Experimental study on group effect of perfobond strip connectors encased in UHPC

Abstract

The group effect on the shear capacity of perfobond strip (PBL) connector group embedded in ultrahigh performance concrete (UHPC) in the steel–concrete joints of hybrid structures was studied experimentally. Push-out tests were performed on 26 encased PBL specimens parameterized by the concrete type, row (or hole) number, and row spacing of connectors. The test results revealed that the failures of all the connections were characterized by the shear fracture of the reinforced concrete dowels. The average ultimate capacities per row of shear connectors in UHPC without steel fibers and with 2% volume fraction of steel fibers were approximately 19% and 42% higher, respectively, than those in C55 normal concrete, owing to the high shear strength of the matrix in UHPC and further enhancement by steel fibers. The effect of increasing the row number from 1 to 3 was a decrease of approximately 17% in the average ultimate load per row of connectors. Similarly, a decrease in row spacing from 3.85 to 2.0 times the hole diameter caused an approximately 14% decrease in the average ultimate load per row. With a reduction coefficient accounting for the group effect introduced, an alternative equation for the ultimate capacity of multirow PBLs was proposed, verified, and adopted in the simplified shear safety evaluation.