STRENGTH AND DEFORMATION CHARACTERISTICS OF R.C. SECTIONS SUBJECTED TO FLEXURE AND AXIAL LOADS

Abstract

The need for ductile behavior of various structural components during any major earthquake has been acutely felt and demonstrated amply during several seismic events. Although it is preferable to dissipate seismic energy by post-elastic deformations in beams, column hinging cannot be avoided entirely in most buildings during severe earthquakes. To achieve sufficient ductility in columns, their potential plastic hinge regions should be reinforced with appropriately designed and detailed longitudinal and lateral confining steel. Although various building codes have specified design equations which can be used to determine the requirement of confining steel in these potential plastic hinge regions, but these equations have some limitations. Most of the equations are valid for normal strength concrete with low axial load coefficient and low curvature ductility demands. These design equations do not incorporate all factors affecting the requirement of the confining steel in potential plastic hinge regions of reinforced concrete columns such as curvature ductility demand, axial load level, mechanical reinforcement ratio, yield strength of lateral steel and grade of concrete. In this thesis the deformation characteristics of RC sections under flexure and axial load were investigated using the program XTRACT. Finally, an effort has been made to develop confining reinforcement requirements for sections under flexure and axial load for a desired level of curvature ductility. The experimental investigation was planned to fully establish the structural response of confined concrete columns. The experimental investigations involved; a) casting and testing of unconfined NSC specimens (10 cylinders of 100mm X 200mm size) and b) confined concrete columns (10 square columns of size 200mm X 200mm X 800mm) under monotonically increasing axial compression. While the test variable of the study on confined concrete is spacing of the transverse reinforcement. For all the confined specimens in general, the reduction of spacing of lateral steel increased the strength and ductility values. A marginal gain in the strength and appreciable increase in the deformability is observed. It has been concluded that the proposed analytical model provide a good correlation between predicted and experimental results.