FRP-Wood-Concrete Composite Bridge Girders

Abstract

Traditional timber bridges designs, while economical and durable, often have difficulty producing adequate stiffness for longer spans. Addition of FRP reinforcement has been shown to improve stiffness to a limited extent, but not nearly as much as it improves strength. To address the stiffness issue, a combined analytical/experimental pilot study is being conducted on a reinforced FRP glulam/concrete composite beam section. The section consists of a glued-laminated beam reinforced on the tension face with E-glass fiber reinforced composite. On the compression face, lag screws were driven into the wood beam before pouring the concrete slab to make the glulam beam and concrete slab composite. The stiffness of the beam was modeled using first order shear deformation theory based on available material properties. The load-deflection ratio was predicted for the limit case of a fully composite concrete slab and the limit case of no concrete slab. A nonlinear model based on moment-curvature analysis was developed and run to help quantify the increased strength and stiffness of the composite beam. An experimental program has been designed to better quantify the beam response and determine whether the strength and stiffness gained through the addition of the concrete in the compression zone sufficient to make up for the additional dead load. The wood used in the glulam was eastern hemlock, a low grade but abundant New England species. A longitudinal E-glass reinforcement mat was bonded to the wood with a phenolic adhesive through the wet lay up method. In order to control shear failure, some of the specimens were wrapped at the ends with additional E-glass shear reinforcement. To date, one beam has been loaded in three point bending within the linearly elastic range, and the results indicate that the stiffness gains are significant. Future tests will examine failure modes and the effects of shear reinforcing, as well quantifying strength gains based on economical amount of FRP reinforcing.