Self-stressing of expansive concrete filled steel and FRP tubes

Abstract

This study investigates expansive recycled aggregate concrete (RAC) confined by steel tubes and fiber-reinforced polymer (FRP) shells and places both systems on a common lateral-pressure scale using thin-cylinder relations. A compact dataset is compiled from tests that either report core self-stress in concrete-filled steel tubes (CFST) or provide initial hoop pre-strain in prefabricated FRP shells filled with expansive grout/concrete. Directly reported CFST self-stress clusters near 5 MPa and coincides with measurable gains in axial capacity, particularly in slender members. For FRP shells, converting the measured hoop pre-strain with laminate stiffness and thickness yields active confinement of roughly 0.9–3.4 MPa for typical GFRP/CFRP stacks, consistent with observed improvements in strength and ductility over ordinary infill. A thin-walled RAC baseline without expansive action shows a capacity shortfall relative to natural-aggregate mixes, framing the performance gap that controlled expansion can recover under confinement. The resulting pressurescale mapping offers a transparent, data-lean way to compare steel and FRP encasements and to plan targeted experiments and laminate selections.