Seismic performance of reinforced concrete columns with lap splices in plastic hinge region

For convenient bar placement, longitudinal bars in columns are often lap-spliced at the bottom of the columns where plastic hinge forms. In this study, the seismic performance of lap-spliced columns was investigated through cyclic loading tests. The bar splice length and shear span-To-height ratio were considered as the primary test variables. The test results showed that after flexural yielding, bond-splitting cracks propagated along the lap-spliced bars during repeated load cycles. The strength, ductility, and failure mode of the columns were significantly affected by the bar splice length and shear span-To-height ratio (or moment gradient). Based on the results, effects of moment gradient on the bond demand of spliced bars were studied, and a reduced splice length addressing the moment gradient was proposed. Furthermore, recommendations for the design and detailing of lap splices in the column plastic hinge region such as splice length, bar offset, and confining transverse reinforcement were provided.