复杂高层结构基于增量动力分析法的地震易损性分析

增量动力分析法(Incremental Dynamic Analysis,IDA)是一种以动力弹塑性时程分析为基础的参数分析方法,计算结构在不同地震动强度作用下的响应,能够反映结构体系随地震动强度的变化,经历弹性、弹塑性直至倒塌的全过程性能.而建筑结构的地震易损性是指在不同强度地震作用下结构达到或超过某种极限状态的条件概率.因此,增量动力分析的结果提供了结构地震易损性分析所需的数据.本文在增量动力分析的基础上,结合地震易损性分析,提出基于IDA的地震易损性分析方法,并采用该方法对某复杂超限高层结构进行抗震性能评估,得出该结构在3个地震水准下,超越5个极限状态的概率.研究表明,基于增量动力分析的易损性分析结果,可为预测重大工程结构的地震破坏和损失提供有力的科学依据.     

基于增量动力分析(IDA)方法的地震易损性工程实例分析

增量动力分析法(Incremental Dynamic Analysis,IDA)是一种以动力弹塑性时程分析为基础的参数分析方法,而建筑结构的地震易损性分析是指在不同强度地震作用下结构达到或超过某种极限状态的概率。文章基于IDA分析方法,通过选取一定数量的地震动记录,指定地震动强度指标并做归一化处理,利用OpenSees软件平台向结构碰撞数值模型输入地震动数据,计算得出结构倒塌概率,以地震动参数为随机变量,对数据进行拟合分析,建立倒塌概率易损性曲线,验证IDA方法的可靠性以及Opensees软件对于该类问题的适用性。     

自适应顺序采样Kriging方法及其在增量动力分析中的应用

复杂结构的增量动力分析（IDA）对于结构的抗震设计和分析有着重要意义,但需对结构进行大量的非线性时程分析,计算量成本高。本文结合Kriging元模型和自适应顺序采样并用于结构增量动力分析以提高其计算效率和精度,其中:Kriging元模型用于预测结构的地震响应,顺序采样根据候选点的熵值补充非线性时程分析逐步增加Kriging模型的预测精度。借助本文方法,IDA曲线可通过少量的时程分析实现较高的精度。为了校验本文方法的可行性与有效性,对二层和九层钢框架结构模型应用直接IDA、hunt&fill方法和本文方法分析并比较了上述三种方法的计算误差、计算效率和IDA曲线差别。在此基础上本文将自适应顺序采样Kriging方法用于考虑结构不确定性参数的IDA分析,并和传统的蒙特卡洛方法进行比较。结果表明:该方法具有较高的计算效率,可以保证IDA曲线的精度。     

基于IDA方法的交河故城金刚宝座式塔土建筑遗址地震易损性分析

增量动力分析（IDA）作为动力形式的静力推覆法,被广泛应用于建筑结构的抗震能力分析和性能评估中,但其在土建筑遗址地震易损性分析中的应用甚少。基于IDA方法尝试对交河故城塔林区金刚宝座式塔土建筑遗址进行在地震作用下的易损性和抗震能力分析,以谱加速度S_a（T₁,5%）作为地震动强度指标,最大层间位移角θ_max作为结构损伤指标进行IDA分析,得到土建筑遗址在一系列调幅地震动作用下的IDA曲线、地震需求概率模型和易损性曲线,计算出模型的倒塌率和CMR值。通过以上分析得出金刚宝座式塔的易损性和抗震能力,为今后土建筑遗址抗震保护提供理论基础和分析思路。     

近场地震作用下考虑二阶效应的混凝土框架抗震分析

利用钢筋混凝土柱的试验结果,验证OpenSees程序用于钢筋混凝土结构非线性分析的可行性。以此为基础,对钢筋混凝土框架结构在远场地震、近场非脉冲地震与近场脉冲地震作用的性能进行非线性时程分析,研究框架结构在三类地震作用下的反应以及二阶效应对结构反应的影响。针对近场脉冲地震对结构进行增量动力分析(IDA)和易损性分析,分别得到结构的IDA曲线、易损性曲线和近场脉冲地震作用下二阶效应对结构抗震性能的影响。分析结果表明,在三类地震作用下,近场脉冲地震导致的二阶效应对结构抗震性能的影响最为显著,结构抗震设计中宜考虑二阶效应的影响。     

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。     

按现行规范设计的Ⅷ度区RC框架结构的倒塌性能评估

选取按照现行规范设计的既有建筑进行有限元建模,考虑地震动的不确定性对其进行大量增量动力分析(IDA),得到模型的IDA曲线簇。在此基础上对其进行地震需求概率分析和概率抗震能力分析,拟合得到结构的易损性曲线,据此对结构的倒塌概率进行定量评估,并比较基于非线性分析与性能评估软件PERFORM-3D的纤维模型和塑性铰模型的分析结果。结果表明:按照我国现行规范设计的钢筋混凝土(RC)框架结构,在预期的罕遇地震作用下倒塌概率较小,可满足"大震不倒"的要求;基于PERFORM-3D的截面纤维模型所得的RC框架结构,经非线性分析所得的倒塌概率相对保守,安全储备更高。     

