Bridges And Structures | Washington State Transportation Center

Liquefaction-Induced Downdrag on Drilled Shafts

This study developed an analytical method that can account for the liquefaction-caused settlement of deep foundations, in particular a structure’s drilled shafts. During and following liquefaction caused by an earthquake, sandy soil layers shrink in volume and settle. Depending on the site conditions, the changes in forces that result from liquefaction-induced soil settlement and downdrag can significantly affect the performance of drilled shafts, even damaging the structure. The new analytical method, based on the neutral plane method, proved successful in application to a case study of downdrag observed during the February 2010 8.8-magnitude earthquake in Maule, Chile.

Shear Design Expressions for Concrete-Filled Steel Tubes and Reinforced Concrete-Filled Tube Components

Concrete-filled steel tubes (CFSTs) and reinforced concrete-filled steel tubes (RCFSTs) are increasingly used in transportation structures as piers, piles, caissons, or other foundation components. CFSTs combine steel and concrete to create efficient and economical composite structural members. Because currently accepted methods for calculating the shear capacity of CFSTs and RCFTs are adapted from shear strength equations used for structural steel or reinforced concrete components, they likely significantly underestimate the shear capacity of the composite section, potentially increasing undesirable conservatism and cost. This research used integrated experimental testing methods, combined with high-resolution analytical models, to investigate the shear capacity of CFST and RCFST members and to develop an improved and more accurate shear strength expression. The resulting new expression provides a total CFST shear strength of 2 times that produced by WSDOT’s currently used expression and is proposed for implementation in WSDOT’s Bridge Design Manual.

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