关于工程场地地震安全性评价中设计地震动反应谱的讨论

本文对目前上海市工程场地地震安全性评价工作中设计地震动反应谱的确定方法进行了讨论。根据上海市地震环境和场地条件,以及地震安全性评价工作中尚存在的一些问题,对设计地震动反应谱的确定方法提出了建议。     

场地脉动卓越周期在工程抗震中的应用

根据工程项目场地地震安全性评价工作中所进行的场进脉动卓越周期试和剪切波速测试结果,以及地震反应分析计算结果的研究分析,根据现行工程抗震设计规范,将场地脉动卓越周期作为工程抗震中场地土类型,场地类别划分的参考标准,以及与工程场地震反应分析计算结果回归分析,结合场地地震危险性概率分析,估算场地地震动峰值加速度,应用于工程抗震设计中。     

中国长线工程场地地震安全性评价工作中的活动构造问题

长线工程场地一般都得穿经活动构造带,因而活动构造研究在该类场地的地震安全性评价工作中尤为重要。为此,文中对长线工程场地对地震安全性评价工作的要求和活动构造的研究现状进行了总结和分析,在此基础上,提出了长线场地地震安全性评价工作中活动构造研究宜开展的研究内容、技术指标、技术路径和成果提交等工作要点。最后,对长线场地震安全性评价工作中活动构造研究目前存在的一些问题进行了初步的分析和探讨     

加速度反应谱规准化对场地位移时程的影响

文中以某一实际工程为例,讨论工程场地地震安全性评价中加速度反应谱规准化对工程场地地震位移时程所带来的影响。数值结果表明,根据规准化加速度反应谱得出的位移时程存在很大的误差。建议在工程场地地震安全性评价工作中,不宜进行加速度反应谱的标定工作。     

1631年常德地震与太阳山断裂带活动性分析

地震成因类型的研究可以为未来地震趋势的估计、烈度区划和重大工程场地地震安全性评价等提供重要科学依据.作为华南内陆的较大地震之一的常德63/4级地震成因探讨更具现实的意义.近年来,湖南和湖北及附近地区在进行重大工程(核电站,水火电站,大型水库,桥梁,速公路及高层建筑等)的场地地震安全性评价工作,及编制地震动区划图时都对常德63/4级地震予以了高度的重视.     

海域工程场地地震安全性评价的特殊问题

本文探讨了海域工程场地地震安全性评价涉及的几个特殊问题,如考虑中深源地震影响的地震危险性分析、海底软弱土层场地地震反应分析等方面的问题。借鉴春晓气田群开发建设项目地震安全性评价和其它工作的实践经验,分析了对这些问题处理的对策,给出了一些建议。     

工程场地中活动断层和场地地震安全性评价

综述了工程场地地震安全性评价中活动断裂评价和场地评价的方法和步骤,指出了评价方法中存在的问题,并提出了解决方案。     

地震工程地质条件勘测中钻探相关工作探讨

依据《工程场地地震安全性评价GB17741-2005》、《岩土工程勘察规范GB50021-2001》等现行国家规范,对地震工程地质条件勘测中钻探相关工作的基本要求和存在的问题进行了探讨,并提出了具体措施和建议。给出了土样深度、土层分层深度、标准贯入试验点深度等钻孔相关深度数据的测量方法。归纳了地震工程地质单元层的划分原则,并介绍了应用该原则编制钻孔柱状图的步骤。     

场地地震效应及其预测的某些考虑

本文从场地地震危险性评价,地震危险性概率分析、场地地震工程地质单元划分、地震反应分析、活断层工程分类等五个方面、论述场地地震效应及其预测中基本原理和方法。根据工程地震危险性评价和分析、地震小区划等地震工程实践,对场地地震效应及其预测提供一些基本考虑和经验     

北京地区中硬场地地震动效应研究

依据典型工程场地的地震安全性评价报告,研究北京地区中硬场地地震动效应。首先,统计分析了地震安全性评价结果中的场地地震动放大效应。再利用201个工程场地的钻孔资料进行土层地震反应计算,分析不同地震动输入下的场地地震动放大效应。结果表明,北京地区中硬场地地震动放大效应明显,得到的场地地震动峰值加速度转换系数Ka高于《中国地震动参数区划图》（GB18306-2001）中的值,大震水准下更为突出。因此,如在北京地区直接采用《中国地震动参数区划图》（GB18306-2001）中的调整系数,可能会低估北京地区中硬场地的地震动放大效应,降低抗震设防标准。最后指出,场地地震动峰值加速度转换系数明显具有区域性,应根据详细的场地地震动效应研究结果,合理地确定场地地震动转换系数。     

