Seismic Performance of RC Columns with Lap Splices at Plastic Hinge Region

소성힌지 구간에서 겹침이음된 RC기둥의 내진성능

For small buildings designed to primarily resist gravity load, lap splices of longitudinal reinforcement are used in columns at the regions (e.g. at the bottom of the $1^{st}$ floor) where flexural yielding is anticipated. Although not allowed under cyclic loading repeated in large inelastic range, such splices can be used as an alternative for the convenience of construction in small buildings where a limited ductility is required. In this study, cyclic loading test was performed for columns using lap splices at the plastic hinge regions. The length and offset bar details of lap splices and the ratio of shear span and section height (or aspect ratio) were considered as the test parameters. Non-seismic hoops of 90-degree end hooks were provided over the lap length. Test results showed that the strength and ductility of columns were significantly varied depending on the offset bar details and length of lap splices. In addition, the aspect ratio also had significant impact on the performance of lap splices due to change of the bond demand in the splice zone. The columns lap spliced in the plastic hinge zone were vulnerable to vertical cracking (or concrete splitting) along the lap length. Based on the test results and the review of existing studies, design recommendations for calculating lap spliced length of columns at plastic hinge zone were proposed.