected as a numerical application, is subjected to a set of as-recorded near-fault and far-fault strong ground motion records. The Concrete Damaged Plasticity (CDP) model including the strain hardening or softening behavior is employed in nonlinear analysis. Nonlinear dynamic response and seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. Both local and global damage indices are established as the response parameters. The results obtained from the analyses of the dam subjected to each fault effect are compared with each other. It is seen from the analysis results that the near-fault ground motions, which have significant influence on the dynamic response of dam–reservoir–foundation systems, have the potential to cause more severe damage to the dam body than far-fault ground motions.     

循环往复加载的地下结构Pushover分析方法及其在地震损伤分析中的应用

考虑到地震作用下地下结构往往受到双向往复荷载作用,本文提出了循环往复加载的地下结构Pushover分析方法.介绍了该方法的实施步骤、基本功能与特点.该方法考虑了地震作用下地下结构双向受力的特点,利用多点位移控制的推覆分析算法进行地震作用下正向加载-卸载-反向再加载的全过程分析.该方法将一次循环加载过程近似看作一次地震作用过程,提出了基于循环往复加载Pushover分析的损伤模型,避免了对土-结构整体模型进行复杂的动力相互作用分析;通过一次循环往复加载的Pushover分析,根据结构构件刚度的改变对结构损伤进行有效评估.结合实际工程进行算例分析初步验证了循环往复加载Pushover分析及地震损伤模型的有效性.     

基于推覆分析的钢框架结构地震倒塌判别准则研究

结构地震倒塌判别准则是工程结构强震分析的关键问题。在层损伤模型的基础上,建立了基于推覆分析的建筑结构整体损伤模型,并以国内某2层2跨平面钢框架结构拟静力试验为背景,应用有限元程序ABAQUS对平面钢框架进行了强震倒塌数值模拟。分析了钢框架结构的倒塌破坏过程,基于建议地震倒塌判别准则研究了钢框架结构的损伤演化规律。结果表明:钢框架结构在强震作用下的损伤发展顺序与塑性发展顺序一致;基于推覆分析的结构整体损伤模型能较好的体现强震作用下钢框架结构的损伤演化规律,且在上下界处收敛;强震作用下,钢框架结构的初始损伤主要由结构的残余侧移引起,而后期损伤主要由结构的承载力和刚度退化引起。     

Fast performance uncertainty estimation via pushover and approximate IDA

Approximate methods based on the static pushover are introduced to estimate the seismic performance uncertainty of structures having non‐deterministic modeling parameters. At their basis lies the use of static pushover analysis to approximate Incremental Dynamic Analysis (IDA) and estimate the demand and capacity epistemic uncertainty. As a testbed we use a nine‐storey steel frame having beam hinges with uncertain moment–rotation relationships. Their properties are fully described by six, randomly distributed, parameters. Using Monte Carlo simulation with Latin hypercube sampling, a characteristic ensemble of structures is created. The Static Pushover to IDA (SPO2IDA) software is used to approximate the IDA capacity curve from the appropriately post‐processed results of the static pushover. The approximate IDAs allow the evaluation of the seismic demand and capacity for the full range of limit‐states, even close to global dynamic instability. Moment‐estimating techniques such as Rosenblueth's point estimating method and the first‐order, second‐moment (FOSM) method are adopted as simple alternatives to obtain performance statistics with only a few simulations. The pushover is shown to be a tool that combined with SPO2IDA and moment‐estimating techniques can supply the uncertainty in the seismic performance of first‐mode‐dominated buildings for the full range of limit‐states, thus replacing semi‐empirical or code‐tabulated values (e.g. FEMA‐350), often adopted in performance‐based earthquake engineering. Copyright © 2009 John Wiley & Sons, Ltd.     

