Concrete-filled steel tube to concrete pile cap connections: verification of analysis/design methodologies

Abstract

This research project focuses on the structural behavior of concrete-filled steel tube (CFST) to concrete pile cap connections, a critical component in many Montana bridges. A series of four experimental pile cap connection specimens were designed and tested to assess the influence of key parameters such as specimen scale, concrete strength, and the incorporation of U-bars on the overall connection performance. The findings from this research revealed that all specimens, barring the specimen with U-bars, displayed consistent moment-drift responses, damage progression, and failure mechanisms within the concrete cap. The inclusion of U-bars notably increased the connection capacity by about 60%, altering the failure mechanism to a plastic hinge formation in the CFST pile. Additionally, the study validated the efficacy of a novel moment-rotation methodology for predicting the capacity of cap connections, with an average measured-to-predicted ratio of 0.95 and a coefficient of variation of 10%. However, this methodology showed a tendency to overpredict capacities in connections without U-bars and underpredict in those with U-bars. Overall, this research provides valuable insight into the behavior of these critical connections under diverse conditions and demonstrates the efficacy of the moment-rotation methodology.