Destructive Test Study Of FRP Combined Plane Truss

Fiber reinforced composites(FRP)have been promoted and applied in various fields due to their light weight,high strength and other characteristics.With the development of materials science and the continuous strengthening of inter-disciplinary integration,the fiber-reinforced composites(FRP)with good tensile properties as the main load bearing components applied in truss structure can highlight its characteristics of high specific strength and high specific stiffness,which makes full use of the material.This paper is based on the National Natural Science Foundation project "FRP-concrete composite box section double-layer traffic structure system stress mechanism and design method research(project number: 51572836)".Applying FRP profiles as the main load-bearing components to engineering requires two key issues to be addressed: first,the connection between FRP profiles;and second,the anisotropy defects of FRP materials.In order to explore the solutions,we designed two steel-FRP combined plane trusses with different numbers of nodes and different numbers of nodes,and the joints for assembly between the rods can be installed at the end of the FRP round pipe and the steel pipe with a specific connection.The FRP round pipe and the steel pipe with the connecting piece are assembled through the metal ball joint to realize the production of the steel-FRP combined plane truss,and the mechanical performance test of the two trusses is carried out to explore the feasibility of the combination of the steel and the FRP profile;Three kinds of FRP rods with different joints were pulled out to explore a more effective connection method of FRP profiles.The main research contents are as follows:(1)The static load test of steel-FRP combined plane truss with length of 4m and height of 1m is carried out to investigate the reliability,deformation coordination ability and overall mechanical performance of steel-FRP combined plane truss joints.It can be seen from the test results that the variable corrugated wedge pre-tightening toothed joint and the inner and outer double-sleeve joints can effectively transmit the load.The steel-FRP combined plane truss is measured under the vertical load of the mid-span.The relationship between the ratio relationship and the theoretically calculated internal force coefficient is in good agreement.The existing truss calculation theory can be applied to the steel-FRP combined truss,and it is feasible to combine the FRP profile with the steel into a truss structure.(2)To further verify the reliability of the rubber-bolt-variable corrugated wedge pre-tightening hybrid joint and the coordinated deformation ability of the FRP combined truss,fully utilize the existing rods and reduce the truss joints on the basis of the original 4m long truss and the number of rods,a 1m long steel-FRP combined truss was assembled and was taken a static test.The test results of FRP combined plane trusses with different number of joints and different number of rods were compared and analyzed.(3)Pull test was conducted on FRP pipe connected by three different connection forms by glue connection,glue-bolt connection,glue-bolt-variable corrugated wedge pre-tightening tooth.The test results show that: bolt connection should be avoided as far as possible in the design of joint connection for pull-extruded FRP tubes.For thin-walled FRP pultrusion pipes(wall thickness less than 4mm),the internal and external double-sleeve cemented joints can be used to exert the tensile strength of the FRP pipe.The maximum rate can reach 80%,and the rubber-plug-variable corrugated wedge pre-tightening tooth mixed connection specimen exhibits certain ductility when it is damaged.The failure mode is more ideal than the other two connection forms,but the pretension force exerted by the variable corrugated wedge pretension teeth on the FRP tube is affected by many factors,and the extrusion degree of the FRP tube is not well controlled,so it needs to be further improved.