Numerical Analysis of the Axial-Flexural Behavior of CFST Columns with Active Transverse Prestressing

This paper presents a numerical study on the vertical (axial) and lateral (flexure) behavior of CFST (Concrete-Filled Steel Tube) columns with active hoop prestress achieved by bolting together two steel half-tubes. Twelve prototype CFST column specimens differing in the prestressing force (three levels) and in the gravity loading ratio (four levels) are analyzed; they are selected to represent typical ground columns of mid-rise buildings. Their structural behavior is simulated with a nonlinear model implemented in Abaqus; concrete and steel behavior are described with a damage-plasticity and a plasticity model, respectively. The concrete-steel interaction is represented by a hard (compression-only) surface-to-surface contact model. The calculations involve three consecutive loading steps: (i) transverse prestress, (ii) axial force, and (iii) lateral loading (shear force and bending moment). The calculation results show that the axial-flexural capacity of the prototype CFST columns is adequate. However, the hoop prestress benefit on axial compressive performance is not outstanding because the tube transverse Poisson expansion impairs the concrete confinement. The benefit in the flexural performance is smaller, due to the lack of sectional lateral expansion during bending. Preliminary studies on mid-rise buildings equipped with the prototype CFST columns show that their gravity and wind capacities are largely enough; conversely, their seismic strength is sufficient only for moderate earthquakes.

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