Static Experimental Research On Prefabricated FRP-Glulam-UHPC Composite Beams

In response to the problems of high self-weight,large long-term deformation,and poor durability of conventional timber-concrete composite beams,this dissertation introduces ultra-high performance concrete(UHPC)and fiber-reinforced polymer(FRP)into the composite structure,proposing a fully prefabricated FRP-glued laminated timber-UHPC composite beam structure that can be lifted and transported in one piece.The new composite beam structure is expected to solve the above problems and provide a new idea for the green development and technological innovation of small and medium span bridges in China,which can promote the construction industry and sustainable development.In this dissertation,a fully-prefabricated FRP-glued laminated timberUHPC composite beam(FTU)and a fully prefabricated glued laminated timber-UHPC composite beam(TU)were designed and produced,and a set of glued laminated timberUHPC joint surface specimens connected by flat steel plates and bolts were pushed out for static load tests.The mechanical properties of the new composite beam were compared and analyzed through theoretical calculations and numerical simulations.The specific work contents are as follows:(1)By pushing out the joint surface of glued laminated timber-UHPC,the slip modulus,failure mode,and shear bearing capacity of the flat steel plate and bolt connection of glued laminated timber-UHPC joint surface were studied.The experimental results show that the joint surface is sheared off in glued laminated timber and exhibits-good-post-peak ductility behavior.(2)By conducting static load destructive tests on two fully prefabricated FRPglulam-UHPC composite beams,the strain characteristics,displacement change rules,relative slip characteristics of the glulam-UHPC bonding surface,failure mode,and bearing capacity of the composite beams were tested and analyzed,and the mechanical properties of the composite beams were studied.The test results showed that under the four-point bending static load test the failure mode of the fully prefabricated glulamUHPC test beam was bending failure,while the failure mode of the fully prefabricated FRP-glulam-UHPC test beam was shear failure of the end glulam.And the difference in the two failure modes is greatly related to the position of the finger joint of the glulam beam.(3)The flexural stiffness and flexural capacity of the composite beams were analyzed and calculated using the "γ" method and the equivalent section method in Eurocodes 5.The results showed that the errors in calculating the flexural stiffness of the FTU beam using the "γ" method and the equivalent section method were 3.1%and 9.6%,respectively.The errors in calculating the flexural stiffness of the TU beam were 1.5%and 6.7%,respectively.The errors in calculating the flexural capacity using the "γ"method and the equivalent section method were 1.54%and 6.83%,respectively.The results showed that the "γ" method in Eurocodes 5 had small errors in calculating the flexural stiffness and capacity of the composite beams and had higher accuracy when used for calculations.The formula for the shear capacity of the timber-UHPC bonding interface from the previous research was used to calculate the shear failure mode at the end of the composite beams.The results showed that the error of the glulam shear failure formula is 18.59%.(4)A finite element model of the fully prefabricated timber-UHPC composite beam was established using Abaqus.Finite element numerical simulation analysis is carried out for the composite beam,After comparing and analyzing the model with the experimental results,the model was calibrated.A wide range of parameter analyses were conducted based on the finite model to clarify the influence of different parameters on the bearing capacity of the fully prefabricated timber-UHPC composite beam.The main parameters analyzed included the spacing of the shear connectors,the reinforcement ratio of the FRP bars,the height of the timber beam,and the thickness of the UHPC slab.The results showed that the reinforcement ratio of the FRP bars and the height of the timber beam had a greater impact on increasing the ultimate bearing capacity of the composite beam.