InTrans / Aug 14, 2018

Field performance of timber bridges: 3. Birchlog Run and Tumbling Rock Run stress-laminated deck bridges

The Birchlog Run and Tumbling Rock Run bridges were constructed in the summer of 1990 on the Monongahela National Forest in West Virginia. The bridges are simple span, single-lane, stress-laminated deck superstructures, and each bridge is approximately 30 ft long and 13 ft wide. The bridges are located approximately 1/2 mile apart and are nearly identical in design. However, the Birchlog Run bridge is constructed of Southern Pine (softwood) lumber, and the Tumbling Rock Run bridge is constructed of Northern Red Oak (hardwood) lumber. The close proximity of the bridges provided an opportunity to compare the performance of stress-laminated decks constructed of softwood and hardwood species under similar environmental conditions. Performance of the bridges was monitored for 3 years, beginning at the time of installation. This monitoring involved gathering and analyzing data relative to the wood moisture content, force level of the stressing bars, vertical bridge creep, and behavior of the bridges under static-load conditions. In addition, comprehensive visual inspections were conducted to assess the overall condition of the bridges. Based on 3 years of field monitoring, the bridges are performing well with no structural or serviceability deficiencies.