Effect of lap-splice details for reinforced concrete columns under cyclic loading

Lap splices of column bars are frequently used at the base of columns in low-rise buildings where plastic hinges may form. The splice length and details of column bars are determined by considering seismic performance, such as load-carrying capacity and displacement ductility, and energy dissipations. To investigate the performance of spliced columns, reversed cyclic load tests were conducted with various splice lengths (ls=30d b~50d b) and splice details (lower bar offset splice, upper bar offset splice, and side-by-side lap splice). In the spliced column with l s=50d b, satisfying the splice length requirement in ACI 318, the nominal flexural strength was attained with ductile behavior. However, when the provided lap-splice length was decreased to 30d b or 40d b, inelastic deformations and energy dissipations of spliced columns were degraded due to early bond failure with severe splitting cracks along splice regions. Lap-splice details have a significant impact on seismic performance. The lower bar offset splice exhibits lower flexural strength but greater ductility and energy dissipation. Conversely, both upper bar offset splice and side-by-side lap splice exhibit greater flexural strength but lower displacement ductility and energy dissipation with bond-splitting failure. The average bond demands of spliced bars decrease with increasing moment gradients due to the significant variation of tensile stresses along splice regions in columns. To reduce the splice length required in current design codes, a modified lap-splice length model for lap-spliced columns considering moment gradients along splice regions was proposed. The reduced splice length was found to correlate well with the present and existing cyclic test results of columns with lap splices.