低延性中心支撑钢框架结构振动台试验

中心支撑钢框架结构是一种典型的双重抗侧力体系,强震作用下支撑失效会引起结构承载力和刚度的折减,支撑失效后,结构剩余部分作为储备体系能够继续承担地震作用。为深入了解低延性中心支撑钢框架结构在地震作用下的非线性反应,研究在支撑失效后结构储备体系的抗震性能,开展了3层中心支撑钢框架结构模型的振动台试验。模型结构为3榀2跨结构,中间榀布置一跨低延性人字形中心支撑(截面宽厚比超出我国规范限值),模型长度缩尺比为1∶6. 5,分别采用硬土、软土场地的地震波单向激励,峰值加速度逐级增加。结构在7度罕遇地震作用下发生底层支撑失效,储备体系避开了硬土场地地震波的卓越周期,加载至超过9度罕遇地震后依然未出现明显损伤。储备体系对软土场地地震波(宁河波)更为敏感,在8度罕遇地震作用下濒临倒塌。结构2、3层支撑始终未发生屈曲和破坏。研究结果表明,当储备体系设计合理时,低延性中心支撑钢框架结构具有良好的抗震性能和抗倒塌能力。

Shaking table test on low-ductility concentricallybraced steel frames

Concentrically braced steel frames (hereafter known as CBFs) are used extensively in buildings as a lateral resistance system. Under the rare earthquakes, buckling and failure of brace would lead to the decrease of bearing capacity and stiffness of the CBFs. The frame of structure as the reserve system provides reserve stiffness and reserve strength after failure of braces. Shaking table tests were performed on three-story CBF to investigate the non-linear reactions of low-ductility CBF under earthquakes and the seismic behavior of reserve system after the failure of braces. The model structure was a 1∶6.5 scaled three-story, three-bay and two-span chevron CBF with low-ductility braces. The braces with large width-to-thickness ratio cannot meet the requirements of seismic detailing according to Chinese seismic code. Two ground motions stand for hard and soft soil sites were loaded unidirectionally and amplified by degrees. The braces in first story fracture under rare earthquake of intensity seven. The reserve system avoids the predominant period of hard soil site earthquake after brace failure, and thus has no obvious damage under rare earthquake up to intensity nine. The reserve system is sensitive to ground motions of soft soil site. The structure is near to collapse under rare earthquake of intensity eight. The second and third stories remain elastic all the while. This test shows that, with rational design of reserve system, the low-ductility steel CBF has favorable seismic performance and considerable collapse prevention performance.