Timber Bridges: Benefits and Costs

Deterioration of bridges in Western Pennsylvania accelerated after the inception of the use of deicing agents two decades ago. These bridges were constructed primarily of reinforced concrete and steel with no provisions in their design for protection from deicing agents. These agents chemically attack unprotected steel and concrete and ultimately cause weakening of the bridge structure. The benefit of the resistance of timber to the effects of deicing agents led to the reconstruction of three highway bridges using modern timber design. Details of two cases of highway bridge reconstruction are presented: (1) A deck replacement over steel stringers; and (2) a beam and deck replacement using existing abutments. The case of replacement of a railroad overpass is also presented. A primary consideration in this project was the minimization of railroad service disruption time. This was accomplished by fabricating timber members on site to accommodate uncertain field conditions. In this case, the use of steel or concrete would have resulted in an unacceptably lengthy service disruption.