Analytical and experimental investigations of shell structures utilized as bridges
F. Wayne Klaiber
Bridges are a vital element of the surface transportation system. According to Federal Highway Administration, approximately 40% of the 578,000 highway bridges in the United States are rated deficient or functionally obsolete. Thus, a critical need exists for an innovative bridge system that is economical, relatively easy to construct and can be used to construct emergency bypass bridges as well as permanent bridges;Previous analytical studies at Iowa State University indicated that segmental, integrated shell-deck bridges are a potential solution for constructing economical bridges. The proposed cross-section was modified to achieve better economy and a one-third scale concrete model was designed and constructed. The model was used to study the problems associated with shell bridge construction, to determine regions of stress concentration that can not be determined by the finite element analysis and to determine the behavior of the interface between adjacent segments;The model consisted of six reinforced concrete segments that were externally post-tensioned together to form a 34 ft. long, 10-ft. wide simple-span model bridge. End segments were provided with a 4 inch thick reinforced concrete diaphragm. For ease of erection, testing and instrumentation, steel-truss elements, rather than concrete elements, were used to connect the curbs to the shell edge beams. This system permitted various configurations of the truss elements to be tested so that the most effective configuration could be determined. The model was tested using single concentrated loads at numerous critical locations to determine the model's behavior, deflections and strains. The model was also tested using concentrated loads which simulated truck loading at various critical locations;The construction of the laboratory model verified the feasibility of constructing segmental shell bridges; segments of the bridge can be precast and transported to the site where they can be post-tensioned together to form a bridge. Connecting the curbs to the shell edge beams was effective in decreasing the deflections, increased the torsional stiffness of the model and reducing the strains. However, using inclined diagonals as a connection was found to be more effective than using vertical truss elements.