Research On The Damage Identification Of Beam Bridge And Truss Structures Based On Conjugate Gradident Methods

At present，the bridge construction are entering a rapid development in our country，especially with the rapid development of the city，the construction of urban rail bridges andhighway bridges also meet in the opportunity of development.However，with the quickeningpace of bridge construction，some of the old bridge were operated over fixed number of yearand the overload that is buried under the significant hidden danger to the safe operation of thebridge，so the safety of the bridge test is imminent.Firstly，according to the structure frequency and modal of damaged，modal residualforces vector equation is established.It makes use of generalized inverse (Moore—Peng Nuoinverse) and the minimum rank method separately to solve the modal residual forces vectorequation， which damage structure the change of the stiffness matrix(K) isacquired.According to the sparse nature of the matrix roughly identify structural damagelocation.Secondly，it makes use of the modal residual forces vector to define damage positionindicators which identify the location of the element.Because the experiment can only bemeasured the response to finite degree of freedom，so this article will be the generalizedinverse、the minimum rank and damage position indicators methods respectively combinedwith modal expansion method which identify structural damage location.According to the damage location positioning，the sine moving load respectively act onsimply supported beams and the three span continuous beams，it measure accelerationresponses to the limited degree of freedom.According to the response data，it make use of theconjugate gradient method(time domain method)and genetic algorithm to identify the damagedegree of elements.Structural damage identification belongs to inverse problemssolving.when single element damage，it can only need to make use of the conjugate gradientmethod and arbitrary assumption initial damage value，through iteration，modified stiffnessparameter models can get good identification effect.The conjugate gradient is combined withthe genetic algorithm when multi-element are damaged,the initial value of the conjugategradient method is obtained by the genetic agorithm，and then it is solved by iteration toachieve identification of the damage degree.About the truss structure,whether it’s single or multi-element damage，it can only make use of the conjugate gradient methods to identify thestructure damage.To simulate the actual situation，considering noise factor，it test the noiseresistance ability of the hybrid method.To compare the method of frequency domains with time domain methods，this articleswill combine element stiffness modification method (frequency domain method) withimproved condensation methods.Element stiffness damage factors can acquire throughsolving modals residual vector equations with least square method，which identify structuraldamage location and degree.The identification result shows that vertical modal data ontobeam can very good identification of structural damage.Add noise interference，it is a littleimpact on identification results，which shows that the method can resist to noise interferencestrongly.Theoretically，this paper the time domain identification method and frequencydomain identification method can better identify structural damage.Finally, it is the simulation damage experiment of simply supported beams which verifytime domains and frequency domains identification method’s feasibility of structural damageidentification.