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。     

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。     

RC框架结构地震倒塌易损性分析的实用方法

基于增量动力分析(IDA)的倒塌易损性分析方法是评估建筑结构抗地震倒塌能力的精细方法,但分析过程比较繁杂且非常费时。为了较快地评估建筑结构的抗地震倒塌能力,首先利用静力非线性(pushover)分析,获得结构倒塌能力的初步估计值aS*,然后将每个地面运动记录调整到aS*,对结构进行动力时程分析,记录结构的动力时程反应,利用IDA的思想得到结构的中值数倒塌谱强度?CTS。该方法与传统的增量动力分析方法相比较,可提高计算效率,计算精度也满足要求。     

增量动力弹塑性分析方法的改进及其应用

本文主要对增量动力弹塑性分析(IDA)方法的两个方面作了改进:(1)以增量动力弹塑性分析方法的基本原理为基础,以快速非线性时程分析(FNA)方法为计算工具,形成快速增量动力弹塑性分析(FIDA)方法。(2)仅以IDA分析结果为基础,建立地震易损性曲线及地震破坏概率计算的离散型式。为了校验本文方法的可行性与有效性,应用增量动力弹塑性分析、模态增量动力弹塑性分析与快速增量动力弹塑性分析计算一个14层筒中筒结构试验模型,比较了用上述三种方法的计算误差与计算效率,比较了传统方法与本文方法计算该模型结构的地震易损性曲线的差别。     

结构附加粘滞阻尼器的抗震设计

本文结合抗震设计规范反应谱,给出了一个附加非线性流体粘滞阻尼器结构的抗震设计方法。研究了非线性阻尼器的力学特性,引入了非线性流体阻尼器的等效线性阻尼比,给出了计算最大加速度时刻附加非线性流体阻尼器结构反应的荷载组合系数,提出了按阻尼力的水平力分量与楼层剪力成正比的原则分配阻尼器阻尼系数的方法。同时给出了基于抗震规范设计反应谱附加非线性阻尼器结构的设计流程,通过一个算例说明了使用该方法设计附加非线性粘滞阻尼器结构的全过程。算例分析表明,这种设计方法适合于手算,便于设计人员掌握,在初步设计阶段可以快速、有效地设计满足给定性能水平的附加非线性流体阻尼器体系。     

隔震减震主次结构体系非线性随机地震反应分析

为研究隔震、减震装置非线性恢复力特性对2自由度主次结构体系均方根位移反应的影响规律,以隔震、减震装置微分型恢复力模式的滞回参数为变量,地震地面运动模拟成高斯白噪声过程,利用等效线性化方法得到主体结构和二次结构均方根位移反应的表达式.分析表明,主体结构隔震装置非线性恢复力特征对主、次结构的均方根位移反应的影响占主导地位;隔震、减震装置的恢复力特征产生适度非线性有利于减小主、次结构的均方根位移反应.     

基于向量式有限元的网壳结构地震易损性分析

为解决网壳结构地震易损性研究中,增量动力分析(incremental dynamic analysis, IDA)所面临的结构非线性分析耗时长且求解困难的问题,提出了一种基于向量式有限元的IDA方法。首先,以一个Kiewitt-8型单层球面网壳为例,验证了向量式有限元方法求解结构地震响应的准确性,其次选取12个不同参数的Kiewitt-8型单层球面网壳为研究对象,并考虑材料不确定性进行IDA分析,以地震峰值加速度与结构最大节点位移比为参数,绘制了结构在地震作用下的IDA曲线和轻微破坏、严重破坏及倒塌这三种性态下的易损性曲线。结果表明：向量式有限元能高效且准确的求解网壳结构的地震响应,屋面质量和矢跨比的增加均会增加三种性态点的超越概率;对于本文的网壳结构算例,求解时间仅为传统有限元方法的1/15,误差在3%以内,屋面质量和矢跨比的改变导致地震危险性最大增加了75%。     

基于单自由度等效线性化模型的RC结构地震易损性分析

通过有限元方法进行非线性动力时程分析获取解析的易损性曲线,计算量大且耗时。本文采用一种简化的计算方法,即基于单自由度的等效线性化模型,对钢筋混凝土框架结构进行地震易损性分析,并研究了该方法在结构高度上的适用性。通过选用5种典型的等效线性化模型对3栋不同高度的钢筋混凝土框架结构进行增量动力分析（IDA）,得到了不同高度的结构在不同强度地震作用下结构的反应和易损性,并与OpenSees程序的计算结果进行对比,研究了等效线性化模型应用于RC框架结构易损性分析在高度上的适用性。分析结果表明:对于10层及以下的框架结构,基于单自由度的等效线性化模型在结构地震易损性分析中具有较好的适用性;对于更高层数的结构,由于高阶振型反应对整体结构反应的影响增大,基于单自由度等效线性化模型的易损性分析结果会出现明显的偏差。     

