Seisimic performance of a precast concrete column with threaded mechanical splices

Abstract

One of the main reasons for the failure of precast structures under seismic actions is insufficient strength and ductility of their connections. The use of ductile mechanical splices in precast connection is expected to provide sufficient ductility and energy dissipation to the structure as well as to improve the buckling behavior of the column reinforcing bars. In this study, threaded mechanical couplers were developed. The splices are allowed to fail with a sufficient amount of energy dissipation in prior to the main reinforcements. Hence, the repair of structures after an earthquake event will be simplified by replacing new couplers. The coupler thicknesses and the gap lengths between the coupler and threaded bars were set to be the main parameters in this study. The couplers are produced from SS400 steel and the threaded bars are made from 20-mm-diameter steel bars with the SD50 grade. The coupler thickness is varied from 3.0 mm to 4.5 mm and the coupler gap length is varied from 30 to 102 mm, equivalent to 1.25 to 4.25 times coupler thread size, 24 mm. In compression, the mechanical splices exhibit higher compressive strength with more post-buckling resistance than the plain control bar by about 11.8%. In addition, the energy dissipation of the splice is 4.9 times the plain bar. However, in the monotonic tensile test, the ductility of plain bars is approximately 5 times of the splices. The energy dissipation of the mechanical splices increases when the coupler gap length increases. The section analysis of the monolithic and precast columns was conducted. The curvature ductility of the precast columns with mechanical splices is approximately 2-2.5 times the curvature ductility of the RC column. In addition, the difference of maximum moment capacity is 10%. The failure of both RC and precast column is due to the buckling of the bar and splice under compression. The sensitivity study is conducted by increasing the volumetric ratio of lateral reinforcement from 0.77% to 1.78%. The RC column has slightly more curvature ductility than the precast columns. It is because the tension rupture of couplers limits the ductility in columns.