Effect of cyclic loading on the mechanical properties of CFRP tendons

Carbon fiber reinforced polymer (CFRP) tendons applied in the bridge engineering are generally sustained with cyclic load, which may bring degradation of the tendons' mechanical properties. The initial mechanical properties of CFRP tendons were tested through static load testing firstly. Then the effect of cyclic load on elastic modulus, relaxation and tensile strength of CFRP tendons under every stage was investigated through fatigue tests. The results show that the elastic modulus of the tendons under ultimate tensile state is about 5% higher than initial condition. Therefore, when the deformation of CFRP tendons has a significant impact on internal force of structure, the nonlinear problem of CFRP material is strongly recommended to be considered during structure designing stage. Two million times of normal service cyclic loading has little effect on elastic modulus, relaxation and tensile strength of CFRP tendons. Under the cycle loading with the stress range of 4.3% of ultimate tensile strength, the tensile strength of CFRP tendons increases by 1.2%. However, when the stress range reaches to 7%, there is no significant change in tensile strength compared with that under the initial condition.