Research On Health Evaluation System Of Spatial Steel Structure Based On Monitoring

It is of great significance to carry out a whole-life health monitoring for spatial steel structures which are usually used in large public buildings.The research of structural health monitoring technology in the field of spatial steel structure has been focused on the aspects of signal sensing,acquisition,transmission and data statistics.Data post-processing analysis,grasping structures' service status,comprehensive evaluation of health status and other aspects are lack of research.This means that only half of the work has been done in structural health monitoring.The current structural evaluation standards lack the evaluation indexes and systems for spatial steel structures which has the characteristics of large scale,huge number of components and remarkable influence of overall performance.In this paper,an evaluation index system based on structural monitoring is established for the spatial steel structures,which provides a feasible and practical method for comprehensive evaluation of health status.In this paper,the construction and calculation of each evaluation index is based on the basic data of stress,strain,deflection and vibration frequency.According to the characteristics of long-term stress and strain monitoring data of spatial steel structures,the missing data can be interpolated by one or multiple linear regression methods.Regressions are based on the relationships between the stress and the temperature or the stresses of different measuring points.Different seasons and times should be considered separately.When the data loss rate is less than 30%,the interpolation result is desirable and the error can be controlled within 10%.In this paper,a method of component importance analysis based on sensitivity analysis and load combination is proposed.According to the degree of importance,the components on which there are measuring points and their weights are determined.Based on the requirements of standards for components' strength and stability,according to the different stress modes,the static and stable performance evaluation indexes are constructed:static performance strength index of axial force component Ics,ba,static performance strength index of flexural component Ics,be,stability performance index of axial compressive component Icb,ba,stability performance index of compressive-bending component Icb,be.According to the value of evaluation indexes,the component performances are divided into four levels:a,b,c,d.In this paper,the evaluation method of the whole static,stable and dynamic performance of the structure is presented.Based on measured value of structural deflection and static deflection limit specified in the standards,the overall static performance index of structure Iss is constructed.Based on stability ultimate bearing capacity calculated by static modified model,the structural stability performance evaluation index Isb is constructed.Based on the maximum deflection value under the combined load of earthquake calculated by dynamic modified model and the limit of this deflection specified in the standards,the structural dynamic performance evaluation index Isd is constructed.The model is modified by using BP neural network method to optimize the main parameters that affect the performances of the structure.Based on the analytic hierarchy process(AHP),a four level evaluation indexes system for spatial steel structures is constructed.The first level is the general index of structural health evaluation.The second level has two system evaluation indexes of component and structure.The third level includes static,dynamic and stability performance indexes of structure or component.The fourth level is basic index calculated directly or indirectly by measured data.The weight ratio method is used to calculate the weight coefficient of third level performance indexes,and weight calculation method and weight sum method are used for evaluation.The weights of other comprehensive indexes of the evaluation system are calculated by AHP.First scale values should be determined according to the relative importance of each index and then the judgment matrix is constructed.The steps of the fuzzy comprehensive evaluation method are as follows.First the trapezoidal distribution and triangular distribution are chosen as the membership function.Then the membership vector and membership matrix are constructed based on which the fuzzy evaluation vector is calculated.The vector is integrated analyzed and finally the fuzzy comprehensive evaluation index is calculated.The comprehensive index of structural health evaluation can be divided into four levels:healthy,sub-healthy,unhealthy and sick.The calculation of the indexes and the structural health comprehensive evaluation process are demonstrated by some examples.The results show that the indexes system and evaluation method for spatial steel structure based on monitoring in this paper are feasible and effective.And the evaluation method is applied in the health monitoring program of Hangzhou Olympic Sports Center Stadium.Finally,the shortcomings in this paper are summarizes,and the directions of further research are put forward.