水平双向加载下钢筋混凝土柱抗震性能试验研究

针对双向水平地震作用下钢筋混凝土框架柱的抗震性能，开展了9个钢筋混凝土框架柱的水平双向拟静力试验研究，考察轴压比、体积配箍率、纵筋配筋率以及加载路径对柱抗震性能的影响，对双向加载下柱的受力特点、承载力变化、位移延性和极限侧移角等指标进行分析。结果表明：相对于水平单向加载，双向加载对柱的抗震性能存在显著不利影响：柱的抗弯承载力及极限位移均明显减小，损伤程度明显加重；随加载方式由单向-十字-菱形-方圈变化，相同位移下柱的强度退化与抗弯承载力下降幅度均有所增加。考虑双向受力后，典型技术标准给出的RC框架结构极限层间侧移角限值的安全冗余度显著降低。基于试验结果初步提出结构设计及分析建议：考虑双向水平地震动影响时，框架柱的抗震设计宜适当降低轴压比、增加约束箍筋、适当折减柱的抗弯承载力；采用层间侧移角进行结构倒塌判别时，可取双向地震动作用下结构最大层间侧移矢量的大小作为判别位移，并根据分析性质（结构设计或既有结构分析）选取恰当的极限层间侧移角判断标准。

Experimental investigation on seismic performance of reinforced concrete columns under horizontally bi-directional cyclic loading

Bi-directional quasi-static tests on 9 reinforced concrete (RC) frame columns were carried out to study the seismic performance of the columns under horizontally bi-directional seismic loading. The effects of axial compression ratio, volume stirrup ratio, longitudinal reinforcement ratio and loading paths on the mechanical properties of columns were investigated. The mechanical characteristics, bearing capacity, ductility and ultimate drift angle of the columns under bi-directional loading were also analyzed. It is shown that the bi-directional loading has detrimental effect on the seismic performance of RC columns compared with the uniaxial loading. That is, the bi-directionally loaded columns exhibit more severe damage and more degradation in bending capacity and ultimate displacement. With the loading path alternating from uniaxial to cross to rhombic to square ring, strength degradation, damage degree and bending capacity degradation of the column at the same displacement may increase to some extent. It is mainly affected by the stress concentration of the cross section of column under bi-directional loading and the correlation of mechanical properties in two horizontal directions. Analysis also shows that by considering the bi-directional seismic actions, safety redundancy of story ultimate drift angle of the RC frame structure proposed by typical technical standards may be significantly reduced. Hence, the recommendations of structural design and analysis can be proposed based the preliminary experimental results. That is, in the seismic design of RC frame columns under bi-directional seismic actions, the compression ratio should be appropriately decreased, the stirrup ratio for constraint should be increased and the bending capacity of column should be adequately reduced. When the story drift angle is used for judging the structural collapse, the magnitude of the maximum story lateral displacement vector under the bi-directional seismic actions is taken as the judgment displacement, and the judgment criterion of ultimate story drift angle is selected according to the seismic analysis (structure design or analysis of existing structure).