عملکرد لرزه ای ستون های RC مستطیل مقیاس بزرگ CFRP تحت بارگذاری جانبی Seismic Performance of CFRP-Retrofitted Large-Scale Rectangular RC Columns under Lateral Loading in Different Directions

1. Introduction As the main vertical members, columns are critical elements for the seismic performance of buildings. In the majority of earthquake cases, the collapse of reinforced concrete (RC) frame buildings is mainly caused by the failure of columns [1]. Therefore, numerous studies have been conducted on the seismic performance of RC columns [2-7]. It has been found that the most common causes of failure or severe damage of the RC columns are the lack of transverse confinement and ductility, inadequate shear or flexural capacity, and the strong-beam weak-column mechanism. In the past two decades, the use of externally bonded fiber-reinforced polymer (FRP) composites in the hoop direction has been found to be an effective strengthening/retrofitting method for improving the seismic performance of RC columns. As a result, considerable investigations on the seismic performance of RC columns strengthened/retrofitted with FRP have been conducted [8-17]. The majority of existing studies on the seismic performance of both RC columns and FRP-strengthened/retrofitted RC columns have been concentrated on the lateral loading in the principal direction of the columns. However, actual structures generally are subjected to multiaxial earthquake excitation. The seismic excitation loading can be in any direction. Moreover, the skewness also is another cause of maximum seismic response of FRP-retrofitted columns not being in the principal direction [18-19]. Consequently, it is essential to evaluate the effect of multi-directional lateral loading on the seismic performance of RC columns to develop more reliable design and strengthening/retrofitting procedures. Thus far, the studies on the seismic performance of both RC columns and strengthened /retrofitted RC columns under multi-directional lateral loading are very limited, especially for FRP-strengthened/retrofitted RC columns. The limited available studies on RC columns have demonstrated that the failure mechanism of RC columns was significantly dependent on the loading path/direction. The ductility and energy dissipation capacity of the columns were also strongly affected by the loading path/direction. In addition, the biaxial cyclic lateral load was found to increase the strength and stiffness degradation when compared to the uniaxial load.