Investigation of prestressed hollow core concrete slabs at elevated temperatures

This paper investigates the behaviour and design of full-scale prestressed hollow core one-way spanning concrete slabs under fire conditions. The hollow core slabs were simply-supported and reinforced with 9.3mm nominal diameter seven-wire mono-strand tendons. Nonlinear 3-D finite element models were developed for the analysis of prestressed hollow core concrete slabs at elevated temperatures. The finite element models were based on a nonlinear finite element modelling approach adopted by the author over the last eight years for the analysis of different structures under fire conditions. The mechanical and thermal material nonlinearities of the concrete and prestressing tendons have been carefully inserted into the model. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the prestressed hollow core slab. In addition, gap elements were used to model the thermal behaviour of the hollow cores, which ensures, for the first time, correct temperature distributions in the regions surrounding the cores. The temperature distribution throughout the prestressed hollow core concrete slab, time-deflection behaviour, time-longitudinal expansion and failure modes of the slabs were predicted by the model and verified against test data. A parametric study was conducted to investigate the effects on the global structural behaviour due to the change in the prestressed hollow core slab geometries, hollow core shapes, load ratios during fire and different fire curves.