Behavior of Hollow-Core Composite Columns under Torsion Loadin

The effect of torsional loads could be significant along with axial and flexural loads on bridge columns during earthquake excitations. The present study presents the torsional behavior of hollow-core steel-concrete-steel columns (HC-SCS) and hollow-core fiber reinforced polymer-concrete-steel columns (HC-FCS). The HC-SCS comprises of sandwiched concrete shell between two steel tubes whereas in HC-FCS column, the outer steel tube of HC-SCS column was replaced by the FRP tube. Both columns have stay-in place permanent form-work to the concrete shell in the form of outer and inner tubes. The steel tubes serve as longitudinal and shear reinforcement to the column. Finite element models of HC-SCS columns were developed using LS-Dyna and the analysis results were validated with an average error of 4.8% against the experimental results in predicting the HC-SCS column's torsional capacity. An extensive parametric study was conducted with seven parameters to better understand the column's torsional behavior. A simplified analytical model was developed to predict the column's torsional capacity with an accuracy of 90%. A large-scale HC-FCS column was constructed and tested under constant axial load and cyclic torsion loading. The column outer diameter was 24 inch with an aspect ratio of 4. The FRP tube was placed on the surface of the footing while the steel tube was embedded into the footing to a length of 1.8 times the diameter of the steel tube. The experimental investigation revealed that the torsional capacity of the HC-FCS column significantly depends on the friction exerted between the steel tube and concrete shell and concrete footing. Furthermore, the HC-FCS column had undergone higher rotational drift compared to the corresponding reinforced concrete column.