Cyclic test on a precast reinforced concrete column-to-foundation grouted duct connection

Abstract

A full-scale specimen of a column-to-foundation grouted duct connection suited for buildings and industrial structures is tested in cyclic bending combined with axial compression. The positioning of the steel ducts along the sides of the column cross-section allows for using traditional reinforcement cages for the column, with longitudinal bars at both mid-side and corners of the cross-section. Splice length and amount of transverse reinforcement along the splice are defined based on Eurocode 2 provisions for laps of reinforcing bars. A total of 19 loading cycles are carried out, achieving a drift of 5.3% in correspondence of a degradation of 15% of the peak resistance. The shear slip measured at the column-foundation interface results to be smaller than 5% of the deflection. Conversely, to predict accurately the test results, the slip of the projecting bars within their ducts cannot be neglected. It is proposed to take account of this slip by introducing an apparent strain. For the tested specimen, the apparent strain turns out to be equal to the yield strain of the reinforcement. A comparison with a monotonic bending test, previously conducted on the same connection, shows a strongly smaller deformability when the loading protocol is cyclic. Hysteretic energy and drift ductility for the proposed connection are close to those concerning a cast-in-place specimen of comparable capacity, which was described in a recent paper. The test results show an over-strength of 1.4 and a gain in ductility of 1.8 compared with the design values of bending resistance and curvature ductility computed for the cross-section at the column-foundation interface.