SEISMIC EFFECTS OF CORNICE PROJECTION IN MASONRY-INFILL REINFORCED CONCRETE BUILDINGS IN BHUTAN

Abstract

Bhutan is located in utmost active seismic zone in the belt of the Himalayan region. However, there is a prevailing architectural requirement of cornice projections away from the perimeter columns at each floor proportional to the floor level to increase floor area and retain Bhutanese architectural style. This irregular projection with thick solid brick walls resting at the edge of cantilever projection affects the structural response during a strong earthquake. To date, there is not adequate investigation on the effects of such cornice projection on seismic performance of buildings. In this study, Nonlinear Response History Analysis (NLRHA) using vertical ground acceleration of relevant earthquakes was performed to assess performance of a three-dimensional three-story typical school building, which represents stock of structures in Bhutan. This study compares response parameters of the bare frame, in-filled frame, and six models with different projection lengths to comprehend the collective effects. Relevant global and local response parameters such as lateral story displacements, inter-story drifts, internal force demands, vertical deflections and its amplifications were assessed. The results indicate that bending moment and vertical deflection of the cantilevered beams are significantly affected due to the presence of cornice projection under vertical acceleration. The bending moment is amplified by a factor of 1.65, whereas the vertical deflection is amplified by a factor of 1.80, compared to the effect of gravity load alone. Based on typical design and acceptance criteria of ACI codes, the cornice projection length should not exceed 1.4m.