Stressed decks are constructed by squeezing lumber laminations using galvanized steel bars with ultimate strengths of 155 ksi. Bridges of longer span lengths using stressed-deck concepts are feasible with two different methods: (a) increasing the number of layers of lumber laminations of the stressed deck; and (b) adding stringers anddiaphragms to the stressed deck. The stressed-bridge systems developed and presented include (a) slab or solid stressed deck, (b) tee, (c) bulb-tee, and (d) box. Only tee, bulb-tee, and box systems were tested. The tee, bulb-tee, and box with laminated veneer lumber (lvl), glulam, and fiber-reinforced plastic stringers are tested for bending under three different load conditions and their responses are evaluated. The significant performance characteristics (such as lamination separation caused by transverse bending, vertical slip caused by direct vertical load, lamination rotational slip at butt joints caused by longitudinal bending, and the minimum transverse prestress levels in laminations) are checked. The tested systems (tee, bulb-tee, and box) are compared for their stiffness. The systems' compositeaction, diaphragm effects, and load sharing are evaluated. In addition, ultimate load characteristics are studied by taking the specimens to failure. Gangarao's analytical model with orthotropic materialproperties is verified with the experimental results. This paper appears in transportation research record no. 1291, Fifth international conference on low-volume roads, may 19-23, 1991, raleigh, north carolina, volume 1.
Abstract