The Technology Of Structural Damage Identification Based On The Modal Parameter

With the expeditious development of science and technology,the scale and constructing difficulty of structure,such as water-power engineering,harbor engineering,ocean engineering of hydraulic structure and bridge,tunnel,industrial and civil construction of civil engineering structure,is increasing.The structure will have problems of material deterioration and damage accumulation when it is charged with the design load and varieties of environmental factors in using time.That will have effect on security and stability of the structure.Direct or indirect economic losses caused by failure or sudden destruction will be serious.Therefore,the damage identification and the real-time monitoring of important structures have important theoretical and practical significance.Actuality of damage identification for structures is expatiated firstly and comments are made on the methods of them.These methods include natural frequency,displacement modal,COMAC,flexibility matrix,wavelet analysis,nerve network and genetic algorithms etc.An approach of structural damage identification based on difference of the strain modal is discussed,which is used in numerical simulation of the damage for a simple supported beam and a continuous beam.The damage of structure is simulated by rigidity reduction of the element,and the mode shape of damage and undamaged are calculated by the software of FEM.Comparing with graphs of the difference of strain modal computed by central difference method,the damage is identified.An experimental investigation of crack identification is conducted to a cantilever,which further proves that using strain modal to identify structural damage is rational and feasible,and numerical simulation is accurate.The strain modal is sensitive parameter to structural damage identification is proved.It can be used to determine the location of structural damage and qualitative assess the degree of damage in a small number of lower order modes.When the structure is analyzed in the same order strain modal,the difference of strain modal is increased with the increase of the degree of damage.For the same degree of damage, the difference of strain modal has the trend of increasing with the increase of the strain modal order.The research on damage identification either can be used to monitor and evaluate the condition of structure,or change the existing structural design concept by using the research results.Security measures of structure design are taken in the position where easy to damage at the early stage of structural design.The research of this paper proves that the strain modal technology used to the structural damage identification is feasible and it has theoretical and practical value in structure health monitoring.