Seismic performance analysis and design suggestion for frame buildings with cast-in-place staircases

Many staircases in reinforced concrete （RC） frame structures suffered severe damage during the Wenchuan earthquake. Elastic analyses for 18 RC structure models with and without staircases are conducted and compared to study the influence of the staircase on the stiffness, displacements and internal forces of the structures. To capture the yielding development and damage mechanism of frame structures, elasto-plastic analysis is carried out for one of the 18 models. Based on the features observed in the analyses, a new type of staircase design i.e., isolating them from the master structure to eliminate the effect of K-type struts, is proposed and discussed. It is concluded that the proposed method of staircase isolation is effective and feasible for engineering design, and does not significantly increase the construction cost.

Effect of seismic design details on hysteresis performance of SRC-RC transfer columns

Four types of seismic design details were tested using 11 transfer column specimens and one comparison specimen of RC under low cyclic reversed loading. Test results show that diagonal cracks control the failure pattern and damage occurs mainly in the RC section with weak shear capacity in the transfer columns. There is a large difference in the bearing capacity and ductility of the transfer columns according to the test results, which indicates that the strengthening effect of diverse structural measures is quite different. The section ratio of I-section-encased steel and the axial compression ratio also have a great influence on the bearing capacity and ductility. Although the bearing capacity of transfer columns with additional longitudinal bars and additional X bars is relatively large, they have poor deformation capacity. Setting more stirrups along the columns is the best structural measure to enhance the seismic performance. The studs on the I-sectionencased steel by welding can help to complete the stress transfer between the steel and concrete, and avoid performance degradation of the two materials due to bonding failure.

Performance-based seismic design of nonstructural building components:The next frontier of earthquake engineering

With the development and implementation of performance-based earthquake engineering,harmonization of performance levels between structural and nonstructural components becomes vital. Even if the structural components of a building achieve a continuous or immediate occupancy performance level after a seismic event,failure of architectural,mechanical or electrical components can lower the performance level of the entire building system. This reduction in performance caused by the vulnerability of nonstructural components has been observed during recent earthquakes worldwide. Moreover,nonstructural damage has limited the functionality of critical facilities,such as hospitals,following major seismic events. The investment in nonstructural components and building contents is far greater than that of structural components and framing. Therefore,it is not surprising that in many past earthquakes,losses from damage to nonstructural components have exceeded losses from structural damage. Furthermore,the failure of nonstructural components can become a safety hazard or can hamper the safe movement of occupants evacuating buildings,or of rescue workers entering buildings. In comparison to structural components and systems,there is relatively limited information on the seismic design of nonstructural components. Basic research work in this area has been sparse,and the available codes and guidelines are usually,for the most part,based on past experiences,engineering judgment and intuition,rather than on objective experimental and analytical results. Often,design engineers are forced to start almost from square one after each earthquake event: to observe what went wrong and to try to prevent repetitions. This is a consequence of the empirical nature of current seismic regulations and guidelines for nonstructural components. This review paper summarizes current knowledge on the seismic design and analysis of nonstructural building components,identifying major knowledge gaps that will need to be filled by future research. Furthermore,considering recent trends in earthquake engineering,the paper explores how performance-based seismic design might be conceived for nonstructural components,drawing on recent developments made in the field of seismic design and hinting at the specific considerations required for nonstructural components.

Peak displacement patterns for the performance-based seismic design of steel eccentrically braced frames

Performance-based seismic design(PBSD) aims to assess structures at different damage states. Since damage can be directly associated to displacements, seismic design with consideration of displacement seems to be logical. In this study, simple formulae to estimate the peak floor displacement patterns of eccentrically braced frames(EBFs) at different performance levels subjected to earthquake ground motions are proposed. These formulae are applicable in a PBSD and especially in direct displacement-based design(DDBD). Parametric study is conducted on a group of 30 EBFs under a set of 15 far field and near field accelerograms which they scaled to different amplitudes to adapt various performance levels. The results of thousands of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis in order to recognize the major parameters that influence the peak displacement pattern of these frames. Results show that suggested displacement patterns have relatively good agreement with those acquired by an exact nonlinear dynamic analysis.

