Cyclic stress development in substandard beam–column joint

This paper investigates the failure, bond, strain and stress development of steel bars in a cyclically loaded substandard reinforced concrete beam–column joint. A seismic assessment of 17 existing buildings in a low seismic zone was conducted to study correlations among column size, column depth to bar diameter ratio, bond index and column tributary area. Four half-scale specimens, representing beam–column joints in buildings with various column tributary areas, were tested under quasi-static cyclic loading. The test results reveal brittle joint shear failure in specimens with small and medium column tributary areas and beam flexural failure in specimens with a large column tributary area. By unbonding longitudinal beam bars in the joint, joint shear failure can be prevented. Local pull-out bond and anchorage bond were also studied. All the specimens studied demonstrated the existence of anchorage bond, but local pull-out slip cannot be prevented in all specimens regardless of column depth to bar diameter ratio.