Concrete-Filled Steel Tubes for Accelerated Bridge Construction

Abstract

Concrete-filled steel tubes (CFSTs), which are steel tubes with concrete infill, have increased strength, stiffness, and deformability relative to comparably sized reinforced concrete columns. The steel is at its optimal location and thus maximizes strength and stiffness while minimizing weight and material requirements and providing confinement to the concrete infill. In turn, the infill delays local and global buckling of the tube. In addition to their high resistance and stiffness properties, CFSTs are easily and rapidly constructed and eliminate the need for formwork and reinforcement. In bridge design, CFSTs may be used for bridge piers, shafts, caissons, and columns. However, the use of these tubes is limited in part because AASHTO design specifications for CFSTs are dated and in part because few validated, constructible connections exist. The American Institute of Steel Construction (AISC) includes more recent updates to CFST design provisions than does AASHTO. This paper compares current CFST design provisions with experimental results, noting limitations and deficiencies. Proposed provisions to improve the AISC provisions are introduced. These improved provisions are used as the basis of new AASHTO specifications for use of CFSTs in bridge design. Connections, which are a second limitation in CFST design, are also discussed. A foundation connection capable of developing the composite capacity of a CFST was evaluated experimentally and resulted in design expressions. A preliminary study of CFST column–to–cap beam connections using numerical simulation is introduced. This paper presents significant advancement and practical methods for the use of CFSTs in bridge design.