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.

Optimization for performance-based design under seismic demands, including social costs

Performance-based design in earthquake engineering is a structural optimization problem that has, as the objective, the determination of design parameters for the minimization of total costs, while at the same time satisfying minimum reliability levels for the specifi ed performance criteria. Total costs include those for construction and structural damage repairs, those associated with non-structural components and the social costs of economic losses, injuries and fatalities. This paper presents a general framework to approach this problem, using a numerical optimization strategy and incorporating the use of neural networks for the evaluation of dynamic responses and the reliability levels achieved for a given set of design parameters. The strategy is applied to an example of a three-story offi ce building. The results show the importance of considering the social costs, and the optimum failure probabilities when minimum reliability constraints are not taken into account.

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.

Probabilistic Performance-Based Optimum Seismic Design Framework: Illustration and Validation

In the field of earthquake engineering,the advent of the performance-based design philosophy,together with the highly uncertain nature of earthquake ground excitations to structures,has brought probabilistic performance-based design to the forefront of seismic design.In order to design structures that explicitly satisfy probabilistic performance criteria,a probabilistic performance-based optimum seismic design(PPBOSD)framework is proposed in this paper by extending the state-of-the-art performance-based earthquake engineering(PBEE)methodology.PBEE is traditionally used for risk evaluation of existing or newly designed structural systems,thus referred to herein as forward PBEE analysis.In contrast,its use for design purposes is limited because design is essentially a more challenging inverse problem.To address this challenge,a decision-making layer is wrapped around the forward PBEE analysis procedure for computer-aided optimum structural design/retrofit accounting for various sources of uncertainty.In this paper,the framework is illustrated and validated using a proof-of-concept problem,namely tuning a simplified nonlinear inelastic single-degreeof-freedom(SDOF)model of a bridge to achieve a target probabilistic loss hazard curve.For this purpose,first the forward PBEE analysis is presented in conjunction with the multilayer Monte Carlo simulation method to estimate the total loss hazard curve efficiently,followed by a sensitivity study to investigate the effects of system(design)parameters on the probabilistic seismic performance of the bridge.The proposed PPBOSD framework is validated by successfully tuning the system parameters of the structure rated for a target probabilistic seismic loss hazard curve.The PPBOSD framework provides a tool that is essential to develop,calibrate and validate simplified probabilistic performance-based design procedures.

Discussion on uncertainties，attenuation of ground motion and aseismic design criterion

The usually calculated exceedance probability curves of ground motion are reduced as cumulative probability curves of normal distribution on some assumptions in this paper. These curves clearly displayed the variation of curve shape with the variance of attenuation relation and its physical implication. Similar investigation is also made on uncertainties of hypocenter locations and magnitudes of future earthquakes. The larger the uncertainty,the flatter the exceedance probability curve is. In a broad sense, the less people know future earthquakes, the flatter is the curve. Due to the rich or poor data sets available, the uncertainties of attenuation relation are different from region to region. The acceleration attenuation relations in these regions with no enough strong earthquake records can be obtained by conversion from other region, but with larger uncertainty. The uncertainty contains systematic difference between the two regions in addition to common stochastic error. A method to check and adjust the converted attenuation relation by using the local data is proposed in this paper. If the uncertainty of attenuation relation is too large, the result of seismic hazard assessment may be unaccepted sometimes.In order to realize that the structures do not collapse in large earthquakes, be repairable under moderate ones and without destruction in small earthquakes, this paper suggests that it may be reasonable to get the first and the third levels of aseismic design parameters by some empirical relation on the basis of the second level not by fixing the risk probability levels (63%, 10% and 3%). A particular aseismic design criterion is not only a balance between economic cost and seismic risk but also suited to the human's knowledge of nature.

