Linear and Nonlinear Static Analysis for Assessment of Progressive Collapse Potential of Multistoried Building

Abstract

Explosions almost instantaneously damage the structures. The direct action of the high intensity blast on the exposed surfaces of the building may causes damage to the primary structural components like columns and structural walls. Damage can be in form of loss of non-structural element, damage to structural components, and collapse of structural element leading to progressive failure of part or whole building. The failure of a member in the primary load resisting system leads to redistribution of forces to the adjoining members and if redistributed load exceeds member capacity it fails. This process continues in the structure and eventually the building collapses. This phenomenon is referred as progressive collapse of the structure. When a multi storey building is subjected to sudden column failure, the resulting structural response is dynamic, typically characterized by significant geometric and material nonlinearity. Analysis methods used to evaluate the potential of progressive collapse varies widely; ranging from the simple two dimensional linear elastic static procedures to complex three dimensional nonlinear dynamic analyses. In the present study the demand capacity ratios of reinforced concrete four storey and ten storey frame structure are evaluated as per GSA guidelines. The linear static and nonlinear static analyses are carried out using software SAP2000. For progressive collapse analysis, a nonlinear static analysis method employs a stepwise increment of amplified vertical loads which can be referred as vertical pushover analysis. The demand capacity ratios found using linear static analysis at critical locations are compared with the hinge formation obtained from nonlinear static analysis. Comparison of linear static and nonlinear static analysis reveals that hinge formation starts from the location having maximum demand capacity ratio calculated from static analysis.