Push-out tests for perfobond strip connectors with UHPC grout in the joints of steel-concrete hybrid bridge girders

This paper aims at examining the structural behavior of perfobond strip (PBL) connectors for steel-concrete joint of hybrid girders with ultra-high performance concrete (UHPC) as grout for such connectors. Twenty-four push-out specimens fabricated according to the design used for the connectors in the steel-concrete joint in a hybrid cable-stayed bridge have been investigated. Effects of several parameters such as (i) the interface bond between perforated plate and concrete, (ii) dowels inside the holes in the plate, and (iii) volume of steel fibers in the UHPC on the behavior of PBL were discussed in depth. Experimental results indicated that the use of a 2% volume fraction of steel fibers in the UHPC, increased the average bond strength at the plate/concrete interface and the shear resistant-capacity of concrete dowel by 82% and 50%, respectively, as compared to UHPC specimens without the fibers. The concrete dowel played an important role in developing the desired loading resistant-capacity of the PBL, and about 34-41% of the overall resistance of a standard PBL embedded in UHPC were supplied by the concrete dowel surrounding transverse rebar. The source of the achieved ductility of PBL was mainly determined by the action of transverse rebars, and the ductility in the specimens having transverse rebars was about eleven times the ductility of similar specimens without the rebars. Furthermore, the experimental ultimate strength values of PBL were compared with available equations in literatures published recently, and an analytical model for PBL/UHPC was developed and appropriate parameters were derived from present data and used to provide reliable prediction of ultimate resistant-capacity of PBL in the hybrid girders' steel-concrete joints.