Experimental Series 2
Experimental soil–foundation–bridge pier interaction: towards a reversal of capacity design
The new seismic design philosophy, which takes advantage of soil “failure” to protect the superstructure was investigated. A reversal of conventional “capacity design” was introduced, through intentional under-designing of the foundation. A simple but realistic bridge model was used as an illustrative example of the effectiveness of this new philosophy. Two alternatives were compared : one in compliance with conventional capacity design, with over-designed foundation so that the plastic “hinge” develops in the superstructure ; and one with under-designed foundation, so that the plastic “hinge” may occur in the soil. The seismic performance of the two alternatives was investigated through shaking table testing. It was shown that the performance of both alternatives is totally acceptable for moderate seismic motions. For large intensity seismic motions, the performance of the new scheme is shown to be advantageous, not only avoiding collapse but hardly suffering any inelastic structural deformation. Naturally, there is always a price to pay, which is none other than increased foundation settlement and residual rotation. These tests have provided a first “proof-of-concept”.