Numerical Assessment of the Fire Behavior of Steel Posttensioned Moment-Resisting Frames

Abstract

Steel self-centering moment-resisting frames (SC-MRFs) are a class of low-damage seismic-resistant structural systems, which use posttensioned high-strength steel bars to provide self-centering capability and yielding or friction-based devices that are activated due to rocking in the beam-column interfaces, to dissipate seismic energy. Until now, research has mainly focused on the assessment of the earthquake resilience of SC-MRFs, while their fire behavior is unknown. To fill this gap in knowledge, this paper studies the fire behavior of different versions of a five storey SC-MRF. The first research objective is to reveal the main factors that affect the behavior of the SC-MRF at elevated temperatures. For that purpose, three-dimensional (3D) finite-element models are developed, and transient thermal/structural analyses are conducted to simulate the behavior of the SC-MRF under fire conditions. The second objective is to study how specific structural details of the beam-column connections affect the fire resistance of the SC-MRF. For that purpose, the structural details of the connections are modified and/or are considered fire protected. Based on the results of parametric analyses, suggestions for the enhancement of the fire resistance of SC-MRFs are provided. In all the transient thermal/structural analyses, the thermal problem is solved by adopting the closed cavity option, which allows simulating the radiative transfer of heat between surfaces during fire. The effectiveness of such an approach was validated through direct comparison with the provisions of Eurocode as well as with existing experimental data from fire tests on steel beams.