Incremental dynamic analysis of woodframe buildings

The collapse of wood buildings was one of the main contributors to the heavy death toll and economic losses during the 1995 Hyogo‐ken Nanbu (Kobe) earthquake in Japan. In California, half of the property loss from the 1994 Northridge earthquake was attributed to wood construction. Based on damage observed in recent earthquakes, the seismic vulnerability of existing wood buildings under maximum credible seismic events is uncertain. The main objective of this study is to quantify the seismic collapse fragilities and collapse mechanisms of a two‐story townhouse and three‐story woodframe apartment building through numerical analyses. Three construction quality variants (poor, typical and superior) were considered for each building in order to assess the effects of construction qualities on seismic collapse fragilities. The buildings were also re‐designed according to the 2006 edition of the International Building Code to quantify the seismic fragilities of modern woodframe construction. The results obtained suggest that the construction quality, excitation direction and wall finish materials can influence significantly the collapse fragilities of woodframe buildings. Copyright © 2008 John Wiley & Sons, Ltd.     

芦山M_S7.0与九寨沟M_S7.0地震灾区房屋震害特征对比研究

通过实地调研“4.20”芦山7.0级地震灾区和“8.8”九寨沟7.0级地震灾区建筑物破坏情况,对灾区内框架结构、砖混结构和简易结构三种类型的建筑物震害特征进行了对比。结果表明:两次地震中相同结构类型的建筑物在同级别地震作用下其破坏程度不同,其中砖混结构和简易结构震害特征差异性较大,分析认为除地震本身作用外,灾区房屋的抗震性能不同也是造成两次地震建筑物震害特征差异较大的原因。最后提出了建议以供灾区恢复重建、农村民居安全建设等借鉴和参考。     

强震作用下砌体结构倒塌过程仿真分析

四川汶川地震中大量砌体房屋倒塌,造成巨大人员伤亡。为研究和预防砌体结构震害,本文概述了多层砌体房屋的主要震害特点,研究了砌体结构地震倒塌分析方法、失效单元与结构倒塌等关键技术问题。利用动力有限元程序LS-DYNA模拟了砌体结构的倒塌过程。仿真计算的结果与真实倒塌过程吻合较好,说明通过合理选取计算参数和计算模型,可以对这种特殊的复杂破坏过程进行模拟分析和仿真。通过再现倒塌过程,发现了结构在强震作用下的薄弱环节,为提高砌体结构抗震性能研究、建立结构防倒塌机制提供了有力的技术支撑。     

汶川地震震中某钢筋混凝土框架结构的非线性地震反应分析

2008年5月12日,四川省汶川县发生了里氏8.0级地震,造成了巨大的人员伤亡以及工程结构震害。位于震中映秀镇的漩口中学教学综合楼是按照《建筑抗震设计规范(GB50011-2001)》进行设计的,按7度进行抗震设防。在此次地震中,该建筑破坏严重,工程震害典型。为此,本文考虑了钢筋混凝土与砌体的材料非线性性质,建立了框架填充墙结构的非线性分析模型,进行了非线性有限元时程分析,分析了结构破坏的原因,讨论了填充墙体对结构抗震性能的影响,为该类结构的抗震设计提供了一定的依据。     

Seismic fragility assessment of RC frame structure designed according to modern Chinese code for seismic design of buildings

Following several damaging earthquakes in China,research has been devoted to find the causes of the collapse of reinforced concrete(RC) building sand studying the vulnerability of existing buildings.The Chinese Code for Seismic Design of Buildings(CCSDB) has evolved over time,however,there is still reported earthquake induced damage of newly designed RC buildings.Thus,to investigate modern Chinese seismic design code,three low-,mid-and high-rise RC frames were designed according to the 2010 CCSDB and the corresponding vulnerability curves were derived by computing a probabilistic seismic demand model(PSDM).The PSDM was computed by carrying out nonlinear time history analysis using thirty ground motions obtained from the Pacific Earthquake Engineering Research Center.Finally,the PSDM was used to generate fragility curves for immediate occupancy,significant damage,and collapse prevention damage levels.Results of the vulnerability assessment indicate that the seismic demands on the three different frames designed according to the 2010 CCSDB meet the seismic requirements and are almost in the same safety level.     

