The effect of lap-splice configuration on seismic performance of substandard RC columns

Abstract

A considerable amount of existing reinforced concrete (RC) buildings in developing countries possess vital deficiencies such as incorporating poor quality of concrete and insufficient transverse reinforcement, and use of plain reinforcing bars without proper detailing, such as inadequate configurations of lap-splices at critical plastic hinging zones. While these can affect the strength and ductility of structural members adversely under seismic actions, research on such substandard structural members is scarce. As such, further information is valuable for the assessment of the seismic safety of such substandard columns constructed with inadequate lap-splice configurations of plain round bars. Therefore, this study aims to investigate the effects of different lap-splice configurations of plain bars on the seismic performance of substandard RC columns and contribute to the development of assessment codes for such existing substandard buildings. Towards this aim, three full-scale columns were constructed to represent typical characteristics of substandard RC columns. The columns were subjected to constant axial loading (with an axial load to capacity ratio of 0.3) and reversed cyclic displacement reversals simultaneously representing gravity loads and seismic actions, respectively. The test program included i) one reference column with continuous longitudinal bars (no lap-spliced connection), ii) one lap-spliced column with an overlap length of 20 times the longitudinal bar diameter without any hook and iii) one lap-spliced column with an overlap length of 20 times the longitudinal bar diameter with a 180-degree hook. Test results demonstrated that columns with lap-splices did not reach their flexural strength and experienced more remarkable strength degradation with respect to the column reinforced with continuous longitudinal bars. On the other hand, presence of a 180-degree hook at the ends of spliced bars reduced the negative influence of inadequate lap-splice length in terms of strength and ductility.