随机地震作用下特高压换流站阀厅非线性动力可靠度研究

通过模态分析研究了抗震设防烈度为8度（0.3g）的混合结构与全钢结构两种阀厅结构方案的动力特性,基于地震动的地震学模型与概率密度演化法分析了全钢阀厅的非线性随机动力可靠度,根据阀厅角柱柱顶位移响应得到了全钢阀厅动力影响的概率密度曲面及典型时刻的概率密度曲线。研究结果表明:阀塔对结构整体刚度影响较小,工程中可采用无阀模型进行简化计算;高烈度设防地区,推荐采用结构布置相对规则的钢结构方案;随机动力分析相比于确定性分析更能反应地震作用下阀厅动力响应的客观规律;阀厅钢结构方案在罕遇地震作用下可靠度较高,结构安全可靠。     

大震下被动与智能隔震结构动力可靠度的对比

对被动及智能隔震结构在“大震”条件下的动力可靠度进行探讨。将被动及智能隔震体系均取作弹塑性模型,并用退化Bouc-W en滞变模型描述上部结构的恢复力,用非退化Bouc-W en模型描述隔震层的恢复力。采用虚拟激励法计算结构的随机响应,根据我国抗震规范中“大震不倒”的设防目标,采用各层最大层间位移峰值响应和累积滞变耗能构造双参数的随机疲劳累积损伤指数,作为功能状态指标。假定各层失效相关,用串联系统计算体系动力可靠度。通过数值算例,对比了被动隔震、智能隔震与非隔震体系的条件失效概率,从动力可靠度角度显示了智能隔震体系的减震优势。     

罕遇地震作用下的框架-摇摆刚架结构体系动力可靠度研究

针对钢筋混凝土框架结构的受力特点,采用增设摇摆刚架的抗震设计方法,以提高罕遇地震下建筑结构的安全性。建立了框架一摇摆刚架结构体系的计算模型,结合状态空间法与虚拟激励法,求解结构的平稳随机响应,并根据计算所得随机响应对框架一摇摆刚架体系的动力可靠度进行分析。以西部地区某已建成的6层框架结构为算例,探讨了罕遇地震作用下不同刚度比的摇摆刚架对新结构体系动力可靠度的影响。结果表明,通过增设不同刚度比的摇摆刚架,可以有效协调结构体系的变形模式,充分发挥结构的耗能能力,降低整体结构的条件失效概率。     

大跨度斜拉桥在随机地震激励下的动力可靠性分析

以随机振动理论为基础,以苏通长江公路大桥为背景,对超大跨度斜拉桥在随机地震荷载作用下的动力可靠度展开研究。根据结构随机振动分析得到的响应统计量,采用结构可靠度分析的JC法(一次二阶矩法)和首次超越破坏理论,分析苏通大桥主梁关键截面上正应力的动力可靠度,并评价结构的抗震性能,分析结果证明该结构可靠性满足桥梁抗震需求。计算结果可为大跨度斜拉桥抗震可靠性分析提供参考。     

基于性能的基础隔震钢筋混凝土框剪结构的倒塌可靠度分析

利用基于性能的结构可靠度分析方法,对基础隔震钢筋混凝土框剪结构进行分析研究。选取20条实际地震动记录,以0.2g为步长对结构地震动参数PGA进行调幅后,建立了140个结构-地震动样本空间。选取上部结构的最大层间位移角、隔震层位移为量化指标,对每一个样本进行动力非线性时程分析后,将结构响应进行统计得到结构在各地震动强度下超越极限破坏状态的概率,将其绘制成基础隔震钢筋混凝土框剪结构的易损性曲线并利用整体可靠度方法分析结构发生倒塌的可靠度指标。该方法直观地反映了结构发生倒塌的概率,为结构的地震损失评估提供依据。     

基于响应面法的连续刚构地震可靠度分析

地震可靠度是桥梁抗震研究中的重要问题。基于随机分析的响应面理论和规范反应谱法,提出了一种分析具有随机结构参数的桥梁地震可靠度的方法,研究了结构的破坏准则及其极限状态方程,计算了高墩大跨连续刚构桥在地震激励下设计基准期内的动力可靠度。分析时考虑了结构参数和场地土的随机性,分别计算了连续刚构在多遇地震、设防地震和罕遇地震作用下的失效概率,得到了结构在设计基准期内,"三水准设防标准"条件下的地震可靠度。结果表明,该桥设计满足抗震规范要求。     

基于破坏指标界限值的结构抗震可靠度分析

结构抗震可靠性的分析一般即采用动力可靠度的研究方法进行。本文提出了进行结构抗震可靠度分析与计算的一种新方法,即基于破坏指标界限值的结构抗震可靠度分析方法。该方法在标定结构破坏指标范围进行破坏等级划分的基础上,采用JC法对结构在不同烈度地震作用下的各破坏状态概率进行计算,从而完成对结构抗震可靠性的分析。计算实例表明,该方法与经典动力可靠性分析所得结论相一致,这表明了本文方法的正确与可靠。     

多高层建筑结构层间位移和层剪力的动力可靠度计算

在虚拟激励法的基础上推导了多高层建筑结构剪切层模型在地震作用下层间相对位移和层地震剪力的自功率谱密度函数的解析表达,通过数值积分获得层间相对位移和层地震剪力的各阶谱矩和标准差,基于随机动力响应过程跨越安全界限次数为泊松过程和两态马尔可夫过程的假设,计算了层间相对位移和层地震剪力的动力可靠度,并用Matlab语言编制了动力可靠度的计算程序.算例表明该方法是高效的和有效的.     