汶川8.0级地震中汶川县城房屋震害及其加固情况分析

依据5.12汶川地震中汶川县城(威远镇)11个区域共522栋房屋的房屋安全鉴定报告,深入统计分析房屋的震害情况及特点。结果表明,县城房屋倒塌较少,但破坏程度较重。破坏多集中在低层房屋以及砌体结构和木结构,而钢筋混凝土框架及高层房屋破坏较轻。结合房屋的破坏情况,对县城房屋的维修和加固情况进行分类统计,分析维修加固中出现的问题,并提出了相应建议。     

A rapid seismic safety assessment method for mid-rise reinforced concrete buildings

The majority of existing buildings are not safe against earthquakes in most of the developing countries. Existing building stocks should be assessed with a seismic safety assessment method before a devastating earthquake. Cheaper and quicker rapid seismic safety assessment methods can be used instead of code-based assessment methods to determine the seismic performance of existing buildings. In this study, an approach was introduced to determine the seismic performance of existing mid-rise reinforced concrete buildings with fewer parameters and process steps than code-based detailed assessment procedures. Calibration and regulation of the introduced method were conducted on the 39 collapsed buildings’ projects in 1999 Kocaeli, Turkey, earthquake. Finally, 55 existing buildings located in Eskisehir, Turkey, assessed with this calibrated method and the results were compared with the results of a code-based detailed assessment method; the results showed a very good agreement of about 83%. This study shows that the proposed method can be applied for the determination of the seismic performance of existing mid-rise reinforced concrete buildings quickly and without compromising reliability.     

Seismic performance evaluation of typical dampers designed by Chinese building code

Adding dampers is a commonly adopted seismic risk mitigation strategy for modern buildings, and the corresponding design procedure of dampers has been well established by the Chinese Building Code. Even though all types of dampers are designed by the same procedure, actual seismic performance of the building may differ from one to the others. In this study, a nine-story benchmark steel building is established, and three different and typical types of dampers are designed according to the Chinese Building Code to realize structural vibration control under strong earthquake excitation. The seismic response of the prototype building equipped with a viscoelastic damper, viscous damper and buckling-restrained brace(BRB) subjected to 10 earthquake records are calculated, and Incremental Dynamic Analysis(IDA) is performed to describe progressive damage of the structure under increasing earthquake intensity. In the perspective of fragility, it shows that the viscoelastic damper has the highest collapse margin ratio(CMR), and the viscous damper provides the best drift control. Both the BRB and viscoelastic dampers can effectively reduce the floor acceleration responses in the mid-rise building.     

Lessons learned from the ＂5.12＂ Wenchuan Earthquake： evaluation of earthquake performance objectives and the importance of seismic conceptual design principles

Many different types of buildings were severely damaged or collapsed during the May 12, 2008 Great Wenchuan Earthquake. Based on survey data collected in regions that were subjected to moderate to severe earthquake intensities, a comparison between the observed building damage, and the three earthquake performance objectives and seismic conceptual design principles specified by the national ＂Code for Seismic Design of Buildings GB50011-2001,＂ was carried out. Actual damage and predicted damage for a given earthquake level for different types of structures is compared. Discussions on seismic conceptual design principles, with respect to multiple defense lines, strong column-weak beam, link beam of shear walls, ductility detailing of masonry structures, exits and staircases, and nonstructural elements, etc. are carried out. Suggestions for improving the seismic design of structures are also proposed. It is concluded that the seismic performance objectives for three earthquake levels, i.e., ＂no failure under minor earthquake level, ＂＂repairable damage under moderate earthquake level＂ and ＂no collapse under major earthquake level＂ can be achieved if seismic design principles are carried out by strictly following the code requirements and ensuring construction quality.     

