Improvement of the earthquake resistance of R/C beam-column joints under the influence of P-△ effect and axial force variations using inclined bars

Abstract

In this study, theoretical and experimental results are presented which were obtained during an investigation of the influence of the <TEX>$P-{\Delta}$</TEX> effect that was caused by the simultaneous changing of the axial load P of the column and the lateral displacement <TEX>${\Delta}$</TEX> in the external beam-column joints. The increase or decrease of <TEX>${\Delta}$</TEX> was simultaneous with the increase or decrease of the axial compression load P and caused an additional influence on the aseismic mechanical properties of the joint. A total of 12 reinforced concrete exterior beam-column subassemblies were examined. A new model, which predicts the beam-column joint ultimate shear strength, was used in order to predict the seismic behaviour of beam-column joints subjected to earthquake-type loading plus variable axial load and <TEX>$P-{\Delta}$</TEX> effect. Test data and analytical research demonstrated that axial load changes and <TEX>$P-{\Delta}$</TEX> effect during an earthquake cause significant deterioration in the earthquake-resistance of these structural elements. It was demonstrated that inclined bars in the joint region were effective for reducing the unfavourable impact of the <TEX>$P-{\Delta}$</TEX> effect and axial load changes in these structural elements.