基于一致倒塌风险的建筑抗震评价方法研究

建筑结构的抗震能力、尤其是抗倒塌能力设计目标应根据其所在场地未来一定设计使用年限内可能遭遇的地震危险性来设定。首先介绍了基于动力增量分析（IDA）的结构倒塌易损性分析方法,随后结合地震危险性分析,分别给出了结构抗倒塌能力和结构所面临地震危险性的概率模型,进而根据结构在未来一定设计使用年限内的倒塌概率,对建筑结构的抗地震倒塌风险进行定量评价,并给出了相应的计算方法。以一座7度抗震设防的RC框架结构为例,计算了该RC框架结构在3个同为7度抗震设防而地震危险性不同地区的地震倒塌风险,指出仅以抗震设防烈度作为建筑结构抗震设计的依据所存在的不足,建议应基于一致倒塌风险进行结构抗震设计,并提出了相关结构抗震设计方法需开展的研究工作。     

基于统一倒塌风险的建筑抗震设计方法研究

为了研制基于一致倒塌风险的建筑抗震设计方法,首先对建筑结构地震倒塌风险表征参数及其控制水准进行了研究,认为在工程设计与控制中,可采用规范GB 50011-2010的弹塑性层间位移角限值作为倒塌的判别标准,采用弹塑性层间位移角限值的超越概率表征建筑的地震倒塌风险,风险控制水准建议取10％;其次对基于统一地震危险的抗震设计...     

Protection of our bridge infrastructure against man-made and natural hazards

Blast mitigation research on a series of bridge components to date has shown both similarities and differences between seismic events and explosive loads in terms of structural response. Similarities on the load side include the fact that both blast and earthquake loads are largely unknown in terms of location, magnitude, intensity, type, etc., and both have characteristics of rapid attenuation with distance from the source mechanism. In terms of consequences, both actions can result in progressive structural collapse, requiring redundant structural systems for mitigation. Significant differences in these two extreme event scenarios also exist; these include load duration and associated strain rate effects and the extent of initial damage or excitation. The similarities and differences between blast and seismic hazards and their responses are explored in a series of blast mitigation field tests, laboratory tests, and computational analyses to form the basis for multi-hazard mitigation in bridge structures.     

填充墙钢筋混凝土框架结构基于位移的改进抗震设计方法

按现行抗震规范设计的底部空框架填充墙钢筋混凝土框架结构,可能无法实现“强柱弱梁”的预期延性破坏机制。为此,建立了填充墙与主体框架协同作用的等效斜撑-框架模型,改进等效单自由度体系阻尼比与刚度的确定方法,提出了填充墙钢筋混凝土框架结构基于位移的抗震设计方法;针对底部为空框架的填充墙钢筋混凝土框架结构进行不同性能目标下的静力推覆分析,实现其“使用良好”、 “修复后使用”和“防止倒塌”性能水平的抗震设计。采用动力弹塑性时程分析方法和能力谱法验证了基于位移的改进抗震设计方法的有效性。分析表明,应用基于位移的改进抗震设计方法,可综合考虑填充墙对主体框架的利弊作用,实现结构性能抗震设计目标。     

钢筋混凝土梁式构件抗爆分析的改进等效单自由度方法

爆炸荷载作用下钢筋混凝土梁式构件可能会出现多种破坏模式，主要有弯曲破坏、直剪破坏和弯剪联合破坏等。现有结构构件抗爆分析方法主要考虑爆炸荷载下结构构件的弯曲破坏，对直剪破坏和弯剪联合破坏研究较少，尤其缺少快速准确的抗爆分析方法。基于等效单自由度模型理论，改进了钢筋混凝土梁抗爆分析的直剪单自由度方法，提出了直剪、弯剪联合破坏的判定准则，给出了两种破坏模式下钢筋混凝土梁动态响应的计算方法。进一步考虑爆炸荷载作用下钢筋混凝土梁的弯曲破坏、直剪破坏和弯剪联合破坏，提出钢筋混凝土梁式构件抗爆分析的改进等效单自由度方法，并给出了其分析步骤。该方法可以直接评估爆炸荷载下钢筋混凝土梁式构件的破坏模式，并计算其动态响应。通过有限元软件LS-DYNA数值模拟了不同爆炸工况下钢筋混凝土梁式构件的动态响应和破坏模式，与改进的等效单自由度方法的计算结果进行了对比，验证了提出的改进等效单自由度分析方法的正确性。     

Numerical simulation and analysis for collapse responses of RC frame structures under earthquake

In this paper, a discrete element model for collapse simulation of RC frame structure is constructed by discretizing the structure into a few elements and spring groups. This model introduces special hysteretic models of connected springs for arbitrary loading path and also takes into account reasonable failure criteria for springs considering coupling effect of shear and axial force. Based on the discrete element model, a computer program is developed to simulate the whole process of RC frame structures from initial state to collapse under earthquakes. Particularly, the contact-impact problem between discrete elements has been treated with effective measures. Then, the program is employed to study the collapse mechanism of a real building in Wenchuan earthquake-hit area; the result of which shows that the simulation program developed based on the new model can realistically simulate the seismic collapse process of RC frame structures.     

