Numerical simulation of beam-column knee joints with mechanical anchorages by 3D rigid body spring model

There is as yet no clear design method for a rational reinforcement arrangement in a beam-column knee joint with mechanical anchorages because internal stresses, internal cracks, and the failure process have not been well understood. Previous experiments have shown that local reinforcement along the anchorages or the placing of an additional concrete block on the top surface of the joint can prevent anchorage failure due to local stresses from the anchorage plates. In this study, a meso-scale discrete analysis using 3D rigid body spring model (RBSM) is conducted to investigate the failure process and to investigate the effect of these measures. By studying the internal stresses and cracks in a beam-column joint with mechanical anchorages, the failure process is revealed: with bonding along the development length of the anchorages, diagonal cracks begin to occur and these cracks propagate to the top surface of the beam-column joint where they open at the surface, and finally, the opening of diagonal cracks takes place. Local reinforcement placed along the anchorages is shown to have two effects: to increase bond performance along the development length of the anchorages and to restrict the opening of the diagonal cracks. An additional concrete block placed on the top surface of the beam-column joint also has two effects: to increase bond performance along the development length of the anchorages and to restrict crack penetration to the top surface of the joint.