Behavior of hollow-core composite columns under torsion loading

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\u27s torsional capacity. An extensive parametric study was conducted with seven parameters to better understand the column\u27s torsional behavior. A simplified analytical model was developed to predict the column\u27s 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 --Abstract, page iv

Torsional Behavior of Hollow-Core FRP-Concrete-Steel Bridge Columns

This paper presents the behavior of hollow-core fiber reinforced polymer-concrete-steel (HC-FCS) column under pure torsion loading with constant axial load. The HCFCS consists of outer FRP tube and inner steel tube with concrete shell sandwiched between the two tubes. The FRP tube was stopped at the surface of the footing and provided confinement to the concrete shell from outer direction. The steel tube was embedded into the footing to a length of 1.8 times to the diameter of the steel tube. The longitudinal and transversal reinforcements of the column were provided by the steel tube only. A large-scale HC-FCS column with a diameter of 610 mm and height of applied load of 2,438 mm with aspect ratio of 4 was investigated during this study. The study revealed that the torsional behavior of HC-FCS column mainly depended on the stiffness of the steel tube and the interactions among the column components (concrete shell, steel tube, and FRP tube)

Hollow-Core FRP-Concrete-Steel Bridge Columns under Torsional Loading

This paper presents the behavior of hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) columns under cyclic torsional loading combined with constant axial load. The HC-FCS consists of an outer fiber-reinforced polymer (FRP) tube and an inner steel tube, with a concrete shell sandwiched between the two tubes. The FRP tube was stopped at the surface of the footing, and provided confinement to the concrete shell from the outer direction. The steel tube was embedded into the footing to a length of 1.8 times the diameter of the steel tube. The longitudinal and transversal reinforcements of the column were provided by the steel tube only. A large-scale HC-FCS column with a diameter of 24 in. (610 mm) and applied load height of 96 in. (2438 mm) with an aspect ratio of four was investigated during this study. The study revealed that the torsional behavior of the HC-FCS column mainly depended on the stiffness of the steel tube and the interactions among the column components (concrete shell, steel tube, and FRP tube). A brief comparison of torsional behavior was made between the conventional reinforced concrete columns and the HC-FCS column. The comparison illustrated that both column types showed high initial stiffness under torsional loading. However, the HC-FCS column maintained the torsion strength until a high twist angle, while the conventional reinforced concrete column did not

Behavior of Hollow-Core Steel-Concrete-Steel Columns Subjected to Torsion Loading

The torsional behavior of hollow-core steel-concrete-steel (HC-SCS) columns is presented using finite-element (FE) and analytical approaches. The HC-SCS columns consist of a concrete shell sandwiched between two steel tubes. Software was used to develop a three-dimensional model of an HC-SCS column that was subjected to torsional loading. The FE results were validated against the experimental results collected from six HC-SCS columns tested under pure torsion. The average error from the FE analysis was 4.8%, compared with experimental results, when predicting the column\u27s torsion strength. The study revealed that the interaction between the steel tube\u27s stiffness and concrete shell\u27s thickness controls the behavior of the column. A parametric study was conducted to further analyze each parameter affecting the column\u27s torsion behavior. The parametric analysis concluded that the torsional behavior of the column mainly depends on the outer steel tube\u27s properties and the thickness of the concrete shell. A simplified equation was developed to predict the torsion strength of the member using a direct method of stress analysis. The proposed equation predicted the members\u27 torsion strength with an accuracy greater than 90%

Seismic Behavior of Hollow-Core FRP-Concrete-Steel Bridge Columns

This paper presents the behavior of precast hollow-core fiber reinforced polymer (FRP)-concrete-steel tubular columns (HC-FCS) under combined axial and lateral loading. The HC-FCS column consisted of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. Two large scale columns, RC-column and HC-FCS column were investigated during this study. The steel tube of the HC-FCS column was embedded into the footing while the FRP tube was stopped at the top of the footing level, i.e., the FRP tube provided confinement only. The hollow steel tube is the only reinforcement for shear and flexure inside the HC-FCS column. The FRP in HC-FCS ruptured at lateral drift of 15.2% while the RC-column displayed 10.9% lateral drift at failure. The RC-column failed due to rebar rupture and the moment capacity suddenly dropped more than 20% after that. However, the HC-FCS suffered gradual failure due to concrete crushing, steel local buckling and yielding, followed by FRP rupture

