Theoretical and Experimental Analysis of GFRP Bridge Deck under Temperature Gradient

The temperature difference between the top and bottom of a glass fiber reinforced polymer (GFRP) composite deck, $\sim 65°\mathrm{C}$ $(\sim 122°\mathrm{F})$ , is nearly three times that of conventional concrete decks $\sim 23°\mathrm{C}$ $(\sim 41°\mathrm{F})$ . Such a large temperature difference is attributed to the relatively lower thermal conductivity of GFRP material. In this study, laboratory tests were conducted on two GFRP bridge deck modules (10.2 and $20.3\mathrm{cm}$ deep decks) by heating and cooling the top surface of the GFRP deck, while maintaining ambient (room) temperature at the deck bottom. Deflections and strains were recorded on the deck under thermal loads. Theoretical results (using macro approach, Navier-Levy, and FEM) were compared with the laboratory test data. The test data indicated that the GFRP deck exhibited hogging under a positive temperature difference (i.e., $T_{\mathrm{top}}>T_{\mathrm{bottom}}$ , heating test; $T_{\mathrm{top}}$ and $T_{\mathrm{bottom}}$ are temperatures at top and bottom of the deck, respectively) and sagging under a negative temperature difference (i.e., $T_{\mathrm{top}}<T_{\mathrm{bottom}}$ , cooling test). Deflections of the deck increased with an increasing magnitude of temperature difference. Typically in the field, tensile strains are induced in the top surface of GFRP deck when exposed to sunlight. Based on the field data, for a temperature gradient of $20°\mathrm{C}$ $(36°\mathrm{F})$ at the deck top and $5.6°\mathrm{C}$ $(10°\mathrm{F})$ at the deck bottom, the induced thermal stress was about $0.6\mathrm{MPa}$ $\left(90\mathrm{psi}\right)$ . However, for a critical temperature gradient of $39°\mathrm{C}$ $(70°\mathrm{F})$ the induced thermal stress on GFRP decks is $6.2\mathrm{MPa}$ $\left(900\mathrm{psi}\right)$ .