Research On Structural System And Joint Connection Performance Of The FRP-Truss-UHPC-Deck Composite Bridge

The ultra-high specific strength,super durability and excellent designability of fiber reinforced composites make them meet the needs of modern bridge engineering for light weight,high strength and durability.The existing studies at home and abroad show that pultrusion molding process is the most economical and suitable for large-scale production of bridge engineering.At present,pultruded FRP has been widely used in bridge engineering,using FRP pultruded profile as the main bearing component of bridge has become one of the goals pursued by bridge researchers.However,there are still two technical bottlenecks when it is used in bridge engineering:(1)the longitudinal shear strength of web is very low.Due to the unidirectionality of pultruded FRP material,the shear strength,interlaminar tensile strength and interlaminar shear strength are relatively small,and the probability of longitudinal shear failure is high.(2)Due to the small section size of FRP pultruded profiles,the existing pultruded forming process cannot be used for the production of super large section FRP pultruded profiles for bridges.In addition,due to the low elastic modulus,it is difficult for the FRP beam structure to break through the stiffness limit.As a result,the design of FRP profile bridges is generally controlled by deformation,and the strength utilization rate of FRP materials is relatively low.FRP-Truss-UHPC-Deck composite beam is a new structural system formed by the combination of FRP top chord or special joints with interface shear key and concrete bridge deck.Reasonable joint connection technology is the core problem to realize the structural system.This project has carried out the experimental research on the structural system and joint connection performance of FRP-Truss-UHPC-Deck composite beam,the failure mechanism of FRP profile connection,the connection technology and design method of new large load-bearing FRP pultruded profile truss joint,the connection performance of FRP-UHPC interface,and the mechanical characteristics of FRP-Truss-UHPC-Deck composite beam bridge are systematically studied.(1)Multi-scale mechanical properties and theoretical analysis method of FRP pultruded profiles.Combined with material property test and numerical simulation,the macro/micro mechanical properties of FRP pultruded profiles were studied from different aspects,such as basic material components,single-layer plates and laminates,the micro numerical model of representative volume element(RVE)of FRP pultruded profiles was established.The mechanical properties of single-layer plates were successfully predicted based on the material properties of components,the prediction accuracy of RVE numerical simulation method and other meso theoretical analysis models for each engineering elastic constant is compared and analyzed.Numerical model of progressive failure of FRP pultruded profiles considering Hashin damage criterion is established,which directly reveals the progressive damage mechanism of composite pultruded profiles.(2)Studies on static behavior of the novel FRP pultruded profiles truss joints.The FRP pultruded profile truss joints connected by the U-shaped steel sleeve is innovatively proposed,the influence of structural parameters such as joint type,profile thickness,bolt diameter,pretension moment,steel sleeve length,steel sleeve(plate)thickness and adhesive layer setting on the mechanical properties of truss joints,such as bearing capacity,joint stiffness,deformation capacity and failure mode,is systematically studied through thirteen groups of static performance tests of FRP pultruded profile truss joints.A refined numerical model of FRP pultruded profile truss joints under static loading is established,the progressive failure analysis method considering Hashin damage criterion is used to reveal the failure mechanism and damage development law of truss joints connected by U-shaped steel sleeve.(3)Design and calculation method for the novel FRP pultruded profiles truss joints.Based on the calculation method of the bearing capacity of the new joint based on the strength of the pultruded section bar,the joint design method based on the strength of the gusset plate and the joint design requirements considering the buckling of the steel plate based on the thin plate theory,performance of the novel FRP pultruded profile truss joint is analyzed in depth from several aspects.Furthermore,the joint design method considering material strength,key geometric parameters and buckling resistance is established,and the detailed design process of the novel FRP pultruded profile truss joint is proposed.(4)Mechanical properties test and flexural/shear provisions analysis of FRP-Truss-UHPCDeck composite bridge.Nine groups of flexural performance tests and eight groups of shear performance tests of UHPC deck were completed,and the effects of reinforcement ratio,curing mechanism,shear span ratio,aggregate particle size and other parameters on the flexural/shear capacity,failure mode,structural ductility,stiffness degradation and other post cracking properties of UHPC deck were studied.The calculation method of flexural/shear bearing capacity of UHPC deck considering fiber tensile contribution is proposed and compared with the current flexural/shear provisions.(5)Experimental study on interface connection performance of FRP-Truss-UHPC-Deck composite bridgeThe effects of bolt arrangement,adhesive layer setting,perforated plate thickness,connecting bolt diameter,U-shaped steel sleeve size and the number of perforated bars on the shear bearing capacity,shear stiffness,failure mode and deformation capacity of FRP-Truss-UHPC-Deck composite interface shear connection were studied through eleven groups of push-out tests on the performance of FRP-Truss-UHPC-Deck interface shear connection.By analyzing the mechanical characteristics of UHPC-steel sleeve PBL connection interface and FRP profile-steel sleeve bolt connection interface,the whole process static failure mechanism of interface shear resistance is revealed,and the calculation method of interface shear capacity based on different failure modes is proposed.(6)Experimental study on mechanical behavior and structural system of FRP-Truss-UHPCDeck composite bridge.A new type of FRP-Truss-UHPC-Deck composite structure system is proposed and reasonable spatial structure connection method is given.The three-point bending test of the FRP-Truss-UHPCDeck composite test beam and truss element beam is carried out,the structural response of the FRPTruss-UHPC-Deck composite beam subjected to bending is systematically analyzed.Refined finite element model of FRP-Truss-UHPC-Deck composite test beam is established,and the influence of different structural parameters such as truss height,profile thickness,width and thickness of bridge deck and different working conditions such as single point bending,four point bending and uniform load on damage evolution,failure mode and bearing capacity of FRP-Truss-UHPC-Deck composite bridge is studied by using parameter analysis method.The integrated design process from material to structure of FRP-Truss-UHPC-Deck composite bridge is proposed to provide a systematic design method for its engineering application.