Comparison of Perception versus Reality in Timber Bridge Performance

Bridge material selection is one of the most difficult decisions an engineer has to make. Many factors and individuals are often involved in choosing the proper bridge material for a given site and location. Physical factors such as strength and lifespan of material, and also site specific factors like roadway alignment and traffic count, play important roles in material selection. Often state Department of Transportation engineers, private consulting engineers, and local highway officials all play roles in the material selection process. Each individual may have his/her own perception of bridge materials based upon past experience and education, and little is known about how these perceptions influence the choice of materials. In this study, perceptions of engineers and highway officials toward timber as a bridge material in four selected states were compared to the actual performance of timber as reported in the National Bridge Inventory. Highway officials and engineers in Mississippi, Virginia, Washington, and Wisconsin were surveyed by mail and personally interviewed to capture their perceptions toward timber as it compared to other major bridge materials (prestressed concrete, steel, and reinforced concrete). This information was compared with the actual performance data obtained from the National Bridge Inventory. The results indicate that there is a strong correlation between highway officials' perceptions toward bridge materials and the reported performance of these materials.