Study On Fatigue Performance Of Bonded Anchorage For CFRP Tendons Affected By Temperature And Moisture

Carbon fiber reinforced polymer(CFRP)has excellent performance,such as light weight,high strength,corrosion resistance,fatigue resistance,low thermal expansion coefficient and good earthquake resistant performance.While the anisotropy and low lateral compressive strength limit its application.The bonded anchorage can minimize the damage of tendons and is widely applied.However,in some cross-sea bridges and ocean-going structures,prestressed anchorage for CFRP tendons may be subjected to seawater erosion at different temperatures.The interfacial and mechanical performance of the resin-based anchor zone may decline severely under cyclic loading,and there are few studies on the fatigue performance of anchoring system for CFRP tendons under the above working conditions.Based on the national natural science foundation project(Project ID: 51508235),the main contents and results of this study are as follows:1.Static load test of the adhesive anchorage system for CFRP tendonIn this paper,sodium chloride solution with a mass fraction of 5% is used to simulate the seawater environment,and the anchoring performance of the system under four different moisture and temperature conditions(i.e.,salt solution immersion at 23? for 30 days,salt solution immersion at 23? for 60 days,salt solution immersion for 50? for 30 days,salt solution immersion for 50? for 60 days,)is studied.Based on the test results,the following conclusions are drawn:(1)The water absorption of the anchoring system at 23? and 50? follows Fick's second law.With that,a prediction model for the ultimate tensile capacity of the bonded anchorage was established,and the model is in line with the experimental results substantially.(2)The ultimate tensile capacity and the interfacial shear strength of the bonded anchorage decrease with respect to the temperature and immersion duration.The ductility and interfacial performance of anchoring system are reduced with respect to hygrothermal conditions.The temperature is especially significant for the damage development in the anchor zone.2.Fatigue test of the adhesive anchorage system for CFRP tendonBased on the static load test results,the effects of moisture,temperature and fatigue stress amplitude on the fatigue performance of the anchoring system were analyzed,and the changes of system slip,stiffness,fatigue life and the strain of steel sleeve during cyclic loading were studied.Based on the test results,the following conclusions are drawn:(1)The immersion time,temperature and fatigue stress amplitude have significant effects on the fatigue performance of the anchoring system.Long-term immersion in salt solution makes the interface between the CFRP tendon and resin mortar gradually fail,thus it is more likely to cause matrix cracking or interfacial debonding during fatigue loading.(2)The microstructure damage develops rapidly and the fatigue life is relatively shortened when the maximum stress level is 50% and the fatigue stress amplitude is 340 MPa.(3)The immersion beyond normal temperature damages the anchoring system more seriously: the system slip and the stiffness at initial loading is significantly reduced,but the strain of steel sleeve remains stable when the maximum stress level is 50% and the fatigue stress amplitude is 174 MPa.(4)The fatigue performance of the anchoring system under moisture and temperature conditions is seriously declined compared with the anchoring system in the dry state.3.Fatigue damage mechanism and life predictionThe fatigue phenomenon of the anchoring system under moisture and temperature conditions shows that the moisture and temperature seriously affect the performance of the resin matrix and the interface between the tendon and bonding medium.The damage in the anchor zone develops and the fatigue performance deteriorates significantly under cyclic loading.The combination of the constant life curve and the S-N curve can quickly predict the fatigue life of the anchoring system under different load conditions.The shape parameter? of the constant life curve and the slopeb of the S-N curve can be modified by experiments to evaluate the fatigue life of the bonded anchoring system under moisture and temperature environments.