SEISMIC PERFORMANCE OF A MULTIPLE STEEL PIPES BRIDGE PIER INTEGRATED BY PILE FOUNDATION WITHOUT A FOOTING USING SHAKING TABLE TESTS

Abstract

 A multiple steel pipes bridge pier integrated by pile foundation without a footing has been proposed to design a rational foundation of the bridge pier structure. Based on the past achievements, the proposed substructures possess an excellent advantage of reduction of strain at the column through strain decentralization at footing point. In addition, reduction in footing weight contributes to decrease pile strain. On the other hand, the proposed substructure has some disadvantages i.e. increase in strain and displacement of piles. But it has been revealed that the strain generated at piles can be minimized by using underground beams around pile heads in the ground. In this paper, the seismic performance of the proposed bridge pier structure grounded in dry sand and liquefiable sand is evaluated based on the large-scale shaking table tests using bridge pier and foundation models with the scale of 1/20. As with the past achievements, the proposed structure has advantages of strain reduction of column by strain decentralization at footing point. It is recognized that it has high seismic performance and high toughness in view of the fact that the main members (columns and piles) hold a large residual strength after yielding of the shear panels.