Utilização da análise dinâmica linear no estudo do colapso progressivo de edifícios de concreto armado

Abstract

The progressive collapse of a structure occurs due to the propagation of a local damage to a larger part of the structure. Although it is an event with small occurrence rate and very few discussed by Brazilian structural design standards, its occurrence can cause irreparable damages, from total loss of the structure to human losses. With the increasing interest in failure criteria, structural safety and structural performance, the prevention of progressive collapse has become a concern for designers and researchers. Regulators from several countries address three methods of structural analysis: linear static, non-linear static and non-linear dynamic. Because it is a dynamic phenomenon, static approaches do not actually represent the progressive collapse phenomenon. On the other hand, the dynamic non-linear analysis adds the aspects of vibration, damping and the physical and geometric non-linear behavior of the structure, being the most reliable model of the phenomenon. Nevertheless, it is a highly complex analysis, which incurs high computational cost. Thus, this work proposes to assess the feasibility of the use of linear dynamic analysis for verification of the resistance of reinforced concrete structures to progressive collapse. This approach presents an intermediate complexity between the use of linear static analysis and non-linear analysis. We applied the proposed method in a regular reinforced concrete structure, designed by NBR 6118:2014, to evaluate the dynamic behavior of the structure. The impact of considering the occurrence of progressive collapse in a structure designed by the Brazilian code, measuring efforts and displacements was also assessed. We compared the results with a static analysis, but the non-linear behavior of the structure was not considered. In addition, the capacity of the structure to resist progressive collapse using the procedure presented in the GSA guide of the years 2003 and 2013 was adopted as a bibliographic source. The results showed that the structure designed by NBR 6118:2014 was not able to withstand the removal of a column, which would lead to the collapse of the structure. Thus, we resized the structure to withstand the phenomenon of progressive collapse, presenting substantial increase in the concrete volume and reinforcement when compared with the originally designed section. From the obtained results, we can conclude that the Brazilian standard should consider an addition of dynamic effects with more criteria.