Shuya NAITO

Effect of Material Deterioration on Mechanical Properties of Steel-Concrete Composite Structures

Takumi SHIMOMURA

The mechanical properties of shear connectors used in the joints of steel-concrete composite structures have been extensively studied under normal conditions. However, there are few studies that have investigated the effects of corrosion on these connectors. Therefore, this study focuses on the joints with headed studs, which are widely used as shear connectors, and examines the hypothesis that when corrosion-induced cracks connect between studs, they act as pre-existing cracks, leading to premature failure of the concrete.
To verify this hypothesis, three push-out test specimens were prepared according to the push-out test method proposed by the Japan Society of Steel Construction (JSSC) for headed studs. Each specimen had two rows of studs, spaced at 100 mm, which is the minimum spacing specified in the Standard Specifications for Composite Structures.
To induce corrosion, the specimens were immersed in a 3% saline solution and subjected to electrolytic corrosion. The corrosion levels were categorized into three stages: no corrosion (0%), crack propagation and rust leakage between studs (7.76%), and further corrosion progression until crack widening had ceased (17.95%).
After inducing corrosion, push-out tests were conducted. The results indicated that for the 7.76% corrosion specimen, where cracks fully penetrated the concrete block, the shear strength was lower than the calculated value that considered only section loss. In contrast, the 17.95% specimen exhibited lower shear strength than the non-corroded specimen but did not fall below the section-loss-based calculation, as the cracks did not penetrate the concrete block. While the calculated values predicted failure due to stud fracture, both the 0% and 17.95% specimens failed by stud fracture, whereas the 7.76% specimen failed due to concrete splitting. These findings confirm the hypothesis that corrosion-induced cracks connecting between studs can act as pre-existing cracks, leading to early concrete splitting.
Finally, based on these results, the implications of stud corrosion for the maintenance of steel-concrete composite bridges with corrugated steel webs were discussed, and future experimental plans were presented.