The development of precast concrete beam-to-column connections under static, cyclic and sustained loading

This study investigates the experimental and theoretical behaviour of an exterior precast concrete beam-column (PCBC) connection. The experimental test specimens consisted of a precast reinforced concrete beam, a precast reinforced concrete column, interlocking bars and cast-in-place (CIP) concrete. The aim of this study was to develop a ductile exterior PCBC connection, which will be comparatively simple to construct on site and be suitable for building structures in seismic zones. Five PCBC connection specimens (namely: P1, P2, P3, P4 and P5) were tested. Two principal factors were investigated: the applied loadings and the steel fibre content contained in the CIP connections. Specimens P1, P2 and P5 contained no steel fibre (Vf = 0%) in the CIP concrete. Specimens P3 and P4 contained 0.5% and 1% of steel fibre content in their CIP concrete, respectively. Specimen P1 was subjected to static loading. Specimens P2, P3 and P4 were subjected to quasi-static loading. Specimen P5 was subjected to long-term loading. All specimens had identical reinforcement details and dimensions. The beam column joint was designed based on ACI 318-2011 Sec. 21, which is proposed for earthquake-resistant structures. The connection performance was evaluated in terms of the load carrying capacity, energy dissipation, stiffness and crack propagation. The results showed that the exterior PCBC connections failed in flexure when they were subjected to static and quasi-static loadings. Plastic hinges formed in the end of the beam (adjacent to the column); these satisfied the seismic resistant moment resisting frame requirements. The PCBC connection had 67% of the joint rigidity in comparison with a monolithic beam-column joint; this led it to have less secant stiffness and greater beam deflection. In spite of this the connection satisfied the acceptance criteria stated in ACI 374.1.-05. The rotation of the beam-column connection did not stop when the initial loading was applied; it continued during sustained loading, which generated a bigger deflection of the PCBC connection. A modification of the ACI long-term deflection equation has been proposed taking into account 67% of the joint rigidity. As a result of the modification the theoretically predicted deflection was found to be in agreement with that measured in experiments. The steel fibre contained in the CIP connection delayed the onset of cracking and slowed down the rate of crack propagation, causing shorter cracks in the joint core and the beam core. Furthermore, SFRC improved the energy dissipation of the connections. A finite element analysis was performed on an exterior PCBC connection using MIDAS FEA software under static loading. The results showed that the model could predict the load-deflection relationship until the yield point under static loading. A further finite element analysis was performed on an interior PCBC connection. The results showed that the interior PCBC connection behaved in a similar manner to a conventional reinforced concrete member under static loading.