BEHAVIOR OF RECTANGULAR COLUMNS WITH LOW LATERAL CONFINEMENT RATIO

摘要

Main objective of the study is to examine the seismic capacity of rectangular reinforced concrete columns having non-seismic detailing. Six column specimens in 1:3 scale have been tested under cycles of lateral load. The column specimens were characterised by high axial load (40%-65% of the axial load-carrying capacity), low lateral confinement ratio (0.001-0.003) and low to moderate shear span ratio (1.5-3.0). An ultimate drift ratio is introduced to quantify the seismic capacity. Poor performances were observed on column specimens with low shear span when subjected to cyclic lateral loads. Four column specimens failed under shear, and flexural failures were observed in the other two column specimens with lateral confinement ratio at 0.003 and moderate shear span. An increase in the axial load ratio within the range 0.4-0.65 resulted in a reduction in the lateral load-carrying capacity by about 10% and a reduction in the ultimate drift capacity by about 30%. Lateral confinement has significant influence on the ultimate drift, of which an increase from 0.001 to 0.003 could increase the ultimate drift capacity by up to 100%. At low to moderate shear span, contributions of shear and bond slip to the deformation must be considered. However, deformation outside the plastic region could be neglected for a column with low shear span ratio.