TMD结构基于双过滤白噪声随机地震激励的系列响应的简明解

针对既有方法在分析TMD结构基于双过滤白噪声激励下结构响应的解表达式复杂而导致计算效率低的问题,提出了一种简明封闭解法。首先,利用双过滤白噪声谱的滤波方程与TMD结构的地震动方程联立,可将TMD结构基于复杂的双过滤白噪声激励准确的表示为易于求解的运动方程;其次,基于复模态法获得TMD耗能结构位移、层间位移的系列响应的复特征值及复模态参与系数;然后基于随机振动理论获得了TMD结构随机地震动系列响应（相对于地面绝对位移和结构层间位移）的功率谱统一形式的二次正交解,进而获得了TMD结构系列随机响应的0-2阶谱矩和方差的简明封闭解。最后研究了基于首超破坏准、Markov过程假设及串联失效模式的TMD结构的体系动力可靠度。通过一算例分析,表明了本文方法的正确性和高效性。因此,本文方法可用于各类线性结构基于复杂的随机地震动响应的分析及其动力可靠度计算。     

隔震结构"小震不坏"的动力可靠度分析

本文探讨叠层橡胶隔震体系在“小震不坏”条件下的动力可靠度分析。基于等效线性化的隔震工程设计参数,建立非比例阻尼隔震结构模型。采用双过滤白噪声功率谱模型描述地震动,并用林家浩虚拟激励法进行随机响应分析。以各层的最大层间位移响应作为控制指标,取结构的弹性位移限值作为位移极限值,建立功能状态方程。根据一次二阶矩方法,用串联模式计算体系的总体可靠度。文末选用了一个7层隔震框架作为数值算例,探讨了隔震阻尼、寒冷环境、节点构造误差所引起的隔震层刚度上升,以及场地土类别等对体系动力可靠性的影响。     

全非平稳地震作用的结构随机反应与可靠度分析

在平稳地震动过程的Clough-Penzien功率谱基础上,采用林家浩非均匀调制函数建立全非平稳地震动过程的演变功率谱。根据我国现行的《建筑抗震设计规范》进行全非平稳地震动演变功率谱的参数识别研究。应用非平稳随机过程模拟的谱表示-随机函数方法,生成建筑结构抗震设计所用地震动的代表性样本集合。通过代表性样本集合的二阶统计值及地震反应谱与目标值的拟合比较,验证本文方法的有效性。最后结合概率密度演化方法,进行以层间位移角为控制准则的结构随机地震反应分析与抗震可靠度计算。     

Nonstationary stochastic response of structural systems equipped with nonlinear viscous dampers under seismic excitation

Nonlinear viscous dampers are supplemental devices widely used for enhancing the performance of structural systems exposed to seismic hazard. A rigorous evaluation of the effect of these damping devices on the seismic performance of a structural system should be based on a probabilistic approach and take into account the evolutionary characteristics of the earthquake input and of the corresponding system response. In this paper, an approximate analytical technique is proposed for studying the nonstationary stochastic response characteristics of hysteretic single degree of freedom systems equipped with viscous dampers subjected to a fully nonstationary random process representing the seismic input. In this regard, a stochastic averaging/linearization technique is utilized to cast the original nonlinear stochastic differential equation of motion into a simple first‐order nonlinear ordinary differential equation for the nonstationary system response variance. In comparison with standard linearization schemes, the herein proposed technique has the significant advantage that it allows to handle realistic seismic excitations with time‐varying frequency content. Further, it allows deriving a formula for determining the nonlinear system response evolutionary power spectrum. By this way, ‘moving resonance’ effects, related to both the evolutionary seismic excitation and the nonlinear system behavior, can be observed and quantified. Several applications involving various system and input properties are included. Furthermore, various response parameters of interest for the seismic performance assessment are considered as well. Comparisons with pertinent Monte Carlo simulations demonstrate the reliability of the proposed technique. Copyright © 2014 John Wiley & Sons, Ltd.     

Wavelet-Hilbert transform-based simulation of pulse-like ground motion

In nonlinear dynamic structural analysis, a suite of pulse-like ground motions is required for the performance-based design of structures near active faults. The dissimilarity in the amplitude and frequency content of the earthquake time series referred to nonstationary properties in temporal and spectral, respectively. An approach is proposed based on the nonstationary properties of the far-field records and the seismological information in an event for simulating pulse-like records. The pulse-like earthquake time history is estimated via the superposition of the residual part of the earthquake with the estimated pulse. The wavelet-based Hilbert transform is utilized to characterize the nonstationary properties, the instantaneous amplitude, and frequencies of far-field records to model residual part. The effects of near-fault and pulse are estimated based on the seismological properties of the region. The validation of the procedure is indicated by comparing simulated time-series, response spectra, and Arias intensity with recorded pulse-like records in two different earthquakes in California; the M_w 6.7 1994 Northridge and the M_w 6.5 1979 Imperial valley.

