Restraint mechanisms in precast concrete double-tee floor systems subjected to fire

This paper examines restraint mechanisms in precast, prestressed concrete structures under fire loading. The focus of the study is a prototype precast, prestressed double-tee beam typically used for precast concrete parking structures. The study examines idealized (simple and fixed) single-span restraints and three realistic restraint mechanisms: multiple-span successive spans gravity support elements (for example, spandrels or inverted-tee girders) flange connectors The analytical approach included nonlinear heat transfer analysis of temperatures throughout a double tee at different fire durations and nonlinear structural analyses of restraint forces and flexural strengths. The strengths were found to vary significantly with boundary condition and fire duration. The strength is significantly less when only the flange is restrained compared with when only the web is restrained and when the entire cross section is restrained. The flexural strength of a beam restrained by spandrels or inverted-tee girders is only slightly greater than that of a simply supported beam. Finally, the strength of a beam restrained by any practical number of flange connectors is only slightly higher than that of a simply supported double-tee beam.