Experimental And Theoretical Research On Joint Connections And The FRP-Truss-UHPC-Deck Hybrid Bridge System

Pultruded FRP shapes and UHPC can adequately satisfy the sustainable requirement regarding light, high-strength and durable in the future bridge engineering, and have been widely used in the bridge engineering at home and abroad. The FRP-truss-UHPC-deck hybrid bridge system, proposed by this paper, complies with the development trend of pultruded FRP shapes, UHPC and their hybrid structure in the bridge engineering, and overcomes the disadvantages, such as web shear failure of FRP profiles, low stiffness of FRP hybrid structure and low wear-resisting performance of the pure FRP truss bridge deck. Through model test, theoretical analysis and fine element methods, this paper presents studies on the failure modes, anti-slipping stiffness and ultimate bearing capacity of the two types of joint connections under varied influence factors, also presents experimental research and fine element analysis on the FRP-truss-UHPC-deck hybrid bridge system, and gives comparison between FRP-truss-UHPC-deck hybrid bridge system and other 6 types of bridges. The main research contents are as follows:(1) Experimental research and analysis on FRP bolted connectors20 FRP bolted connectors are conducted to investigate the effect of shear form, bolt diameter, bolt number, plate geometry parameter, pre-tightening force, and structural adhesive bond on failure mode, anti-slipping stiffness and ultimate bearing capacity. FRP bonded/bolted connectors take the advantages of bolt connectors and bonded connectors, and hold many characteristics, such as high rigidity, good ductility. Shear damage of FRP plate is the main failure mode in FRP bolted connectors, and its crack starts from the 45° direction of bolt hole, then extending along the direction of fiber and eventually destroyed. Through experimental and theoretical analysis, the anti-slipping stiffness mode of FRP bolted connectors and FRP bonded/bolted connectors is proposed by this paper, and the formula about the ultimate bearing capacity of FRP bolted connectors is also presented under shear failure mode.(2) Experimental research and analysis on FRP shear connectors10 FRP push-out specimens are tested to investigate the effect of bolt number, bolt diameter, bolt height, reinforcement ratio of UHPC plate, concrete grade on failure mode, anti-slipping stiffness and ultimate bearing capacity. The ultimate bearing capacity of FRP-UHPC push-out specimens is higher than the FRP-NC push-out specimens, and the average bearing capacity of single bolt increased by 80%, the average anti- slipping stiffness increased by 130%. Shear damage of FRP wing plate and direct shear destruction of bolt are the two main failure modes of FRP push-out specimens. Based on different failure modes, two anti-slipping modes are proposed by this paper. Verified by the experiment, the ultimate bearing capacity of the FRP push-out specimens, under the direct shear destruction of bolt, can be calculated by the formula proposed by this paper.(3) Experimental research and analysis on FRP-truss-UHPC-plate hybrid bridge systemThe FRP-truss-UHPC-plate hybrid bridge system is tested to study its mechanical property under three kinds of load actions. This hybrid bridge system can meet the design requirements very well, showing good linear mechanical performance under the monotonic load, and good resume performance under the cyclic load. The results calculated by finite element numerical model conform to the experimental value, so the finite element numerical model can be well applied to predict the mechanical performance of the FRP-truss-UHPC-plate hybrid bridge.(4) Mechanical property analysis and comparison of FRP-truss-UHPC-plate hybrid bridge systemFinite element parametric analysis is carried out to study the mechanical property of FRP-truss-UHPC-plate hybrid bridge system. The change of the FRP bottom chord's section size, the FRP web member's section size and the hybrid bridge's height have a bigger influence on the stiffness of FRP-truss-UHPC-plate hybrid bridge system. Using the UHPC material as the hybrid bridge's deck can improve the anti-slipping stiffness of FRP-UPHC interface, and the bending stiffness of the FRP-truss-UHPC-plate hybrid bridge system. Compared with the three typical FRP truss bridges at home and abroad, this hybrid bridge is lighter, using less FRP materials, and its relative stiffness is bigger. Compared with the other three highway bridges of the same span, this hybrid bridge is also lighter, convenient to construct, possessing great application advantage in coastal area and marine environment.