Simple Moment-Rotation Methodology for Predicting the Capacity of Concrete-Filled Steel Pipe Piles to Concrete Cap Connections

This study focuses on the development of an analysis methodology for predicting the ultimate seismic capacity of a concrete-filled steel tube (CFST) to reinforced concrete pile cap connections. This methodology is similar in form to a moment–curvature analysis. The first step involves discretizing the connection elements in the cap into individual fibers and then imposing a rigid body rotation of the embedded CFST. The strains in the individual fibers in the cap are then obtained from this rotation based on strain–displacement compatibility, and the resulting stresses are determined using nonlinear material responses. Equilibrium is then enforced between the associated force resultants and the external shear and moment delivered by the CFST. Specifically, a double-iterative procedure is used in which both the rotation angle and the axis of the rotation location are varied until equilibrium is achieved. Once developed, a set of experimental tests was used to preliminarily calibrate the methodology and demonstrate its feasibility for predicting the ultimate capacity of the CFST to concrete pile cap connections. The average ratio of the measured-to-predicted capacities was 0.99 with a coefficient of variation of 5.4% for the nine test specimens in the test series.

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