Glulam timber bridges for local roads

•This study facilitates the field deployment of glulam girder and glulam slab bridges.•Full-scale tests were performed to investigate the glulam bridge system performance.•Current design methods for timber bridges were found sufficient with non-composite assumption.•Superstructure costs of glulam bridges are less than those for typical prestressed bridges.•Both glulam girder and glulam slab bridges are low-cost and viable for local roads. Glued-laminated (glulam) and cross-laminated timbers are gaining interests in bridge engineering community due to their improved strength and enhanced durability compared to sawn lumber. The main bridge type on South Dakota local roads is a precast prestressed double-tee girder bridge, which has only one supplier in the state. In an attempt to provide more bridge type selection options for local governments, the system performance of two types of glulam timber bridges was investigated through full-scale experiments. One glulam girder bridge and one glulam slab bridge were tested under fatigue and strength loading. Both bridge types showed minimal damage during the fatigue testing and the bridge stiffness remained constant. Strength testing of the two bridge systems confirmed that the AASHTO method of design for timber bridges is adequate. Girders of glulam girder bridges should be designed as fully non-composite members. A cost analysis showed that the superstructure cost of glulam timber bridges can be 30–50% lower than the precast prestressed double-tee bridge superstructure cost. Based on the construction, testing, and cost analysis, it is concluded that both types of glulam timber bridges are viable alternatives to precast prestressed double-tee bridges to be used on local roads.