考虑结构不确定性的多层框架结构地震易损性分析

文中选取常见的六层钢筋混凝土框架结构作为研究对象,考虑地震动与结构模型的双重不确定性,基于拉丁超立方抽样和正交设计相结合的试验方法针对结构模型建立了27个结构样本,应用OpenSees分别对每个样本开展增量动力分析,分别计算出每个样本在27条地震动的12次调幅作用下的各算例所对应的最大层间位移角。并对最大层间位移角与峰值加速度结果进行回归分析。以结构最大层间位移角作为损伤指标得到结构地震易损性曲线,并对比分析了地震动记录条数与模型不确定性对结构地震易损性的影响。结果表明,文中提出的分析方法能够较好的考虑地震动不确定性与结构自身不确定性,是一种有效的理论易损性求解方法;结构模型自身的不确定性对结构地震易损性结果具有较大的影响,这种影响对结构在大震作用下的抗倒塌能力尤为明显;文中的研究结果可为评估多层框架结构的地震灾害损失提供基础数据。     

考虑多维地震作用的高耸钢筋混凝土烟囱结构易损性分析

竖向地震作用对高耸烟囱结构动力响应有不可忽略的影响。选用240m高的某钢筋混凝土烟囱作为研究对象,考虑结构损伤,通过有限元软件ABAQUS,采用复合壳单元建立相应的非线性有限元分析模型。为考虑地震动的不确定性,根据谱相容性原则,选择20条合理地震动记录,进行增量动力分析。输入的地震动分别为一维、二维、三维。分别以材料应变和地面峰值加速度作为结构地震需求参数和地震动强度参数,结合增量动力分析获得的结构地震响应,采用能力需求比模型的曲线拟合法计算易损性曲线。通过钢筋和混凝土的材料应变定义四个损伤状态限值,最终得到在不同维数地震动输入时高耸钢筋混凝土烟囱结构的地震易损性曲线和倒塌概率曲线。研究结果表明,考虑多维地震作用比只考虑一维地震作用时高耸烟囱的结构易损性和倒塌概率增大。     

模型参数不确定性对结构抗地震倒塌能力影响的定量估计

以设计基准期内地震倒塌的概率作为工程结构抗震设防的目标,已经成为国际抗震领域研究的重要方向,而预测结构地震倒塌概率时应充分考虑结构参数不确定性的影响。为此,本文以RC框架结构为基本研究对象,基于非线性动力时程分析,采用IDA方法和中心点法,估计模型参数不确定性对RC框架结构抗地震倒塌能力的影响。结合4个RC框架结构算例,分析了结构在地震作用下抗倒塌能力对10个主要模型参数的敏感性。分析表明,源于模型参数的不确定性bMDL对抗倒塌能力的影响可达到地震动不确定性bRTR的50%~65%,应予以合理考虑。其中,结构抗倒塌能力对混凝土极限强度fu、混凝土极限压应变eu的取值最为敏感。     

基于结构典型失效模式的地震侧向倒塌易损性分析

基于结构系统可靠度理论,提出了一种基于结构典型失效模式的地震侧向倒塌易损性分析方法。该方法通过将结构体系近似假设为串-并联混合体系,从而将确定结构体系的地震倒塌概率这一复杂问题简化为确定不同典型失效模式的发生概率。以一栋5层钢筋混凝土框架结构为例对所提出方法进行了应用研究。研究考虑了屈服失效、极限变形失效和剪切失效3类失效机制,共计选取了7种结构典型失效模式。通过与基于增量动力分析(IDA)方法得到的结构地震倒塌易损性曲线对比发现:随着地震动强度的增加,基于典型失效模式计算得到的地震倒塌易损性曲线一直处于基于IDA方法得到的地震倒塌易损性曲线的上方。这表明该方法计算得到的地震倒塌易损性结果高估了结构在地震作用下发生倒塌的可能性,可将其视为倒塌易损性真实结果的上限值。     

