POST CRACKING BEHAVIOUR OF R. C. INFILLED FRAMES

Abstract

The unabated migration of rural population to urban areas, especially to the metropoliton cities, and the sky rocketting land prices have made the vertical cons-truction almost a compulson. Reinforced concrete rigid frame is the most commonly employed structural system for the constitution of low rise buildings. In the traditio-nal design of such frames only biSe frame is designed and the effect of infill panels .s and partition walls etc. m disregarded. Studies (1) have shown that inplane stiffness of the frame increases significantly due to beneficial interaction between the frame and the infill. The researches in this field in, the last 2-3 decades have provided many different formulations ranging from approximate equivalent strut method$ to linear and non-linear finite element method for the analysis of such a structure. Recently (2) the influence of the different interface bonding material on the overall behaviour cif Muffled frames has also been investigated. In the .present dissertation a non-linear finite element formulation has been presented to predict the complete response of infilled R.C. frames. Three different types of elements namely 8 noded isopararnetric element for the modelling of concrete member and masonry Milli, a 3 noded bar element to model reinforcing steel and a six noded interface element to simulate interface.boundary have been used. An existing finite element program for linear analysis of Muffled frames have been modified to include bar elements for the discrete modelling of reinforcing steel, and to include effect of material non-linearity due to cracking/crushing of concrete and masonry and yielding of steel. The effect of interface failure due to shear or tensiOn has also been included. The progr.am written in Fortran IV used a mixed incremental iterative procedure for the non-linear analysis to economise on computer .time. In order to validate the proposed formulation, two models double storeyed infilled frames have been tested in the laboratory up to near ultimate load.. Different interface bonding materials namely cement slurry and epoxy sand mortar have been used to study their influence on the ultimate load and the general behaviour in the pre and post-cracking phases. On the basis of the comparison of the experimental results and the theoretical results using the proposed program, it is established that complete load deflection behaviour and zones of distress can be predicted satisfactorily