Research On Failure Mechanism Of Joint Connection And Design Method Of The FRP-Truss-Concrete-Deck Hybrid Bridge System

The FRP-truss-concrete-deck hybrid bridge system which adapts to the trends of Chinese bridge engineering is developing new types of high-performance bridge systems.It is also a bridge system that can fully exploit the mechanical characteristics of pultruded profiles.To promote the use of this hybrid structural system in bridge engineering,it is necessary to scientifically understand the failure mechanism of its joint connection and accurately predict its bearing capacity.This thesis focuses on the scientific key question which is the bearing failure of FRP pultrusion profile joints under static load.Through theoretical analysis and numerical simulation methods,this thesis presents studies of multi-scale elastic constant calculation method for FRP pultruded profiles,the progressive damage failure mechanism and the prediction method of bearing capacity of bolt joints in FRP truss and the design method of FRPtruss-concrete-deck hybrid bridge system.The main research contents are as follows:(1)Theoretical and Numerical Analysis of Multi-scale Mechanical Properties of FRP MaterialsThe theory of mesomechanics for elastic constants of unidirectional composite material is studied.Supplementary formulae of third dimension for modified blending model are proposed.Numerical model of representative volume element is established and a program for calculation of elastic constants is made.Prediction accuracy rate among modified blending model,homogenization theory and RVE numerical model is analyzed and an optimization proposal for the calculation of elastic constants of unidirectional composite material is made.A calculation method of the three-dimensional equivalent engineering constant of the composite laminate material based on the classical laminated plate theory is established and Matlab computational program is made,which indicates that the theoritic results are in good agreement with the experimental values.Furthermore,Composite laminate numerical models with different scales are established and their accuracy is also compared.Corresponding recommendations are provided according to the features of each model.(2)Analysis of Progressive Damage Failure and Bearing Capacity of FRP Bolt ConnectionsA progressive damage analysis process of FRP bolt connection is established based on equivalent laminated stress analysis model,Hashin-Rotem failure criterion,Matzenmiller stiffness degradation model and bolt joint failure evaluation method.In addition,a progressive damage numerical model of single-bolt FRP connection is built.The load-displacement curves of the double-shear specimens from the numerical model are basically consistent with the curves from test results and the error of the failure load is 4.75%.Mechanical performance between specimens with different shear forms is compared and the causes of the error of the single-shear specimens are analyzed.The freatures of stress and the entire process of damage initiation,damage propagation,and ultimate failure of each FRP layer are analyzed.Based on the bearing capacity prediction function of the progressive damage numerical model,the influence of geometric parameters on the connection strength is investigated and the geometric optimal design method for FRP bolt connection is proposed.(3)Analysis of Mechanical Behavior of Joint Connection of FRP-Truss-ConcreteDeck Hybrid Bridge SystemThe structure of open profile clamping node connection is put forward and the connection area is designed according to the geometric optimal design method for FRP bolt connection.The equivalent lamination model of the opening profile clamping node is established and the failure load and the damage initial load of the node connection structure are predicted as the design basis for the joints of the FRP-truss-concrete-deck hybrid bridge system.The trend of the stiffness degradation of the web-vertical and the web-slanted joints under tensile and compressive loads is analyzed.The relations between the damage trends and the "fiber-bolt extrusion angle" of each layer.A shear strength design method for bolted joints of FRP-concrete interface based on single bolt bearing capacity tested by experiments is proposed.(4)Design Method of FRP-Truss-Concrete-Deck Hybrid Bridge SystemThe design method and design procedure of FRP-truss-concrete-deck hybrid bridge system are proposed.A FRP-truss-concrete-deck hybrid bridge including its hybrid section,truss fa?ade,truss bolt joints and FRP-concrete interface connection is designed.A numerical model of FRP-truss-concrete-deck hybrid bridge is established and checking calculation of deflection,deck stress,bearing capacity of truss bolt joints and shear capacity of FRP-concrete interface connection are performed.