Code Provisions to Limit Plan Area Projections in RC Buildings with Complex Plan Geometry

Abstract

Buildings with varied plan geometries and projections are influenced by their torsional effects, reentrant corners, and floor flexibility, and they have experienced severe damage or collapse in past earthquakes. Building code provisions do not explicitly define the requirements for plan geometries but rather specify individual upper limits for torsional effects, reentrant corners, and floor flexibility. Reentrant corners in buildings with poor plan geometry are critical aspects that influence their damage or collapse. Code provisions place an upper limit on projection in buildings based on either (1) the percentage of projection using lateral dimensions, ranging from 15% to 40% [e.g., BNBC 2020, GB50011, IS 1893(1), Iran Standard 2800, E.030, SIA 261, Venezuela 58. etc.] or (2) percentage area of projection using gross area, ranging from 5% to 30% (e.g., Eurocode 8 and Venezuela 58). Due to the disparity in the projection ranges specified in different code provisions of various countries, parametric studies have been conducted in this research to identify the acceptable range in a reentrant corner building. The analysis includes H-shaped buildings with a length of projection 10%, 17%, 25%, and 33%, and two other unsymmetric buildings in T and L-shape with 11% and 14% projection ratios. Elastic and inelastic behaviors are studied using modal, response spectrum, nonlinear static and dynamic analyses. An increase in the projection ratio can lead to increased damage or complete collapse of the building. Additionally, it is advisable to restrict the reentrant corners in building code provisions by imposing limitations based on both percentage lateral dimension (A/L≤10%) and area (Ao/Ag≤5%).