United States Department of Transportation
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Abstract:Structural Composite Lumber (SCL) is reconstituted with high grade presorted veneers to enhance properties including higher and more uniform strength and stiffness than conventional lumber. Parallel Strand Lumber (PSL) is mainly constituted of wood strands of up to 66 ft long bonded together using an adhesive under pressure. Different structural elements including plates and beams can be produced from PSL. PSL is free of natural wood defects such as checks, knots and decay, and less susceptible to water since the adhesive used in the manufacturing process is water resistant. The mechanical characterization of Parallam was performed through various testing methods that included bending, shear, aging and fatigue. CFC-WVU developed a design procedure for bridge decks utilizing Parallam composite wood panels, manufactured by Trus Joist, Buckhannon, WV. Spring connectors were designed and tested before using them as mechanical means to connect the Parallam deck to steel stringers. After establishing the mechanical properties of the Parallam, CFC utilized its expertise to design two short span bridges: Peel Tree and Hackers Creek bridges. Peel Tree Bridge is simply supported with a span of 29 ft. It carries a single traffic lane on county road 20/3 in Barbour County, WV consisting of five W14 × 90 stringers spaced at 2'-9" and the bridge width is 15 ft. The bridge was built in FY2005. Hackers Creek Bridge is simply supported with a span of 31 ft. It carries a single traffic lane on county road 119/2 in Barbour County, WV. The bridge consists of three W24x94 steel stringers with 6 ft c/c spacing. Hackers Creek Bridge was built in FY2005. Both the bridges are designed to carry AASHTO HS-25 truck load. After construction, CFC-WVU started a monitoring program to evaluate the load carrying capacity and serviceability of the two bridges. Four live load tests (static and dynamic) were conducted on each bridge using dump trucks provided by the WVDOH. The tests were performed mainly to evaluate the Dynamic Load Allowance, Transverse Load Distribution, Live Load Deflection as well as the stresses under service conditions. Also, visual inspection and moisture measurements in decks were performed to evaluate the overall service condition of the two bridge decks and the deck-to-stringer connectors. Static deflections of the two bridges were within the allowable limits under a truck load 15% higher than HS-25 AASHTO load. Also, the dynamic as well as the static strains were within the allowable limits under the test truck load. Visual inspection of Peel Tree Bridge revealed wear problems at the top of the deck due to lack of wearing surface. Hackers Creek Bridge had nine failed deck-to-stringer connectors. Moisture content measurements were taken on the decks of both bridges. The average moisture content of both decks was below the 19% limit provided by AASHTO bridge design specifications (LRFD & Standard).
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