Experimental Study on Flexural Behavior of Concrete Filled Steel Tube Girder Bridges

Concrete Filled Steel Tube (CFT) is a structure in which the steel tube is filled with concrete material. Such structure enables to achieve mechanical effects like increased bearing capacity and improved deformability compared to single steel tube structure or RC structure presenting the same section. Even if CFT structure has been developed to improve the ductility and bearing capacity of columns receiving mainly axial compressive forces in buildings, its applicability as flexural member like bridge girder is evaluated regard to its remarkable bearing capacity, excellent deformability (ductility), inhibition of noise and vibration. This study intends to develop a new steel composite bridge structure using the CFT member as girder. Accordingly, the results of member and full-scale bending tests performed on a CFT girder-slab composite section in order to assess the flexural behavior of the CFT member are presented. Specimens were manufactured considering several parameters such as the strength of filling material, the eventual presence and number of inner shear connectors to evaluate the bending bearing capacity of CFT member. The specimen filled by lightweight and low strength air-mortar with compressive strength of 8 MPa exhibited strength increased by about 20% compared to hollow steel tube, and the introduction of ┐-shaped perfobond rib inside the tube to improve the composite effect increased the strength by 50%. Moreover, the filling of the steel tube augmented significantly the flexural strength and ductility compared to the hollow tube, which showed that the confinement effect of the tube supplemented the brittleness of concrete. The adoption of inner shear connector prevented sliding at the interface between the filling material and the tube, and allowed the section to behave as a composite section. The stiffening effect of the ┐-shaped perfobond rib is seen to contribute relatively to the increase of the bending bearing capacity.