Effects of the slab casting sequences and the drying shrinkage of concrete slabs on the short-term and long-term behavior of composite steel box girder bridges. Part 1

In this study, the time-dependent behavior of composite steel girder bridges was investigated both theoretically and experimentally. The layer approach was used as an analytical model to determine the equilibrium conditions in a section, and to effectively consider the different material properties across the sectional depth. The effect of creep was studied in accordance with the first-order algorithm based on the expansion of a degenerate kernel of compliance function. In addition, the shrinkage effect of concrete was accounted for by the volume change of the concrete slabs. To verify the analytical results, field tests were performed on two actual bridges under construction. Strain values on the top and bottom flanges were monitored 30 days after the deck concrete had been placed. Analytical results compared well with the experimental results. The ultimate shrinkage strain recommended in the specifications can be significantly different from the actual rate of drying shrinkage, depending on field conditions such as concrete slump, the ambient temperature, and the relative humidity.