核电厂考虑结构参数不确定的 地震易损性分析

为考虑核电厂结构参数不确定对结构地震易损性的影响,基于一次二阶矩法(First-Order Second-Moment, FOSM)进行地震易损性分析。以核电结构中混凝土材料的密度、弹性模量,泊松比和抗拉强度为不确定参数,建立有限元模型,并与试验结果对比,以验证模型的准确性。基于有限元数值模拟方法,通过增量动力法计算核电厂模型在多条地震记录下不同峰值加速度的动力响应,同时基于FOSM得到参数不确定下的对数标准差,进而得到核电厂结构考虑参数不确定的地震易损性曲线。结果表明,结构参数的不确定对核电结构有一定的影响,未考虑参数不确定的地震易损性结果会低估结构的失效概率。该方法可为核电结构基于参数不确定下的易损性分析提供一定的理论依据与实用价值。     

基于IDA的隔震桥梁易损性分析

针对目前减隔震技术在我国桥梁领域的推广应用,建立一座隔震桥梁,基于增量动力分析(IDA)方法研究了桥梁在单条地震动下的动态响应,得到了桥墩以及支座在地震动作用下的响应曲线(IDA曲线)。以桥墩位移延性系数和支座剪应变作为损伤指标,对IDA曲线进行损伤状态区间的划分。通过IDA曲线发现隔震桥梁具有良好的抗震性态,支座比桥墩更容易损伤。最后,将支座和桥墩综合考虑计算得到桥梁结构整体易损性(DS)。     

基于IDA的方钢管混凝土框架-SPSW核心筒结构地震易损性研究

为研究方钢管混凝土框架-钢板剪力墙（SPSW）核心筒结构在不同强度地震下破坏概率,使用拉杆模型作为钢板剪力墙等效模型,与已有试验对比验证各参数有效性。以地震动峰值加速度（PGA）作为地震动强度参数,按照场地条件等要求选择11条地震动记录。以结构最大层间位移角作为损伤指标,对一典型方钢管混凝土框架-钢板剪力墙核心筒结构进行增量动力分析（IDA）,得到IDA曲线簇。基于增量动力分析进行易损性分析,得到易损性曲线,并计算结构的抗倒塌储备系数。结果表明:8度多遇地震作用下,此结构处于正常使用状态。8度设防地震作用下,处于修复后可使用状态。8度罕遇地震作用下,处于生命安全状态。表明该结构具有良好的抗震性能,满足规范中“小震不坏”、“中震可修”和“大震不倒”的抗震设防目标。该结构抗倒塌储备系数大于规范建议值,具有较好的抗倒塌能力。     

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.     

基于IDA方法的框架结构震害风险评估

为了评估不同抗震设防烈度区建筑结构震害风险,即场地地震危险性与结构地震易损性的卷积,本文以典型框架结构为例,对其震害风险进行研究。依据抗震设计规范,分别按照6度、7度和8度设计3个3跨10层框架结构模型,采用动力增量分析方法（Incremental Dynamic Analysis,IDA）对其进行地震易损性分析。同时,基于我国地震烈度概率分布特点,应用MATLAB软件生成符合极值Ⅲ型分布的地震烈度,并将其转化为地震加速度峰值,联合地震易损性结果评估模型震害风险。通过划分震害风险等级,为建筑结构抗震防灾对策的制定提供借鉴。     

Cloud to IDA: Efficient fragility assessment with limited scaling

Incremental dynamic analysis (IDA) leads to curves expressed in terms of structural response versus intensity, commonly known as the IDA curves. It is known that implementation of IDA usually involves significant computational effort and most often significant scaling of the original records to various intensity levels. Employing as the performance variable the critical demand to capacity ratio (DCR) throughout the structure, which is equal to unity at the onset of the limit state, facilitates the identification of the intensity values at the onset of a desired limit state and hence the implementation of the IDA procedure. Employing the structural response to un‐scaled records and the corresponding regression‐based response predictions (a.k.a., the “Cloud Analysis”) helps in identifying the range of intensity values corresponding to demand to capacity ratio values in the vicinity of unity. The Cloud to IDA procedure for structural fragility assessment is proposed on the premise of exploiting the Cloud Analysis results to obtain the IDA curves both with minimum number of analyses and minimum amount of scaling. The transverse frame of a shear‐critical 7‐story older RC building in Van Nuys, CA, which is modeled in Opensees with fiber‐section considering the flexural‐shear‐axial interactions and the bar slip, is employed as a case study. It is demonstrated, by comparing the results to IDA and other state of the art non‐linear dynamic procedures based on no scaling or spectral‐shape‐compatible scaling, that the Cloud to IDA procedure leads to reliable results in terms of structural fragility and risk for the prescribed limit state.     

