Experimental study of prefabricated RC column-foundation assemblies with two different connection methods and using large-diameter reinforcing bars

Abstract

Prefabricated reinforced concrete (RC) column-to-foundation connections are typically located at the critical region of the columns and are subjected to a combination of large compression and bending deformation under earthquake actions. The seismic behaviour of these connections affects the structural behaviour of precast concrete frames as a whole. The prefabricated column-to-foundation connections using grouted sleeves (PC-S) and grouted corrugated ducts (PC-C) were two typical connections. However, up to now the researches on the seismic performance of the two typical connections are mainly concentrated on small-diameter reinforcing bars used in the connections. The use of large-diameter high-strength reinforcing bars in the large size precast columns has clear advantages in precast structures as it helps improve the construction efficiency due to a reduced number of connected longitudinal bars and less congestion of the reinforcing bars. In this study, two full-scale prefabricated column-foundation assemblies with different connection methods, designated as PC-S and PC-C, respectively, along with one cast-in-place reference specimen, were prepared and tested under quasi-static cyclic loading. In all three specimens, large-diameter high-strength reinforcing bars were adopted as the longitudinal reinforcing bars. The test results showed that both types of connections exhibited similar strength as compared to the cast-in-place specimen. In specimen PC-S, buckling of the longitudinal bars and rupture of stirrups at the top of the grouted sleeves were observed, and this led to lower ductility with an ultimate lateral drift ratio of 4.5%. In specimen PC-C, a more pronounced pinching behaviour was observed after a lateral drift ratio of 2%, which was due to significant bond-slip displacements of large-diameter high-strength longitudinal bars in the overlap region. The three specimens exhibited different plastic hinge mechanisms at the column bases as demonstrated from the measured steel strains, cracking patterns and failure modes. Based on the experimental results, further improvements of using large-diameter high-strength reinforcing bars in the two types of prefabricated column-to-foundation connections are recommended.