Statistical evaluation of the damage potential of earthquake ground motions

This study focuses on the damage potential of earthquake ground motions based on the inelastic dynamic response of equivalent single degree of freedom structures. Their yield resistances are selected in accordance with seismic design codes. An index accounting for the accumulation of damage due to inelastic excursions is used to represent structural damage. A set of 94 ground motions are employed for this analysis, which are all scaled to the same peak ground acceleration of 0.4 g. Earthquake ground motions are classified with respect to both the ratio of peak velocity to peak acceleration (V/A ratio) and their effective excitation duration. The effect of these parameters on damage potential is investigated by using sensitivity analysis and probabilistic techniques. It is concluded that both V/A ratio and effective duration significantly influence the damage potential of earthquake ground motions, although they are not represented appropriately by the spectral definitions of earthquake excitations in seismic design codes.     

Assessment of damage in mountain tunnels due to the Taiwan Chi-Chi Earthquake

Tunnels, being underground structures, have long been assumed to have the ability to sustain earthquakes with little damage. However, investigations of mountain tunnels after the Chi-Chi Earthquake in central Taiwan revealed that many tunnels suffered significant damage to various extents. This work describes the findings of a systematic assessment of damage in the mountain tunnels in Taiwan after the earthquake. It was found that among the 57 tunnels investigated 49 of them were damaged. The damage patterns are summarized based on the characteristics and the distribution of the lining cracks. This systematic investigation, involving geological conditions, design documents, construction and maintenance records of these tunnels, has been conducted to assess the potential factors that may have influence on the various damage patterns and the earthquake loading for tunnels. The results show that the degree of damage is associated with the geological condition and structural arrangement of the tunnel. A tunnel passing through a displaced fault zone will definitely suffer damage. The extent of geological weak zones, distance from the epicenter, and the existence of a slope face are also significant influencing factors. The seismic capacity of the tunnel is influenced by its structural arrangement, type of lining, invert setup, lining reinforcement, and other parameters.     

大跨度网壳结构强震失效机理研究

随着大跨度网壳结构近些年在重大工程中的大量应用,该结构在强震作用下的失效机理问题也逐渐突出,为空间结构学者所关注。在总结了近些年大跨度网壳结构强震失效机理领域的研究进展基础之上,介绍了适用于网壳结构强震失效机理分析的基于荷载域全程响应的分析方法,以及在该方法中引入材料损伤累积的研究过程;定义了网壳结构在强震作用下的两类失效模式,即由几何非线性引起的动力失稳和由过度塑性损伤导致的动力强度破坏;论述了基于模糊数学中模糊综合判断理论的判别网壳结构强震失效模式的方法;在此基础上,对网壳结构动力损伤模型的建立也进行了阐述,并对网壳结构在强震下失效极限的确定方法进行了总结。图5表3参20     

攀枝花里氏6.1级地震建筑震害调查与分析

2008年8月30日攀枝花发生里氏6.1级地震后,四川大学相关人员根据四川省的要求作为专家小组之一赴攀枝花开展了为期一个月的房屋应急评估工作.评估了攀枝花市及其下辖仁和区和盐边县房屋的受损情况,根据建筑不同结构类型和不同场地地震烈度进行了建筑的震害统计,结合典型工程震害案例,分析了震害特征和破坏原因,并提出了一些提高房屋建筑抗震的建议.     

强震下单层柱面网壳损伤及失效机理研究

基于结构损伤理论,对单层柱面网壳在强震下的失效机理进行研究。单层柱面网壳在强震下不仅会发生动力失稳,也可能由于过度塑性发展导致动力强度破坏的模式。对于动力强度失效的研究,应当在分析中考虑材料损伤累积以及断裂效应的影响。为在有限元分析中包含这一影响因素,编制了基于通用有限元软件ABAQUS的用户材料子程序,具有较高的计算精度和较好的收敛性。应用其对单层柱面网壳在强震下的响应进行参数研究,并与基于理想弹塑性材料时的响应对比,讨论考虑材料损伤对网壳失效特征的影响。将单层柱面网壳在强震下失效时刻的多项特征响应进行统计分析,拟合了能够表征网壳损伤程度的损伤模型,建立单层柱面网壳在强震下的失效判别准则。针对实际工程抗震设计中采用损伤累积本构模型计算的困难,提出网壳结构失效极限的简化判别方法。     

