The Performance of Structural Steel Beams Subject to a Localized Fire

Abstract

This paper presents the results from the open flame, localized fire tests conducted on 6.17 m long, simply supported W16×26 beam specimens. The cross sections at midspan (i.e., expected plastic hinge zone) of the beam specimen were directly exposed to the natural gas fire. Two different tests were conducted: (1) firethermal tests to evaluate the effects of the prescribed heat release rates (HRR), provided by the 1 m2 natural gas burner, on the thermal responses of the specimen and (2) structural-fire test to evaluate the fire effects on the overall behavior and the loadbearing capacity of the specimen. The test results indicated that the prescribed heat release rates from the burner affected the heating rate of the specimen. When the HRR-time relationship of the burner followed a step function, the fire-exposed region of the beam specimen was heated essentially linearly with increasing time of fire exposure. When the HRR was set to a target magnitude of 400 kW throughout the test, the fire-exposed region was heated nonlinearly until it reached a steady-state temperature condition. When the beam specimen was subjected to linearly increasing flexural loads at a maintained HRR of 700 kW, combined flexural and lateral torsional failure of the specimen was exhibited. The lateral deformations in the compression flange at the fire-exposed critical sections initiated at 124 ± 5 kN-m, which is 39% of the plastic moment capacity at room temperature. The peak moment capacity was 171 ± 9 kN-m (54 % of the plastic moment capacity at room temperature), while the maximum temperature was 642 ± 28 ˚C at the HRR of 700 kW. The test results from the present study can be used for developing or calibrating analytical models, which can be eventually used for evaluating the performance of structural members subjected to a localized fire