Study On Fatigue Of Transmission Tower-Line Coupled System With The Coupling Effect Between Corrosion And Fatigue Vibration

Transmission tower-line system belongs to the important lifeline engineeringwhich is a project with enormous investment and profound influence. Transmissiontower-line system has the feature of high-rise structure and large-span structure,therefore, it is sensitive to wind. During the whole service stage, the structure wouldproduce fatigue damage accumulation affected by enviorment corrosion and windinduced vibration，which leads to the resistance and property of the system graduallydeteriorating. The capacity of the structure to resist the extreme load would bedecreased. In this paper, we should do research on the fatigue properties of transmissiontower-line system under the enviorment corrosion and wind-induced fatigue on the baseof theoretical derivation and experimental study. Mainly include the following contents:1) Based on the influence law of experimental results about Q345equilateral steelangle, a parameters degradation model of the material mechanic capability isestablished. Firstly, an acid rain corrosion model is established based on the rainfall ofchongqing and distributional characteristics.The change low of corrosion rates of Q345studied by this corrosion model varying with acid rain ph value、corrosion means andcorrosion time. A corresponding degradation model is establised on the base of theelastic modular, ultimate strength、elongation and so on.2) Based on the experimental results and improved single point-likelihood method,the S-N curve model which is about corrosion fatigue of Q345equilateral steel angle isestablised.A improved regression analysis method is given to ascertain S-N curveexpression argument on the base of improved single point-likelihood method. Theeffects of the corrosion time on the corrosion state of member and the fatigue damagemode are analyzed by fatigue experiment results. The P-S-N and γ-P-S-N curve modelof members is establised on the change law of members’ fatigue life with corrsion time.Based on the change law of parameter with time, the t-P-S-N curve model of membersis establised. The change law of fatigue life of Q345equilateral steel angle duringdifferent corrsion time is investigated by the model.3) By means of improved Single Point-Group Method based on the experimentalresults, this article establishes corrosion fatigue S-N curve model of the Q345equalangle steel under the action of different corrosion ways. This article proposes theregression analysis method of S-N curve expression parameters and its implementation algorithm based on the improved Single Point–Group Method, and observes thecorrosion state and fatigue failure model of the member in every corrosion wayaccording to the results of the Q345equal angle steel fatigue experiment under theaction of different corrosion ways, and establishes the corresponding member P-S-Nand γ-P-S-N curve model by analyzing the varying pattern of the member fatigue life inevery corrosion way, and explores the influence pattern that corrosion way to the fatiguelife of the Q345equal angle steel member under different reliability conditions usingthe P-S–N curve model of the Q345equal angle steel member that established bycombining theoretical derivation and parameters analysis under the action of differentcorrosion ways.4) The model of material mechanical properties under the effect of corrosion andfatigue will be taken out in the dissertation through the low cyclic loading test results ofQ345equilateral angle steel components. Those components above got differentdamage by corrosion, fatigue or corrosion couple with fatigue effect. First the specimenwill be treated with the damage of corrosion, fatigue or corrosion couple with fatigue inthree groups. Then all of the components in the three groups and some non-damagespecimen will be taken the low cyclic loading tests. The capacity of strength, stiffness,ductility and hysteretic behavior can be proved by the test of the components underdifferent damage condition before. The damage degradation model will be establishedthrough the test result. Finally, the combination parameters damage model of bothcorrosion and fatigue was established. This joint model of the degradation of thecorrosion and fatigue damage must be modified based on the actual variation of the testresults. So far the model of the degradation of the mechanical parameters in differentdamage was complimented.5) Based on the component fatigue S-N curve model and the performancedegradation model established by the test results, the fatigue properties of thetransmission line system and structural performance degradation are definitively studied.According to the S-N curve model of Q345equal angle steel established by the testresults, this paper analyzes the variation law of corrosion way and time to thetransmission tower structure fatigue damage and fatigue life. At the same time, thispaper establishes the tower line system by different corrosion conditions of materialparameters, and then, does the time-history analysis of the previous tower line system.Further, this paper analyzes the variation law of tower component fatigue performance at the different conditions. Based on the calculation results of two above-mentionedmethods, this paper comparatively analyzes the Wind-induced vibration fatiguedifferences of the material fatigue model and the component fatigue model intransmission towers system. According to the component performance degradationmodel affected by corrosion, fatigue and coupling corrosion fatigue, this paper analyzesthe degradation of the structure resisted external loads in different injury cases of thetransmission towers system.6) The fatigue property of transmission tower-line system has been studied basedon the proposed S-N models and adaptive response surface method. The jointdistribution model for both wind direction and wind speed is obtained by multiplyingthe distribution model of wind speed and wind direction together. Then the method forcalculating the wind-induced fatigue of transmission tower-line coupled system isproposed by combined with the joint distribution model and the Miner law. At last, thewind-induced fatigue of ultra-high voltage transmission tower-line coupled system isalso studied by the proposed method. A criterion for judging the existence of cross termsis derived mathematically in the present work. Combing this criterion with quadraticpolynomial of all possible terms via an indicative function, an adaptive response surface,which is more rational than traditional response surface, is proposed. And animplementation algorithm for judging criterion is put forward; the Structural reliabilityof ransmission tower-line system has been studied by the adaptive response surfacemethod.