Experimental study on effectiveness of retrofitting via normal strength concrete filling on damaged circular steel tubes subjected to axial and horizontal loads

- A damaged steel tube is retrofitted by filling it with normal strength concrete.
- Concrete filling improves load-carrying capacity of a damaged steel tubes.
- The progression of local buckling deformation is suppressed by infilled concrete.
- Concrete filling is an effective retrofitting for a damaged steel tube.

Following an idea derived from the concrete-filled steel tube (CFT), this research aims to enhance the structural responses of a damaged hollow steel tube by filling it with concrete. A series of experiments are conducted to investigate the effectiveness of this technique, simulating repair but more importantly retrofitting after the tube is damaged by accidental loads such as earthquakes. To this end, loading tests are performed on the modeled specimens. The level of damage induced on the steel tube by loading is one of the parameters investigated. Concrete filling is found to improve the load-carrying capacity as well as the stiffness and ductility of a damaged hollow steel tube even with severe local buckling. The load-carrying capacity of the retrofitted steel tube is more than 1.5 times that of a hollow steel tube and was 72-89% of that of a traditional concrete-filled steel tube calculated using the design codes presented by Japan Society of Civil Engineers. From these experimental results, concrete filling promises to be an effective means of enhancing the structural response of a damaged hollow steel tube.