Impact of Layout and Height on EBFs under Fire: AI Optimization Insights

Abstract

Considering the response of structures to intense heat is crucial when designing for potentially life-threatening fires, such as wildfires and postearthquake fires. The attention paid to structural thermal reaction following several disasters has increased in recent years. Eccentrically braced frame (EBF) structures in seismic conditions are widely used for many buildings because of their excellent performance in seismic areas. However, little research has been conducted on their behavior during fires, mainly due to the complicated nonlinear behavior of link beams. OpenSees is a software framework for developing applications to simulate the performance of structural systems subjected to earthquakes and fires. Using this software and the elements and materials developed for it, modeling the nonlinear behavior of the link beam in EBFs is possible. For the purpose of this paper, 36 different buildings containing a varying number of bays and stories were analyzed under extreme thermal conditions to provide adequate data for the hypothesis. First, all the buildings are modeled in three dimensions, and all members of the structure are designed. Then, the final structures are analyzed under the applied loads, and the nodal forces are calculated. Then, one braced frame from each building is modeled in OpenSees and analyzed under gravity loads and two fire scenarios. Heat transfer analysis was used to calculate the temperature distribution in members’ sections to increase modeling accuracy. Steel has high thermal conductivity relative to that of concrete. For the consideration of extreme events, heat transfer analysis was completed using steel beams supporting a concrete slab. The results show that the number of bays does not directly correlate to structures resistant to fire; however, the number of stories does. As a structure increases its floor count, its behavior in a fire improves. Observations showed that braced bays with at least one or more adjacent braced bays remained stable as fire compromised a single bay.