STRENGTH AND DUCTILITY OF BRIDGE SUBSTRUCTURES

Extensive test results for bridge columns subjected to axial load together with inelastic reversals of lateral displacements are presented. Section shapes tested included square, octogonal, diagonally loaded square, hollow circular and hollow square columns. Other variables included axial load level, amount of confining steel, aspect ratio, and yield strength of the confininf reinforcement. Results indicated that current design practice is conservative. In particular, current methods for predicting flexural strength invariably underestimated the true flexural strength by substantial margins, particularly when axial load levels were high. Tests on strength and ductility of prestressed concrete and steel encased piles are described, which indicate that both methods of piling have adequate reserves of ductility. Theoretical aspects of the shear strength of bridge columns are discussed, and preliminary experimental results are reported, which indicate that current design methods for circular columns are conservative. Limited dynamic testing indicates a possible reduction of shear strength by comparison with static test results. The findings of the research are summarised in a simple design approach which should result in substantial reductions in the size and reinforcement requirements for bridge piers designed for seismic resistance. (TRRL)