Experimental study on the interfacial bond behavior of UHPC filled circular stainless steel tubes

As the interfacial bond property is of great significance to derive the composite action between stainless steel tube and UHPC for the Ultra-High Performance Concrete Filled Stainless Steel Tubular (UHPCFSST) columns, the push-out tests were conducted in this program, which includes 8 specimens having different stainless steel tube diameter and tube thickness. Based on the test results, the damage patterns and the full range load-slip curves are analyzed in detail, and the interfacial bond stress constitutes at different loading stages were also identified and evaluated. On top of that, the longitudinal strain of the stainless steel tube was analyzed based on elastic theory to derive the non-dimensional bond stress distribution law along the steel-concrete interface. The comparison between test results and the predictions from current code specification or the available empirical formulas indicate a large discrepancy and inconsistency. Therefore, the bond strength and corresponding slippage value of UHPCFSST columns were predicted by a new equation based on regression analysis. The research discovery obtained from this study provides theoretical significance and practical value for improving the design theory and application of UHPCFSST columns in practical engineering.