Study On Interfacial Bonding Properties Of FRP Strengthened Brick Masonry Structures

In recent years,fiber reinforced polymers（FRP）are more and more widely used in the field of structure reinforcement,and the related researches on FRP are increasing day by day,the study on FRP reinforced brick masonry structure has also appeared.However,the existing research has not highlighted the influence of the mortar joints,so that the research results and the actual reinforcement project has a deviation..In this paper,40 groups of FRP reinforced brick masonry specimens were made,among which 20 groups were strengthened with carbon fiber reinforced polymers（CFRP）and the other 20 groups were strengthened with basalt fiber reinforced polymers（BFRP）.The experiment takes single brick and masonry prism as the reinforcement object,considers the impact of fiber sheet material type,bond length,bond width,mortar joints and end anchorage on the interface bond performance,and focuses on the influence of mortar joints on the interface bond performance.The influence of mortar joints on interfacial bonding performance mainly includes:the existence of mortar joints will make the ultimate bonding capacity of masonry prism specimen 10.4%～37.5%lower than that of single brick;The presence of mortar joints makes the load-displacement curve show a"discontinuous"linear increase,and the curve value will decrease by 7.5%～34.0%at the mortar joints.Based on the equilibrium principle of force and continuous boundary condition,the shear stress of mortar joints is analyzed,it is concluded that the shear stress at the mortar joints in the masonry prism is smaller than that in the brick block,which is also the reason why the effective bonding length of the masonry prism is longer than that of the single brick.In order to consider the influence of mortar joints on the bearing capacity of interface,the ratio coefficient of brick-mortar area（χ）was put forward.Strain distribution method and superposition principle are used to draw strain distribution diagram and experimental bond-slip curve,and the deformation extension of FRP and debonding mechanism of FRP are expounded.The debonding process of FRP can be divided into three stages:linear elastic stage,microcrack stage（softening stage）and macrocrack stage（debonding stage）.Based on the crack propagation energy principle,the energy release rate G theoretical expressions of failure modeⅠ,Ⅱand failure modeⅤare obtained respectively.The peak value and integral value of the test stress-slip curve were calculated,using fitting regression method to get bilinear stress-slip law key parameters₈（6）,₀ expression,substituting the expression of energy release rate G into the general model to obtain the empirical formula of interface bearing capacity,and the empirical formula of interface bearing capacity was compared with the experimental results,the mean error of the predicted value was 8.9%,the predicted value curve of the model agrees well with the experimental curve.In the improved model,the ratio coefficient of brick-mortar area is introduced to consider the influence of mortar joints on the bonding capacity of the interface,which is more in line with the actual engineering situation,it can be used as a reference for the application of fiber reinforced masonry structure.