Demonstration Timber Bridge Design and Testing Performance of Deck Asphalt Overlay

Serviceability issues associated with timber bridges have recently become more of a focal point of research directed at promoting the increased use of timber bridges in our nation’s transportation systems. Previous work conducted by the Bridge Engineering Center (BEC) at Iowa State University (ISU) in cooperation with the United States Department of Agriculture (USDA) Forest Products Laboratory (FPL), in conjunction with this work has been directed at improving asphalt wearing surface performance on glued-laminated timber girder bridges with transverse glued-laminated panel decks through modifications to the deck. Differential panel deflection was identified as a significant factor affecting the deterioration of asphalt wearing surfaces on timber bridges. Research showed that the use of a layer of plywood on top of the deck provided approximately a 50 percent reduction in these relative deflections. In order to evaluate the full benefits and durability of this detail, the plywood overlay was implemented on a demonstration bridge with an asphalt wearing surface. The full-scale glued-laminated timber girder bridge was designed and constructed and is currently being used as a test facility for the plywood detail developed and tested in previous laboratory work. This paper provides quantitative information on several complementary projects prior to the implementation of the demonstration bridge and also provides preliminary results from the initial testing and evaluation of the Demonstration Bridge.