Performance Testing Of The Fatigue Life Gauge Steel Bridge Fatigue Life Estimates

The fatigue life gauge is a resistance-fatigue response sensor. The electric resistance value of the fatigue life gauge increases and accumulates automatically with the fatigue experience so that the bridge fatigue life can be evaluated based on the resistance change. In this thesis, the fatigue life estimation of steel bridges is investigated by using this new type of fatigue sensor-fatigue life gauge, which includes the mechanism of fatigue life gauge, the key techniques to process the fatigue life gauge, the method to measure the resistance-fatigue response performance of this new sensor and the procedure to estimate steel bridge fatigue life. The main work and results include:1. The process method of fatigue life gauge foil is discussed, including alloying component design, alloying method, cold roll technique and the processing parameter control of heat treatment.2. The procedure utilizing the alloy foil to produce fatigue life gauge is discussed, including the choice of backing material, frame design of grid, the jointing of down-lead and the technique of capsulation of the gauge.3. The resistance-fatigue response behavior of fatigue life gauge for 14MnNb bridge steel is tested in the laboratory. With these tests, the resistance-cycle number model is established by several-month fatigue experiments, including the strain threshold, the resistance-cycle number curves and the technique to transform the varied strain amplitude into the constant strain amplitude.4. How to implement the resistance response model of the fatigue life gauge to evaluate the residual fatigue life of steel bridges is studied. The proposed procedure includes three steps: (1) to determine the strain loading spectrum of critical points; (2) to equal the strain spectrum with that obtained from fatigue life gauge; and (3) to evaluate the bridge fatigue life with the help of S-N curve. 5. The proposed method with the resistance response model of the fatigue life gauge has applied to the Tsing Ma Bridge to estimate the fatigue life. Meanwhile, the fatigue life estimation is carried out by using BS5400 code. It is demonstrated that both results are quite agreeable.