Experimental evaluation of composite floor assemblies under fire loading

Emily Irene Wellman, Purdue University

Abstract

The use of composite floor systems is a common practice in the construction of steel structures due to structural and economic advantages. Research performed abroad into the behavior of these systems under fire loading within a complete structure has indicated a potential for cost savings in construction by leaving secondary steel beams without fire protection. The goal of this research was to determine the structural behavior of U.S. designed composite beam floor systems subjected to both gravity and thermal loading through experimental testing, specifically focusing on the failure mechanisms of the components of the system (the connection, composite beam, and composite girder). This document presents the response of these systems with both protected and unprotected beams under both standard and realistic fire loading and considers two different types of beam-to-girder shear connections. Three specimens were tested, each 3.96 m by 4.57 m in plan with beam-to-girder shear connections. Composite beams were W10X15 (W250X25.3) with W12X16 (W310X23.8) supporting girders. Beams and girders acted compositely with a 38 mm deep ribbed steel deck composite with 64 mm of lightweight concrete. Specimens were tested with two different shear connection types, under design and realistic fires, and with and without fire-protection on the interior beams. Through testing, no failure was observed in the shear studs. The removal of fire-protection from the interior beam increased deflections at the beam mid-span, but only nominally affected the temperatures in the protected girders and connections. The replacement of the design fire conditions with slower cooling conditions caused slower cooling of all elements in the system and increased permanent deformations in the girders. Although the slab transferred a significant portion of the shear from the beam to the girders, it was not able to support the steel members once they had lost their stiffness, indicating that membrane action was not at play in the behavior of these slab systems.

Degree

M.S.C.E.

Advisors

Varma, Purdue University.

Subject Area

Civil engineering

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