Institute for Transportation

Several hardwood timber bridges were constructed in Pennsylvania
during the early 1990s. This report summarizes the long-term field performance of seven stress-laminated deck bridges over a 4-year period beginning August 1997 and ending July 2001. Data collected include lumber moisture content, static load test deflection measurements, and bridge condition assessments. In addition, stressing bar force, temperature, and relative humidity conditions were monitored several times per day by a remote data acquisition system installed at each bridge site. Superstructure lamination moisture content ranged between 20% and 40% after nearly 10 years of service. The field performance of four bridges was unsatisfactory. Loss in prestressing bar force necessitated bar re-tensioning at the Millcross Road bridge (Lancaster County), and live load deflection limits were exceeded at the Brookson Road (Crawford County), Laurel Run (Huntingdon County), and Jacobs (Huntingdon County) sites. Several serviceability and/or maintenance deficiencies need immediate attention to achieve satisfactory field performance.