Experimental investigation on seismic performance of rigid frame tied-arch bridge with split-piers

A novel seismic design method, namely split-pier seismic design, is proposed. A vertical gap and connect elements are set in split-piers. The lateral stiffness of piers is reduced by cracking of the connect elements under severe earthquake, and the seismic response of bridges is reduced by avoiding the site predominant periods. A model of tied-arch rigid frame bridge with split-piers was designed. Seismic performance was investigated by pseudo-static experimentation on the scale model, The failure process of split-piers, the hysteresis characteristic and the effect of split-piers on the superstructure are presented. Results show that the split-pier has better seismic performance than common ductile piers do.

A simplified methd of evaluating the seismic performance of buildings

This paper presents a simplified method of evaluating the seismic performance of buildings. The proposed method is based on the transformation of a multiple degree of freedom (MDOF) system to an equivalent single degree of freedom (SDOF) system using a simple and intuitive process. The proposed method is intended for evaluating the seismic performance of the buildings at the intermediate stages in design, while a rigorous method would be applied to the final design. The performance of the method is evaluated using a series of buildings which are assumed to be located in Victoria in western Canada, and designed based on the upcoming version of the National Building Code of Canada which is due to be published in 2005. To resist lateral loads, some of these buildings contain reinforced concrete moment resisting frames, while others contain reinforced concrete shear walls. Each building model has been subjected to a set of site-specific seismic spectrum compatible ground motion records, and the response has been determined using the proposed method and the general method for MDOF systems. The results from the study indicate that the proposed method can serve as a useful tool for evaluation of seismic performance of buildings, and carrying out performance based design.

Probability-Based Seismic Performance Evaluation for Buildings

Recent developments in earthquake engineering indicate that probabilistic seismic risk analysis (PSRA) is becoming increasingly useful for the evaluation of structural per-formance in accordance with building codes. In recent years, the field of seismic resis-tance design has been undergoing a critical shift in focus from strength to performance. However, current earthquake resistant design procedures do not relate building performance to probability. A lack of sufficient empirical data has highlighted gaps in this research. This study integrated results from the analysis of structural fragility and seismic hazard in Taiwan to perform PSRA to examine the effectiveness of building code in mitigating the risks associated with earthquakes. Factors taken into account included the effect of construction materials, building height, and building age. The results of this study show that the probability of exceeding damage associated with the CP level in buildings of light steel, pre-cast concrete, and masonry, exceeds 2%. These buildings fail to meet the performance objectives outlined in FEMA-273.

Ground Motion and Site Effects on Performance-Based Design

The objective of Performance-Based Earthquake Engineering （PBEE） is the analysis of performance objectives with a specified annual probability of exceedance. Increasingly undesirable performance is caused by increasing levels of strong ground motion having decreasing annual probabilities of exceedance. The development of this methodology includes three steps： （1） evaluation of the distribution of ground motion at a site; （2） evaluation of the distribution of system response; （3） evaluation of the probability of exceeding decision variables within a given time period, given appropriate damage measures. The work has taken a systematic approach to determine the impact of increasing levels of detail in site characterization on the accuracy of ground motion and site effects predictions. Complementary studies have investigated the use of the following models for evaluating site effects： （1） amplification factors defined on the basis of generalized site categories, （2） one-dimensional ground response analysis, and （3） two-dimensional ground response analysis for surface topography on ground motion. The paper provides a brief synthesis of ground motion and site effects analysis procedures within a Performance-Based Design framework. It focuses about the influence on the evaluation of site effects in some active regions by different shear waves velocity measurements Down Hole （D-H）, Cross Hole （C-H）, Seismic Dilatometer Marchetti Test （SDMT） and by different variation of shear modulus and damping ratio with strain level and depth from different laboratory dynamic tests for soil characterization： Resonant Column Test （RCT）, Cyclic Loading Torsional Shear Test （CLTST）.

