Qilin Zhao

Research on the shear failure load of composite pretightened tooth connections by the characteristic lengths

In the conventional methods, the shear failure load of composite pretightened tooth connections is determined by experiment. To determine the shear failure load of the composite pretightened tooth connection without performing experiments, a method based on the characteristic lengths is presented in this paper. This method involves three steps: first, the characteristic lengths of the composite are determined; second, the stress distribution of the composite joint is analyzed by the use of a finite element method; finally, the failure load is predicted by the stress distribution of the characteristic length and failure criterion. The failure loads based on the characteristic lengths are validated by the test results for composite joints with different parameters. In comparison with the experimental data, this method provides higher magnitudes of failure load with a difference of <11% of the test value, except one with 11.6%. Good agreement was observed among the results of the present numerical method and the test. The method in the present work can be directly used in the design of pretightened tooth connections.

Experimental and theoretical research on the compression performance of CFRP sheet confined GFRP short pipe.

The axial compressive strength of unidirectional FRP made by pultrusion is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. A theoretical iterative calculation approach was suggested to predict the ultimate axial compressive stress of the combined structure and analyze the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure. In this paper, the experimental and theoretical research on the CFRP sheet confined GFRP short pole was extended to the CFRP sheet confined GFRP short pipe, namely, a hollow section pole. Experiment shows that the bearing capacity of the GFRP short pipe can also be heightened obviously by confining CFRP sheet. The theoretical iterative calculation approach in the previous paper is amended to predict the ultimate axial compressive stress of the CFRP sheet confined GFRP short pipe, of which the results agree with the experiment. Lastly the influences of geometrical parameters on the new combined structure are analyzed.

Evaluation of the torsional mechanism by analytical solution for a hybrid fiber-reinforced polymer–aluminum triangular deck truss beam

The hybrid fiber-reinforced polymer–aluminum triangular deck truss beam composed of modular structural units has the advantages of lightweight, high-bearing capacity, and faster installation. Although the analysis-oriented studies have been carried out by laboratory tests, numerical simulations, and theoretical analyses, the design-oriented study convenient for the application of the novel structure subjected to pure torsion is still lacking. Based on previous researches, some reasonable assumptions are presented to obtain a simplified analytical model. Analytical solutions of the torsional angle and torsional stiffness for the hybrid triangular deck truss beam subjected to pure torsion are derived. The derivation procedures and formulae are experimentally and numerically calibrated, finding that the formulae can be used to design with a satisfactory accuracy. The accuracy of the torsional stiffness predicted reaches to more than 90%. It is concluded that for the new hybrid triangular deck truss beam, the applied torsional moment is primarily resisted by the bending of its bilateral vierendeel trusses and the torsion of the fiber-reinforced polymer lower chords, which contribute approximately 37% and 62% for the total torsional stiffness, respectively.

Experimental investigation of a novel connection for pultruded composites: Hybrid bolt-tooth connection

Due to the insufficient connection efficiency of the bolted connection of pultruded composites, a novel composite connection technique called hybrid bolt-tooth connection was proposed. The paper presents a series of experiments studying the bearing capacity and the failure mode of the hybrid bolt-tooth connection by comparing with the pure bolted connection. Furthermore, the influences of the depth, the length and the number of the teeth on the connector’s failure mode and bearing capacity were studied. The results indicate that compared with the pure bolted connection, the hybrid bolt-tooth connection has a higher connection efficiency thanks to the load sharing of the teeth. The number, the depth and the length of the teeth exhibit a significant influence on the bearing capacity and failure modes. With the increase of the number and the length of the teeth, the bearing capacity is improved effectively; the bearing capacity of the connection with shallow teeth is significantly higher than that with deep teeth. Therefore, the hybrid bolt-tooth connection is an effective jointing method and has a good application prospect.

Influence of off-axis ply orientation on the axial compression behaviour of CFRP tubes

This paper presents an experimental investigation of the compression behaviour of Carbon Fiber Reinforced Plastics (CFRP) tubes with different off-axis ply orientations. A series of compression tests with effective end-reinforcement were conducted on [04/±theta] CFRP tubes, with θ equal to either 0°, 30°, 45°, 60°, or 90°. Various failure progressions and fracture morphologies were measured using a high-speed camera and a scanning electron microscope. The failure modes and mechanisms of CFRP tubes with different stacking sequences were analysed in detail. The results indicate that the off-axis ply orientation greatly influences the compression behaviour. The adopted end-reinforcement ensures that nearly all of the CFRP tubes fail within the gauge length. When θ < 45°, the tubes exhibit various failure modes, and the scatter of strength is large. However, when θ ≥ 45°, the sole failure mode is a shear fracture of the inner 0° layers, and their scatter of strength is minor. A new shear failure mechanism is instrumented: the shear fracture direction changes from inclining along the circumferential direction to inclining along the radial direction when θ varies from 45° to 90°. The failure strength and off-axis ply orientation display a complex non-linear relationship. When θ = 60°, the compression strength becomes maximum at an average value of 602 MPa, and the scatter of strength is 2.71%.

Analysis of Interfacial Bond Stress of Bonding Anchors for FRP Tendon

An analytic interfacial bonding stress solution of bonding anchors for FRP tendon�» loaded by axial force, is studied in this article. Based on the assumptions and differential equations of force equilibrium, the distribution of shear stress through the thickness of the anchors is derived, the calculating formula of interfacial bonding Stress is obtained. The presented calculating formula agrees well with the result of finite element analysis (FEA). Furthermore, based on the analytic solution, the factors affecting the distribution of interfacial bonding stress are discussed, including elastic modulus of material and geometry parameters. 1 INTRODUCE To the bond anchor for FRP tendon, many researchers focus on measuring the interfacial bond stress distribution and ultimate tensile strength etc by experiment. The research suggests: the bond anchors transfer the load by interfacial shear stress, the shear failure of tendon material close to or within the anchorage zone is most common mode of failure, this failure is induced mainly by the anchorage geometry and the degree of stress concentration exerted by the anchorage on the tendon. this mode of failure decreases greatly the efficiency of transfer load (1) (2) (3) Therefore, the research on distribution of bond stress and how to decrease the degree of concentration stress are very important. The experimental research is basic and essential; However, using a great deal of experiment to optimize and develop anchorage systems is too expensive and time-consuming. In the field of analytic theory, However the recent analysis not only simplify the columned anchors to the plate problem (4) (5) , but also the effect of grouted material and steel tube to interfacial bond stress are not considered. In this paper, considering the effect of grouted material and steel tube, according to the cylindrical coordinate, the distribution of the shear stress through the thickness of anchors was derived; The calculating formula of interfacial bond Stress of grouted material,FRP tendon and steel tube was obtained.