The use of Artificial Neural Networks to estimate seismic damage and derive vulnerability functions for traditional masonry

This paper discusses the adoption of Artificial Intelligence-based techniques to estimate seismic damage, not with the goal of replacing existing approaches, but as a mean to improve the precision of empirical methods. For such, damage data collected in the aftermath of the 1998 Azores earthquake (Portugal) is used to develop a comparative analysis between damage grades obtained resorting to a classic damage formulation and an innovative approach based on Artificial Neural Networks (ANNs). The analysis is carried out on the basis of a vulnerability index computed with a hybrid seismic vulnerability assessment methodology, which is subsequently used as input to both approaches. The results obtained are then compared with real post-earthquake damage observation and critically discussed taking into account the level of adjustment achieved by each approach. Finally, a computer routine that uses the ANN as an approximation function is developed and applied to derive a new vulnerability curve expression. In general terms, the ANN developed in this study allowed to obtain much better approximations than those achieved with the original vulnerability approach, which has revealed to be quite non-conservative. Similarly, the proposed vulnerability curve expression was found to provide a more accurate damage prediction than the traditional analytical expressions.     

某框架结构建筑震害分析及加固设计研究

根据地震现场考察,介绍了云南盈江5.8级地震某7层框架结构建筑的震害情况;从施工、设计等方面系统的分析了震害原因,并在此基础上进行了震损修复及抗震加固设计,加固设计从建筑物的结构体系受力特性出发,采用规范化的标准加固设计模块,分析对比加固前后计算结果,保证了加固实施的合理性及安全性,总结了防御和减轻震害应注意的一些问题,可为同类工程提供参考。     

Free vibration analysis of bridges

Most bridges are designed using a static analysis, adjusted by a dynamic amplification factor which is a function of the first flexural frequency. This method is imprecise but continues to be used, partly because of the apparently complex processes required to estimate accurately and to provide for the levels of vibration in a bridge. This paper investigates the natural frequencies and associated mode shapes of bridge superstructures. It compares field observations with theoretical idealizations and finds that, while a single beam idealization is accurate for straight, nonskewed bridges and for some continuous superstructures, many other bridges require an eigenvalue analysis of a finite beam element grillage. A simplified method for estimating the natural frequency of vibration is developed. An application of the Rayleigh method to a grillage model of the bridge, it is quick to apply and accurate to within 10%. The paper also compares the effects of using the static and dynamic moduli of elasticity of concrete in estimating the natural frequency of vibration, and concludes that the dynamic modulus is more appropriate. Finally, it debates the significance of certain types of support stiffness in estimating the fundamental frequency, and finds that their effect is negligible.     

Regional loss estimation due to hurricane wind and hurricane-induced surge considering climate variability

This paper presents a framework to assess the potential hurricane damage risks to residential construction. Studies show that hurricane wind, frequency and/or hurricane-induced surge may change as a result of climate change; therefore, hurricane risk assessments should be capable of accounting for the impacts climate change. The framework includes a hurricane wind field model, hurricane-induced surge height model and hurricane vulnerability models. Three case study locations (Miami-Dade County, FL; New Hanover County, NC and Galveston County, TX) are presented for two types of analyses: annual regional loss estimation and event-based regional loss estimation. Demographic information, such as median house value and changes in house numbers, and distribution of houses for different exposures, is used to estimate the time-dependent probability of damage with or without possible climate change-induced change in wind speed, frequency and/or surge height. Through both analyses, it was found that climate change may have a significant impact on regional hurricane damage losses.     