基于IDA的阀厅结构地震易损性分析

尽管近年来大型换流站阀厅结构越建越多,但是对阀厅结构的易损性研究仍十分缺乏。考虑到大型换流站阀厅结构在电力系统中的重要性,对这类结构易损性开展深入地研究是十分必要的。在数值模型正确性得到验证基础上,对阀厅结构开展在不同类型地震动作用下的增量动力分析(IDA),基于增量动力分析结果建立阀厅结构处于不同破坏状态的地震易损性曲线。研究结果表明当地震动峰值加速度小于0.5g时,阀厅结构刚度降幅比较缓慢,而随着峰值加速度增大,其刚度降幅逐渐增快。由地震易损性曲线可知,在罕遇地震作用下阀厅结构处于不同破坏状态的超越概率均小于5%,该阀厅结构抗震设计满足要求并具有较大安全储备。     

极罕遇地震作用下剪力墙结构地震易损性分析

为深入研究极罕遇地震作用下剪力墙结构的整体抗震性能,文中依据我国现行规范设计了不同设防烈度、不同高度的9个剪力墙结构,在SAP2000中对其进行数值建模,通过对其他试验进行数值建模并对比数据结果,验证了建模方法的合理性与实用性.基于所建数值模型,采用增量动力分析(IDA)方法,模拟了剪力墙结构从弹性、塑性、倒塌全过程的...     

采用不同减震结构体系的RC框架结构地震易损性分析

采用消能减震技术能有效提高结构的抗震性能,而不同减震结构体系减震效果不同。为了评估不同减震结构体系下的抗震性能,本文以某6层RC框架结构为研究对象,采用基于增量动力分析法的地震易损性分析方法,分别研究了增设防屈曲约束支撑、软钢阻尼器、粘滞阻尼器3种不同减震结构体系的抗震性能。研究结果表明：在同一减震目标下,3种不同的减震结构体系均能有效控制结构的地震响应,其中防屈曲约束支撑结构在不同损伤状态下的超越概率最小,抗倒塌储备系数最大,说明该阻尼器的控制效果最佳,其次是软钢阻尼器,最后是粘滞阻尼器。     

考虑倒塌概率修正的钢筋混凝土框架结构地震易损性分析

为研究倒塌概率对非倒塌极限状态的影响,提出了考虑倒塌概率修正的结构地震易损性分析方法。基于全概率定理,将结构极限状态划分为倒塌状态和非倒塌状态两类,若结构发生倒塌则认为结构发生非倒塌极限状态破坏的概率为100%。考虑倒塌概率修正的地震易损性分析方法包含直接方法和间接方法,其中,直接方法是直接对传统地震易损性函数进行修正,而间接方法仅修正地震易损性函数中的概率地震需求参数。以4榀不同高度不同设防烈度的钢筋混凝土平面框架结构作为研究对象,选择100条实际地震动记录作为输入,分别采用直接方法和间接方法开展考虑倒塌概率修正的地震易损性分析。结果表明：倒塌概率对轻微破坏和中等破坏极限状态的影响较小,而对严重破坏极限状态的影响较大;在地震动强度较小时,两种方法对地震易损性的修正结果相差较小;随着地震动强度的提高,两种方法对地震易损性修正结果的差距逐渐增大。     

空心高墩铁路桥梁地震易损性分析

为了评价某钢筋混凝土圆形空心高墩铁路桥梁的抗震能力,本文以各墩柱控制截面的截面曲率为损伤指标,采用增量动力分析方法,分析了圆形空心高墩在纵桥向和横桥向地震动作用下的地震响应,得到了桥梁构件和桥梁整体结构控制截面在不同损伤状态下的超越概率,建立了圆形空心高墩铁路桥梁的地震易损性曲线.分析结果表明:纵桥向地震动作用下,各墩...     

