Effect of thermal loading on the performance of horizontally curved I-girder bridges

Effect of Thermal Loading on the Performance of Horizontally Curved I-Girder Bridges Kevyn C. McBride As the amount of infrastructure in the United States continues to grow and older infrastructure is replaced or updated, bridge designers are faced with increasing space and geometrical limitations. Curved bridges have become a popular design alternative to the traditional straight girder or chorded bridges as they can provide the designer a more cost effective solution to complicated geometrical limitations or site irregularities. However, the volume of research and knowledge on the behavior of curved bridges is lacking compared to straight and chorded bridges, especially in terms of their response to changing thermal conditions. In most cases, it is assumed that bearing design allows expansion and contraction of the superstructure that relieves thermal stresses, but in reality this is rarely true. Bridge curvature complicates the structures response to thermal loading as the bearing configuration must handle a larger degree of expansion and contraction in the transverse, or radial, direction. Failure to properly design bridge bearings to accommodate thermal loads will lead to unaccounted for deformations and stresses in the superstructure. This research begins with two small scale parametric studies, performed using finite element modeling, that investigate how uniform thermal loading effects web deformations and web and flange stresses of a single curved steel I-girder and also of a section consisting of two curved steel I-girders connected with cross frames. The major focus of this research is a case study on the response of the Buffalo Creek Bridge, located in Logan County, West Virginia, to changing thermal conditions prior to any in-service loading. Two detailed 3D finite element models of the bridge were created, one modeling the piers as rigid members and one modeling the piers as flexible members, and both models were subjected to uniform temperature increase and decrease. Results indicate that uniform thermal loading leads to global and local buckling along the Igirder web centerlines, lateral distortional buckling in the web cross section, and thermal stresses in the I-girder webs. Although pier flexibility is shown to reduce the magnitude of thermally induced local and lateral distortional buckling and thermal stresses, I-girders experience larger global buckling when the piers are flexible. The results indicate that the introduction of pier flexibility did not relieve all the thermal stresses in the I-girder webs. At some locations, when the piers are rigid, the I-girder stresses exceed the AASHTO web bendbuckling capacity as well as the overall stress capacity of the section. This study shows that uniform thermal loading will lead to increased out-of-plane web deformations and increased web stress levels, which will both combine to decrease the load carrying capacity of the bridge when subject to subsequent live-loading conditions. This dissertation outlines a methodology that should be utilized by bridge designers and/or owners to validate the integrity of traditional bridge designs, especially in the case of more complicated bridge structures.