从抗震设防类别探讨室内地震应急避难场所的选择

区分建筑物的抗震设防类别是进行抗震设计的前提和依据。本文针对当前我国室内地震应急避难场所认定面临的现有建筑的抗震安全性问题,根据不同版本的《建筑工程抗震设防分类标准》和《建筑抗震设计规范》,对现有体育、会展、教育建筑等设计、施工时依据的抗震设防类别、标准、规范进行分析研究,以为室内地震应急避难场所的选择提供参考,从而推动室内地震应急避难场所的认定工作。     

评估结构抗震性能的能量方法

在抗震概念设计中，虽然确立了一些准则，但这些准则基本上是定性的，目前尚缺乏简明的定量评估准则。本文结合抗震设计规范提出了一种对结构抗震性能评估的能量方法，可用于抗震设计方案的定量评估和比较，以及场地对结构影响的定量评估，减震方案的评估。该方法在实际工程设计中的应用取得预期效果。     

Seismic safety of low ductility structures used in Spain

The most important aspects of the design, seismic damage evaluation and safety assessment of structures with low ductility like waffle slabs buildings or flat beams framed buildings are examined in this work. These reinforced concrete structural typologies are the most used in Spain for new buildings but many seismic codes do not recommend them in seismic areas. Their expected seismic performance and safety are evaluated herein by means of incremental non linear structural analysis (pushover analysis) and incremental dynamic analysis which provides capacity curves allowing evaluating their seismic behavior. The seismic hazard is described by means of the reduced 5% damped elastic response spectrum of the Spanish seismic design code. The most important results of the study are the fragility curves calculated for the mentioned building types, which allow obtaining the probability of different damage states of the structures as well as damage probability matrices. The results, which show high vulnerability of the studied low ductility building classes, are compared with those corresponding to ductile framed structures.     

Estimation of the behavior factor of existing RC-MRF buildings

In recent years, several research groups have studied a new generation of analysis methods for seismic response assessment of existing buildings. Nevertheless, many important developments are still needed in order to define more reliable and effective assessment procedures. Moreover, regarding existing buildings, it should be highlighted that due to the low knowledge level, the linear elastic analysis is the only analysis method allowed. The same codes (such as NTC2008, EC8) consider the linear dynamic analysis with behavior factor as the reference method for the evaluation of seismic demand. This type of analysis is based on a linear-elastic structural model subject to a design spectrum, obtained by reducing the elastic spectrum through a behavior factor. The behavior factor (reduction factor or q factor in some codes) is used to reduce the elastic spectrum ordinate or the forces obtained from a linear analysis in order to take into account the non-linear structural capacities. The behavior factors should be defined based on several parameters that influence the seismic nonlinear capacity, such as mechanical materials characteristics, structural system, irregularity and design procedures. In practical applications, there is still an evident lack of detailed rules and accurate behavior factor values adequate for existing buildings. In this work, some investigations of the seismic capacity of the main existing RC-MRF building types have been carried out. In order to make a correct evaluation of the seismic force demand, actual behavior factor values coherent with force based seismic safety assessment procedure have been proposed and compared with the values reported in the Italian seismic code, NTC08.     

按现行规范设计的Ⅷ度区RC框架结构的倒塌性能评估

选取按照现行规范设计的既有建筑进行有限元建模,考虑地震动的不确定性对其进行大量增量动力分析(IDA),得到模型的IDA曲线簇。在此基础上对其进行地震需求概率分析和概率抗震能力分析,拟合得到结构的易损性曲线,据此对结构的倒塌概率进行定量评估,并比较基于非线性分析与性能评估软件PERFORM-3D的纤维模型和塑性铰模型的分析结果。结果表明:按照我国现行规范设计的钢筋混凝土(RC)框架结构,在预期的罕遇地震作用下倒塌概率较小,可满足"大震不倒"的要求;基于PERFORM-3D的截面纤维模型所得的RC框架结构,经非线性分析所得的倒塌概率相对保守,安全储备更高。     

Seismic vulnerability evaluation of RC moment frame buildings in moderate seismic zones

A multi‐level seismic vulnerability assessment of reinforced concrete moment frame buildings located in moderate seismic zones (0.25g) is performed on a set of ductile versions of low‐ to mid‐rise two‐dimensional moment frames. The study is illustrated through application to comparative trial designs of two (4‐ and 8‐story) buildings adopting both space‐ and perimeter‐framed approaches. All frames are dimensioned as per the emerging version of the seismic design code in Egypt. These new seismic provisions are in line with current European norms for seismic design of buildings. Code‐compliant designs (CCD), as well as a proposed modified code design relaxing design drift demands for the investigated buildings, are examined to test their effectiveness and reliability. Applying nonlinear inelastic incremental dynamic analyses, fragility curves (FC) for the frames are developed corresponding to various code‐specified performance levels. Code preset lower and upper bounds on design acceleration and drift, respectively, are also addressed along with their implications, if imposed, on the frames seismic performance and vulnerability. Annual spectral acceleration hazard curves for the case study frames are also generated. Estimates for mean annual frequency (MAF) of exceeding various performance levels are then computed through an integration process of the data resulting from the FC with the site hazard curves. The study demonstrates that the proposed design procedure relaxing design drift demands delivers more economic building designs relative to CCDs, yet without risking the global safety of the structure. The relaxed design technique suggested herein, even though scoring higher, as expected by intuition, MAF of exceeding various code‐limiting performance levels expressed in terms of interstory drift ratios, still guarantees a reasonably acceptable actual margin against violating code limits for such levels. Copyright © 2010 John Wiley & Sons, Ltd.     

