Assessment of Redundancy Factors for the Seismic Design of Special Moment Resisting Reinforced Concrete Frames

Abstract

A parametric study devoted to assess the impact of increasing the structural redundancy in ductile reinforced concrete (RC) moment framed buildings is presented. Among the studied variables were the number of stories and the number of bays. Studied models were 4, 8, 12 and 16-story frames with a story height h=3.5 m (11.5 ft). Nonlinear static analyses were used to evaluate numerically redundancy factors. Based on the results of this research and previous studies reported in the literature, it can be concluded that it is justified to account directly structural redundancy in the design by using a redundancy factor, as proposed and done in some international building codes.

Redundancy Factors for the Seismic Design of Ductile Reinforced Concrete Chevron Braced Frames

“…As shown by Tena-Colunga and Cortés-Benítez (2015), lack of redundancy could lead to a premature structural collapse due to fail of one or some specific elements. Despite of the poor seismic performance of weakly-redundant buildings observed during past earthquakes, this practice is still used in regions of Mexico with high seismic risk (Fig.…”

“…Therefore, it is clear the need to develop clear and easy to apply global code design parameters in the design process, in order to promote a good structural behavior when buildings are subjected to strong earthquakes and prevent the collapses observed in past earthquakes. As commented by Tena-Colunga and Cortés-Benítez (2015), despite the acquired knowledge over years, in the last two decades the impact of redundancy has been oversight in building codes and in the seismic design of structures. As previously commented, there are just few research studies available where the impact of redundancy has been evaluated.…”

“…Results obtained were compared with the currently proposed values in the Manual of Civil Structures (MOC-08), a model code of Mexico. In this study, the adopted definition of redundancy is based on the proposal by Tena-Colunga and Cortés-Benítez (2015), in which redundancy refers to a characteristic of structures in which multiple continuous paths of resistance to loads exists, which causes a high degree of static indeterminacy, and has impact on both deformation capacities and strength. …”

“…According to Liao and Wen (2004) and Tena-Colunga and Cortés-Benítez (2015), a reliability/redundancy factor for the seismic design of buildings, ρ, was first introduced in NEHRP 97, UBC 1997, and IBC 2000. This factor was used as a multiplier of the lateral design earthquake load and took into account only the floor area and maximum element-story shear ratio in its first version.…”

“…Obviously, this philosophy would lead buildings to experience damage during the occurrence of a strong earthquake, and that the earthquake-resistant structural system must be able to accommodate without experiencing collapse (collapse prevention limit state). As it is well known, redundancy contributes to an adequate structural performance, since as the number of resisting elements located in a given direction increases, better plastic stresses redistribution is allowed, contributing to develop a stable collapse mechanism (Tena-Colunga and Cortés-Benítez 2015).…”