Investigating the behaviour of steel framed-tube and moment-resisting frame systems exposed to fire

Abstract

This paper investigates the behaviour of two popular structural systems subjected to overheating and column removal cases, which may follow fire incidents. A typical 15–storey steel building is designed with two types of structural system framed-tube and moment-resisting frame. The nonlinear behaviour of these structures under different fire scenarios is investigated using OpenSees Software. The results indicate that deflection of heated beams is insignificant below 400 °C but after that, degrading mechanical properties of steel material leads to large deflection and runaway of heated beams at temperatures below 600 °C. Also, heating the beams of structures initially induces large axial forces in the beams due to restraints on thermal expansion. Thermal expansion of heated floors induces large horizontal displacement and consequently causes additional bending moments in the exterior column. So columns reach their elastic limit at the early stages of fire. Columns of the framed-tube system reach their elastic limit at lower temperatures (130 °C) but fail at higher temperatures (380 °C) compared to columns of the moment-resisting frame system (210 °C). In addition, the lower storey and interior columns are more vulnerable to progressive collapse and fail at lower temperatures (330 °C) due to carrying more gravity loads. In most fire scenarios, beams and columns of framed-tube systems fail at higher temperatures and perform well in the fire than moment-resisting frame systems. In column removal scenarios, mid-span displacement of the heated beam increases significantly, leading to downward movement of upper stories. Also, column removal in the framed-tube system is more destructive than in the moment-resisting frame system. In general, in both structural systems, column removal scenarios, which may follow fire, induce more damage to the structures than general temperature rise in considered fire scenarios.