A probabilistic performance‐based approach for mitigating the seismic pounding risk between adjacent buildings

Existing design procedures for determining the separation distance between adjacent buildings subjected to seismic pounding risk are based on approximations of the buildings' peak relative displacement. These procedures are characterized by unknown safety levels and thus are not suitable for use within a performance‐based earthquake engineering framework. This paper introduces an innovative reliability‐based methodology for the design of the separation distance between adjacent buildings. The proposed methodology, which is naturally integrated into modern performance‐based design procedures, provides the value of the separation distance corresponding to a target probability of pounding during the design life of the buildings. It recasts the inverse reliability problem of the determination of the design separation distance as a zero‐finding problem and involves the use of analytical techniques in order to evaluate the statistics of the dynamic response of the buildings. Both uncertainty in the seismic intensity and record‐to‐record variability are taken into account. The proposed methodology is applied to several different buildings modeled as linear elastic single‐degree‐of‐freedom (SDOF) and multi‐degree‐of‐freedom (MDOF) systems, as well as SDOF nonlinear hysteretic systems. The design separation distances obtained are compared with the corresponding estimates that are based on several response combination rules suggested in the seismic design codes and in the literature. In contrast to current seismic code design procedures, the newly proposed methodology provides consistent safety levels for different building properties and different seismic hazard conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic hazard level reduction for existing buildings considering remaining building lifespans

Seismic hazard levels lower than those for design of new buildings have been permitted for seismic evaluation and retrofit of existing buildings due to the relatively short remaining lifespans. The seismic hazard reduction enables costeffective seismic evaluation and retrofit of existing buildings with limited structural capacity. The current study proposes seismic hazard reduction factors for Korea, one of low to moderate seismicity regions. The seismic hazard reduction factors are based on equal probabilities of non-exceedance within different remaining building lifespans. A validation procedure is proposed to investigate equality of seismic risk in terms of ductility-based limit states using seismic fragility assessment of nonlinear SDOF systems, of which retrofit demands are determined by the displacement coefficient method of ASCE 41-13 for different target remaining building lifespans and corresponding reduced design earthquakes. Validation result shows that the use of seismic hazard reduction factors can be permitted in conjunction with appropriate lower bounds of the remaining building lifespans.     

On the design and seismic response of RC frame buildings designed with Eurocode 8

Performance-Based Seismic Design is now widely recognized as the pre-eminent seismic design and assessment methodology for building structures. In recognition of this, seismic codes may require that buildings achieve multiple performance objectives such as withstanding moderate, yet frequently occurring earthquakes with minimal structural and non-structural damage, while withstanding severe, but rare earthquakes without collapse and loss of life. These objectives are presumed to be satisfied by some codes if the force-based design procedures are followed. This paper investigates the efficacy of the Eurocode 8 force-based design provisions with respect to RC frame building design and expected seismic performance. Four, eight, and 16-storey moment frame buildings were designed and analyzed using the code modal response spectrum analysis provisions. Non-linear time-history analyses were subsequently performed to determine the simulated seismic response of the structures and to validate the Eurocode 8 force-based designs. The results indicate the design of flexural members in medium-to-long period structures is not significantly influenced by the choice of effective member stiffness; however, calculated interstorey drift demands are significantly affected. This finding was primarily attributed to the code’s enforcement of a minimum spectral ordinate on the design spectrum. Furthermore, design storey forces and interstorey drift demand estimates (and therefore damage), obtained by application of the code force-based design procedure varied substantially from those found through non-linear time-history analysis. Overall, the results suggest that though the Eurocode 8 may yield life-safe designs, the seismic performance of frame buildings of the same type and ductility class can be highly non-uniform.     

基于性态的建筑工程抗震设计——《建筑工程抗震性态设计通则》述评

《建筑工程抗震性态设计通则(试用)》对抗震设计具有重要的指导意义,其中的抗震设计理念同以往的抗震设计规范在抗震设防的思路、概念和方法上有较大的区别。从工程实践的角度,比较了《通则》和现行抗震设计相关规范的区别并对具体应用提出一些看法。