DESIGN METHODOLOGY FOR SEISMIC UPGRADING OF TORSIONALLY UNBALANCED EXISTING R.C. BUILDINGS

This paper presents a design methodology for the seismic upgrading of rotationally sensitive existing R.C. buildings. The first part of the methodology deals with the elimination of the effect of torsional coupling on modal periods and shapes. The second part aims at the modification of the response shape of the building in each direction so as to achieve a near – uniform distribution of interstorey drift along the building height. A three-storey building constructed in the early 1970s with old type reinforcement detailing is selected as a case study. After being assessed, the proposed methodology is implemented and the various steps involved are described in detail. The validity of the proposed methodology was assessed by carrying out inelastic analyses with the use of a three-dimensional finite element model of the retrofitted structure. The results indicate the efficiency of the proposed design methodology for the seismic upgrading of existing torsionally unbalanced R.C. buildings.