Dynamic response limit of high-speed railway bridge under earthquake considering running safety performance of train

Due to the wide railway network and different characteristics of many earthquake zones in China,considering the running safety performance of trains(RSPT)in the design of high-speed railway bridge structures is very necessary.In this study,in order to provide the seismic design and evaluation measure of the bridge structure based on the RSPT,a calculation model of RSPT on bridge under earthquake was established,and the track surface response measure when the derailment coefficient reaches the limit value was calculated by referring to 15 commonly used ground motion(GM)intensity measures.Based on the coefficient of variation of the limit value obtained from multiple GM samples,the optimal measures were selected.Finally,the limit value of bridge seismic response based on RSPT with different train speeds and structural periods was determined.

Multi-hazard performance assessment of a transfer-plate high-rise building

Many urban areas are located in regions of moderate seismicity and are subjected to strong wind. Buildings in these regions are often designed without seismic provisions. As a result, in the event of an earthquake, the potential for damage and loss of lives may not be known. In this paper, the performance of a typical high-rise building with a thick transfer plate （TP）, which is one type of building structure commonly found in Hong Kong, is assessed against both earthquake and wind hazards. Seismic- and wind-resistant performance objectives are first reviewed based on relevant codes and design guidelines for high-rise buildings. After a brief introduction of wind-resistant design of the building, various methodologies, including equivalent static load analysis （ESLA）, response spectrum analysis （RSA）, pushover analysis （POA）, linear and nonlinear time-history analysis （LTHA and NTHA）, are employed to assess the seismic performance of the building when subjected to frequent earthquakes, design based earthquakes and maximum credible earthquakes. The effects of design wind and seismic action with a common 50-year return period are also compared. The results indicate that most performance objectives can be satisfied by the building, but there are some objectives, such as inter-story drift ratio, that cannot be achieved when subjected to the frequent earthquakes. It is concluded that in addition to wind, seismic action may need to be explicitly considered in the design of buildings in regions of moderate seismicity.

Application of consequence-based design criteria in regions of moderate seismicity

Current design criteria and prineiples of earthquake engineering design are reviewed,including safety factors, probabilistic approach,and two-level and muhi-level functional design ideas.The modern multi-functional idea is discussed in greater details.When designing a structure,its resistance to and the intensity of the earthquake action are considered. The consequence of failure of the structure is considered only through a rough and empirical factor of importance,ranging usually from 1.0 to 1.5.This paper suggests a method of'consequence-based design,'which considers the consequences of malfunctioning instead of simply an importance factor.The main argument for this method is that damage to a structure located in different types of societies may have very different consequences,which are depeudant on its value and usefulness to the society and the seismicity in the region.

Effect of URM infills on seismic vulnerability of Indian code designed RC frame buildings

Unreinforced Masonry (URM) is the most common partitioning material in framed buildings in India and many other countries. Although it is well-known that under lateral loading the behavior and modes of failure of the frame buildings change significantly due to infill-frame interaction, the general design practice is to treat infills as nonstructural elements and their stiffness, strength and interaction with the frame is often ignored, primarily because of difficulties in simulation and lack of modeling guidelines in design codes. The Indian Standard, like many other national codes, does not provide explicit insight into the anticipated performance and associated vulnerability of infilled frames. This paper presents an analytical study on the seismic performance and fragility analysis of Indian code-designed RC frame buildings with and without URM infills. Infills are modeled as diagonal struts as per ASCE 41 guidelines and various modes of failure are considered. HAZUS methodology along with nonlinear static analysis is used to compare the seismic vulnerability of bare and infilled frames. The comparative study suggests that URM infills result in a significant increase in the seismic vulnerability of RC frames and their effect needs to be properly incorporated in design codes.