Research on performance-based seismic design criteria

The seismic design criterion adopted in the existing seismic design codes is reviewed. It is pointed out that the presently used seismic design criterion is not satisfied with the requirements of nowadays social and economic development. A new performance-based seismic design criterion that is composed of three components is presented in this paper. It can not only effectively control the economic losses and casualty, but also ensure the building's function in proper operation during earthquakes. The three components are: classification of seismic design for buildings, determination of seismic design intensity and/or seismic design ground motion for controlling seismic economic losses and casualties, and determination of the importance factors in terms of service periods of buildings. For controlling the seismic human losses, the idea of socially acceptable casualty level is presented and the 'Optimal Economic Decision Model' and 'Optimal Safe Decision Model' are established. Finally, a new method is recommended for calculating the importance factors of structures by adjusting structures service period on the base of more important structure with longer service period than the conventional ones. Therefore, the more important structure with longer service periods will be designed for higher seismic loads, in case the exceedance probability of seismic hazard in different service period is same.

Performance-based global reliability assessment of a high-rise frame-core tube structure subjected to multi-dimensional stochastic earthquakes

When evaluating the seismic safety and reliability of complex engineering structures,it is a critical problem to reasonably consider the randomness and multi-dimensional nature of ground motions.To this end,a proposed modeling strategy of multi-dimensional stochastic earthquakes is addressed in this study.This improved seismic model has several merits that enable it to better provide seismic analyses of structures.Specifically,at first,the ground motion model is compatible with the design response spectrum.Secondly,the evolutionary power spectrum involved in the model and the design response spectrum are constructed accordingly with sufficient consideration of the correlation between different seismic components.Thirdly,the random function-based dimension-reduction representation is applied,by which seismic modeling is established,with three elementary random variables.Numerical simulations of multi-dimensional stochastic ground motions in a specific design scenario indicate the effectiveness of the proposed modeling strategy.Moreover,the multi-dimensional seismic response and the global reliability of a high-rise frame-core tube structure is discussed in detail to further illustrate the engineering applicability of the proposed method.The analytical investigations demonstrate that the suggested stochastic model of multi-dimensional ground motion is available for accurate seismic response analysis and dynamic reliability assessment of complex engineering structures for performance-based seismic resistance design.

Development of Performance-Based Tunnel Evaluation Methodology and Performance Evaluation of Existing Railway Tunnels

The concept of performance-based design, which mainly focuses on mechanical performance, has become the international standard, as in the case for ISO. The standardization of tunnel design has not been achieved because it requires integration of separate specialized fields, such as geotechnical engineering, structural engineering and concrete engineering. It is also required to clarify performance-based criteria for tunnel structures to suit specific use purposes (objectives), establish the concept of survey, planning, design, construction and maintenance based on such criteria, and develop proper management systems for operation and maintenance to suit specific tunnel use purposes. To this end, it is vital to develop a methodology for evaluating and verifying the performance of existing tunnels. This paper presents a new concept of performance requirements for tunnel structures and describes the method of quantitatively evaluating the total performance of existing tunnels in relation to the required performance, assuming the total performance to be based on the Analysis Hierarchy Process.

支架固定馆藏人物俑文物的抗震优化设计研究

为优化支架固定馆藏人物俑文物的抗震效果,选取不同尺寸和体态的典型地震易损人物俑文物复制品(武士俑和唐三彩人物俑),开展文物复制品-优化组合措施(支架和卡固件)抗震系统振动台试验,获得影响文物复制品运动状态的关键优化参数、文物复制品与支架相互作用规律,并检验组合措施对较大体积人物俑文物的抗震固定效果。建立文物复制品-组合措施相互作用系统数值分析模型,通过参数分析,获得支架与文物间安装缝隙、在安装缝隙内填充不同种类隔震垫对文物动力响应的影响、文物复制品与固定措施相互作用规律及采用独立支架/组合措施有效固定人物俑的最小支架尺寸,为兼顾安全性及最小干预原则的固定措施优化设计提供必要依据。结果表明:相比独立支架,组合措施能够有效降低人物俑文物动力响应,有效提高固定效果;为保证人物俑文物安全,建议支架与文物间安装缝隙不大于5 mm;在缝隙中填充橡胶垫及硅胶垫可使文物与支架间相互作用力降低50%~75%,有效防止文物局部损伤;当人物俑文物体型超过一定限值,独立支架不再适用,建议选择支架和随形卡固件组合措施。