漾濞6.4级地震外廊式教学楼震害调查与分析

外廊式教学楼是中小学校典型的建筑形式。汶川地震后,外廊式教学楼震害引起大量研究人员重视。2021年5月21日21时48分,云南大理州漾濞县发生6.4级地震,本文作者详细调查了位于漾濞县的4所典型框架结构外廊式教学楼,以震害较为严重的漾濞一中和花椒园小学为例,分析了结构各部位发生破坏的原因。以震害现象为佐证,得出以下结论:由于横墙的约束,楼板沿纵向平动,各轴构件的本构关系可在同一坐标系下进行对比分析,结构破坏取决于构件沿纵向的极限位移。并在此基础上,从新的角度探讨了多层建筑的抗震能力。     

建筑结构地震反应观测台阵的发展现状及展望

我国城市化进程的加快使人口与财富高度集中,城市向大型化、复杂化发展,在地震面前变得越发脆弱,而我国多数城市位于地震高危险区,灾害风险迅速攀升。充分借鉴国际减轻地震灾害风险先进理念,结合当今智能技术,开展地震风险评估与监测技术研究,已成为我国当前防震减灾工作的重中之重。国家重点研发计划项目“区域与城市地震风险评估与监测技术研究”以研发高性能区域与城市地震灾害监测及组网观测技术为手段,建立融合工程结构性态、社会和经济等多元信息的区域与城市大震风险动态评价指标体系、评估技术和软件系统平台,并开展应用示范,实现区域与城市地震灾害风险科学化、精准化和动态化评估,为显著提升我国抗御地震灾害风险能力提供关键技术支撑。经过两年的研究,设计并生产了MEMS加速度计样品,提出了观测网络优化布置方法、典型结构台阵优化布设方案和改进的数据多跳路由算法数据传输模式;构建了RC构件可视损伤识别的卷积神经网络Damage-Net,引入强跟踪滤波算法,实现了建筑结构体系时变物理参数的有效追踪,并建立了建筑抗震韧性评价方法;提出了基于计算机视觉的数据异常探测方法、桥梁结构基于弹塑性耗能差率的损伤指数模型和基于卷积神经网络和递归图的桥梁损伤识别方法,建立了桥梁地震破坏监测和性态评估标准 Benchmark模型;分别建立了基于遥感数据的建筑物提取技术、单体建筑结构和区域建筑群结构性能水平恢复函数模型和结构恢复能力计算方法,构建了区域和城市大震风险评估指标体系和风险动态评价模型;提出了基于物联网大震灾害监测系统总体架构、考虑多损伤状态的参数化桥梁地震灾害风险评估模型,开发了建筑群地震灾害仿真系统;初步完成了示范建筑地震监测方案设计,完成了示范桥梁地震监测网络建设和三河市多元信息的数据库建设;初步设计了三河市区域地震灾害监测网络。     

混凝土高层建筑结构地震破坏抗毁能力评估

提出基于构件性能的混凝土高层建筑结构地震破坏抗毁能力评估方法,采用强度与延性法分析混凝土高层建筑构件强度和变形,以对强震作用下混凝土高层建筑结构性能实施准确描述。基于建筑结构性能以及多条地震波情况下高层建筑结构倒塌极限状态的分析规范,采用IDA方法设置建筑结构抗倒塌能力系数,并依据该系数获取基于构件性能的混凝土高层建筑结构地震破坏抗毁能力评估流程,实现建筑结构地震破坏抗毁能力的准确评估。实验结果说明,所提方法实现了混凝土高层建筑结构地震破坏抗毁能力的准确评估。     