Numerical simulation and analysis for collapse responses of RC frame structures under earthquake

In this paper, a discrete element model for collapse simulation of RC frame structure is constructed by discretizing the structure into a few elements and spring groups. This model introduces special hysteretic models of connected springs for arbitrary loading path and also takes into account reasonable failure criteria for springs considering coupling effect of shear and axial force. Based on the discrete element model, a computer program is developed to simulate the whole process of RC frame structures from initial state to collapse under earthquakes. Particularly, the contact-impact problem between discrete elements has been treated with effective measures. Then, the program is employed to study the collapse mechanism of a real building in Wenchuan earthquake-hit area; the result of which shows that the simulation program developed based on the new model can realistically simulate the seismic collapse process of RC frame structures.     

不同极限位移BRB的RC框架结构#br# 抗地震倒塌性能研究

设计6个装有不同极限位移BRB的RC框架结构,基于OpenSees建立相应的有限元模型并验证模型的可行性和BRB模拟准确性,对装有不同极限位移BRB的RC框架结构模型进行增量动力分析和地震易损性分析,研究不同极限位移BRB的RC框架结构抗地震倒塌性能。研究表明：随着BRB极限位移的增加,结构抗倒塌性能得到提升;当系数小于1.2倍时,罕遇地震下结构中出现BRB失效概率大于5%,当系数大于1.2倍时,BRB极限位移提高对结构抗倒塌性能提高有所下降;《建筑消能减震技术规程》（JGJ 297—2013）对消能减震装置极限变形取12倍安全系数是合理的。     

Probabilistic approach for failure assessment of steel structures in fire by means of plastic limit analysis

The issue of fire scenarios approach to fire protection is often subject of ongoing discussions within the fire safety engineering community. The choice of an adequate number and type of fire scenarios is not always univocal and straightforward. The fire scenarios to be used in structural assessment are quite complicated to obtain. Their definition often involves significant large-scale fire tests and sophisticated numerical simulations, taking into account numerous factors. For this reason, it seems appropriate to introduce probabilistic tools to assess the most probable fire scenarios. This work proposes a probabilistic approach integrating the Monte Carlo simulation with plastic limit analysis in order to assess the probability of failure of a structure subjected to fire. The underlying assumptions related to spatial–temporal evolution of the fire action and the response of materials and structural members comply with Eurocode provisions. The procedure, mainly devoted to identify the most critical fire scenarios for the structural response, is illustrated by means of a case study represented by a steel braced structure, used as parking. Beyond the limitations related to the simplified assumptions, the outcomes of the analyses demonstrate the potential of the approach for choosing fire scenarios by means of a probabilistic procedure and for evaluating the probability of fire-induced progressive collapse.     

Seismic reliability assessment of a two-story steel-concrete composite frame designed according to Eurocode 8

Recent earthquakes have shown that some buildings designed primarily for life safety according to the seismic provisions of current building codes could be subjected to severe damage to structural and non-structural elements and building contents. In order to overcome this drawback, the scientific community is developing more accurate methodologies to assess seismic performances of structures. In this framework, the present paper aims at the evaluation of mean annual frequency (MAF) of exceeding a limit state (limit value of interstory drift ranging from 0.002 to 0.05) following the probabilistic approach introduced by Pacific Earthquake Engineering Research Center adopting (PEER) the application procedure suggested by Jalayer and Cornell. Reference is made to a single two-story steel-concrete composite frame, designed according to Eurocode 8 and tested in real scale at the ELSA Laboratory of Ispra. The reason for investigating this frame is related to the availability of results both of pseudo-dynamic tests performed on 3D steel-concrete composite frame and of monotonic and cyclic tests performed on internal and external beam-to-column joint sub-assemblages belonging to the building. As a consequence, it has been possible to assess the seismic reliability of a 3D steel-concrete composite building, designed according to Eurocode 8, taking into account both randomness and uncertainty.     

