| The strength of bridges predicted by most current design codes is based on the philosophy of computing the capacity of individual members for various force effects (e.g., negative bending, positive bending, and shear). However, bridges (especially those with steel superstructures) have significant load redistribution capability; thus, the ultimate load that may be resisted by the system is likely significantly higher than the ultimate load that is computed based on the strength of individual members. While the ultimate capacity of individual bridge members is fairly well understood, the ultimate capacity of a bridge "system" is not.; The objective of the research discussed herein is to provide insight into the plastic behavior of multi-girder bridges by evaluating the load redistributed to other girders when one girder begins to yield. The insight gained from the very limited number of previous destructive tests is now being applied to the planning of the destructive test of Bridge 7R. Using a refined set of testing procedures, this destructive test will provide information on the ultimate capacity and plastic behavior of the bridge system. Through the use of a diagnostic field test of the current structure, coupled with a detailed finite element analysis, accurate predictions regarding the ultimate capacity and distribution effects of the structure have been evaluated. Based on the analyses, protocols for the destructive test have been developed. The testing of the bridge will require over 3 million pounds of load to successfully plastify the entire cross section. This is equivalent to 41 HS-20 design trucks. The test is expected to yield very valuable information about the system behavior of bridges. The information gained will be used to aid in the future design, construction, and rating of our nation's bridge infrastructure. |