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。     

地下结构地震作用的简化分析方法研究

随着地下结构建设的飞速发展,地下结构工程师不仅面临众多的地下结构静力设计问题,同时也面临着抗震设计问题。目前,利用大型商业软件对地下结构的动力时程分析及模型试验研究已开展较多,但其研究成果还较难应用于实际的地下结构抗震设计之中。同时,我国抗震设计规范还处于研究、发展阶段。因此,建立一套便于工程应用的简化抗震设计方法是十分必要的。本文首先从地下结构拟静力解析解方面着手,采用弹性解析解的方法探讨了自由场变形与地下结构变形之间的相互关系;然后,采用数值模拟的方法,对自由场与地下结构的动力反应特性进行了系统研究,提出了地下结构简化设计方法的基本思路,在此基础上,基于子结构法分别对反应位移法、静力有限元法进行了理论推导及方法改进;最后,介绍了地下结构弹塑性分析方法,并对地下结构拟静力实验进行了数值模拟。本文主要研究工作及研究成果如下:(1)基于解析解的自由场与地下结构变形拟静力关系研究。基于平面弹性复变函数理论分别对圆形地下结构和矩形地下结构进行拟静力解析求解,明确了地下结构拟静力解析求解的基本方法。同时,对Wang、Penzien、Bobet、Park和Huo的方法进行了系统分析,并探讨了接触条件和泊松比对地下结构变形系数的影响。(2)自由场与土-地下结构散射场关系研究。采用数值模拟的方法,研究了在P波和S波作用下,含地下结构散射场及相应的自由场的动力反应,对比分析了地下结构顶板与底板相对位移及自由场相应位置处相对位移最大时刻对应的加速度、应力等动力特征及整个时程的最大值的特征规律。通过这些动力特征分析,找出自由场与土-地下结构散射场二者的动力特性之间的联系,并以此探讨了地下结构简化抗震设计方法的可行性及研究方法。(3)反应位移法理论推导及改进。基于子结构法对反应位移法的原理进行了理论推导,提出了地基弹簧系数的多种求解方法并对地震荷载(剪应力、土层位移差等效荷载以及惯性力)的求解方法进行改进,通过算例对改进的反应位移法与规范中的反应位移法和整体动力时程分析方法进行对比分析,验证了改进反应位移法的实用性。(4)静力有限元法理论推导及改进。基于子结构方法对静力有限元方法进行了理论推导,对现有的静力有限元方法(强制边界位移法、反应加速度法、反应应力法)进行了对比研究,提出了静力有限元计算模型,并验证了该方法的实用性。(5)地下结构弹塑性简化分析方法。采用地基刚度衰减的方法,对规范中反应位移法、改进反应位移法以及静力有限元法在土体弹塑性条件下的计算结果与动力时程方法进行对比,验证了这3种方法在土体弹塑性条件下的计算精度。同时,采用数值模拟的方法,模拟了地下结构拟静力条件下的弹塑性反应。     

Direct estimation of the seismic demand and capacity of oscillators with multi‐linear static pushovers through IDA

SPO2IDA is introduced, a software tool that is capable of recreating the seismic behaviour of oscillators with complex quadrilinear backbones. It provides a direct connection between the static pushover (SPO) curve and the results of incremental dynamic analysis (IDA), a computer‐intensive procedure that offers thorough demand and capacity prediction capability by using a series of nonlinear dynamic analyses under a suitably scaled suite of ground motion records. To achieve this, the seismic behaviour of numerous single‐degree‐of‐freedom (SDOF) systems is investigated through IDA. The oscillators have a wide range of periods and feature pinching hysteresis with backbones ranging from simple bilinear to complex quadrilinear with an elastic, a hardening and a negative‐stiffness segment plus a final residual plateau that terminates with a drop to zero strength. An efficient method is introduced to treat the backbone shape by summarizing the analysis results into the 16, 50 and 84% fractile IDA curves, reducing them to a few shape parameters and finding simpler backbones that reproduce the IDA curves of complex ones. Thus, vast economies are realized while important intuition is gained on the role of the backbone shape to the seismic performance. The final product is SPO2IDA, an accurate, spreadsheet‐level tool for performance‐based earthquake engineering that can rapidly estimate demands and limit‐state capacities, strength reduction R‐factors and inelastic displacement ratios for any SDOF system with such a quadrilinear SPO curve. Copyright © 2006 John Wiley & Sons, Ltd.     

