Experimental and numerical studies on hybrid bolted connection of steel box girders: Bending mechanism

The non-axial force connection used in the earth-anchored cable-stayed bridge, consisting of the outer box girder, steel box girder inside and support system, allows the sliding behaviour of the steel box girder to release longitudinal deformation and secondary stress induced by the temperature and seismic effect at the mid-span of bridge. Hybrid bolted connection proposed to assemble the steel box girder can reduce the residual and construction deformation to guarantee the sliding performance. However, the structural behaviours of the steel box girder with hybrid bolted connection are unclear due to the lack of relevant studies, whose bending behaviour and moment-transferring mechanism are crucial to the design of the non-axial force connection. This paper presents experimental and numerical studies on the steel box girder with hybrid bolted connection to reveal its bending behaviour and the moment-transferring mechanism. Two 1/3 downscaled specimens S1 and S2 are tested to obtain the comprehensive bending behaviours and failure modes of the steel box girder with hybrid bolted connection. Finite element (FE) models considering ductile fracture criterion are established to reveal the comprehensive bending mechanism. Three stages of the bending mechanism are revealed and demonstrated: the bending moment of the steel box girder is mainly sustained by the inner flange connection and steel girder over 45 % and 35 % respectively, but the partial moment is carried by the friction behaviour of the single-lap connection at Stage I. The yielding of high-strength bolts on the inner flange connection results in the initial stiffness reduction when reaching the elastic capacity. Stage II: the inner flange connection reaches its ultimate bending capacity with the single-lap connections overcoming the friction limitation, and the structural response of specimens is determined by steel girder and the single-lap connection. At Stage III, steel girder reaches the ultimate moment resistance with 40 % of the total bending moment, and the bending moment and stiffness of the steel box girder with hybrid bolted connection are dominated by the single-lap connections. Besides, the moment-transferring mechanism of hybrid bolted connection is completely illustrated for the following structural design, calculation and optimization.