地震作用下纵筋屈曲的研究进展

在地震作用下,钢筋混凝土结构中的墩柱在承受竖向力的同时,通常还会受到往复荷载作用下的水平力,若结构中横向约束不足,纵筋可能会发生明显的横向变形,使得结构承载力和延性显著降低,修复困难.因此,研究纵筋在受压时的屈曲机理对结构设计以及施工都有着重要的指导意义.鉴于此,对基于单根钢筋直压试验的纵筋屈曲研究进行总结,分析得出钢筋屈曲的主要影响因素是长细比和屈服强度;概括总结基于RC (reinforced concrete)短柱直压试验的纵筋屈曲问题的研究进展,阐述在复杂相互作用下纵筋屈曲可能受到的各种影响因素;结合土木发展现状,对使用新材料/新构造的墩柱中的纵筋屈曲研究进行讨论.现阶段对纵筋屈曲的研究中没有给出判断钢筋屈曲方向和范围的理论方法,对纵筋的整体屈曲以及新型结构中的纵筋屈曲问题仍有待进一步研究,且应在后续研究中综合考虑锈蚀、加载历程、截面形式以及各材料相互作用等因素对纵筋屈曲的影响.

地下结构抗震设计反应位移法的研究综述

近年来,反应位移法在地下结构抗震分析中的应用渐趋广泛。简要介绍了反应位移法的基本原理和应用现状,从地层变形、地基弹簧和结构模型等关键因素的角度详细总结了反应位移法的发展过程和最新研究进展,厘清了方法的完善思路,指出地层-结构相互作用是影响计算精度的重要误差来源。此外,在上述基础上论述了当前反应位移法应用过程中存在的突出问题,提出了反应位移法在进一步拓展应用场景、提升结果代表性过程中需要深入研究的关键问题。

基于震害调查的土石坝震陷规律和关键影响因素分析

基于国内外典型地震中155个土石坝地震震害调查样本数据,分析了土石坝震陷规律,并基于灰色关联度分析法对土石坝地震关键影响因素进行了研究。结果表明:震陷率上包线随地震动峰值加速度和震级的增大而增大,随震中距的增大而减小,近场范围内震陷率较大,震中距达到100~150 km时,震陷率已很小;土坝的震陷率上包线值最大,其次是心墙堆石坝,面板堆石坝最小;修建时间越早,震陷率上包线值越大,反映出施工设备和筑坝施工方式的演变所带来的大坝填筑质量的差异;地震动峰值加速度、震级、坝型、修建年份、震中距5项因素对震陷率的影响依次减小,但不存在绝对主导因素。依据震陷规律和关键影响因素分析结果,结合水工抗震规范对土石坝地震残余变形预测和控制进行了讨论,给出了土石坝抗震安全变形控制标准及设计原则,可为土石坝抗震设计、地震残余变形预测和控制提供指导。

混合联肢PEC墙结构基于合理失效模式的性能化设计方法研究

基于性能化设计理念,提出了混合联肢PEC墙结构基于合理失效模式的性能化设计方法:以结构达目标位移时实现合理失效模式作为性能目标,基于能量平衡原理确定结构设计基底剪力,并给出符合失效模式的侧向力分布;依据给定目标塑性耦连比分别求解钢连梁和PEC墙肢底部加强区内力需求;采用塑性设计方法设计钢连梁和PEC墙肢底部加强区截面,采用弹性设计方法设计PEC墙肢非加强区截面,保证结构实现预期性能目标。依据提出的基于合理失效模式的性能化设计方法,设计了12层混合联肢PEC墙算例结构,对其进行Pushover分析和弹塑性动力时程分析,验证了该方法的可行性。基于合理失效模式的性能化设计方法设计的混合联肢PEC墙结构抗震性能良好,地震作用下,各层钢连梁首先剪切屈服耗散能量,然后PEC墙肢底部形成弯曲塑性铰,塑性铰分布及发展过程符合预期,实现了“两阶段耗能体系”设计目标。