RC框架结构超强系数与地震经济损失风险分析

基于现行的中国抗震设计规范,设计了6个不同参数的钢筋混凝土框架结构模型,利用静力弹塑性（Pushover）分析方法求得各个框架结构的超强系数;同时,利用基于性能的抗震设计（PBSD）的方法,通过增量动力分析（IDA）、易损性分析和地震损失风险分析等,定量的求出各个框架结构的经济损失风险,并比较了不同框架结构超强系数和经济损失风险的变化情况。结果表明:在层高相同的情况下,当抗震设防烈度逐渐增大时,超强系数减小,经济损失风险逐渐增大;在抗震设防烈度相同的情况下,当层高增大时,超强系数减小,经济损失风险逐渐增大。     

地震波参数对柱顶隔震体系的水平向减震性能影响研究

为了研究地震波参数对柱顶隔震体系的水平向减震性能的影响,选取台湾集集地震中8条地震波作为输入,进行了柱顶隔震体系模型的振动台试验。分析了柱顶隔震体系的水平向动力响应特点,研究了地震波的PGV/PGA、卓越周期、平均周期和断层距及幅值对其水平向减震性能的影响,并进行了数值模拟的对比分析。结果表明:柱顶隔震体系的水平向减震性能良好。相同地震强度下地震波参数的PGV/PGA、卓越周期、平均周期和断层距对柱顶隔震体系水平向减震性能的影响明显,其中:PGV/PGA的影响程度最大,可以作为主要的分析指标;随着地震动强度的增大柱顶隔震体系的水平向减震效果更加明显,地震动强度达到一定幅值后,减震率缓慢下降;与远场地震相比,近场地震不利于柱顶隔震体系的水平向减震性能的发挥,脉冲型近场地震作用下其减震效果更差。振动台试验结果与数值模拟结果基本一致,表明分析结果的可靠性。     

Overstrength of dowelled CLT connections under monotonic and cyclic loading

This paper presents an evaluation of overstrength based on an experimental study on dowelled connections in Cross Laminated Timber (CLT). Connection overstrength needs to be well understood in order to ensure that ductile system behaviour and energy dissipation can be achieved under seismic loading. Overstrength is defined as the difference between the code-based strength, using characteristic material strengths, and the 95th percentile of the true strength distribution. Many aspects contribute to total connection overstrength, which makes its definition challenging. In this study, half-hole embedment tests were performed on CLT to establish embedment strength properties and three point bending tests were performed to determine the fastener yield moment. Different connection layouts, making use of mild steel dowels and an internal steel plate, were tested under monotonic and cyclic loading to evaluate theoretically determined overstrength values and study the influence of cyclic loading on overstrength. Experimental results were compared with strength predictions from code provisions and analytical models for ductile response under monotonic loading. It was found that cyclic loading does not significantly influence overstrength for connections that respond in a mixed-mode ductile way indicating that in future more expedient monotonic test campaigns could be used. This work also provides further experimental data and theoretical considerations necessary for the estimation of a generally applicable overstrength factor for dowelled CLT connections.     

Seismic response evaluation of base-isolated reinforced concrete buildings under bidirectional excitation

This paper reports on an investigation of the seismic response of base-isolated reinforced concrete buildings, which considers various isolation system parameters under bidirectional near-fault and far-fault motions. Three-dimensional models of 4-, 8-, and 12-story base-isolated buildings with nonlinear effects in the isolation system and the superstructure are investigated, and nonlinear response history analysis is carried out. The bounding values of isolation system properties that incorporate the aging effect of isolators are also taken into account, as is the current state of practice in the design and analysis of base-isolated buildings. The response indicators of the buildings are studied for near-fault and far-fault motions weight-scaled to represent the design earthquake (DE) level and the risk-targeted maximum considered earthquake (MCE_R) level. Results of the nonlinear response history analyses indicate no structural damage under DE-level motions for near-fault and far-fault motions and for MCE_R-level far-fault motions, whereas minor structural damage is observed under MCE_R-level near-fault motions. Results of the base-isolated buildings are compared with their fixed-base counterparts. Significant reduction of the superstructure response of the 12-story base-isolated building compared to the fixed-base condition indicates that base isolation can be effectively used in taller buildings to enhance performance. Additionally, the applicability of a rigid superstructure to predict the isolator displacement demand is also investigated. It is found that the isolator displacements can be estimated accurately using a rigid body model for the superstructure for the buildings considered.