高速铁路自复位摇摆桥墩抗震性能分析

基于OpenSEES平台分别建立4跨高速铁路传统简支梁桥和摇摆桥墩简支梁桥系统的有限元模型,并依据摇摆桥墩的基本抗震设防目标,设计摇摆桥墩耗能构件的面积和承载力。在考虑地震动随机性基础上,进行自复位摇摆桥墩在高铁桥梁系统中的抗震性能研究。结果表明:罕遇地震下自复位摇摆耗能装置能够有效降低墩底最大弯矩,减震率达20.26%,进而减少墩身损伤,但碰撞效应使墩底最大轴力放大了74.7%;墩底耗能构件基本进入塑性但未完全被破坏,可实现震后快速修复;摇摆桥墩的最大墩顶位移比传统桥墩增加了66%,但位移组成中可自复位的刚体旋转变形远大于弯曲变形,因此震后残余位移减少了35%;摇摆耗能机制对支座最大变形的减震率达12.3%,使主梁最大变形增大了约49%,但对其残余变形的影响在1 mm内;轨道约束会削弱桥墩摇摆行为,使墩顶最大位移减少了14%,但对墩顶残余位移无明显影响。

长持时地震动对建筑结构抗震影响的研究进展

该文综述了长持时地震动作用下建筑结构抗震性能的研究进展。介绍了长持时地震动的定义和特性;梳理了长持时地震动作用下建筑结构数值模拟、试验研究和理论分析的研究进展;详细综述了长持时地震动作用下建筑结构的延性性能、耗能能力、易损性和抗倒塌性能的研究进展。此外,介绍了考虑长持时地震作用影响的建筑结构抗震设计方法,梳理了国内外建筑结构抗震设计规范对长持时地震作用的考虑方法,并对长持时地震动作用下建筑结构抗震性能的研究进行了展望。建议关注长持时地震动作用下建筑结构的抗震性能,进一步研究长持时地震动的定义和特性,改进长持时地震动作用下建筑结构的数值模拟、理论分析和试验研究方法,深入探讨长持时地震动作用下各类建筑结构的地震响应、易损性和抗倒塌性能,为未来结构抗震设计及评估中考虑长持时地震作用的影响和规范修订提供参考。

桥梁抗震设计关键内容与减震、隔震技术的应用

为避免因发生地震而出现的桥梁结构失稳、倒塌问题,该文针对桥梁工程的抗震设计进行详细分析,结合桥梁结构出现的震害,提出桥梁抗震设计的关键点、减隔震技术的运用对策,旨在以桥梁工程为例,对比减隔震技术相较于非减隔震技术在提升抗震性能、降低震害风险等方面起到重要作用。这一研究将为桥梁抗震设计,合理运用减隔震技术提供重要参考。

变滞回性能阻尼器的抗震性能及其在RC排架墩中的应用

为了实现分级保护主体结构同时减小传统耗能阻尼器在强震作用下的残余变形的目的,提出一种基于形状记忆合金(shape memory alloy,SMA)板环的新型变滞回性能阻尼器(variable hysteresis performance damper based on shape memory alloy,SMA-VHD)。首先阐明了新型阻尼器的基本构造,揭示了其变滞回性能工作机理和自复位原理。通过对SMA板材进行材性试验确定了SMA板材的关键性能参数,进而建立阻尼器精细化有限元模型,系统研究阻尼器的滞回性能及参数影响规律。最后将新型阻尼器应用于RC排架墩中,通过动力时程分析研究附加阻尼器桥墩结构的分阶段抗震性能。研究结果表明:SMA板材应力应变关系呈“旗帜型”,具有良好的自复位能力;SMA-VHD滞回曲线呈现明显分级平台,随着阻尼器变形的增加,其滞回曲线由饱满的矩形变为具有自复位功能的“旗帜型”,表明该阻尼器具有变滞回性能的特性;将SMA-VHD应用到RC排架墩中,可有效实现结构的分级抗震,提高桥墩结构的抗震性能水平。

