Localized Heating of Post-tensioned Concrete Slabs Research Program

Abstract

Performance-based design is the growing paradigm in contemporary structural engineering, and structural fire safety engineering is no exception. Advocates of performance-based methodologies seek to adopt sophisticated fire strategies tailored to individual building needs. In particular, these strategies are being applied to optimized reinforced concrete buildings, including post-tensioned (PT) structures. The current understanding of prestressing steel behavior based largely on outdated research that fails to properly account for material property changes at elevated temperatures. Furthermore, real fires in real PT concrete buildings have the potential to induce unique failure mechanisms that cannot be observed or accounted for using standard fire tests, as seen through case studies of real fires (see Chap. 3). Current modelling tools used to establish structural fire safety engineering strategies lack realistic experimental validation and verification, leading to the development of potentially unconservative performance-based strategies for PT concrete buildings. In order to enable credible performance based design of PT concrete buildings current modelling capabilities need to be improved, through the analysis of densely instrumented experiments, which incorporate as many relevant structural properties (post-tensioning, continuity, restraint, realistic scale, unbonded reinforcement, etc.) of as-built PT construction as possible. This need is partly addressed in the current chapter by presenting experiments on three 3-span continuous, restrained PT concrete slabs (slab strips). The slabs were put under sustained service loading and exposed to severe localized heating using radiant heaters. This chapter considers an extensive recent experimental program conducted for this book over the years 2011–2013. This experimental program compliments those discussed in previous chapters. Three novel large-scale tests on locally heated, continuous PT concrete slab strips are detailed. In real and contemporary multiple bay and continuous unbonded post tensioned (UPT) concrete slabs exposed to fire, structural actions may play significant (often inter-related) roles influencing the response of this construction. This response is studied and explained herein.

If we attempt to develop the fire endurance of a construction system in actual buildings under fire conditions we would not obtain a single-valued answer, but rather we would have to measure a range of performance levels depending upon methods of structural framing existing in a single building as well as the methods of structural framing of any and all buildings into which the construction system under consideration could be incorporated….

—RW Bletzacker (1967)