RC框架基于典型相关分析的地震动多元破坏势评估

为了更加全面地评估地震动对结构的潜在破坏势,考虑多个地震动强度参数和多个结构损伤参数对地震动破坏势的影响,提出一种基于典型相关分析的地震动多元破坏势评估方法。为说明所提方法,以具有不同高度和不同抗震设防水平的16个钢筋混凝土框架结构为研究对象,采用100条真实地震动记录作为地震输入。将与地震动加速度、速度和位移相关的8个地震动强度参数进行对数线性组合,构造成地震动多元强度参数的典型变量。将结构最大层间位移角、整体损伤指数、最大楼层加速度进行对数线性组合,构造成结构多元损伤参数的典型变量。通过使地震动强度参数的典型变量和结构损伤参数的典型变量的相关系数达到最大,获得可以较好评估地震动破坏势的复合地震动参数。研究结果表明：相比于单一地震动参数,复合地震动参数可以更好地评估地震动的破坏势,其与结构损伤的相关性也更强。     

Study on the damage propagation of surrounding rock from a cold-region tunnel under freeze–thaw cycle condition

Using an equipment with CT (computerized tomography), the characteristics of damage propagation of rock from a cold-region tunnel were studied under different conditions with freeze–thaw cycles, and the results were described by CT images and CT values. The relationships between damage development and the amount of water-supply, and loading or unloading process were also discussed during the repeated freeze–thaw, respectively, as well as the intensity change; moreover, the rate of breakage was also put forward. It was shown that the CT values and CT images could directly express the damage situation of rock, and the results were expected to provide a referenced basis for numerical computation and the safe running of cold-region tunnel.     

汶川8.0级地震中各类建筑结构地震易损性统计分析

阐述汶川地震中不同类型建筑结构的破坏特点,并对破坏原因进行简要分析。在现场科学调查的近5000个建筑物破坏样本的基础上,对汶川地震中不同烈度区的建筑物的破坏特点进行分析。取得以下成果:掌握了设防砌体结构和未设防砌体结构、底框架结构、钢筋混凝土框架结构的破坏特点,并对上述结构的破坏原因进行初步的分析;统计分析不同烈度区内各建筑物的破坏率;对比分析上述结构在不同烈度区中的易损性。对我国地震工程界认识不同类型结构以及设防与非设防结构的破坏形态及今后修订抗震设计规范有着重要的参考价值。     

Seismic fragility assessment of effectiveness of viscous dampers in R/C buildings under scenario earthquakes

Fragility curves are used to represent the probabilities that the structural damages, under various level of seismic excitation, exceed specified damage states by means of earthquake intensity–damage relations. In this study, the fragility curves have been developed for comparative seismic evaluation of several retrofitting measures by incorporation of fluid viscous (VS) dampers applied to a representative high-rise reinforced concrete (R/C) office building located in Istanbul. In the retrofitting strategies considered, similar type of VS dampers was used and designed to provide the structure with three different effective damping ratios of 10%, 15%, and 20%. In the fragility analysis, a set of 240 artificially generated earthquake ground motions compatible with the design spectrum selected to represent the variability in ground motion was employed to study nonlinear dynamic responses of the structures before and after retrofit. Four damage states: slight, moderate, major, and collapse were defined to express the condition of damage. The fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of peak ground acceleration (PGA), spectral acceleration (S_a), spectral displacement (S_d). Comparison of the fragility curves indicated that the VS dampers were very effective in attenuating seismic structural response under various earthquake ground motions. It was also found that a two-fold reduction in the probability of exceeding damage states might be achieved by introducing passive VS damper systems.     

1995年日本阪神地震大开地铁车站震害原因及成灾机理分析研究进展

1995年日本阪神地震中,大开、长田、三宫、上泽和新长田等地铁车站以及区间隧道发生了程度不同的震害,特别是大开地铁车站震害极为严重,是迄今为止人类历史上首次记录到的几乎完全塌毁的大型地下结构震害事例,引起了人们对地下结构抗震问题的关注和重视。围绕大开地铁震害事例,国内外已开展了大量的理论、数值和试验研究工作,对震害机理和破坏模式等进行了深入、系统的解析,深化了对地下结构抗震性能的理解,但由于研究者们各自侧重的角度不同,资料的掌握和分析模型与方法上的差异,仍存在一些认识上的歧义,迄今并未形成一种系统性的共识。本文较为系统地从研究者们所采用的分析方法、分析模型及获得的相应结论等角度,回顾了围绕大开车站震害事例开展的研究工作,总结了地震动、场地特性及结构构造因素等对大开车站震害影响的分析成果,并对进一步深入分析大开车站震害现象以及地下结构抗震应解决的关键问题提出了建议。     

