Damage Identification Of Freely Supported Beam Based On Modal Parameters

The reliability and safety of civil engineering structure related to the economy of annation and the security of people’s life and property.During the enlistment of the structure,under the influence of environment, load and so on, the structure come into being damage ofdifferent degree easily, how to identify structural damage accurately, is the premise job ofstructure’s diagnosis, assessments, and reinforcement. For engineering structure, its modalparameters (frequency, vibration mode and damp, etc) are the functions of its physicalparameters (mass, stiffness, etc.), when the physical parameters of the structure changed, themodal parameters were changed certainly, too. The structure’s modal parameters can bemeasured through the metrical instruments, so through the modal parameters changes ofstructure to identify their physical parameters changes, is the theoretical basis of damageidentification based on the modal of structure. This paper carried on an investigation into thedamage identification of the freely supported beam model made by I-steel, in the following Ihave carried the three aspects of work through:(1)Damage identification technology that based on the mode of the structure is theengineering damage identification and diagnosis methods developed in recent decades, theacademicians home and abroad did a lot of research. This paper expatiated detailed the theoryof foundations of damage identifications based on frequency, vibration mode, flexibilitymatrix, energy method and wavelet transform.(2) This paper carried the value analysis of the freely supported beam model made byI-steel through, adopted the methods based on “gradually orienting” of frequency changesquare ratio, vibration mode curvature difference and flexibility curvature difference toidentify the damages of the structure. It turned out that the methods of “gradually orientation”could identify the location of the freely supported beam structure’s one damage accurately,for two damages, the identification was not obvious, for the degree of only one damage wasnot obvious else; the method based on vibration mode curvature difference could identify onedamage or several damages, besides the degree of these damages in the same locations, butthe method could identify the degree of damages qualitatively only; the method based onflexibility matrix curvature difference could identify one damage or several damagesobviously, it could identify the degree of damages in the same locations qualitatively only too.When adopt the methods based on vibration mode curvature difference and flexibility matrixcurvature difference to identify the damages of freely supported beam, the identification resultwith the first-order mode was better than it with high order mode.(3) This paper carried the experimentation analysis of three freely supported beams madeby I-steel through. When the freely supported beams occurred one damage, adopted themethod “gradually orienting” to identify structure, the identification result validated the valueanalysis conclusion. When orientated the damage of the freely supported beams, achieved frontal three order modes of frequency to draw the graph of frequency change square ratio,then divided the structure model into three units, to simulate every unit’s damage, to draw thegraph of frequency change square ratio of every damage condition, to orientate the damagesin different units; second, divided the damaged unit modal into three units, to simulate everyunit’s damage, to go a step further, to orientate the damages in different units; like this,divided the modal smaller. When the primal structure modal was divided into81units,simulated the damage location accurately, the identification result was well, the error rangewas within3%.