基于增量动力分析方法的空间掉层框架结构的抗地震倒塌能力研究

参照GB 50011—2010《建筑抗震设计规范》和GB 50010—2010《混凝土结构设计规范》设计了7度(0. 10g)区非掉层框架以及掉层框架原型结构,并采用PERFORM-3D软件对相应的平面和空间模型10个算例进行对比分析。基于增量动力分析方法对非掉层框架和掉层框架结构进行了抗地震倒塌能力研究。按照FEMA 350倒塌判定准则对比了两种模型的倒塌易损性曲线规律,同时考察了各算例的抗倒塌安全储备系数,统计了结构的各层间峰值位移角、倒塌模式及倒塌概率。分析结果表明:1)对于第一种倒塌极限状态,在平面模型中,非掉层框架结构安全储备系数值小于掉层框架结构,而在空间模型中则相反; 2)在第二种倒塌极限状态下,非掉层框架结构的抗地震倒塌能力远远弱于掉层框架结构,而且在此极限状态下结构的抗地震倒塌能力、倒塌概率以及倒塌模式都与地震动的输入方向有关; 3)地震动方向对掉层框架结构的抗地震倒塌能力及相应的安全储备影响较大,双向地震作用下,结构可能出现不同于平面模型和单向地震作用下的新倒塌模式,抗地震倒塌安全储备更小。     

考虑碰撞效应的相邻框架结构地震易损性分析

针对间距不足和高度不等的相邻钢筋混凝土框架结构,设置考虑碰撞刚度和阻尼非线性的碰撞单元,通过对三维非线性有限元模型的时程分析研究地震碰撞效应,并开展增量动力分析,分别以所有层和碰撞层最大层间位移角为工程需求参数,提出考虑碰撞效应的地震易损性分析方法。以6层和4层、6层和5层、6层和3层相邻钢筋混凝土框架结构为例,对比分析不同周期比下考虑与不考虑碰撞效应的相邻结构地震易损性曲线。结果表明：对于6层和4层相邻结构,考虑碰撞效应后,6层结构所有层的最大层间位移角对应的失效概率略有减小,4层结构的反之,而较低结构的碰撞层及较高结构的碰撞层以上层的最大层间位移角对应的失效概率明显增大,即碰撞效应对结构整体响应影响不明显,而对局部响应影响显著;6层和5层、6层和3层相邻结构地震易损性曲线具有类似规律,且相邻结构自振周期越接近,碰撞对结构地震易损性影响越小。     

Seismic partitioned fragility analysis for high‐rise RC chimney considering multidimensional ground motion

In order to identify the vulnerable parts and areas of the high‐rise reinforced concrete chimney, this paper presents an effective method, which called partitioned fragility analysis. One 240‐m‐high reinforced concrete chimney was selected as the practical project, and its analytical model was created with ABAQUS software. The selected high‐rise chimney structure was divided into 17 parts, and then the damage probability of each part in different damage states was obtained with the fragility analysis considering multidimensional ground motions. Twenty ground motion records were taken from the Next Generation Attenuation database as the input motions, and the peak ground acceleration was selected as the intensity measure. The response of the chimney structure under multidimensional ground motions was obtained based on incremental dynamic analysis. The maximum strains of concrete and steel bars were defined as the damage limit states of the chimney structure. The fragility curves and surfaces obtained from this analysis showed that the vulnerable areas of the chimney structure appear at 0–20 m, 90–130 m, and 150–200 m along the height of the chimney respectively. Based analytical results, these vulnerable parts can be retrofitted to enhance the seismic resistance of existing chimney structures. And the partitioned fragility analysis method can also be used to improve the design of new chimney structures.     

结构抗倒塌能力简化评估方法及其应用

针对增量动力分析(IDA)计算实际结构倒塌时常会遇到的工作量大、数值收敛困难等问题,提出结构抗倒塌能力的简化评估方法.该方法根据Pushover曲线与IDA曲线在定义结构倒塌极限状态上的相关性,通过单向和往复的Pushover分析确定结构的骨架参数和滞回特性,构建倒塌分析的等效单自由度模型,快速计算结构的倒塌强度.对一榀三跨六层钢框架和一榀三跨六层混凝土框架进行分析,结果显示简化方法得到的响应曲线和倒塌易损性曲线与IDA的结果接近,可以近似评估以第1振型为主的结构的抗倒塌能力.     