改进的基础隔震结构地震作用简化计算方法

在《建筑抗震设计规范》(GB50011-2001)关于隔震结构的简化计算方法中,水平向减震系数的表达式和定义有些不符,假定的隔震结构地震作用分布规律也与实际情况略有出入。本文基于水平向减震系数的定义和实际隔震结构的地震作用分布规律提出了一种改进的隔震结构水平向减震系数、隔震结构总地震作用、隔震结构上部地震作用分布的计算方法,并提出了总水平地震作用减震系数的新概念。本文提出的改进方法具有表达准确、物理意义明确的特点。将本文提出的改进算法计算结果与时程分析计算结果比较,结果显示,改进方法的计算结果与时程分析结果接近,且分布规律一致。     

Earthquake safety in India: achievements,challenges and opportunities

The Indian subcontinent has suffered some of the greatest earthquakes in the world. The earthquakes of the late nineteenth and early twentieth centuries triggered a number of early advances in science and engineering related to earthquakes that are discussed here. These include the development of early codes and earthquake-resistant housing after the 1935 Quetta earthquake in Baluchistan, and strengthening techniques implemented after the 1941 Andaman Islands earthquake, discovered by the author in remote islands of India. Activities in the late 1950s to institutionalize earthquake engineering in the country are also discussed. Despite these early developments towards seismic safety, moderate earthquakes in India continue to cause thousands of deaths, indicating the poor seismic resilience of the built environment. The Bhuj earthquake of 2001 highlighted a striking disregard for structural design principles and quality of construction. This earthquake was the first instance of an earthquake causing collapses of modern multi-storey buildings in India, and it triggered unprecedented awareness amongst professionals, academics and the general public. The earthquake led to the further development of the National Information Centre of Earthquake Engineering and the establishment of a comprehensive 4-year National Programme on Earthquake Engineering Education that was carried out by the seven Indian Institutes of Technology and the Indian Institute of Science. Earthquake engineering is a highly context-specific discipline and there are many engineering problems where appropriate solutions need to be found locally. Confined masonry construction is one such building typology that the author has been championing for the subcontinent. Development of the student hostels and staff and faculty housing on the new 400-acre campus of the Indian Institute of Technology Gandhinagar has provided an opportunity to adopt this construction typology on a large scale, and is addressed in the monograph. The vulnerability of the building stock in India is also evident from the occasional news reports of collapses of buildings under construction or during rains (without any earthquake shaking). Given India’s aspirations to be counted as one of the world’s prosperous countries, there is a great urgency to address the safety of our built environment. There is a need: to create a more professional environment for safe construction, including a system for code enforcement and building inspection; for competence-based licensing of civil and structural engineers; for training and education of all stakeholders in the construction chain; to build a research and development culture for seismic safety; to encourage champions of seismic safety; to effectively use windows of opportunity provided by damaging earthquakes; to focus on new construction as opposed to retrofitting existing buildings; and to frame the problem in the broader context of overall building safety rather than the specific context of earthquakes. Sustained long-term efforts are required to address this multi-faceted complex problem of great importance to the future development of India. While the context of this paper is India, many of the observations may be valid and useful for other earthquake-prone countries.     

点支式玻璃建筑结构地震损伤评估模型研究

地震对建筑结构的损伤轻则影响建筑完整性,重则导致建筑崩塌。近几年,地震损伤评估问题得到地震工程研究领域的高度重视,但对点支式玻璃建筑结构的损伤评估研究较少。为此,构建一种点支式玻璃建筑结构地震损伤评估模型。采用基于HHT变换的结构损伤部位识别方法判断地震中点支式玻璃建筑损伤部位,建立点支式玻璃建筑结构地震损伤评估多元联系数模型,评估点支式玻璃建筑损伤部位的损伤情况。结果表明,该评估模型对某地区点支式玻璃建筑结构地震损伤评估情况与实际结果一致,且该模型可控性较强,评估范围全面,评估效率明显优于其他评估模型,应用价值较高。     

Seismic behavior of single‐story asymmetric‐plan buildings under uniaxial excitation

