Seismic behaviour and size effect of column base joints with inverted exposed grouted sleeves

To solve the problems of invisible grouting processes and grouting defects in the vertical connection of traditional grouted sleeves, four inverted exposed grouted sleeve (IEGS) column base joint specimens are designed and manufactured. Experiments on the specimens under low cyclic loading with constant axial compression ratios are then conducted. The effects of different section sizes and different secondary pouring materials on the seismic performance of the IEGS column base joints are studied. The results show that the failure mode of all the columns is bending, the plastic hinge moves up to the top of the grouted sleeves, and the longitudinal rebar inside the grouted sleeves is not pulled out. With an increase in the section size of the column, the bearing capacity of the specimen is greatly improved, and the hysteretic curve is more pinched. The yield load and peak load are increased by 9.97% and 6.31%, respectively, after the concrete is replaced by a high strength (f(cu) = 67.60 MPa) cement-based grouting material in the secondary pouring area. The relative nominal flexural strength and energy dissipation coefficient exhibit obvious size effects by decreasing as the column size and the strength of the secondary pouring materials increase. In addition, IEGS column base joints are simulated using the finite element analysis software ABAQUS. The analytical study is conducted and compared with the experimental results, which is essentially consistent with the experimental data. According to the comprehensive analysis of the test and simulation results, the stress of the rebar is mainly concentrated in the plastic hinge; thus, it is appropriate to strengthen the stirrup at the sleeves and extend the stirrup densification area appropriately.