Mechanical Response of a Composite Steel, Concrete-Filled Pile

Abstract

A steel pipe-pile section, filled with concrete, was instrumented and tested under axial load. Two types of strain gages, resistive and vibrating wire, were mounted to the steel-pipe pile and checked by determining the known Young’s modulus of steel E^s. The steel section was filled with concrete and a resistive embedment gage was placed in the concrete during the filling process to measure axial strain of the concrete. The axial load – axial strain responses of the steel (area A^s) and concrete (area A^c) were evaluated. The stiffening of concrete, related to curing, was also studied. Assuming the boundary condition of uniform axial displacement, i.e., equal axial strain in the steel and concrete, εz^s = εz^c = εz, the sum of the forces carried by the two materials, F^s + F^c, where F^s = εz * E^s * A^s and Fc = εz * E^c * A^c, provides a reasonable estimate – within 3% – of the pile force. For the particular specimen studied (12 in. ID, 0.25 in. wall thickness), the stiffness of the composite section of steel and concrete was about three times larger compared to the steel section without concrete. Further, the concrete carried about 70% of the load, but the axial stress in the concrete, at an applied force of 150,000 lb, was less than 20% of the compressive strength of the concrete.