Incremental dynamic analysis with consideration of modeling uncertainties

Incremental dynamic analysis (IDA) has been extended by introducing a set of structural models in addition to the set of ground motion records which is employed in IDA analysis in order to capture record‐to‐record variability. The set of structural models reflects epistemic (modeling) uncertainties, and is determined by utilizing the latin hypercube sampling (LHS) method. The effects of both aleatory and epistemic uncertainty on seismic response parameters are therefore considered in extended IDA analysis. The proposed method has been applied to an example of the four‐storey‐reinforced concrete frame, for which pseudo‐dynamic tests were performed at the ELSA Laboratory, Ispra. The influence of epistemic uncertainty on the seismic response parameters is presented in terms of summarized IDA curves and dispersion measures. The results of extended IDA analysis are compared with the results of IDA analysis, and the sensitivity of the seismic response parameters to the input random variable using the LHS method is discussed. It is shown that epistemic uncertainty does not have significant influence on the seismic response parameters in the range far from collapse, but could have a significant influence on collapse capacity. Copyright © 2008 John Wiley & Sons, Ltd.     

Fragility estimation and sensitivity analysis of an idealized pile-supported wharf with batter piles

The main objective of the present study is to develop seismic fragility curves of an idealized pile-supported wharf with batter piles through a practical framework. Proposing quantitative limit states, analytical fragility curves are developed considering three engineering demand parameters (EDPs), including displacement ductility factor (µ_d), differential settlement between deck and behind land (DS) and normalized residual horizontal displacement (NRHD). Analytical fragility curves are generated using the results of a numerical model. So, the accuracy and reliability of resulted fragility curves directly depend on how accurate the seismic demand quantities are estimated. In addition, the seismic performance of pile-supported wharves is highly influenced by geotechnical properties of the soil structure system. Hence, a sensitivity analysis using the first-order second-moment (FOSM) method is performed to evaluate the effects of geotechnical parameters uncertainties in the seismic performance of the wharf.Herein, the seismic performance of the wharf structure is simulated using the representative FLAC2D model and performing nonlinear time history analyses under a suit of eight ground motion records. Incremental dynamic analysis (IDA) is used to estimate the seismic demand quantities. As a prevailing tool, adopted fragility curves are useful to seismic risk assessment. They can also be used to optimize wharf-retrofit methods. The results of sensitivity analysis demonstrate that uncertainties associated with the porosity of loose sand contribute most to the variance of both NRHD and µ_d. While in the case of differential settlement, the friction angle of loose sand contributes most to the variance.     

基于耐震时程法的进水塔结构抗震性能分析

进水塔结构作为水电站的进水建筑物,其抗震性能对水电站的安全运行有重要意义。以沙牌水电站的高耸独立进水塔结构为研究对象,应用3条耐震时程曲线对其进行抗震性能分析与评估,并将计算结果与天然地震动下的增量动力分析结果进行比较,对比分析进水塔塔顶位移、基底剪力及地震损伤历程。实例研究表明：耐震时程法可以较好地分析结构的抗震响应,与增量动力分析结果的均值相匹配。耐震时程法可以利用较少的时程分析得到不同动力强度作用下的结构响应,且计算结果精度好、效率高,为进水塔结构的抗震性能分析提供一种新的手段。     

Analytical fragility assessment using unscaled ground motion records

It is desirable that nonlinear dynamic analyses for structural fragility assessment are performed using unscaled ground motions. The widespread use of a simple dynamic analysis procedure known as Cloud Analysis, which uses unscaled records and linear regression, has been impeded by its alleged inaccuracies. This paper investigates fragility assessment based on Cloud Analysis by adopting, as the performance variable, a scalar demand to capacity ratio that is equal to unity at the onset of limit state. It is shown that the Cloud Analysis, performed based on a careful choice of records, leads to reasonable and efficient fragility estimates. There are 2 main rules to keep in mind for record selection: to make sure that a good portion of the records leads to a demand to capacity ratio greater than unity and that the dispersion in records' seismic intensity is considerable. An inevitable consequence of implementing these rules is that one often needs to deal with the so‐called collapse cases. To formally consider the collapse cases, a 5‐parameter fragility model is proposed that mixes the simple regression in the logarithmic scale with logistic regression. The joint distribution of fragility parameters can be obtained by adopting a Markov Chain Monte Carlo simulation scheme leading directly to the fragility and its confidence intervals. The resulting fragility curves compare reasonably with those obtained from the Incremental Dynamic Analysis and Multiple Stripe Analysis with (variable) conditional spectrum–compatible suites of records at different intensity levels for 3 older reinforced concrete frames with shear‐, shear‐flexure‐, and flexure‐dominant behavior.