Design Criteria for Post and Beam Bents with Drilled Shafts: Fid-Bau Portal

Design Criteria for Post and Beam Bents with Drilled Shafts

B. Robinson / A. Vidot / Y. P. Park / B. Possiel / V. Suarez

The research work presented in the report addresses the potential areas of conservatism in the current practice related to bridge bents supported by drilled shafts and piles. The research encompasses modelingefforts and an experimental program. Modeling includes analysis of existing bridge case studies with drilled shaft foundations to characterize the impact of the current assumptions on sizing the variouscomponents of a bridge bent. An experimental program is performed to evaluate the connection stiffness, and to determine if a given connection has sufficient capacity to develop such stiffness and transfer moment The experimental program includes testing bearing pads in compression and shear to define their index properties. The bearing pads are then tested in a prototype bridge set up to measure their performance under simulated loading. An improved set of design guidelines and recommendations regarding the superstructure- substructureconnections rotational stiffness, shaft/pile top boundary conditions, and resistance factors are proposed along with characterizing the impactof the current practice and various design assumptions on sizing components of bridge bents. Resistance factors are developed for drilledshafts, based on load test data from the states geologic regions, for compatibility with LRFD implementation. Work in the report serves to provide a better understanding of the performance of bents supported by drilled shafts under AASHTO loading conditions. Such understanding serves as a tool that provides NCDOT engineers with the flexibility of specifying the level of conservatism to be built into a specific bridge bent design.