地震序列作用下砌体结构弹塑性动力破坏倒塌情景仿真

Most worldwide seismic codes consider structure design only subjected to single seismic wave. The effects of earthquake sequences have not been considerated carefully. However, multiple earthquakes occur within short time period are always observed in history events, and the structures behave quite differently under single or multiple earthquakes. Sometimes, aftershock becomes the key element for structure collapse. Meanwhile, masonry is one of the most popular structure types in the world. Also, it will become one of the major structure types for aseismic capacity promotion in Chinese rural areas. In order to prevent disastrous collapse of masonry structures under earthquake sequences, it is significant to study the crack growth and collapse mechanics by using numerical simulation and experiments, simultaneously. The effect of earthquake sequences should be evaluated and taken into consideration in seismic codes..It might be insufficient to study collapse mechanics by using traditional macro analysis methods, push-over or seismic fragility without fracture analysis, since stiffness matrix and strain energy will change drastically due to crack growth,also the damage accumulates among earthquake sequences. Based on PDS-FEM (Particle Discretization Scheme Finite Element Method, a three dimensional fracture analysis method), this project will create a platform by developing fast modeling technology for masonry structure, fracture/collapse analysis method, and the eartuquake senario visualization technologies.In order to apply this platform to real structures, parallel computing technology will be applied, and the computation efficiency will be highly advanced. After setting up the platform, a study of a masonry structure under earthquake sequences will be conducted. The findings of this project will be useful to understand the collapse mechanics of masonry structures. Also, it will provide a new viewpoint to understand the efect of multiple earthquakes and how to consider the effect of earthquake sequences in seismic design.

世界多数抗震规范主要考虑单次地震作用下的结构设计，未考虑多次地震动影响。强余震常有发生，而结构在多次与单次地震动作用下的破坏状态不同。余震有时成为其倒塌的关键因素。砌体结构或将成为我国乡镇抗震能力提升的主体结构之一，世界上有广泛分布。研究地震序列作用下砌体结构开裂失效和倒塌机制，在抗震规范中如何考虑地震序列的影响具有重要意义。.结构在多次地震动作用下发生损伤累计，开裂后刚度发生突变，内力重分布，采用传统方法不足以反映其失效过程和破坏机制。本研究以三维断裂有限元方法（PDS-FEM）为基础，创建一个集砌体结构快速建模，弹塑性动力求解，破坏倒塌分析和情景再现技术于一身的分析平台。引入并行计算技术大幅提高计算效率。根据我国国情研究地震序列设定方法。以此为基础研究多次地震动作用下砌体结构破坏倒塌机理，为抗震规范中如何考虑多次地震动影响提供研究方法和理论依据。

在本项目的研究过程中适逢尼泊尔在2015年4月25日发生了7.8Mw大地震。主震后17天内伴随8次超过Mw5.3的余震，尤其是在5月12日发生了7.3Mw的强余震。在实地考察中，发现很多框架结构和砌体结构在主震中发生损伤，在短期无法修复的情况下，在余震中进而发生严重破坏，甚至倒塌。在SCI期刊上发表了一系列文章，总结了各种结构在主余震作用下结构的损伤、破坏、乃至倒塌的情况。.本项目首先进行了两次足尺一层有筋砌体结构振动台实验。由于振动台不允许发生结构倒塌，因此首先进行安全验证实验，采用汶川主震时位于不同烈度区台站记录的强震数据进行单方向加载，结构未发生严重破坏。之后，弱化材料强度增加配重，调幅地震动后采用三向输入，发现结构出现明显开裂，同时在设计地震动输入下结构未发生倒塌，保证振动台安全。.基于断裂破坏分析方法PDSFEM，本项目成功实现了三维弹塑性静、动力分析拓展，基于消息传递并行库，进行了双层并行架构程序设计，并在天河国家超算中心采用840线程完成了包含超过3100万自由度的约束砌体结构弹塑性动力破坏仿真分析。在计算中发现：1，采用Newton-Raphson进行非线性迭代求解时，收敛速度较慢，因此探寻适于应对结构刚度可能发生巨大变化（破坏倒塌），大变形（结构失稳）的非线性迭代算法。最终发现杨永斌院士提出的GDCM方法可以有效求解包括极值点和反弯点等非线性问题。在项目末期刚刚完成该求解算法的程序编译。今后将设计模型进行包含大变形屈曲计算分析，验证该算法的效用；2，采用率无关破坏准则会使结构过早的发生破坏，因此推荐采用Tuler-Bucher率相关破坏准则进行动力破坏分析。.研究内容在14ICF国际会议上进行了发表，总结了两篇文章，分别投向International Journal of Solids and Structures和Structural Engineering & Mechanics，尚未发表。