汶川地震中某RC框架结构的震害分析与模拟

Damage Analysis and Simulation of a RC Frame Structure in the Wenchuan Earthquake

2008年5月12日,四川省汶川县发生里氏8.0级地震,造成了巨大的人员伤亡以及工程结构震害。本文基于江油市某RC框架结构的震害调查,分析了该框架结果出现底层"薄弱层"和"强梁弱柱"的破坏机制的主要原因。采用该框架结构附近三个台站的主震加速度记录作为输入开展了非线性地震反应分析。研究表明,填充墙的竖向不均匀布置改变了框架的抗侧刚度分布,造成底层薄弱层的破坏现象。底层柱子的轴压比相对较大,塑性变形能力及耗能能力相对较差,使得底层柱的变形量更容易达到其塑性变形极限而发生破坏。由于现浇楼板对梁刚度和抗弯承载力的增强,框架结构很难出现规范中"强柱弱梁"的破坏机制。结构基本周期对应的加速度反应谱值是决定结构地震反应的主要参数,基本周期加速度反应谱值的增加会导致结构塑性铰的迅速发展,造成结构出现柱铰机构而整体失稳倒塌。建议设计框架结构时,尽量避免填充墙的不均匀布置。适当增加底层柱的截面面积和配筋率,降低轴压比以保证良好的延性。梁端负向抗弯承载力计算时采用T型截面,并考虑一定范围内楼板配筋的影响。

On 12 May 2008, an earthquake with magnitude 8.0 occurred in Wenchuan, Sichuan Province, China, causing very huge casualties and engineering damages to the buildings. Based on the investigation of a typical RC frame structure damaged in Jiangyou City, the causes of strong beam and weak column and soft story were summarized. Using acceleration records at Jiangyou city, nonlinear dynamic time history analysis were performed to simulate the damage. Analysis showed that non-uniform collocation of the vertical infill walls altered the lateral stiffness distribution, which made the first floor a soft story. Big axial compression ratio of bottom columns leaded to a ductility deficiency, which made the bottom columns more brittle. As stiffness and bending capacity of the beam enhanced by the floor slab, it is difficult to appear framework specified ＂strong column-weak beam＂ failure mechanism. The structural response was mainly controlled by the acceleration response spectrum value at fundamental natural period of the structure. The increasing of acceleration response spectrum value at fundamental natural period would lead to rapid development of the plastic hinges and overall instability or collapse. Some suggestions were given to seismic design as follows. （1） Non-uniform infill wall should be avoided. （2） Appropriately increase the cross-sectional area and the reinforcement rate of the bottom column to decrease the axial compression ratio in order to ensure enough ductility. （3） Use T-sections to calculate negative bending capacity of the beam, and considering the impact of slab reinforcement within a certain range.