Retrofit of External Beam-Column Concrete Joints with Diagonally Crossed Reinforcement: Experimental and Analytical Investigations

Abstract

Experimental research was carried out regarding the flexural behavior under cyclic reversal loading of six full-scale external beam-column concrete joints cast with plain concrete in the presence of shear reinforcements in the joint regions. The types of shear reinforcements adopted in the joint region were horizontal stirrups and inclined bars. All specimens were designed to fail in the joint region. One had only one stirrup in the joint, another had five stirrups in the joint, and three joints had a fix through diagonal bars of diameters 10, 12, and 14 mm subsequently inserted in inclined holes of diameter 20 mm created in the joint region of the existing reinforced concrete (RC) frames, and the holes were filled with epoxy resin. The experimental results indicate that it is possible to increase the shear strength of joint regions with inclined bars. The increase in shear strength was proportional to the increase in the amount of the steel area of the inclined bars, and the overall performances were comparable in terms of strength to that of well-confined joints. From the analytical point of view, a simple model based on the limit state of concrete crushing with transverse stirrups and inclined bars in both the elastic and the yielded states was developed and verified against the experimental results.