Study On Damage Detection Of Structures Based On Modal Strain Energy

Engineering structure safety are key problems to be solved in civil engineering field.Structural damage may cause structural performance degradation or even structure collapse,so the structural damage state to be evaluated in time is particularly important.Bar structures and plate structures are applied as research objects,and intensive and systematical research works on modal strain energy method are introduced in this dissertation.The main contents and conclusions are listed as follow:(1)The rationality of replacing damage structure stiffness matrixes by undamaged structure stiffness matrixes in element fractional modal strain energy method calculation process are explained.After standardizing the element fractional modal strain energy method index,the damage index threshold is presented,which is capable of localizing the damage position effectively.The positioning performance of the index was studied under different damage degree and the level of noise,the example results show that the presented index has good performance in damage localization and noise resistance.(2)Cross modal strain energy method has the advantages of high precision and without iteration in damage quantity identification.Elemental damage was defined by the cross-sectional area reduction,and the mass change also was considered.Elemental stiffness matrix was considered as the combination of stiffness matrices contributed by different sectional properties,the damage identification equation was expanded and multiple indexes were applied to describe structural damage.Numerical results show that considering structure mass change can improve the accuracy in structural damage identification.(3)Modal strain energy indexes value of adjacent elements were relatively large in plate structures damage localization,which was called the “vicinity effect”.The weight coefficient,which was calculating through the ratio of the integrate strain energy index between adjacent nodes and center node,was applied to modify the original modal strain energy index.The noise assessment factors were used to study the presented method performance in plate damage localization.Numerical results show that the revised index can realize the accurate localization of all kinds of damage,weak the “vicinity effect” and has good noise resistance.(4)The current cross modal strain energy method studies mostly focus on one-dimensional beam structure and two-dimensional bar structure,and has been seldom applied in plate structures.Considering the finite element node displacement and strain relations in plate structures,cross modal strain energy method is expanded in damage identification of plate structures.Numerical results show that this method can recognize the damage degree on plate structure in single damage and multiple damage cases.