Seismic fragility assessment of a tall reinforced concrete chimney

In China, a considerable proportion of reinforced concrete (RC) industrial chimneys in operation was designed and constructed in accordance with less rigorous outdated seismic criteria during the end of 19th and early 20th century. However, few research works have been reported till date on a realistic overall assessment of the seismic performance of these existing aging RC chimney structures. Therefore, in this study, fragilities of existing RC chimney were studied. For this purpose, an existing 240 m tall RC chimney was selected and structurally modeled with a lumped mass beam (stick) model by means of the OpenSees analysis program. In order to capture the uncertainties in ground motion realizations, a series of 21 ground motions are selected from the Next Generation Attenuation database as the input motions. To develop the analytical fragility curves, nonlinear incremental dynamic analysis of the studied RC chimney was then carried out using the selected input motions, which were normalized to different excitation levels. The section curvature ductility ratio was considered as the damage index. Based on material strain and sectional analysis, four limit states (LSs) were defined for five damage state. The seismic responses of the all sections were utilized to evaluate the likelihood of exceeding the LSs. Then the peak ground acceleration (PGA)‐based seismic fragility curves of the structure were constructed assuming a lognormal distribution. Finally, under the light of these fragility curves, the damage risks in existing RC chimney were discussed. The analytical results indicated that for design level earthquake of PGA = 0.1 g (g is the gravitational acceleration) and the maximum considered earthquake of PGA = 0.22 g, the probabilities of exceeding the light damage state were around 1.5% and 44%, respectively, while the exceedance probabilities corresponding to moderate, extensive and complete damage states were approximately zero in both cases. On the other hand, fragility analysis revealed that the RC chimney structure had considerable ductility capacity and was capable to withstand a strong earthquake with some structural damages. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic fragility analysis of concrete encased frame‐reinforced concrete core tube hybrid structure based on quasi‐static cyclic test

Concrete‐encased frame‐core tube hybrid structural system has been widely employed in high‐rise buildings. This paper intends to analyze the seismic fragility of this structural system under ground motion excitation. The quasistatic cyclic test on a 1/5‐scaled, 10‐story three‐bay specimen is introduced. Fiber‐based finite element model is developed and integrated with numerical techniques that would be able to simulate the nonlinear response based on the OpenSees program. As the model is verified by the experimental data, a series of incremental dynamic analyses (IDAs) considering different frame‐tube stiffness ratios are carried out. IDA curves are drawn to describe each structural performance state. Fragility curves and probabilistic demand models are proposed for quantifying failure probability. The collapse margin ratio is employed to evaluate the collapse probability. The result shows that the collapse probability under rare earthquake still meets the requirement of Applied Technology Committee‐63 Report. The hybrid structure is proved to perform superior collapse resistance ability. The proper increase in the stiffness of core tube can reduce the collapse probability and enhance the collapse resistance capacity.     

Seismic fragility analysis of reinforced concrete structures considering reinforcement corrosion

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素，会引起结构的自振周期延长、地震需求变化及抗震能力衰减，使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象，分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数，对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平，建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

锈蚀钢筋混凝土结构地震易损性分析

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素,会引起结构的自振周期延长、地震需求变化及抗震能力衰减,使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象,分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数,对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平,建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

Seismic fragility curves for mid-rise reinforced concrete frames in Kingdom of Saudi Arabia

This article is concerned with the development of seismic fragility curves for typical mid-rise plane reinforced concrete moment-resisting frames in Kingdom of Saudi Arabia (KSA), which is considered as low-seismicity area. Two structural models; four- and eight-storey moment-resisting frames were considered. Three cities with different seismic intensities, Abha, Jazan and Al-Sharaf, were selected to cover various values of mapped spectral accelerations in KSA. The 0.2-s spectral accelerations range from 0.21 to 0.66 g, while the 1.0-s spectral accelerations range from 0.061 to 0.23 g. The structural models were designed under dead, live and seismic loads of these cities according to the Saudi Building Code. Incremental dynamic analysis was performed under 12 ground motions using SeismoStruct. Five performance levels, namely, operational, immediate occupancy, damage control, life safety and collapse prevention were considered and monitored in the analysis. Fragility curves were developed for the structural models of the three cities considering the five selected performance levels.