The critical parameters that influence the nonlinear seismic response of asymmetric‐plan buildings are identified by evaluating the effects of different asymmetries that may characterize the structure of a building as well as exploring the influence of the ground motion features. First, the main findings reported in the literature on both the linear and nonlinear dynamic response of asymmetric‐plan buildings are presented. The common findings and the conflicting conclusions reached in different investigations are pointed out. Then, the results of comprehensive nonlinear dynamic analyses performed for evaluating the seismic response of systems characterized by different strength and stiffness configurations, representative of a large class of asymmetric‐plan buildings, are reported. Findings from the study indicate that the building response changes when moving from the linear to the nonlinear range, so that the seismic behavior of asymmetric‐plan buildings, apart from the source of asymmetry, can be always classified as irregular. Additionally, it was observed that as the seismic demands cause amplification of system nonlinearity with increasing earthquake intensity, the maximum displacement demand in the different resisting elements tends to be reached with the same deformed configuration of the system. The resultant of the seismic forces producing such a maximum demand is located at the center of resistance and corresponds to the collapse mechanism of the system that provides the maximum lateral strength in the exciting direction of the seismic action. Copyright © 2008 John Wiley & Sons, Ltd.     

损失分布和非结构损失对房屋建筑地易损性的影响

房屋建筑的地震易损性是地震损失评估和地震巨灾风险模型的基础。作为房屋建筑的重要组成部分,各类非结构构件的损失在现有的易损性模型中并未得到足够重视。本文以一栋典型钢筋混凝土框架结构教学楼为对象,通过将房屋建筑中的各类构件划分为具有不同地震损伤特性和损失后果的易损性组,考察建筑内的损失分布和非结构损失对房屋建筑地震易损性的影响。分析结果表明:由于许多非结构构件在中小地震作用下即可能发生较严重的破坏,房屋建筑在中小地震下的易损性主要受非结构损失控制;随着地震动强度等级的不断提高,结构损伤渐趋严重,结构损失对整体建筑易损性的影响不断增大;在结构进入震后不可修状态之前,建筑不同楼层的损失分布是评估建筑地震损失时不可忽略的因素。     

A PRELIMINARY STUDY ON THE METHOD OF SEISMIC INTENSITY ASSESSMENT BASED ON RESIDENTIAL BUILDING DATA AND HIGH RESOLUTION REMOTE SENSING IMAGES

After destructive earthquakes, the assessment result of seismic intensity is an important decision-making basis for emergency rescue, recovery and reconstruction. This job requires higher timeliness by government and society. Because remote sensing technology is not affected by the terrible traffic conditions on the ground after the earthquake, large-scale seismic damage information in the earthquake area can be collected in a short time by the remote sensing image. The remote sensing technique plays a more and more important role in rapid acquisition of seismic damage information, emergency rescue decision-making, seismic intensity assessment and other work. On the basis of previous studies, this paper proposes a new method to assess seismic intensity by using remote sensing image, i.e. to interpret the building collapse rate of a residential quarter after an earthquake by high-resolution remote sensing images. If there already are detailed building data and building structure vulnerability matrix data of a residential area, we can calculate the building collapse rate under any intensity values in this residential area by using the theory of earthquake damage prediction. Assuming that the building collapse rate interpreted by remote sensing is equal to the building collapse rate predicted by using the existing data, it will be easy to calculate the actual seismic intensity of the residential area in this earthquake event. Based on this idea, according to the relevant standard specifications issued by China Earthquake Administration, this paper puts forward some functional models, such as the calculation model of building collapse rate based on remote sensing, the data matrix model of residential building structure, the prediction function matrix model of residential building collapse rate and the prediction model of residential building collapse rate. A formula for calculating seismic intensity by using remote sensing interpretation of collapse rate is also proposed. To test and verify the proposed method, this paper takes two neighboring blocks of Jiegu Town after the Yushu M7.1 earthquake in Qinghai Province as an example. The building structure matrix of the study block was constructed by using pre-earthquake 0.6m resolution satellite remote sensing image(QuickBird, acquired on November 6, 2004), post-earthquake 0.2m aerial remote sensing image(acquired by National Bureau of Surveying and Mapping, April 15, 2010) and some field investigation data. The building collapse rate in the two blocks was calculated by using the interpretation results of seismic damage from the Remote Sensing Technology Coordinating Group of China Seismological Bureau. The seismic damage matrix of building structures in Yushu area is constructed by using the abundant scientific data of the scientific investigation team of the project “Comprehensive Scientific Investigation of the Yushu M7.1 Earthquake in Qinghai Province” of China Seismological Bureau. On this basis, the collapse rate prediction function of different structures in Yushu area is constructed. According to the prediction function of collapse rate and the building structure matrix of the two blocks, the building collapse rate under different intensity values is predicted, and the curve of intensity-collapse rate function is drawn. By comparing the building collapse rate interpreted by remote sensing and the intensity-collapse rate function curve of this two blocks, the seismic intensity of both blocks are calculated to be the same value: Ⅸ degree, which is consistent with the results of the field scientific investigation of the earthquake. The validation shows that the method proposed in this paper can effectively avoid the influence caused by the difference of seismic performance of buildings and accurately evaluate seismic intensity when using remote sensing technique. The method has certain application value for earthquake emergency work.     