基于机器学习的钢筋混凝土柱失效模式两阶段判别方法增强出版（附加材料可在文章详情页“评审附件”下载）

钢筋混凝土柱在侧向地震力作用下具有弯曲、剪切和弯剪三种失效模式。不同的失效模式下钢筋混凝土柱具有不同的地震损伤特征。因此,准确地判别钢筋混凝土柱的失效模式对于准确评估钢筋混凝土结构的抗震性能具有重要意义。利用已有的钢筋混凝土柱滞回加载试验数据,采用机器学习方法,提出了一种钢筋混凝土柱失效模式两阶段判别方法。其中,第一阶段以钢筋混凝土柱的基本设计参数为输入变量,采用机器学习中的回归算法,建立钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形预测模型。第二阶段以钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形作为输入变量,采用机器学习中的分类算法,对钢筋混凝土柱的失效模式进行自动判别,实现了准确判别钢筋混凝土柱失效模式的目的。研究结果表明：极端随机树、AdaBoost、随机森林和梯度提升算法分别对受弯承载力、受剪承载力、弯曲变形和剪切变形的预测效果最佳;极端随机树、梯度提升算法和最近邻居法分别对弯曲失效、剪切失效和弯剪失效具有最佳的分类效果;相比已有的钢筋混凝土柱失效模式分类方法,提出的两阶段分类方法具有与真实失效模式最为接近的分类结果,分类精度可以达到96%。     

A machine-learning-based two-step method for failure mode classification of reinforced concrete columns

钢筋混凝土柱在侧向地震力作用下具有弯曲、剪切和弯剪三种失效模式。不同的失效模式下钢筋混凝土柱具有不同的地震损伤特征。因此，准确地判别钢筋混凝土柱的失效模式对于准确评估钢筋混凝土结构的抗震性能具有重要意义。利用已有的钢筋混凝土柱滞回加载试验数据，采用机器学习方法，提出了一种钢筋混凝土柱失效模式两阶段判别方法。其中，第一阶段以钢筋混凝土柱的基本设计参数为输入变量，采用机器学习中的回归算法，建立钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形预测模型。第二阶段以钢筋混凝土柱的受弯承载力、受剪承载力、弯曲变形和剪切变形作为输入变量，采用机器学习中的分类算法，对钢筋混凝土柱的失效模式进行自动判别，实现了准确判别钢筋混凝土柱失效模式的目的。研究结果表明：极端随机树、AdaBoost、随机森林和梯度提升算法分别对受弯承载力、受剪承载力、弯曲变形和剪切变形的预测效果最佳；极端随机树、梯度提升算法和最近邻居法分别对弯曲失效、剪切失效和弯剪失效具有最佳的分类效果；相比已有的钢筋混凝土柱失效模式分类方法，提出的两阶段分类方法具有与真实失效模式最为接近的分类结果，分类精度可以达到96%。     

三维地震动输入对IDA倒塌易损性分析的影响

地震作用下建筑结构抗倒塌能力是性能化抗震设计的核心目标,基于IDA的倒塌易损性分析能够定量评价结构的抗地震倒塌安全性.本文通过一个8层RC框架结构和一个20层RC框架-核心筒结构的算例,指出仅考虑地震动单一水平分量的IDA分析会高估结构抗地震倒塌安全性;而三维地震动输入下结构可能出现更多的倒塌模式,可更全面地体现整体结...     

Stochastic seismic collapse and reliability assessment of high‐rise reinforced concrete structures

To provide knowledge beyond the conventional engineering insights, attention in this work is focused on a comprehensive framework for the stochastic seismic collapse analysis and reliability assessment of large complex reinforced concrete (RC) structures. Three key notions are emphasized: the refined finite element modeling and analysis approach towards structural collapse, a physical random ground motion model, and an energy‐based structural collapse criterion. First, the softening of concrete material, which substantially contributes to the collapse of RC structures, is modeled by the stochastic damage constitutive model. Second, the physical random ground motion model is introduced to quantitatively describe the stochastic properties of the earthquake ground motions. And then the collapse‐resistance performance of a certain RC structure can be systematically evaluated on the basis of the probability density evolution method combining with the proposed structural collapse criterion. Numerical results regarding a prototype RC frame‐shear wall structure indicate that the randomness from ground motions dramatically affects the collapse behaviors of the structure and even leads to entirely different collapse modes. The proposed methodology is applicable in better understanding of the anti‐collapse design and collapse prediction of large complex RC buildings.     

