Load Rating by Load Testing on Bridges

Project summary:

Load rating of bridges is presently performed with simplified analysis methods that are generally very conservative. Load testing with vehicles with known axle weights can be used to calibrate or refine these analysis methods, thereby improving both their accuracy and their effectiveness. For example, a load test can be used to obtain a more accurate distribution of load among multiple girders in a bridge superstructure, as well as to account for the additional fixity of parapets and other types of structural components that are often not included in rating analysis. In past research at the University of Minnesota and other institutions, this technique has been successfully used to look at service load behavior for fatigue evaluation of bridges. However, the behavior of the bridge and the distribution of load are not linear with increasing load. For example, bridges with non-composite concrete decks over interior piers often behave as if they are composite throughout the length of the bridge when loaded at service load levels. As the ultimate strength level (i.e., structural limit load) is approached, however, slip will most likely occur between the steel girders and the concrete deck in the negative moment region over the piers, and the behavior will revert to non-composite in that region. Thus, unless the load tests are carried out at a sufficiently high load level, the assumed distribution of load from a service-level load test may be both inaccurate and unconservative. On the other hand, the load test cannot be performed at a load level that would cause permanent deformation or other significant damage. This project will involve the testing of a bridge with heavy truck loads to help evaluate the load rating on the bridge and to help establish a procedure for load rating based upon testing with heavy trucks.