Influence of the concrete structural configuration in the seismic response

Abstract

The recent increase in seismic records in Brazil boosted the publication of NBR 15421 (ABNT, 2006) - Design of Earthquake-Resistant Structures- which requires the seismic loads to be considered in the design due to the dissipation of energy in the inelastic regime structures and seismicity of the Brazilian territory. Many buildings built before the publication of this code were not designed to withstand seismic activity, increasing its fragility and vulnerability to earthquakes of any intensity. Some of these buildings were designed and built with irregular distributions of mass, stiffness or resistance over its height, which can lead to insufficient seismic performance. Therefore, it is essential for engineers to understand the seismic response of structures with irregular distributions of mass, stiffness or resistance along its height, which are referred to in this paper as structures with irregularities. In this sense, the aim of this work is to evaluate the seismic behavior of a reinforced concrete structure with horizontal structural irregularities by observing their influence in the loss of the ability to resist lateral loads and energy dissipation. For this purpose, were used the Equivalent Lateral Force (ELF) Method, Modal Response Spectrum (RSA) Method and Pushover Analysis, described in NBR15421: 2006 [1] standard and the American Standard FEMA 356 [2]. Similarly, the seismic behavior of models using the capacity spectrum method defined in the ATC-40 [3] was calculated. All results were compared with those obtained from a regular structure classified as the reference model or base case, in order to view the various changes caused by irregularities. The proposed study was carried out numerically and the simulations were performed using CSI ETABS Nonlinear (r) v9.5 [4] program. The results show that the ability of the structure to withstand collapse depends on the plasticity of its elements and of the adequate details to permit response without critical loss of strength of the structural system.

Keywords:
seismic analysis; seismic resistant structures; irregular structures