Experimental Research On The Bond Behavior Of FRP Pipe And Concrete At Interface

The durability of traditional material piles such as steel piles, concrete piles and timber piles has become an increasingly prominent problem when they serve as foundations in corrosive environment. The piles require expensive reinforcement and maintenance costs, which means traditional material piles have high life-cycle costs. FRPC pile (Fiber Reinforced Polymer Pile Filled with Concrete) is a new form of foundation, which combines FRP pipe and concrete together. As there are significant differences in properties between FRP material and traditional pile material, mainly in anisotropy, surface hardness, roughness, etc. It is necessary to conduct research on the bond property between FRP pipe and concrete in order to make sure they work together. For this purpose, sponsored by NSFC project "Study on basic characteristic of concrete-filled FRPC composite pile under cyclic horizontal load", the author has conducted a study on the bond behavior of FRP pipe and concrete at interface by means of theoretical analysis and laboratory model experiments. In this paper, the influence of bonding type, slenderness ratio, radius-thickness ratio, concrete strength and concrete type to bonding behavior at interface is discussed. The main contents and achievements of this research are as follows:The author has theoretically analyzed the bond property at interface of FRPC composite pile. Relationship between the bonding stress at interface and the strain on the surface of the FRP pipe was figured out. Beyond that, the theoretical constitutive relation of bond slip between FRP pipe and concrete was worked out.Push-out tests of 33 concrete-filled FRPC composite piles have been carried out, the component of bonding force and the characteristics along with development of adhesive failure were discussed based on the results of the experiments. The characteristics of P-S curve and ?-S curve of test specimens were summed up.By controlling variables method, the influence of bonding type, slenderness ratio, radius-thickness ratio, concrete strength and concrete type to bonding behavior at interface was discussed. The test results are listed as follows:Firstly, the bonding strength of internal-spiral FRPC specimen is the highest, specimen with shear connectors comes the second and direct-bonding specimen has the lowest bonding strength when their geometrical dimensions are the same; Secondly, slenderness ratio has no obvious effect on bond strength of FRPC pile; Thirdly, the smaller the value of radius-thickness ratio is, the better bonding performance FRPC pile gets; Fourthly, concrete strength has positive influence on the bonding strength of direct-bonding FRPC piles but has little effect on internal-spiral FRPC piles and those with shear connectors; Finally, the bonding performance of FRPC pile with expansive concrete is much better than that with common type of concrete.By attaching strain gauges on the surface of FRP pipe along its longitudinal direction, the author explored the distribution regularities of the strain on the surface and the bonding stress at interface. According to the test results, the strain on the FRP pipe surface is triangle-distributed along the height, which means that the bonding stress at interface is approximately uniformly distributed.The author has conducted regression statistical analysis of the ultimate bond strength of internal-spiral specimens and specimens with shear connectors, regression formulas of the ultimate bond strength were finally obtained.Based on theoretical analysis and experimental results, simplified constitutive models of different bonding-type specimens such as direct-bonding specimens, internal-spiral specimens and specimens with shear connectors were put forward.