Cyclic testing of concrete-filled circular steel tube bridge columns having encased fixed-based detail

Concrete-filled steel tube columns have been recognized to have many desirable characteristics that can lead to stable hysteretic energy dissipation during earthquakes. They also have many other properties that make them advantageous for bridge applications (i.e. steel tube provides confinement to the concrete and acts as formwork during construction; concrete enhances the local buckling resistance of the steel tube; construction can be accelerated when the tube alone can carry the dead-loads; no need for stain protection on piers when superstructure is of weathering steel; final aesthetic of the product compatible with current practice, etc.).; A literature review was performed to collect data on the behaviour of concrete-filled steel tubes under axial load, combined axial and bending forces, and cyclic forces. Analytical work was performed to ensure that the test columns chosen would be representative of full-scale bridge piers found in North America. The foundation detail was designed to ensure that the full moment capacity of the composite column could be developed at its base without failure of the foundation.; This study involved testing four concrete-filled steel tubes under a constant axial load and subjected to an increasing cyclic horizontal force applied at the top of the column. All four columns sustained drifts of 7% before failure occurred by the steel tube fracturing at the location of the local buckles. Subsequent analytical work lead to two new proposed design equations. These produce axial-flexure interaction equations in much better agreement with the existing data than the equations for circular concrete-filled steel tubes currently used by the Canadian CAN/CSA-S16.1-M94 standard, or American AISC LRFD 1994 Specifications.