Performance-based methodology for assessing seismic vulnerability and capacity of buildings

This paper presents a performance-based methodology for the assessment of seismic vulnerability and capacity of buildings. The vulnerability assessment methodology is based on the HAZUS methodology and the improved capacity- demand-diagram method. The spectral displacement (Sd) of performance points on a capacity curve is used to estimate the damage level of a building. The relationship between Sd and peak ground acceleration (PGA) is established, and then a new vulnerability function is expressed in terms of PGA. Furthermore, the expected value of the seismic capacity index (SCev) is provided to estimate the seismic capacity of buildings based on the probability distribution of damage levels and the corresponding seismic capacity index. The results indicate that the proposed vulnerability methodology is able to assess seismic damage of a large number of building stock directly and quickly following an earthquake. The SCev provides an effective index to measure the seismic capacity of buildings and illustrate the relationship between the seismic capacity of buildings and seismic action. The estimated result is compared with damage surveys of the cities of Dujiangyan and Jiangyou in the M8.0 Wenchuan earthquake, revealing that the methodology is acceptable for seismic risk assessment and decision making. The primary reasons for discrepancies between the estimated results and the damage surveys are discussed.

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.

Performance-based seismic financial risk assessment of reinforced concrete frame structures

Engineering facilities subjected to natural hazards(such as winds and earthquakes) will result in risk when any designed system(i.e.capacity) will not be able to meet the performance required(i.e.demand).Risk might be expressed either as a likelihood of damage or potential financial loss.Engineers tend to make use of the former(i.e.damage).Nevertheless,other non-technical stakeholders cannot get useful information from damage.However,if financial risk is expressed on the basis of probable monetary loss,it will be easily understood by all.Therefore,it is necessary to develop methodologies which communicate the system capacity and demand to financial risk,Incremental dynamic analysis(IDA) was applied in a performance-based earthquake engineering context to do hazard analysis,structural analysis,damage analysis and loss analysis of a reinforced concrete(RC) frame structure.And the financial implications of risk were expressed by expected annual loss(EAL).The quantitative risk analysis proposed is applicable to any engineering facilities and any natural hazards.It is shown that the results from the IDA can be used to assess the overall financial risk exposure to earthquake hazard for a given constructed facility.The computational IDA-EAL method will enable engineers to take into account the long-term financial implications in addition to the construction cost.Consequently,it will help stakeholders make decisions.

Performance-based concept on seismic evaluation of existing bridges

Conventional seismic evaluation of existing bridges explores the ability of a bridge to survive under significant earthquake excitations. This approach has several major drawbacks, such as only a single structural performance of near collapse is considered, and the simplified approach of adopting strength-based concept to indirectly estimate the nonlinear behavior of a structure lacks accuracy. As a result, performance-based concepts that include a wider variety of structural performance states of a given bridge excited by different levels of earthquake intensity is needed by the engineering community. This paper introduces an improved process for the seismic evaluation of existing bridges. The relationship between the overall structural performance and earthquakes with varying levels of peak ground acceleration （PGA） can successfully be linked. A universal perspective on the seismic evaluation of bridges over their entire life-cycle can be easily obtained to investigate multiple performance objectives. The accuracy of the proposed method, based on pushover analysis, is proven in a case study that compares the results from the proposed procedure with additional nonlinear time history analyses.

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.

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.

Persisting challenges for performance-based building assessment

Intense research and refinement of the tools used in performance-based seismic engineering have been made,but the maturity and accuracy of these methods have not been adequately confirmed with actual data from the field. The gap between the assumed characteristics of actual building systems and their idealized counterparts used for analysis is wide. When the randomly distributed flaws in buildings as they exist in urban areas and the extreme variability of ground motion patterns combine,the conventional procedures used for pushover or dynamic response history analyses seem to fall short of reconciling the differences between calculated and observed damage. For emergency planning and loss modeling purposes,such discrepancies are factors that must be borne in mind. Two relevant examples are provided herein. These examples demonstrate that consensus-based analytical guidelines also require well-idealized building models that do not lend themselves to reasonably manageable representations from field data. As a corollary,loss modeling techniques,e.g.,used for insurance purposes,must undergo further development and improvement.

大连梭鱼湾专业足球场结构计算与分析

大连梭鱼湾专业足球场主体结构采用钢筋混凝土框架结构,罩棚索桁架结构为轮辐式上斜交下径向双层索网体系,索桁架外侧支承于钢压环,内侧设置索拉环,拉环内侧设置钢挑棚,屋盖膜结构采用张拉膜结构体系。外幕墙采用钢桁架+交叉索网支承单层ETFE膜体系。根据整体结构体系特点和构件的重要性,制定了合理的抗震性能目标,通过抗震性能化设计使结构达到预期的结构性能目标,满足相关规范要求。针对本工程复杂多结构体系特点,结构设计时进行多软件、多模型计算分析,对结构进行抗风荷载、抗雪荷载、抗温度作用、抗震等计算分析,以控制结构变形及承载力,确保结构设计安全合理。

《基于保持建筑正常使用功能的抗震技术导则》(RISN⁃TG046-2023)解读

《建设工程抗震管理条例》自2021年9月1日起施行,对位于高烈度设防地区、地震重点监视防御区的新建学校、幼儿园、医院、养老机构、儿童福利机构、应急指挥中心、应急避难场所、广播电视等建筑的抗震性能提出了更高要求,即:要求由“保证安全性”提升到“保持正常使用功能”。因此,住房和城乡建设部标准定额研究所于2023年5月12日颁布了《基于保持建筑正常使用功能的抗震技术导则》(RISN-TG046—2023)。为了帮助使用者更深入地理解《导则》,对《导则》的编制背景、编制过程以及各章节内容进行简要介绍,对《导则》的关键条文进行深入解读,详细说明了震时正常使用建筑的设计流程。《导则》创新提出了通过位移、加速度双控实现结构、非结构、设备三保护的设计理念,为实现建筑震时正常使用提供了科学实用的解决方案。

