Full Session with Abstracts
In its failure investigation of the World Trade Center building 7, the National Institute of Standards and Technology (NIST) showed that the collapse of a 47-story steel frame building could be initiated by cascading failure of composite floor systems subjected to fire. Uncontrolled fires might cause thermal expansion of long-span floor beams which pushed primary girders off from their connections to columns, and eventually led to buckling of some critical columns. Researchers have stipulated that there could be many unknown factors resulting this fire-induced collapse, including thermal expansion of long floor beam spans, asymmetrical framing of floor beams, irregular shape of floors, composite effectiveness of primary girders, and steel connection type.
The NIST has launched a multi-year research project motivated by the need to generate experimental results to study the complex behavior and limit states of real-scale composite floor systems in fire. The test frame suggested for study is a two-story, two bays by three bays gravity frame with each story height of 3.3 m. The test bay measures 6.1 m by 9.1 m. The test bay is hydraulically loaded to service gravity loads as specified in building codes and standards. The fire is produced by natural gas fueled burners with a total maximum capacity of 16 megawatts and is confined to the test bay using enclosure walls. Support columns are protected against severe fire exposure to provide a reliable load path during the test. The first test is a standard fire test to generate baseline data for current U.S. practice. For later test series, a test fire is designed using NIST’s Fire Dynamics Simulator to simulate a fire in an over-loaded office setting up to and beyond a flashover condition, followed by cool-down. Various conventional and advanced measurement tools (thermal imaging, fiber optics technology, and digital image correlation) are used. The measurements include the characteristics of fire in terms of the heat release rates and gas temperatures, the thermal response (temperatures and heat fluxes), and structural responses (displacements, forces, and strains) of composite floor systems.
The experiments conducted at the NIST represent a major advance in real-scale experimentation of steel-concrete composite floor systems under fire and structural loading. The proposed test series capture a broad spectrum of geometric, design, and loading parameters relevant to current construction practice. The temperature and structural response data, measured through heating and cooling phases, will be extremely valuable for validation of computational models predicting structural performance under fire and will provide important steps forward for performance-based standards for fire resistant design of steel buildings.