STRENGTH AND DUCTILITY OF JACKETTED R.C. MEMBERS

Abstract

A large number of RC buildings, in India, have been constructed without giving adequate attention to earthquake forces. These buildings require strengthening. Different strengthening strategies can be used for different structures, depending on the particular conditions and performance levels desired. Strengthening of individual beams and columns using RC jacketing is a commonly used strategy for seismic retrofitting. Seismic safety of a structure demands sufficient strength and ductility. RC members such as beams and columns must possess sufficient strength to resist internal forces generated due to earthquake. At the same time, these members should also have adequate ductility which imparts capacity to undergo large inelastic deformation without significant loss of strength. Generally, the earthquake forces encountered by a structure are much higher than those for which it is 'designed. This deficiency can be partially recuperated, by provision of ductility which induces capacity to absorb energy by hysteretic behavior of member. The ductility in a member can be obtained with ductile constituent materials. Since concrete is brittle, it requires confinement, which imparts ductility to it. Quantification of effect of passive confinement on ductility is very important parameter, which helps the designer to predict the behavior of the member under earthquake load. Generally the strength available in a member is more than that for which it is designed. Exact quantification of this over-strength in member is required for capacity design method, which involves choosing a failure mechanism prior to design. In this dissertation strength and ductility of unjacketed and jacketted beams and columns have been studied. Effect of confinement on ductility has been studied using the Kent and Park model of confined concrete. Effect of axial load on ductility of columns has also been studied. Contribution of original section in the strength of a jacketed column. has been studied and it has been found that ignoring the steel in original column does not make much error, in the normal range of reinforcement. Strength of beams and columns for different material strength i.e., Limit State Strength, Characteristic Strength and Most Probable Strength has been studied and overstrength available has been estimated.