National Fire Research Laboratory Commissioning Project

Résumé du livre

This report presents the experimental design and results of a series of localized fire tests on structural steel I-shaped beams. A total of nine tests were conducted in the National Fire Research Laboratory, including thermal tests (Tests 1 through 5) and four-point bending tests at ambient (Test 6) and elevated temperatures (Tests 7 through 9). The specimens were nominally 6.2-m long W16x26 beams made of ASTM A992 steel. Each specimen was vertically supported with either a (i) simple support condition, or (ii) double-angles bolted to laterally braced support columns. The thermally-loaded specimens were exposed to fire generated using a natural gas burner. The burner had an area of 1 m2 and was located 1.1 m below the bottom flange of the beam at midspan. A four-point flexural loading scheme was used to apply concentrated forces at two locations 2.44 m apart around midspan. The recorded data included temperatures, heat release rates from the burner, and structural measurements including forces, displacements and strains. The repeatability of several measurements was evaluated. The test results indicated that the heating rate of the specimen was sensitive to the prescribed heat release rate versus time relationship used in each test. However, the thermal gradient developed in the fire-exposed cross sections of the beam never achieved linearity under the localized fire exposure. When the exposed (bottom) flange temperature was maintained to 616 ℗ʻC, the load-bearing capacity of the simply-supported beam was reduced to 67 % of its room-temperature capacity. When the same simply-supported beam was initially loaded to 67 % of its room-temperature capacity and then exposed to a growing (t-squared) fire, the exposed flange temperature of the beam at failure was 663 ℗ʻC. When the beam specimen was supported by double-angle connections and subjected to the same bending moment, its fire resistance (failure temperature) was decreased to 90 % of that of the simply-supported beam. Regardless of the connection types and fire conditions (steady-state or transient-state fire), the beam specimens failed by lateral torsional buckling with rapidly increasing vertical displacements.