Seismic reliability assessment of a steel moment-resisting frame with two different ductility levels using a cloud analysis approach

A cloud method for generating percentile engineering demand parameter versus intensity measure(EDP-IM) curves of a structure subjected to a set of synthetic ground motions is presented. To this end, an ensemble of synthetic ground motions based on available real ones is generated. This is done by using attenuation relationships, duration and suitable Gutenberg-Richter relations attributed to the considered seismic hazard at a given site by estimating a suitable distribution of magnitude and site to source distance. The study aims to clarify the significance of the duration and frequency content on the seismic performance of structures, which were not considered in developing percentile incremental dynamic analysis(IDA) curves. The collapse probabilities of two steel moment-resisting frames with different ductility levels generated by IDA and the proposed cloud method are compared at different intensity levels. When compared with conventional IDA, the suggested cloud analysis(SCA) methodology with the same run number of dynamic analyses was able to develop response hazard curves that were more consistent with site-specific seismic hazards. Eliminating the need to find many real records by generating synthetic records consistent with site-specific seismic hazards from a few available recorded ground motions is another advantage of using this scheme over the IDA method..     

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.     

Seismic assessment of concrete gravity dams using capacity estimation and damage indexes

A new concept to determine state of the damage in concrete gravity dams is introduced. The Pine Flat concrete gravity dam has been selected for the purpose of the analysis and its structural capacity, assuming no sliding plane and rigid foundation, has been estimated using the two well‐known methods: nonlinear static pushover (SPO) and incremental dynamic analysis (IDA). With the use of these two methods, performance and various limit states of the dam have been determined, and three damage indexes have been proposed on the basis of the comparison of seismic demands and the dam's capacity. It is concluded that the SPO and IDA can be effectively used to develop indexes for seismic performance evaluation and damage assessment of concrete gravity dams. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficient structural seismic performance evaluation method using improved endurance time analysis

Evaluation of structural performance under seismic excitations from low intensity to high intensity is essential to verify the seismic resistant capacity of a structure, and usually carried out by the incremental dynamic analysis (IDA) method or pushover method. The recently developed endurance time (ET) method is another method that uses dynamic pushover excitations, i.e., endurance time acceleration function, to obtain results similar to those obtained by IDA or pushover methods with low computational cost and acceptable accuracy. This study proposes an improvement on the ET method by considering more restrictions for both the elastic and inelastic response spectra in the generation procedure, and by specifying a target duration. Four reinforced concrete frame structures with 4, 8, 12, and 16 stories are adopted to verify the accuracy of the improved method. Comparison of the results obtained by the proposed method, the ET method and the IDA method shows that the improved method has a higher accuracy than the ET method. For evaluation of structural responses under specific ground motion intensity, which is typically required in seismic design codes, the results obtained by the proposed method are compared with five commonly used ground motion selection methods, and shows the proposed method provides acceptable accuracy for engineering applications.

     

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.     

Accuracy of nonlinear static procedures for the seismic assessment of shear critical structures

The nonlinear behavior of reinforced concrete (RC) members represents a key issue in the seismic performance assessment of structures. Many structures constructed in the 1980s or earlier were designed based on force limits; thus they often exhibit brittle failure modes, strength and stiffness degradation, and severe pinching effects. Field surveys and experimental evidence have demonstrated that such inelastic responses affect the global behavior of RC structural systems. Efforts have been made to consider the degrading stiffness and strength in the simplified nonlinear static procedures commonly adopted by practitioners. This paper investigates the accuracy of such procedures for the seismic performance assessment of RC structural systems. Refined finite element models of a shear critical bridge bent and a flexure‐critical bridge pier are used as reference models. The numerical models are validated against experimental results and used to evaluate the inelastic dynamic response of the structures subjected to earthquake ground motions with increasing amplitude. The maximum response from the refined numerical models is compared against the results from the simplified static procedures, namely modified capacity spectrum method and coefficient method in FEMA‐440. The accuracy of the static procedures in estimating the displacement demand of a flexure‐critical system and shear‐critical system is discussed in detail. Copyright © 2015 John Wiley & Sons, Ltd.     

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.