A series of compartment fire experiments was conducted on long-span steel-concrete composite floor beams designed and constructed following U.S. building codes and standards. The test program consisted of five 12.8 m long composite floor beam specimens with various end support conditions. Each specimen was constructed as a partially-composite beam consisting of a W18×35 steel beam and an 83 mm thick lightweight concrete slab cast on top of 76 mm deep ribbed steel decking units. Test variables included two types of simple shear connections (shear-tab and welded/bolted double-angle connections) and the slab continuity over girders. One specimen with the double-angle connections at the ends was tested at ambient temperature and the remaining four specimens were tested under simultaneous mechanical and fire loading. This report, Part 1, presents details of the test setup, specimens, design basis of fire loading, instrumentation, and the behavior of the composite beam with double-angle connections at ambient temperature. The ambient temperature test indicated that the composite beam specimen failed by a shear stud near the west end, followed by concrete breakout failure and yielding of the steel beam. The measured moment capacity was approximately 80% of the calculated flexural strength. The double-angle connection at the west end failed by weld fracture, which caused collapse of the composite beam. The ambient behavior of the composite beam specimen presented herein will serve as a baseline to compare with the composite beam assemblies tested under combined mechanical loads and fire exposure, which are presented in a subsequent report; Part 2 (Choe et al. 2019). The datasets obtained from these tests provide technical information to advance performance-based design of composite floor assemblies in steel-framed buildings subject to fire.

Structural fire protection design in the United States is based on prescriptive fire-resistance ratings of individual load-bearing elements which are derived from standard fire testing, e.g. ASTM E119. In standard fire testing, a custom-built gas furnace is traditionally used to heat a test specimen by following the gas temperature-time curve prescribed in the ASTM E119 standard. The span length of the test specimen seldom exceeds 6 m due to the size limitations of available furnaces. Further, the test specimen does not incorporate realistic structural continuity. This paper presents a basis for designing an ASTM E119 fire environment in a large compartment of about 10 m wide, 7 m deep and 3.8 m high constructed in the National Fire Research Laboratory of the National Institute of Standards and Technology. Using the designed fire parameters, a full-scale experiment was carried out on December 20, 2018. The measured average upper layer gas temperature curve was consistent with the E119 fire curve. The maximum difference between the measured curve and the E119 fire curve towards the end of the test was about 70 °C (7%). The study indicates that by proper design and control, the time-temperature curve for the standard fire testing may be approximated in a real compartment. The experimental method suggested in this paper would allow to extend the application of the standard fire testing to large-scale structures not limited by the size of furnaces, to experimentally evaluate the thermally-induced failure mechanism of structural systems including connections and frames, and to advance fire protection design methods.

Purpose-The purpose of this paper is to propose a method for Hybrid Fire Testing (HFT) which is unconditionally stable, ensures equilibrium and compatibility at the interface and captures the global behavior of the analyzed structure. HFT is a technique that allows assessing experimentally the fire performance of a structural element under real boundary conditions that capture the effect of the surrounding structure. Design/methodology/approach-The paper starts with the analysis of the method used in the few previous HFT. Based on the analytical study of a simple one degree-of-freedom elastic system, it is shown that this previous method is fundamentally unstable in certain configurations that cannot be easily predicted in advance. Therefore, a new method is introduced to overcome the stability problem. The method is applied in a virtual hybrid test on a 2D reinforced concrete beam part of a moment resisting frame. Findings-It is shown through analytical developments and applicative examples that the stability of the method used in previous HFT depends on the stiffness ratio between the two substructures. The method is unstable when implemented in force control on a physical substructure that is less stiff than the surrounding structure. Conversely, the method is unstable when implemented in displacement control on a physical substructure stiffer than the remainder. In multi degrees-of-freedom tests where the temperature will affect the stiffness of the elements, it is generally not possible to ensure continuous stability throughout the test using this former method. Therefore, a new method is proposed where the stability is not dependent on the stiffness ratio between the two substructures. Application of the new method in a virtual HFT proved to be stable, to ensure compatibility and equilibrium at the interface and to reproduce accurately the global structural behavior. Originality/value-The paper provides a method to perform Hybrid Fire Tests which overcomes the stability problem lying in the former method. The efficiency of the new method is demonstrated in a virtual HFT with 3 degrees-of-freedom at the interface, the next step being its implementation in a real (laboratory) hybrid test.

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