Fire induced progressive collapse of steel building structures: The role of interior gravity columns

Abstract

This paper presents a qualitative assessment of the importance of gravity columns on the stability behavior of a typical mid-rise (10 story) steel building subjected tocornercompartment fires. Two ten-story steel buildings with composite floor systems were designed following the design practices in the US. One of thesebuildings had perimetermomentresistingframes (MRFs) to resist lateral loads while the other buildinghadan interior core of RC shear walls. Effects of gravity loads and fire conditions were simulatedusing the finite element method and numerical analysis techniques.The results from the numerical investigations indicated that gravity columnsgovernthe overall stability of building structures under fire conditions.Gravity columns have the highest utilization ratio, and they are most likelyto reach their critical temperatures first. If gravity column failure occurs, the loadshed or droppedby the failed columnhas to be redistributedto the neighboring columnsto maintain overall structural stability. This axial load redistribution canoccur through the development of alternate load pathsincludingcatenary action. Simulation results indicate that the presence of steel reinforcementin the concrete slabs (inadditionto the minimum shrinkage reinforcement)facilitates uniform redistribution of the axial load dropped by the failed gravity column to the neighboring columns. The additional steel reinforcement improves the flexural and tensile strengths of the composite floor system,which enhances its ability to develop alternate load paths including catenary action in the slab, and thus maintain structural stability after gravity column failure.