A Comparative Study On Damage Identification Methods Of Space Grid Structures

Structural health monitoring is a hot topic in the field of civil engineering.It is the focus of the study to choose the appropriate structural health monitoring method for different structures.It is the basic procedure of structural health monitoring to establish the model and explore the information of structural damage,and use this information to determine the position and degree of structural damage.In this paper,the following research work is mainly carried out: the application of element generalized strain difference method,the static response method with frequency and the residual force method to spatial latticed structures and space tube truss structure,compare and analyze the damage identification results.Conclusions are as follows:1.The damage identification and anti-noise analysis of spatial latticed structures and space tube truss structure are carried out by using the two damage identification methods based on the generalized strain difference proposed in this paper.The first is based on the generalized displacement of the element strain difference damage identification method.In this method,the generalized strain of elements can be deduced from the generalized displacement of nodes by integrating the displacement time history response curve of the structure under impact load.Therefore the change of element generalized strain are presented as new dynamic indicator for damage location of the tuess structure,and the damage degree is determined by the damaged-element generalized strain changes.The second is based on the generalized strain of the element strain difference damage identification method.In this method,the element generalized strain is obtained by the summation of the absolute value of the strain time history curve,which can be deduced from the displacement time history response curve of the structure under impact load.Therefore the change of element generalized strain are presented as new dynamic indicator for damage location of the truss structure,and the damage degree is determined by the generalized strain change values.2.Damage identification and anti-noise analysis of spatial latticed structures and space tube truss structure were carried out by using the static response method with frequency.The structural damage parameters are identified by the response of structure to static loading and the low order natural frequency information,thusdetermining the possible damage location.And the damage function is determined by comparing the difference between the displacement difference before and after the damage and the actual displacement difference,and the damage degree is determined by the concave quadratic function.In order to accurately locate the damage elements with multiple damage conditions,this paper presents a method for secondary identification of multi-damage conditions.The amount of displacement change caused by the damage element in the single damage condition is subtracted from the displacement change caused by the multi-damage condition,and the damage is identified again by using the value as the new reference index.According to the principle of elastic superposition,the damage element under multi-damage conditions can be located accurately.3.Damage identification of spatial latticed structures and space tube truss structure were carried out by residual force method.The damage location can be determined by the residual force vector,and the degree of damage to the structure can be obtained by solving the residual force equation.4.The numerical simulation of the spatial latticed structures and the space tube truss structure shows: the two kinds of damage identification methods based on generalized strain difference can effectively identify the damage of different position and degree of structure,and the anti noise ability is better than the conventional element strain modal method;Combined with the frequency of the static response method has a strong ability to identify damage,but the anti-noise ability is limited;The residual force method can accurately identify the damage element for single damage and multi-damage condition of different damage degree.The shortcomings are the need for complete vibration mode and large data processing capacity.5.Based on the above methods,it can be seen that the anti-noise ability of the element generalized strain difference method is better than that of the static response method with frequencyt.The anti-noise ability of the element strain difference method based on generalized displacement is better than that of the element strain difference method based on generalized strain,and the method has good anti-noise ability for both the spatial latticed structures and the space tube truss structure,and can not only accurately locate the damage element,but also the quantitative identification of damage is very accurate.