Bending performance of wet joints in negative moment zone of prefabricated small-box girder bridges: Experimental and numerical study

Abstract

The prefabricated small-box girder (PSBG) structure adopts the construction method of simple supporting beam transforming to continuous beam, which results in negative bending moment on the box girder supports and large tensile stress on the top of the longitudinal wet joints. Due to the relatively low tensile strength of concrete, the top plate of the bridge in the negative bending moment zone is susceptible to cracking under the load of vehicles, as well as due to the shrinkage and creep of concrete. This poses a risk to the safety, applicability, and durability of the bridge structure and may lead to a reduction in these aspects. Ultra-high performance concrete (UHPC) has excellent tensile performance and stronger crack control capability, which can effectively improve the anti-cracking and durability of the wet joints of the PSBG. In the present study, the research focused on the negative bending moment zone of a three-span continuous small–box girder bridges. This zone was selected as the research object and served as the basis for designing a stepped wet joint girder, where UHPC is partially cast on the top plate. By conducting three-point bending tests, we compared the bending mechanical properties of the joint girders when poured with normal concrete (NC) and UHPC in the joint top area. Further, the key factors affecting the anti-cracking performance and bearing capacity, including the length and thickness of the UHPC layer and the width of the wet joint, were analyzed by finite element simulation. The results show that the contribution of the top plate UHPC to tensile stress cannot be ignored. Compared with the NC joint girder, the UHPC joint girder has better toughness and plasticity, and the cracking load and bearing capacity increased by 28.6% and 9.7%, respectively. According to the simulation results, as the increase of the length and thickness of the UHPC layer and the width of wet joint, the anti-cracking and bearing capacities of the PSBG with the wet joint were enhanced. The thickness and length of the UHPC layer had a significant effect on improving the anti-cracking performance of the wet joint, and the joint width only needed to meet the transfer length of rebar bond stress.