Seismic Performance of Innovative Hollow-Core FRP-Concrete-Steel Bridge Columns

This paper presents the seismic behavior of hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) columns. The typical HC-FCS column consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The inner steel and outer FRP tubes provide continuous confinement for the concrete shell; hence, the concrete shell achieves significantly higher strain, strength, and ductility than unconfined concrete in conventional columns. Three large-scale HC-FCS columns were investigated in this study. Each column had an outer diameter of 610 mm (24 in.) and a height-to-diameter ratio of 4.0. The steel tube was embedded into a reinforced concrete footing with an embedded length of 1.6-1.8 times the steel tube diameter, whereas the FRP tube only confined the concrete wall thickness and truncated at the top of the footing level. In general, the columns exhibited high lateral drift, reaching to 11.6%, and failed gradually as a result of concrete crushing and local steel tube buckling. An equation to determine the steel tube development length of HC-FCS columns was introduced based on an extensive finite-element study. The finite-element analysis was validated with finite-element models. In addition, this paper introduces a quick-repair technique for HC-FCS columns. Guidelines for the preliminary design of HC-FCS columns under seismic loading are also presented to help implement this new technology

Hollow-Core FRP–Concrete–Steel Bridge Columns under Torsional Loading

This paper presents the behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns under cyclic torsional loading combined with constant axial load. The HC-FCS consists of an outer fiber-reinforced polymer (FRP) tube and an inner steel tube, with a concrete shell sandwiched between the two tubes. The FRP tube was stopped at the surface of the footing, and provided confinement to the concrete shell from the outer direction. The steel tube was embedded into the footing to a length of 1.8 times the diameter of the steel tube. The longitudinal and transversal reinforcements of the column were provided by the steel tube only. A large-scale HC-FCS column with a diameter of 24 in. (610 mm) and applied load height of 96 in. (2438 mm) with an aspect ratio of four was investigated during this study. The study revealed that the torsional behavior of the HC-FCS column mainly depended on the stiffness of the steel tube and the interactions among the column components (concrete shell, steel tube, and FRP tube). A brief comparison of torsional behavior was made between the conventional reinforced concrete columns and the HC-FCS column. The comparison illustrated that both column types showed high initial stiffness under torsional loading. However, the HC-FCS column maintained the torsion strength until a high twist angle, while the conventional reinforced concrete column did not

Behavior of Hollow-Core FRP-Concrete-Steel Columns under Static Cyclic Flexural Loading

This paper presents the seismic behavior of hollow-core fiber-reinforced polymer (FRP)-concrete-steel (HC-FCS) columns comparable with the conventional RC column. The typical HC-FCS column consists of a concrete shell sandwiched between an outer FRP tube and an inner steel tube. The HC-FCS column represents a compact engineering system; the steel and FRP tubes act together as stay-in-place formworks. The steel tube acts as a flexural and shear reinforcement. This paper studies three large-scale columns - one RC column having a solid cross section and two HC-FCS columns. Each column has an outer diameter of 610 mm (24 in.) and a shear span-to-diameter ratio of 4.0. The steel tube is embedded into the reinforced concrete footing with an embedded length of 1.6 times the steel tube diameter, whereas the FRP tube only confines the concrete shell and truncates at the top of the footing. The HC-FCS columns exhibits high lateral drift reaching 15.2% and fail gradually due to concrete crushing and local steel tube buckling, followed by FRP rupture. The reference RC column fails at a drift of 10.9% due to rebar fracture. Simple beam theory overpredicts the flexural strength of the columns by an average of 9%