Advanced Structures & Composites Center

Published: 2002

Publication Name: ASCE Structures Congress 2002: Performance of Structures – From Research to Design

Publication URL: https://digitalcommons.library.umaine.edu/etd/2612/

Abstract:

Glulam beams can be reinforced on the tension side to increase their bending strength, and many studies have shown the significant promise of reinforcing wood beams with Fiber Reinforced Polymers (FRPs). However, while FRP tensile reinforcement can significantly increase the bending strength of wood beams, it provides only a modest increase in flexural stiffness. This is a significant issue, since deflections can control the design of long-span glulam bridges.
One method to increase both bending strength and stiffness of glulam girders is to reinforce the tension side with FRP and provide a partially composite concrete deck on the compression side. This project explored the feasibility of this approach to increase both girder stiffness and strength by testing FRP-glulam-concrete composites and designing a bridge. The major tasks that were performed include:
1. Development of a connection to achieve partial composite action between glulam girders and a concrete deck.
2. Experimental Work:
a. Construct and test seven glulam-concrete connections in direct shear I under static and fatigue loads to determine the strength and stiffness of .the composite connector.
b. Construct and test two 30-ft. T-beams with a reinforced glulam web .and a partially composite concrete deck under both static and fatigue loads.
3. Design and preparation of plans for a 70-ft. span FRP-remforced glulam-concrete composite bridge for Fairfield, Maine.
A composite connection was selected to attach a concrete slab to a glulam girder based on cost, ease of installation, and performance. Direct shear tests using this connection gave promising results. The connection withstood large shear forces, even after being subjected to 2,000,000 constant-amplitude fatigue cycles. In fact, the average connector strength in the fatigued specimens was nearly identical to the average connector strength in the control specimens.
Two 30-ft. FRP-reinforced glulam-concrete composite T-beams were subjected to 2,000,000 constant-amplitude fatigue cycles and then loaded to failure quasi-statically. The dimensions and material properties of the glulams were identical, except Beam #2 contained twice the number of connectors as Beam #I. As a result, Beam #2 had a larger interface-stiffness and therefore a higher degree of composite action. Also, the discontinuity of flexural strains at the wood-concrete interface indicated partial composite action between the concrete slab and the FRP-reinforced glulam girder.
Using the results of the direct shear and beam tests, a 70-ft. span by 35-ft. wide bridge superstructure was designed on schedule for the town of Fairfield, Maine. The individual components of the bridge were drafted and were bid on by contractors and distributors. Presently, all of the components have been manufactured and are in the possession of the Maine Department of Transportation in Fairfield, Maine. As soon as the Town of Fairfield completes the substructure, construction of the superstructure will begin.
This project was an attempt to design a wood-girder bridge system that can compete with the steel and concrete bridges that dominate the market today. By combining FRP, glulams, and concrete in a composite section that best utilizes their material strengths, glulam-girder bridges that are aesthetically pleasing can compete in today’s market.