近场脉冲型地震作用下附加支撑双柱式摇摆桥墩的抗震性能研究

为了解决摇摆桥墩承载力和耗能能力不足的问题,该文提出一种附加人字形支撑的双柱式摇摆桥墩结构,支撑为纯耗能支撑或自复位耗能支撑,支撑通过连接装置安装在双柱式摇摆桥墩的盖梁和承台之间。为了研究新型附加人字形支撑双柱式摇摆桥墩的抗震性能,对其进行拟静力分析,将双柱式现浇桥墩和双柱式纯摇摆桥墩作为对比模型,研究附加纯耗能支撑和自复位耗能支撑双柱式摇摆桥墩的滞回性能;分别对这四种桥墩结构进行动力时程分析,探究这四种桥墩在近场对称脉冲、近场非对称脉冲和远场无脉冲地震动作用下的动力响应。研究结果表明:附加支撑的双柱式摇摆桥墩中的墩柱仍具有摇摆机制,可有效避免墩身出现塑性铰发生严重的损伤破坏,同时附加的支撑可以显著提高桥墩的承载能力和耗能能力,有效降低桥墩结构的位移响应,特别是自复位耗能支撑还可额外为桥墩提供自恢复力,有效提高结构的抗震性能。

西安领事馆区丝路国际文化艺术中心剧院结构设计

西安领事馆区丝路国际文化艺术中心剧院结构由钢筋混凝土框架-剪力墙主体与异形空间钢结构外罩组合而成,是具有体型复杂、内部空旷、跨度大等特点的混合结构。主体结构存在楼板不连续、局部不规则两项不规则项。针对不规则项及关键问题,提出加强措施及抗震性能目标。经过计算分析,找出薄弱部分进行加强,验证主体结构满足预设性能目标的要求。通过多模型比较研究发现,钢结构外罩对主体结构的影响不可忽略。对大跨、长悬挑处楼板进行了振动舒适度验算,对大跨转换钢桁架进行了竖向地震工况的补充计算,进行了楼板在温度与地震工况下受力分析。结果表明主体结构满足承载力和正常使用极限状态的要求。

湖北工人文化宫超限结构设计

湖北工人文化宫的主要功能为职工培训和展览等,主体结构采用框架-剪力墙结构,存在扭转不规则、偏心布置、楼板不连续、局部跃层柱等不规则项,属于复杂超限高层建筑。采用抗震性能化设计对主要构件进行复核,采用YJK和MIDAS Building软件对结构进行多遇地震弹性计算和弹性时程分析以及罕遇地震下的动力弹塑性时程分析和楼板应力分析等。分析结果表明,整体结构可以满足规范的要求,达到预定的性能目标。并根据分析结果采取抗震加强措施。在容易产生共振的大跨度预应力楼盖区域,以高阻尼橡胶减振垫作为减振材料,对楼盖在人行激励下和有节奏运动激励下的楼板舒适度进行分析。分析结果表明,楼板舒适度满足规范要求。

高烈度区多层长悬挑钢结构设计

长安乐传媒港是十四届全运会重要配套项目,为南侧带3层大悬挑的不规则复杂结构,最大悬挑长度38.5m。主体结构采用钢结构框架-支撑体系,悬挑部分采用钢桁架结构。针对大悬挑结构设计难点开展了分析和研究;重点介绍了整体结构方案选型、结构整体分析结果以及结构抗震性能化设计结果;也重点介绍了单人行走激励和人群激励下悬挑钢桁架舒适度分析,考虑长悬挑结构安装过程、卸载顺序和楼板刚度形成次序的施工模拟分析,以及长悬挑对基础设计的影响。结果表明,本工程的多层长悬挑构结构具有较高的安全储备,整体结构具有良好抗震性能;长悬挑结构设计中需要特别关注施工过程的影响,基础设计时应考虑竖向构件受拉的不利影响。