9416525 Breen The main objective of this project is the evaluation of the potential effects of vertical ground accelerations, when combined with the horizontal components of motion, on the seismic response of highway bridges. The effects to be examined are the stresses in the piers and girders or the maximum ductility requirements if there is inelastic action, and the potential slippage and permanent displacements at the seats of the girders. Recommendations will be made to incorporate appropriate provisions in bridge design codes to account for them in the seismic design. A series of parametric studies will be conducted on simplified models of highway bridges, assuming first completely linear behavior, incorporating next the nonlinearity associated with the behavior of the bearing pads and the possibility of sliding or uplift of the girders' ends, and including finally the possibility of nonlinear material behavior in the girders and piers. Two-dimensional, in-plane, models and t a more limited extent with three-dimensional models will be used. The parametric studies will be complemented with the analyses of some selected bridges from the Northridge area to compare the theoretical predictions with the observed patterns of behavior and reported damage. Design recommendations will be made in consultation with bridge designers and engineers involved in the code writing process. This study is expected to contribute to a better understanding of the potential effects of vertical ground acceleration and of the conditions under which these effects may become important and should be accounted for in the design. If the results were to indicate that revisions should be made in the present bridge design codes to improve the safety and reliability of highway bridges in the epicentral area, the outcome of the project would have a significant impact on the seismic design. This is a Northridge Earthquake project. ***