高层建筑混凝土结构设计中的抗震设计

随着城镇化的快速发展,高层建筑的需求不断扩大,而我国地震频发,高层建筑抗震设计已作为最核心的要求之一。传统的抗震设计方法遇到了前所未有的挑战,如何提高这些建筑的抗震性能成了一个迫切需要解决的问题。根据最新的抗震设计研究理论,提出了一系列有效策略旨在提升高层混凝土建筑的抗震能力设计,确保高层建筑在面对地震作用时的可靠性与安全性,保障人们的财产安全。

城市高架桥梁延性抗震设计方法研究

桥梁抗震设计是高架桥梁设计的关键之一,在整个桥梁的下部结构设计工作中占据了很大的比重。延性抗震设计方法由于具有经济、耐久、可靠和施工方便等优势,在高架桥梁抗震设计中占据主要地位,故对延性抗震的设计方法及思路进行总结和进一步研究十分必要。以工程实例为背景,给出城市高架桥梁延性抗震的概念设计思路,采用有限元方法建立空间梁单元抗震分析模型,总结了地震作用下各构件的验算方法,并对延性抗震的适用条件进行研究,为相关工程的抗震设计提供参考。

复杂山区隧道群安全玻璃棚洞结构设计及稳定性分析

车辆通过复杂山区隧道群时,洞口段不可避免的会出现明暗效应,影响行车安全。以实际工程为例,采用安全玻璃作为棚洞面板,进行了棚洞上部、下部结构设计,考虑不改变既有隧道机电设施的条件下,在棚洞顶部设置了排烟窗口。采用有限元数值模拟软件对棚洞结构进行了计算分析,结果表明安全玻璃棚洞满足规范要求。

An evaluation of force-based design vs.direct displacement-based design of jointed precast post-tensioned wall systems

The unique features of jointed post-tensioned wall systems, which include minimum structural damage and re-centering capability when subjected to earthquake lateral loads, are the result of using unbonded post-tensioning to attach the walls to the foundation, along with employing energy dissipating shear connectors between the walls. Using acceptance criteria defined in terms of inter-story drift, residual drift, and floor acceleration, this study presents a multiplelevel performance-based seismic evaluation of two five-story unbonded post-tensioned jointed precast wall systems. The design and analysis of these two wall systems, established as the direct displacement-based and force-based solutions for a prototype building used in the PREcast Seismic Structural Systems （PRESSS） program, were performed at 60% scale so that the analysis model could be validated using the PRESSS test data. Both buildings satisfied the performance criteria at four levels of earthquake motions although the design base shear of the direct displacement-based jointed wall system was 50% of that demanded by the force-based design method. The study also investigated the feasibility of controlling the maximum transient inter-story drift in a jointed wall system by increasing the number of energy dissipating shear connectors between the walls but without significantly affecting its re-centering capability.

Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets: artifi cial and historic records

A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011-2001 design spectrum to a parametrically defined evolutionary power spectrum （EPS）. Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned design spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average （ARMA） filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response spectrum is in a close agreement with the considered design spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signals＇ response spectra with the GB 50011-2001 design spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice.

A simplified design method for metallic dampers used in the transverse direction of cable-stayed bridges

The aseismic design of cable-stayed bridges in the transverse direction with newly proposed metallic dampers that can accommodate both longitudinal and transverse movement of the deck has recently been considered.This work focuses on developing a simplified method to design an appropriate metallic damper.The seismic performance of cablestayed bridges with different damper stiffness,main span lengths,tower shapes and types of deck in the transverse direction are investigated.The transverse displacement of the deck of a cable-stayed bridge increases significantly with the increment of the damper stiffness,which proves that the design of the damper stiffness is crucial.A simplified model considering the damper stiffness,cable system and tower in the transverse direction is developed to evaluate the period and lateral displacement of a complicated cable-stayed bridge.Based on the simplified model,a design method is proposed and assessed using two cable-stayed bridges as examples.The results show that metallic dampers can be designed with high efficiency,and the optimal ductility of the damper can be selected.

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.