Transverse load distribution in sawn timber stringer bridges

Six sawn timber stringer bridges, in Cape Breton, Nova Scotia, were tested mainly to see the difference between the results of purely analytical evaluations, and those conducted with the help of data obtained from diagnostic tests an these bridges. Four of these bridges were found by analytical evaluation to have their Live Load Rating Factors (LLRF's) smaller than 1.0, being 0.96, 0.72, 0.72 and 0.87, respectively. It is noted that a bridge should have the LLRF greater than 1.0, if it is not to be posted. The other two bridges had LLRF equal to 1.21 and 1.10, respectively. By using the data from the test results, the LLRF for the four apparently deficient bridges are upgraded to or above 1.00, and those of the other two bridges were also upgraded substantially. It was found that the load distribution characteristics of the tested bridges given by the simplified method of the Canadian Highway Bridge Design Code (CHBDC) were similar to those predicted by a well-tested rigorous method of analysis, being the semi-continuum method of analysis. The observed characteristics were, however, significantly better than those given by both the simplified and rigorous methods of analysis. Improved load distribution characteristics of the sawn timber bridges, leading to smaller live load moments, seem to suggest a significant contribution of the asphalt surfacing in the transfer of loads between stringers.