Influence of soilestructure interaction on seismic collapse resistanceof super-tall buildings

Numerous field tests indicate that the soilestructure interaction （SSI） has a significant impact on thedynamic characteristics of super-tall buildings, which may lead to unexpected structural seismic responsesand/or failure. Taking the Shanghai Tower with a total height of 632 m as the research object, thesubstructure approach is used to simulate the SSI effect on the seismic responses of Shanghai Tower. Therefined finite element （FE） model of the superstructure of Shanghai Tower and the simplified analyticalmodel of the foundation and adjacent soil are established. Subsequently, the collapse process of ShanghaiTower taking into account the SSI is predicted, as well as its final collapse mechanism. The influences ofthe SSI on the collapse resistance capacity and failure sequences are discussed. The results indicate that,when considering the SSI, the fundamental period of Shanghai Tower has been extended significantly,and the collapse margin ratio has been improved, with a corresponding decrease of the seismic demand.In addition, the SSI has some impact on the failure sequences of Shanghai Tower subjected to extremeearthquakes, but a negligible impact on the final failure modes.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

Simplified vulnerability assessment of reinforced concrete circular piers in multi-span simply supported bridges

This paper proposes a simplified procedure for the seismic vulnerability analysis of multi-span simply supported bridges, in the case of single piers with solid circular sections. The proposed method can be applied whenever the seismic response of the whole bridge depends on the most critical pier. For an assigned limit state, the procedure determines the capacity curve of the critical pier as a function of three parameters (elastic stiffness, displacement at yielding, displacement at collapse), starting from the behaviour under combined axial stress and bending, and then taking into account the different possible collapse modes (shear failure; lap splice failure of the longitudinal bars; buckling) and the geometric nonlinearity. A significant numerical example is presented in which the traditional FEM solution is compared with the proposed simplified procedure.     

极罕遇地震作用下建筑结构一致风险抗倒塌设计方法研究

结合当前国际上以“抗倒塌”为目标进行地震动参数区划和以“一致倒塌风险”为设防目标进行结构抗震设计的发展趋势,针对我国现行建筑抗震设计规范体系中抗倒塌能力评估的局限性,建议了四种一致风险抗倒塌设计方法,详细介绍了四种方法的评价指标与计算过程。考虑极罕遇地震作用,基于极罕遇地震一致风险谱对地震动记录进行了挑选与调幅。以RC框-剪结构作为典型案例,采用四种抗倒塌设计方法进行验算,结果表明：同时考虑地震危险性与结构不确定性影响的全概率方法验算未通过,其余验算方法均通过,这说明了忽略结构所在场地危险性影响会造成结构倒塌性能评估的不准确性,未考虑结构体系多种不确定性影响会高估结构的抗倒塌性能,因此有必要推行“一致风险”的结构设计理念。     

考虑结构不确定性的地震倒塌易损性分析

传统的地震倒塌易损性分析中通常只考虑地震动不确定性的影响。在结构临近倒塌时,通常处于高度非线性状态,会出现结构不确定性与地震动不确定性的耦合放大现象。针对这一问题,将平均值一次二阶矩方法（MVFOSM）与逐步增量动力分析（IDA）相结合,提出了一种可以考虑结构不确定性的基于MVFOSM的随机IDA方法。以五层三跨钢筋混凝土框架结构为例,采用基于MVFOSM的随机IDA方法对其进行了地震倒塌易损性分析,并利用“龙卷风图”方法对结构抗地震倒塌能力的灵敏度进行了分析。研究表明：结构不确定性的存在使得结构抗地震倒塌能力的对数标准差增加了70%,因此有必要在地震倒塌易损性分析中考虑结构不确定性的影响。     

A multi-objective structural optimization method for serviceability design of tall buildings

Structural optimization design aims to identify optimal design variables corresponding to a minimum objective function with constraints on performance requirements. To this end, many optimization frameworks have been proposed to determine optimal structural systems that are subjected to seismic and wind hazards in isolation. However, some modern tall buildings are sensitive to seismic and wind excitation owing to their complex structural systems and geographic regions. Therefore, a proper structural optimization method for such buildings is required to ensure that the expected performance is achieved in a multi-hazard scenario. This study proposes a multi-objective serviceability design optimization methodology for buildings in multi-hazard seismic and wind environments by combining optimality criteria and the nondominated sorting genetic algorithm II (NSGA-II). Seismic and wind effects can be instantaneously updated due to changes in the structural dynamic properties during the optimal design process. A neural-network-based surrogate model with self-updating is proposed to predict the structural natural frequency so that the overall computation time of the optimization process can be reduced. The proposed method was used to optimize a 50-story frame-tube building and was compared against the general genetic algorithm and general NSGA-II to verify the feasibility and effectiveness.