基于改进多目标布谷鸟算法的拦沙重力坝结构抗震优化

混凝土重力坝在强震作用下易出现结构安全问题,因而需采用合理经济的工程措施加以防护。将西北地区某拦沙重力坝作为研究对象,基于振型分解反应谱法分析大坝自振特性与动力响应,并综合考虑坝踵拉应力和抗震措施可变造价,采用改进多目标布谷鸟算法(MOCS)进行抗震设计方案的优化。此外,为提高算法性能,通过调整拥挤度距离计算公式、引进多项式变异算子以及动态步长和发现概率等方式进行改进。通过与其他多目标算法在不同测试函数上的对比试验,证明改进MOCS算法具备计算高效和解集均匀等优点。最后,根据Pareto最优解集,对重力坝的设计方案进行合理性评价,并提出工程建议。相关方法与结论对高烈度地震区混凝土重力坝的结构设计具有参考价值。

某复杂高层结构设计分析与探讨

分析本项目建筑的不规则内容,并且运用正确的抗震设计概念,针对该工程特点及结构设计难点,经过全面、可靠的计算分析,提出相应的抗震加强措施。主要包括关键剪力墙全高设置约束边缘构件,满足正截面抗弯承载力中震不屈服、斜截面抗剪承载力中震弹性的性能目标,对关键处楼板进行应力分析,对楼板分析中应力较大的部位加大配筋、连接板截面加大与配筋加强,以及通过改变建筑布局增设连接板等措施。结果表明,采取上述加强措施,该结构设计能实现拟定的抗震性能目标,结构安全可靠。

基于遗传算法的隔震支座优化设计方法

结合我国现有的结构设计规范,对隔震层支座自动设计问题,结合第三代非支配排序遗传算法制定了隔震支座优化设计方法。提出精细化剪切模型作为本次优化的计算模型,与以往的层剪切模型不同的是,将隔震层的各个隔震支座单独建立,可一次性获得满足偏心率的隔震支座布置方案。上述算法在大型通用有限元软件ABAQUS进行了程序实现。对一个5层的框架隔震结构进行优化设计,结果表明本文提出的方法是有效的,可操作的。

《建筑抗震设计规范》和《高层建筑混凝土结构设计规程》抗震性能化设计规定的分析对比

《建筑抗震设计规范》(GB 50011—2010,2016版)和《高层建筑混凝土结构设计规程》(JGJ 3—2010)均有抗震性能化设计的规定且略有不同,工程师在执行中可不避免地产生困惑。本文分析两本规范抗震性能化设计的规定,从荷载-位移曲线的角度阐述性能目标、性能水准的含义,并对比两本规范的设计参数。列举29个采用性能化设计方法的工程实例,分析位移指标的取值依据。根据上述两方面分析,总结两本规范性能化设计规定的不同点,并给出设计建议。

抗震管理条例背景下的建筑减震设计思考

基于《抗震管理条例》提出的“设防地震下正常使用”要求,提出消能减震结构性能化设计的性能目标及构件承载力要求的验算指标,并通过实际算例阐述了消能减震设计的基本流程,反映了消能减震元件的减震效果,实现了预设的减震性能目标。

厦门阳光龙净总部大楼超限结构设计

厦门阳光龙净总部大楼,采用钢筋混凝土框架-核心筒结构体系,存在“扭转不规则”“楼板不连续”“局部的穿层柱和个别构件的转换”“塔楼偏置”四项不规则,属于特别不规则性超限工程。采用YJK和PKPM两种软件,对结构进行小震弹性分析,并采用SAUSAGE对结构进行大震动力弹塑性分析,得到地震作用下结构的变形和损伤情况。针对其薄弱处采取加强措施,保证结构在大震作用下,能满足不倒塌的抗震性能目标。此外,对核心筒剪力墙面外搭梁处的暗柱采用PKPM进行补充验算,供工程设计参考。

某超高层框筒结构的中大震设计分析研究

通过实际工程案例,探讨中震计算对框筒结构的抗震设计作用,找出框筒结构中需要按中震验算设计截面的构件;同时按照中震验算结果调整这些构件在截面设计后进行大震作用下的弹塑性时程分析,考察这些构件在通过中震验算调整后是否能满足“大震不倒”的性能目标,以说明中震设计对于部分框架剪力墙结构设计的重要性。

某高烈度区超限高层住宅结构设计

对天津某高烈度区高层住宅进行结构超限情况判断,发现结构存在高度超限、扭转不规则、凹凸不规则等多项不规则项。针对结构的不规则项,设定合理的结构抗震性能目标,通过不同的结构分析软件研究结构在多遇地震、设防地震、罕遇地震的受力性能,采用弹性时程分析、静力弹塑性(Pushover)分析,深入探讨结构在地震中的反应,找出结构在地震反应中的薄弱位置,对这些薄弱位置进行相应的加强,使结构设计满足预定的性能目标。

地铁运用库上盖结构设计难点分析与工程应用

通过介绍地铁运用库上盖建筑开发的特点,分析了上盖结构体系普遍存在的底部刚度突变、竖向构件大量或全部转换等问题。以厦门第一个地铁上盖开发项目为例,阐述了地铁上盖结构设计的要点、难点,进行了大震下动力弹塑性分析,并对薄弱部位进行加强。根据项目施工存在分期情况,提出了相应的解决措施,可为同类型项目结构设计提供思路和参考。