Effects of Bridge Deck Thickness on Properties and Behavior of Bridge Decks

About two years ago, the Alabama Department of Transportation (ALDOT) increased its minimum bridge deck thickness to 178 mm (7 in.), and thus ALDOT’s deck thicknesses now range from 178 to 197 mm (7–7.75 in.). Even with the upgrade, ALDOT still utilizes the thinnest decks in the country. Thicker bridge decks are stiffer, stronger, and should provide a longer service life; however, they cost more and require a stronger and more costly support girder system. All of the parameters investigated in the parameter sensitivity study, with the exception of two (deck unit weight and initial cost), support increasing Alabama’s minimum bridge deck thickness. An increase in thickness from 178 to 203 mm (7–8 in.) would cause the deck unit weight to increase 287–575 N/m² (6–12 psf), depending on whether the concrete is added to the top or the underside of the deck. This would increase the cost of the bridge deck around $2.15/m² ($1.80/yd²), and would translate into an increase in deck initial cost of around 2–3%. However, increasing the deck thickness from 178 to 203 mm (7–8 in.) would also increase the deck service life, which would reduce the life-cycle cost of the deck/bridge.