Elastomeric Bearings In High Demand Applications

Pot and disk bearings are typically used in high-demand bridge applications where significant demands are imposed on bearings at the supports to accommodate rotations and complex bridge movements from both environmental thermal loads and vehicular traffic. However, past bridge research, design, and installation experience demonstrates that less costly elastomeric bearings are not only easy to install, inspect, and replace, but also more forgiving of installation errors. The use of elastomeric bearings in high-demand applications results in much less structural restraint against bridge thermal deformation than other more sophisticated sliding bearings. Although past bridge design practice includes applications of elastomeric bearings in two steel trapezoidal box girder systems in Central Texas, the use of elastomeric bearings in high-demand application is nevertheless largely impeded by historical and current bearing design provisions at national and state levels that are unduly restrictive for large-sized elastomeric bearings as well as the scantiness of field, laboratory, and numerical investigations on them. This investigation reported in this dissertation is part of a research project including material study, full-scale testing, field monitoring, and finite-element studies, with a focus primarily on finite-element studies of elastomeric bearings in comparison with laboratory and field measurements. A three-dimensional finite-element model capable of simulating the behavior of elastomeric bearings in full-scale compression, shear, and rotation testing was first developed and validated by experimental results from the full-scale testing. More comprehensive parametric finite-element studies of elastomeric layers under axial load and rotational deformation were then carried out leading to the development of a reliable elastomeric bearing design with improved economy and serviceability, based on total shear strain approach. A three-dimensional finite-element study of a continuous curved steel trapezoidal box girder system (IH-35 NB & US-290 EB direct connector) was carried out to investigate the translational movements and rotations imposed on elastomeric bearings under thermal loads with 100-year return period, and validated by instrumentation measurements from field monitoring. Design suggestions were put forward with regard to determining demands on elastomeric bearing s under thermal loads in high-demand applications. A field investigation was finally carried out on elastomeric bearings on the instrumented bridge, two of which were found to be damaged to different extents. The results reveal that the two damaged bearings are subjected to excessive amount of transverse rotation. Further analyses by calculating the maximum shear strain of all bearings using the proposed design approach confirmed that the observed bearing damage is the direct result of the excessive transverse angle of inclination on the concrete bearing seat surface.