Research On Fatigue Crack Growth Mechanism Of Steel Structure Reinforced With Prestressed CFRP Plate

Fatigue cracking of aged steel bridges is a serious threat problem for the bridge serveice.Application of prestressed carbon fiber plate（CFRP）has been proved to be effective in fatigue life extension and retarding the crack propagation.However,a few studies foucus on the crack propagation driving force of steel structures.This thesis briefly reviewed the common crack driving force models and recommends a two-parameter crack driving force model usingΔK_eff^1-αK^α_max.The crack propagation was also simulated using dirving forces in the specimen of the steel tensile plate and beam by means of the interactive application of the fatigue analysis software Franc3D and ANSYS.The main conclusions are as follows:（1）This paper compares the typical crack driving force models includingΔK,ΔK_eff,(ΔK⁺K_max^0.5),ΔK_eff^1-αK^α_max.And a review on the assumptions,application scope and limitations of various driving force models is completed.The results show that the driving force modelΔK_eff^1-αK^α_maxcan provide more accurate prediction of the fatigue life of the steel structures in a wider range of stress ratios.（2）The crack growth simulation of the steel tensile plate is conducted using various driving force models on the damaged steel tensile plate reinforced by prestressed CFRP plate.The results show that the driving force modelΔK_eff^1-αK^α_maxcan well simulate the crack shape.The efftcts of the initial crack shape,location,number on fatigue life are also analyzed,and the results show that the initial crack shape and location are the governing factors.（3）The crack growth simulation of the steel beam is also investigated on the notched steel beams strengthened with prestressed unbounded CFRP plate.The crack growth in the steel beam performs in two stages:crack propagation just in flange and simultaneously in flange and web,and the first stage consumes more than 85%of the total fatigue.The results show that the prediction of the modelΔK_eff^1-αK^α_maxis in a good agreement with the experimental results.The research results would referred to the CFRP reinfrocement of the damaged steel structures and the assessment of fatigue life.