     

Solution of random structural system subject to nonstationary excitation: transforming the equation with random coefficients to one with deterministic coefficients and random initial conditions

This paper deals with the lower order (first four) nonstationary statistical moments of the response of linear systems with random stiffness and random damping properties subject to random nonstationary excitation modeled as white noise multiplied by an envelope function. The method of analysis is based on a Markov approach using stochastic differential equations (SDE). The linear SDE with random coefficients subject to random excitation with deterministic initial conditions are transformed to an equivalent nonlinear SDE with deterministic coefficients and random initial conditions subject to random excitation. In this procedure, new SDE with random initial conditions, deterministic coefficients and zero forcing functions are introduced to represent the random variables. The joint statistical moments of the response are determined by considering an augmented dynamic system with state variables made up of the displacement and velocity vectors and the random variables of the structural system. The zero time-lag joint statistical moment equations for the augmented state vector are derived from the Itô differential formula. The statistical moment equations are ordinary nonlinear differential equations where hierarchy of moments appear. The hierarchy is closed by the cumulant neglect closure method applied at the fourth order statistical moment level. General formulation is given for multi-degree-of-freedom (MDOF) systems and the performance of the method in problems with nonstationary excitations and large variabilities is illustrated for a single-degree-of-freedom (SDOF) oscillator.     

Seismic spatial effects on long-span bridge response in nonstationary inhomogeneous random fields

The long-span bridge response to nonstationary multiple seismic random excitations is investigated using the PEM (pseudo excitation method). This method transforms the nonstationary random response analysis into ordinary direct dynamic analysis, and therefore, the analysis can be solved conveniently using the Newmark, Wilson-θ schemes or the precise integration method. Numerical results of the seismic response for an actual long-span bridge using the proposed PEM are given and compared with the results based on the conventional stationary analysis. From the numerical comparisons, it was found that both the seismic spatial effect and the nonstationary effect are quite important, and that both stationary and nonstationary seismic analysis should pay special attention to the wave passage effect.     

基于结构动态响应统计特征的损伤指标研究

为了提高土木工程结构损伤识别的可靠性和有效性,本文提出一种基于结构动态响应统计特征的损伤指标,并对其可行性进行研究。文中首先在结构随机振动理论基础上推导出结构动态响应（包括位移、速度和加速度）的统计特征（包括均值和方差）与结构损伤位置和损伤程度之间的关系;然后通过敏感性分析确定以结构位移的方差作为结构损伤识别的损伤指标;最后,数值模拟-六层钢筋混凝土框架结构在白噪声激励下的动态响应,观察在不同损伤位置和损伤程度下结构动态位移方差的变化,从而对选择结构位移的方差作为损伤指标的可行性进行评估。研究得出结论,使用结构动态响应的统计特征作为土木工程结构损伤识别的损伤指标是可行的。     

Local site effects on a high-pier railway bridge under tridirectional spatial excitations: Nonstationary stochastic analysis

This paper presents a theoretical nonstationary stochastic analysis scheme using pseudo-excitation method (PEM) for seismic analysis of long-span structures under tridirectional spatially varying ground motions, based on which the local site effects on structural seismic response are studied for a high-pier railway bridge. An absolute-response-oriented scheme of PEM in nonstationary stochastic analysis of structure under tridirectional spatial seismic motions, in conjunction with the derived mathematical scheme in modeling tridirectional nonstationary spatially correlated ground motions, is proposed to resolve the drawbacks of conventional indirect approach. To apply the proposed theoretical approach readily in stochastic seismic analysis of complex and significant structures, this scheme is implemented and verified in a general finite element platform, and is then applied to a high-pier railway bridge under spatially varying ground motions considering the local site effect and the effect of ground motion nonstationarity. Conclusions are drawn and can be applied in the actual seismic design and analysis of high-pier railway bridges under tridirectional nonstationary multiple excitations.     

基于一致可靠度的地震动记录样本容量确定方法研究

确定地震动输入样本容量是开展结构动力地震反应分析的重要环节,目前国内外关于地震动输入样本容量的讨论往往忽略或尚难以定量考虑结构地震反应估计的可靠度水平。以一实际钢筋混凝土框架结构为例,首先分析在大样本地震动作用下结构非线性地震反应的统计特征,研究估计结构地震反应时取样本最大值和平均值的差异,然后借助于假设检验分析结构地震反应的概率分布模型,给出基于一致可靠度的地震动样本容量确定方法,并对比分析单周期点、多周期点、谱值匹配调整地震动及人工合成地震动对样本容量需求的影响,为保证在小样本地震动输入下结构地震反应估计值满足给定可靠度和容许误差提供分析方法和判断依据。本文方法适应于定量确定不同结构类型和不同地震强度水平下的地震动样本容量需求,对建筑结构抗震性能评估及设计规范研究有一定意义。