Computational & Technology Resources
an online resource for computational,
engineering & technology publications
PROCEEDINGS OF THE EIGHTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Simulations of Fire Temporal Thermal Behaviour of Fibre Reinforced Polymer Bridge Decks
W.I. Alnahhal1, M. Chiewanichakorn1, S. Alampalli2 and A. Aref1
1Department of Civil, Structural and Environmental Engineering, University at Buffalo, State University of New York, Buffalo, United States of America
W.I. Alnahhal, M. Chiewanichakorn, S. Alampalli, A. Aref, "Simulations of Fire Temporal Thermal Behaviour of Fibre Reinforced Polymer Bridge Decks", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Eighth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 8, 2006. doi:10.4203/ccp.83.8
Keywords: bridge deck, fibre reinforced polymer, temporal, thermal, finite element method, fire resistance limit.
The United States has one of the largest highway networks in the world. The efficiency and safety of this network plays essential role for the continued economic health of the country. Recently, attention has been focused on Fibre Reinforced Polymer (FRP) as an alternative material for bridge construction. A significant concern in the applications of FRP composite materials is the possibility of an accidental fire. Fire threat can come from many sources at various severity levels. On a bridge, fire may be caused by an oil truck involved in an accident resulting in an oil spill.
Recently, the first FRP deck has been installed to a state highway, located in New York State, to improve the load rating of a 60-year old truss bridge over Bentley Creek in Wellsburg, New York. Aref and Chiewanichakorn  conducted failure analysis of Bentley Creek bridge by performing static-stress analysis up to failure. In addition, thermal-stress analysis was also performed under two scenarios, high ambient temperature gradient and burning truck temperature gradient. Whereby a sequential thermal-stress analysis method was employed. A major disadvantage of this approach was that degradation of material was not taken into account. Hence, the results were too conservative.
The post-fire mechanical properties of FRP bridge decks decrease rapidly with increasing heat exposure time and heat flux due to combustion of the polymer matrix and heat degradation . Dao and Asaro  performed experimental and theoretical studies of compressive failure of single skin composites under fire degradation. As the experimental results indicated, most structural properties of E-glass/vinyl-ester composites used in their study were lost as temperatures approach 130oC.
Finite element method (FEM) has been employed to study the structural behaviour of the FRP bridge deck under thermal effects. The finite element model was verified with the field-test results, provided by New York State Department of Transportation (NYSDOT). This study describes the behaviour of the FRP bridge deck on a truss bridge subjected to thermal loading from truck fire incident combined with mechanical loading from commercial trucks. Fully coupled thermal-stress analyses were performed using FEM to determine fire resistance limit, which is defined as the time period from the initiation of fire until the moment that failure occurs at any part of the FRP deck. The effect of damage on the FRP deck due to accidental incidents that involve fire must be investigated to take appropriate remedial measures to predict the damage and possibility of failure.
Coupled thermal-stress analyses showed that FRP decks are sensitive to the effect of elevated temperatures. As compared with steel or concrete bridges, FRP bridges exhibited lower heat resistance. The most critical fire scenario occurred where the FRP top faceskin started to fail after 440 seconds of burning truck on deck. This implies that any FRP bridge under fire incident has to be vacant from people and vehicles quickly, and the damaged region of FRP bridge should be repaired before any further use.
A simple material degradation relationship was employed in this study because of the lack of material test results. This preliminary attempt to model a full scale FRP deck under fire demonstrated that structural fire modelling is possible and more importantly if actual material degradation are available, the simulation would accurately indicate the actual fire resistance limit. Although the most important factors influencing the fire endurance of FRP composites were thermal conductivity of FRP, CTE of composites, type of resin, and type of glass fibre, the combined effect of these factors was not addressed in this study. Phenolic resin had shown a greater tendency to produce delamination during fire incident according to study done by Dodds et al. . More research is required to investigate the effect of these factors on fire endurance of FRP composites.
purchase the full-text of this paper (price £20)