Damage Detection Of Space Trusses Based On The Change Of Cross-model Modal Strain Energy

Civil engineering structures are usually damaged by various factors such as environmental corrosion,accidental load and fatigue loading during their service process.If the damage can’t be found and repaired timely,the structure may be partially damaged or even overall collapse.In order to ensure the operational safety of working structures,it is vital to develop efficient and accurate damage identification methods.Modal parameters(such as frequency and vibration mode)are often used to establish damage indexes or identification algorithms to achieve structural damage localization or quantitative identification.The research shows that modal strain energy based on vibration mode is sensitive to structural damage.However,most of previous studies that focus on damage identification based on modal strain energy used structural models or physical components that are relatively simple and small in scale,while relatively few studies have been conducted on large structures(such as space trusses)with relatively complex structures and a large number of members.Moreover,the previous damage identification studies based on modal strain energy have some problems such as weak antiinterference ability and large fluctuations in positioning accuracy.The concept of cross model modal strain energy is introduced in this paper.In this paper,the concept of cross-model modal strain energy is introduced to systematically study the damage identification method applicable to spatial structures based on the change of cross-model modal strain energy in order to improve the accuracy of structural damage identification.The concrete work content is as follows:(1)The damage locating ability of indexes constructed by traditional modal strain energy and cross-model modal strain energy was compared.According to the constructive formula of the damage index,it can be judged from the qualitative point of view that the cross-model modal strain energy index has stronger anti-noise ability than the traditional modal strain energy index.The numerical analysis of a space truss also shows that the cross-model modal strain energy index has a more prominent ability to locate damaged structural elements and strong robustness against noise.(2)Furthermore,a new damage location method(WT＿CMSEI)is proposed by combining cross-model modal strain energy with wavelet analysis.Based on the calculation of the crossmodel modal strain energy index(CMSEI)of all elements,the wavelet analysis is performed on the spatial domain sequence composed of the CMSEI indexes of each element.And highfrequency detail coefficients are extracted for signal reconstruction to obtain the new damage index WT＿CMSEI.The greater the WT＿CMSEI index value of an element,the higher the possibility of damage of the element.The numerical analysis of a space truss and a double-layer lattice shell shows that the wavelet analysis can further improve the damage location ability of the cross-model modal strain energy index and can better resist the interference caused by undamaged bars.(3)On the basis of the above research,a two-stage damage identification method based on cross-model modal strain energy is proposed.The suspected damaged element is found using WT＿CMSEI index firstly,and then the reduced sensitivity equation including only the suspected damaged elements is established based on the sensitivity relationship between the cross-model modal strain energy and the element damage.The quantitative identification of structural damage can be achieved by solving the reduced equation iteratively.The numerical analysis of a plane truss,a space truss and a double-layer lattice shell shows the effectiveness of the proposed method.Furthermore,the proposed method can accurately identify the damage degree of the damaged element even considering the misjudgment of positioning.