Research Of Mechanical Properties For Adhesive Interface In GFRP Bridge Deck

Adhesively bonded joint is one of the key parts of GFRP bridge deck.The whole mechanical properties of the GFRP bridge deck and the composite action between GFRP bridge deck and main girder depend on the adhesively bonded joint.In bridge engineering,several failures(e.g.,delamination and cracks)often occur at the adhesively bonded joint of GFRP bridge deck,which have an adverse effect on usability and durability.In order to enhance service behavior of the GFRP bridge deck and promote the application in engineering,systematic research of the mechanical properties for adhesively bonded joint is necessary to perform.The characteristic of interfacial stress distributions for composite single-lap joint(SLJ),feature of non-uniformity distribution of double cantilever beam(DCB)specimen and its effects on mode-I fracture toughness were intensively studied with theoretical analysis,numerical simulation and model test.The aforementioned works can provide theoretical models and practical methods for strength design and anti-fracture design of adhesively bonded joint in GFRP bridge deck.Details of the present study are summarized as follows:(1)A one-dimensional nonlinear model with high accuracy for determining edge moment factor of unbalanced composite SLJ under tensile loading was provided with incorporating the effects of bending-tension coupling and large deformation in overlap.The parametric analyses concerning geometrical parameters and material properties were performed with the on-dimensional model.The applicability and accuracy of the existing models for unbalanced SLJ and the varying pattern of the edge moment factor were studied.Meanwhile,the critical value and theoretical formulas were provided for determining long and short unbalanced SLJ.(2)A two-dimensional model with high accuracy for determining interfacial stress distributions of unbalanced composite SLJ under tensile loading was developed by considering the effects of bending-tension coupling and large deformation in overlap.The effects of the tensile load and material properties on adhesive stress distributions were studied with the present two-dimensional model.The results indicated that the effect of the large deformation in overlap region on adhesive stress distributions can't be neglected.And the stress intensities of adhesive stresses are related with the difference between the flexural stiffness of upper and lower adherends.(3)An equivalent plate model was developed for determining non-uniformity feature of mode-I energy release rate(ERR)distribution along the straight crack front of DCB specimen.The analytical formulas with high accuracy for non-uniformity and variation coefficients were obtained with Kirchhoff plate theory and Rayleigh-Ritz method.The equivalent plate model and virtual crack closed technique(VCCT)were used to analyze the non-uniformity coefficients for the bi-material DCB specimen,which is equal to the average value of the non-uniformity coefficients for the two symmetric DCB specimens composed of upper and lower adherends of bi-material DCB specimen,respectively.(4)The varying patterns of non-uniformity coefficient and deviation of crack length for DCB specimen in initiation and propagation processes and its effects on mode-I fracture toughness were studied.Then,the three classical beam models in existing codes(including ASTM D 5528-01e3)for determination of mode-I fracture toughness were modified.The practical formulas with compact form and high accuracy for determing deviation of crack length in initiation and propagation processes were developed.(5)An improved DCB specimen with curved pre-cracked front was provided.The mode-I ERR distribution along the curved pre-cracked front is uniform.Compared to the traditional DCB specimen with the straight pre-cracked front,mode-I fracture toughness determined by the improved DCB specimen is more reasonable and its calculation is simpler.In order to conveniently and accurately obtain the curved pre-cracked front with feature of uniformity distribution of mode-I ERR,a practical formula with compact form for determination of shape function of curved pre-cracked front was provided.(6)The effect of length of adhesive interface crack on local mechanical properties of GFRP bridge deck in negative moment region of steel-GFRP composite bridge was investigated with multi-scale finite element model and VCCT.And the fracture behavior of adhesive interface crack under three worst-cases of load was evaluated.