Traffic forces and temperature effects on shear key connections for adjacent box girder bridge.

摘要

Adjacent box girder bridges are widespread around the world. They have many advantages such as ease of erection, excellent depth-to-span ratio and speeding up the construction, etc. Usually these kind of bridges are built up by placing the box girders side by side, then pouring grout into an octangular shaped gap between the beams which is called “shear key”. Finally the girders are pulled together by a series of lateral ties (post-tensioning forces may be applied).; The focus of this research is the “shear key” leakage problem, since for the current “shear key” design, the cracking could be easily caused after “shear key” is formed. Those cracks can let salt laden water penetrate through the beam joints, then the load transfer between girders could be lost. That would affect the integrity and the strength of the whole bridge.; The finite element method was applied in this analytical analysis. The finite element program, ANSYS, was first verified to be a valid tool by doing the analysis compared with an experimental test. Then in order to find out the best design for “shear key” connection, ANSYS was used to analyze five “shear key” variations: “Regular keyway”, “Neutral-axis keyway”, “full-depth keyway”, “Regular hinge keyway” and “Neutral-axis hinge keyway”.; Two kinds of material, which are used in grouting shear keys, were involved in this analysis and they are non-shrink grout and hi-flow epoxy. Several load conditions were considered: HS-20 truck load, temperature effect and post-tensioning forces. The combinations of these separate load conditions were also being analyzed. Some analytical results were compared with some previous studies to check the consistency of the analytical results and field experimental data.; According to the result of the analytical analyses, “full-depth keyway” was found to be the best option for shear key design, since it always had the lightest critical stress or cracking condition compared with other four variations. Non-shrink grout was shown to be a better choice than hi-flow epoxy when temperature issue could not be neglected, because the thermal expansion coefficient of hi-flow epoxy is too high. Post-tensioning forces are also recommended to be applied on the adjacent box girder bridges, because in this finite element analysis it was verified that post-tensioning effect could improve the anti-cracking capacity of shear key connections.; So “full-depth keyway” approach with using non-shrink grout, combined with post-tensioning forces, is the proposed design method from this analytical analysis.