Experimental and numerical investigations on direct shear performance of UHPC dry joints

Abstract

Ultra-high performance concrete (UHPC) has great prospects in the field of precast segmental bridges. The excellent mechanical properties of dry joints between the UHPC segmental have become the focus of scholars all over the world. Currently, there are few studies on UHPC dry joints with a compressive strength between 120 MPa and 140 MPa. In this study, the direct shear performance of UHPC dry joints was tested and simulated with parameters of steel fiber content, confining stress, key number, shear key interlocking depth-height ratio (the depth-height ratio was used later), and key height. The results showed that the cracking resistances and ultimate strength of UHPC joints could be significantly improved with the increase of steel fiber content. All the UHPC specimens showed a little brittleness behavior with the average cracking load being 78.4% of the average ultimate load. Different cracking patterns occurred in single-keyed UHPC dry joints, while sequential failure arose for multi-keyed UHPC dry joints. Compared with monolithic specimens, the direct shear strength of keyed UHPC dry joints was reduced with a range of 51.4%–66.0%, and the decreasing trend was alleviated with the increase of the key number. The direct shear capacity of UHPC dry joints increased with the increase of key height and depth-height ratio, and the optimized depth-height ratio was 0.40–0.50. Compared the calculated results of existing formulae with the test results incorporated with the previous studies, it was found that Jiang's formula predicted the shear capacities of UHPC dry joints more accurately than the other formulae. In addition, the influence of the depth-height ratio on the direct shear capacities of UHPC dry joints cannot be reflected by the existing formulae, which need further improvement.