Seismic Design of High Strength Concrete Beam Column Joints with Central Vertical Bars and Confinement Bars as Shear Reinforcement

High strength concrete Beam Column Joints are frequently used in seismic regions of North America and Far East for high rise reinforced concrete frames. Seismic loading results in large shear forces in the exterior beam column joints (BCJ) region. The shear resistance of high strength concrete short beams has proved to be equal or less than that of normal strength concrete1. In experimental work on High Strength Concrete (HSC) short beams2 it was demonstrated that Horizontal Central Bars (HCB) significantly improve shear resistance of the tested short beams. The shear span to the effective depth, in a short beam is analogous to the ratio of the beam lever arm to the column effective depth, in a exterior beam column joint21&22 as shown in figure 1.. In this paper a new design equation for predicting the shear strength of monotonically loaded exterior high and normal strength concrete beam column joints is proposed. The influence of Vertical Central Bar (VCB) on the behaviour of beam-column joints are investigated by studying the available experimental results from tests on a number of HSC short beams with Horizontal Web Bars. The main difference of the proposed design equation as compared to the existing equations is that the proposed equation is taking in to account Vertical Central Bar (VCB) reinforcement which has not been taken into account in the xisting design equations.