Assessing structural vulnerability against earthquakes using multi-dimensional fragility surfaces: A Bayesian framework

The present paper advocates a probabilistic framework for assessing structural vulnerability against earthquakes. This is justified by the significant randomness that characterizes not only the earthquake excitation (amplitude, frequency content, duration), but also the structural system itself (i.e. stochastic variations in the material properties). Performance predictions can readily be summarized in the form of fragility curves which express the probability of exceeding various damage levels (from minor to collapse) with respect to a metric of the earthquake intensity. In this paper, a Bayesian framework is proposed for the derivation of fragility curves which can produce estimates irrespective of the amount of data available. It is particularly flexible when combined with Markov Chain Monte Carlo (MCMC) techniques and can efficiently provide credible intervals for the estimates. Furthermore, a general procedure based on logistic regression is illustrated that can lead in a principled manner to the derivation of fragility surfaces which express the probability of exceeding a damage level with respect to several measures of the earthquake load and can thus produce more accurate predictions. The methodologies presented are illustrated using data generated from computational simulations for a structure on top of a saturated sand deposit which is susceptible to liquefaction.     

雷达遥感建筑物震害信息提取方法综述

合成孔径雷达遥感具有全天时、全天候工作的能力,在地震灾害应急中发挥了重要作用。回顾了雷达遥感建筑物震害信息提取技术的发展历史,总结了各种用于建筑物震害信息提取的雷达卫星的参数特征以及使用雷达遥感提取建筑物震害信息的震例。介绍了目前应用的各种雷达遥感建筑物震害信息提取方法,包括目视解译和计算机自动信息提取两种,其中后者包括基于纹理特征和极化特征的单时相方法、基于强度特征和相干特征的多时相方法。比较了这些方法的适用性和不足,并探讨了雷达遥感建筑物震害信息提取方法的发展趋势。     

超限框支高层抗震墙建筑结构抗震设计

结合工程实例,对超限框支结构设计原则进行简要论述。通过对设计探索过程的剖析,我们试图阐明:对于较为复杂的结构体系,在缺乏较为明确或常规的规范依据情况下,需要回归到结构设计最基本的原理上。先期针对结构不同部位、不同受力状态,分别设定出在小震、中震、大震作用下不同的抗震设防目标,并根据目标期望,进行有目的的结构分析,并取得相对应的、可靠的内力值。这样,才更能够最真实的反应出结构状态,从而确保结构安全。     

Modeling Residual Displacements of Concrete Bridge Columns under Earthquake Loads Using Fiber Elements

Nonlinear dynamic analysis with fiber-element models is now widely used to assess the seismic response of bridge structures. The ability of such models to accurately simulate response parameters for characterizing the postearthquake condition of bridges, namely residual displacements, is assessed by comparison of analyses of dynamically loaded reinforced concrete bridge columns to experimental data. The models are unable to capture residual displacements, and the cause of the inability to capture residual displacements is investigated through dynamic analysis of fiber-element and single-degree-of-freedom (SDOF) models. A certain type of pinching present in the numerical hysteretic response shape is found to lead to poor residual displacement simulation both in the SDOF models and in fiber-element models. When eliminating this pinching, improvements to residual displacement simulation are found. A modified concrete constitutive model representing damage accumulation from cyclic loading is implemented for the fiber-element analysis that incorporates changes to reloading behavior when moving from high tensile strain back to compression. Analysis using the modified concrete constitutive model leads to improvements in the ability of the fiber-element model to capture residual displacements.     

Numerical study on dynamic behavior of slope models including weak layers from deformation to failure using material point method

This paper describes numerical studies on the dynamic behavior of experimental slope models, including various inclined weak layers. These studies were conducted by simulation of shaking table tests using the material point method (MPM), which allows seamless treatment of various considerations, from elastic behavior to discontinuous collapse behavior of slopes, on the basis of an elasto-plastic constitutive law. The simulation results showed that the failure modes, progressive deformation and downward sliding of the numerical slope models, which were similar to that observed in the shaking table tests, can be obtained using the numerical method. In addition, sensitivity analyses of the numerical models used in this study were performed to determine the effects of mesh size, number of particles per cell (PPC) and damping constants on the simulation results. The results of these analyses indicated the use of fine meshes and high damping constants seems to produce sensible results and reduce numerical noises, respectively.     

高铁大跨桥梁设计地震作用与国内外主要抗震规范的比较研究

本文选择了现行国内外主要抗震设计规范,对比了国内外主要抗震设计规范的场地类型划分的差异;考虑地震的重现期与结构的重要性系数等因素,对比分析了我国不同行业抗震规范与《铁路工程抗震设计规范》2009年修正版在多遇地震(小震)、设防烈度地震(中震)和罕遇地震(大震)下各规范反应谱平台取值以及反应谱曲线本身。研究表明我国高铁大跨桥梁在小震的设计取值偏高,中震取值与国内其它规范相当,而大震的取值则偏低。我国高铁大跨桥梁的设计地震作用与欧洲规范Eurocode 8 的对比研究表明,我国的小震(50年重现期)取值小于欧洲规范(90年重现期)、中震(475年重现期)取值也小于欧洲规范(475年重现期)的相应取值。与美国AASHTO规范和加州规范Caltrans(2013)对比研究表明,由于我国规范采用了1.5的重要性系数,小震取值(50年重现期)远高于美国规范的50年重现期的设计地震水平,而与其475年重现期地震水平相当;中震水平(475年重现期)的加速度反应谱平台值略低于Caltrans(975年重现期),但是略高于AASHTO(1000年重现期),我国反应谱曲线与Caltrans大致相当,但是高于AASHTO;对于大震(2475年重现期),AASHTO(2475年重现期)的地震作用取值介于我国的7度 (0.1g) 设防与8度(0.2g)设防之间。总体来说,我国的高铁大跨桥梁的设计地震作用取值偏于保守。     

5·12地震灾区活动板房如何科学防雷

5·12汶川特大地震发生后,在灾区搭建了大量的活动板房,活动板房的所有金属体应做良好接地,且应与其它接地共用接地体.应根据灾区各地的雷暴日数和活动板房的结构,采取相应的防雷措施.在活动板房的上空架设空中避雷线、避雷针的做法不可取.若过渡安置房采用双层彩钢板和金属骨架结构,则在做好整体良好接地的情况下,已能起到防护直击雷的作用.     

地震灾区过渡安置房电气设计点滴

介绍了过渡安置房的建筑特点;依据<地震灾区过渡安置房建设技术导则>,结合当地实际情况,确定了电气设计的标准;采取了保障安置房居民人身安全的技术措施.     

从汶川地震的建筑震害谈结构概念设计的重要性

通过对汶川5.12地震部分灾区的初步考察,本文从建筑震害的现象分析入手,强调了结构抗震概念设计的重要性,并对此进行了思考,希望引起建筑界同仁的重视,切实做好建筑物的抗震防灾工作。     

高层建筑采用基础隔震技术的探讨

随着经济发展,都市土地使用饱和、中心商业区地价高企,势必造成高层、超高层建筑的普遍开发。汶川地震的发生后,人们对安全建筑物的要求越来越迫切。而我国在高层、超高层建筑的基础隔震领域,基本还是空白,处于地震带的大中城市,发展高层、超高层建筑的基础隔震技术,已经迫在眉睫。本文根据现有的技术,对高层,超高层建筑的基础隔震的可行性进行探讨。