An experimental and analytical study of post-tensioned steel-concrete composite bridges.

摘要

The purpose of the research study is to conduct an investigation to understand the performance of a relatively new type of bridge construction that involves prestressed (post-tensioned) steel-concrete composite bridge members. The investigation included experimental as well as analytical evaluations of the short-term and long-term structural behavior. The experimental part involved a series of field measurements of a newly constructed steel-concrete composite bridge which was post-tensioned with high-strength steel tendons. This bridge, which is part of the I-90 Indiana Toll Road, is located in Elkhart County, Indiana. Strain distributions in the composite girders and the elongation of a selected post-tensioning tendon were measured at certain crucial phases of construction. The field monitoring was periodically conducted over a period of about one year after the post-tensioning operation. Analytical solutions were developed to evaluate the structural response due to various types of instantaneous loads, temperature effects and time-dependent factors (creep and shrinkage in concrete deck, and relaxation in steel tendons). The validity and effectiveness of the analytical model were examined by comparing calculated results with data collected from the field.; The long-term structural response was predicted based on the proposed methodology. A design procedure for post-tensioned steel-concrete composite bridges was also developed. The experimental and analysis results both showed that significant compressive stresses will develop along the composite section due to the introduction of post-tensioning as well as the effects of creep and shrinkage in the concrete deck. Consequently, web local buckling is an important issue for designing this type of bridge structure. It was found that the most critical location for web instability occurs near the drape point. The investigation also showed that expected prestress losses in post-tensioned steel-concrete composite bridges are not as significant as those that occur in conventional prestressed concrete bridges. Moreover, the analysis demonstrated that even though creep and shrinkage will result in tensile stresses in the concrete bridge deck, the magnitude of stress is not sufficient to cause cracking.