基于耗能保险丝的桥梁双柱墩减震控制研究

Seismic damage control of bridge bents with double columns based on structural fuses

双柱式排架墩被广泛应用于桥梁下部结构,同时在历次破坏性地震中震害普遍且严重。基于保险丝的损伤控制理念,可通过设置防屈曲支撑(buckling restrained brace,BRB)等可更换的耗能装置来提升双柱墩的侧向承载力和耗能能力。当BRB按人字形和单斜式布置时,其耗能能力不能得到充分利用。该研究将肘节式支撑系统和BRB相结合,发展一种能够放大BRB位移的肘节式耗能减震体系,从而提升了BRB的耗能减震能力,并针对此保险丝体系,推导出由桥墩材料、几何属性和位移放大系数等无量纲参数控制的BRB核心段长度取值范围表达式,还绘制了位移放大系数的三维等高线图用于保险丝的设计。选择具有不同破坏形式的两个双柱墩进行保险丝设计,确定BRB的设计参数,建立动力分析模型并输入4组不同类型的地震动进行增量动力分析,考察了人字形、单斜式和肘节式BRB保险丝体系在不同地震动强度下对双柱墩的减震效果。结果表明:同等设计条件下肘节式BRB体系的减震效果最好,BRB的变形得到了放大并充分发挥了其滞回耗能作用,从而将双柱墩的地震损伤控制在轻微破坏甚至于弹性状态,而对应的人字形BRB体系减震效果则最差。

Bridge bents with double columns are widely used in bridge substructures.However,bents have suffered serious damage in previous destructive earthquakes.According to the damage-control concept based on structural fuse,the lateral load and energy dissipation capacity of double-column bents were improved by implementing replaceable energy dissipation devices.The energy dissipation capacity of the buckling restrained brace(BRB)is good but cannot be used to the full when arranged in chevron or single diagonal type.In the paper,a toggle-BRB system was developed,which can amplify the displacement and improve the energy dissipation of BRB.For this kind of fuse system,the expression of the length range of the BRB core controlled by dimensionless parameters such as material,geometric properties and displacement amplification factor of bents was derived.Three-dimensional contour charts of the displacement amplification factor for reference in fuse design were drawn.Taking two double-column bents with different failure modes as examples for fuse design,the parameters of BRB were determined.The dynamic analysis models were established respectively,and four groups of ground motions with different types were input for an incremental dynamic analysis.The seismic isolation effects of chevron,single diagonal and toggle BRB systems on double-column bents under different intensities of ground motions were investigated.The results show that compared with chevron and single diagonal systems in the same conditions,the toggle BRB system has the best seismic isolation effect.The BRB,whose deformation is amplified,plays a full role in deformation and energy dissipation,and can control the seismic damage of double-column bents keeping in slight damaged or even elastic states.The seismic isolation effect of the chevron BRB system is the worst.