汶川Ms8．0级地震房屋震害调查与分析

四川汶川Ms8.0特大地震发生后,作者在第一时间深入地震灾区,开展了地震灾害评估和建筑物震害调查工作,文章基于现场调查结果,分析了此次地震中房屋震害特点,探讨了其破坏机理,并且对经验教训进行了总结和反思.     

高校建筑中砌体结构震损特征及机理分析

结合高校建筑中砌体结构的特点,在高校砌体结构震害调查统计的基础上,对各类破坏形式进行机理分析,本项工作对高校建筑的加固改造具有指导意义。     

含嵌固墙体古建筑木结构震害数值模拟研究

以四川广元市某古建筑木结构为例,在考虑墙体嵌固作用的基础上,研究了汶川地震下古建筑的震害症状与地震响应状况。采用ANSYS软件对该古建筑榫卯节点的半刚性特征及砖砌体与木构架的嵌固作用进行了模拟,并建立了结构的有限元模型。通过模态分析,获得了结构的基频和主振型;通过将汶川波进行调幅作用于该结构,获得了结构在不同时刻的内力及变形峰值,并获得了典型节点的地震响应曲线。结果表明:考虑墙体的嵌固作用后,该古建筑的基频为1.59Hz,振动形式以第一振型为主,地震作用下木构架产生的位移很小,内力均在容许范围内,且保持稳定的振动状态;墙体由于强度不足,在某些部位将产生破坏,与震害现状基本吻合。     

建筑结构地震灾害损失的动态预测方法

建筑结构地震灾害损失的大小与地震发生的概率及强度、结构的抗震能力有密切的关系。根据地震发生概率及强度的随机性和结构的抗力随时间变化，提出了地震灾害损失动态预测的一般方法。     

Seismic performance evaluation of reinforced concrete hilly buildings under sequence of earthquakes

The present study investigates the effect of earthquake sequences on the response of reinforced concrete hilly buildings having typical configurations, that is, stepback and split-foundation, with three different story ratios. A set of 30 as-recorded mainshock-aftershock sequence of earthquake ground motions is considered for this study. Mainshock acceleration time histories are scaled at two distinct intensity levels to obtain the mainshock-damaged building. These mainshock-damaged hilly buildings are then subjected to aftershocks. A comparative study is performed for various response quantities, such as peak interstory drift ratio, peak floor acceleration, and peak roof displacement of undamaged and mainshock-damaged buildings under aftershocks. Further, fragility analysis is carried out to study the effect of aftershocks on undamaged and mainshock-damaged hilly buildings. Subsequently, component-wise seismic loss estimation due to damage in the non-structural and structural components is performed. It is concluded from the study that the building components that contribute maximum to the expected repair cost ratio vary with respect to the intensity of the aftershocks. Also, the estimated seismic loss is higher in mainshock-damaged split-foundation buildings in comparison to stepback buildings.     

汶川地震中单层钢筋混凝土柱厂房典型震害分析

通过对四川江油市、成都市、彭州市、绵阳市汉旺镇、甘肃天水市、陕西汉中市单层钢筋混凝土柱厂房的震害调查,以及对典型震害的分析,得出以下结论:按抗震规范设计的建筑,钢筋混凝土主体结构破坏轻微;非结构构件震害相对比较严重,特别是纵墙端开间、高大山墙、高低跨悬墙,以及高大设备和基础的连接;未进行抗震设计且未进行加固的老厂房震害一般较严重。为此,要特别加强非结构构件和高大设备的抗震设计,对未进行抗震设计的老厂房要尽快安排抗震加固。