COMPARATIVE STUDY ON THE SEISMIC RETROFIT OF A MID-RISE STEEL BUILDING: STEEL BRACING VS ENERGY DISSIPATION

The paper presents a comparative study of an existing retrofit for a mid-rise steel building using additional stiff steel braced-frames against an alternate retrofit using ADAS (Added Damping and Stiffness) passive energy dissipation devices. The subject building, located near Alameda Park in downtown Mexico City, is a ten-storey office building that was built in the 1950s. The structure was damaged during the 1985 Michoacán Earthquake because of resonant response with the site. The building was later retrofitted using additional braced frames according to the seismic provisions of Mexico's 1987 Federal District Code. The retrofit scheme was planned to take the structure away from resonant responses and to inhibit structural damage. A proposed upgrade using ADAS energy dissipation devices was studied to compare energy dissipation against traditional stiffening using steel braces as retrofit options for mid-rise buildings in Mexico City's lake-bed zone. Different sets of analyses were carried out to compare both alternatives: (a) three-dimensional elastic analyses; (b) limit analyses and; (c) nonlinear dynamic analyses for postulated site ground motions for a M_s=8.1 earthquake. Initial costs of the retrofit schemes were also studied. The comparative studies suggest that a retrofit using ADAS devices would have a better dynamic performance than the one using steel braces. However, the steel bracing retrofit provides more strength and its initial cost of retrofit is less than that of the ADAS retrofit. © 1997 John Wiley & Sons, Ltd.     

Revision of seismic design codes corresponding to building damagesin the “5.12” Wenchuan earthquake

A large number of buildings were seriously damaged or collapsed in the "5.12" Wenchuan earthquake. Based on field surveys and studies of damage to different types of buildings, seismic design codes have been updated. This paper briefly summarizes some of the major revisions that have been incorporated into the "Standard for classification of seismic protection of building constructions GB50223-2008" and "Code for Seismic Design of Buildings GB50011-2001." The definition of seismic fortification class for buildings has been revisited, and as a result, the seismic classifications for schools, hospitals and other buildings that hold large populations such as evacuation shelters and information centers have been upgraded in the GB50223-2008 Code. The main aspects of the revised GB50011-2001 code include: (a) modification of the seismic intensity specified for the Provinces of Sichuan, Shanxi and Gansu; (b) basic conceptual design for retaining walls and building foundations in mountainous areas; (c) regularity of building configuration; (d) integration of masonry structures and precast RC floors; (e) requirements for calculating and detailing stair shafts; and (f) limiting the use of single-bay RC frame structures. Some significant examples of damage in the epicenter areas are provided as a reference in the discussion on the consequences of collapse, the importance of duplicate structural systems, and the integration of RC and masonry structures.