Post-Fire Behavior of FRP Composites

High Temperature Performance of Polymer Composites, First Edition. Yu Bai and Thomas Keller. 

Fire endurance experiment investigation was introduced in Chapter 7, where full-scale beam and column specimens were subjected to true flaming heat (ISO fire curve). The post-fire performance of the survived specimens is evaluated in this chapter and further compared with the results from the proposed modeling approach. 

Pre-Fire, Fire Exposure, and Post-Fire Load-Deflection Responses 

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In this chapter, the post-fire behavior of FRP composites was evaluated and modeled on the stmctural level. Results from the models compared well with results from fuU-scale post-fire experiments on cellular GFRP beam and column specimens that had been subjected to mechanical and thermal loading up to 120 min with inclusion of different thermal boundary conditions. On the basis of the previously proposed thermal and mechanical response models, existing approaches for post-fire evaluation can be applied. Predicted temperature profiles and the conversion degrees of decomposition can be used to estimate the post-fire stiHhess from existing two- and three-layer models. The borders between different layers can be determined either by a temperature criterion or a RRC criterion. 

The recently developed models to predict time and temperature-dependent material properties and post-fire properties showed good agreement with the experimental results. On the basis of the proposed models, the post-fire stiffness of FRP composite materials can be predicted before fire exposure. As a result, the post-fire behavior can be predesigned based on the functionality and importance of the stmcture. 

In this book, it is intended to provide the reader with useful and comprehensive experimental data and models for the design and application of FRP composites at elevated temperatures and fire conditions. The progressive changes that occur in material states and the corresponding progressive changes in the thermophysical and thermomechanical properties of FRP composites due to thermal exposure will be discussed. It will be demonstrated how thermophysical and thermomechanical properties can be incorporated into heat transfer theory and structural theory. The thermal and mechanical responses of FRP composites and structures subjected to hours of reahstic fire conditions will be described and validated on the full-scale structural level. Concepts and methods to determine the time-to-failure of polymer composites and structures in fire will be presented, as well as the post-fire behavior and fire protection techniques. 

The post-fire elastic modulus, E, can be estimated from Eq. (8.2). The recovered elastic modulus for the DuraSpan material used was 88% of Eg, which was obtained from two-mn DMA, see Section 8.2.3. It should be noted that such a modulus recovery is a general behavior for FRP composites cooled down from glass transition, but before decomposition. For comparison, another pultraded GFRP material (from FiberHne, Denmark) is shown in Figure 8.16 [14], which exhibited a recovery to 96% of the initial value. 

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