Study On Seismic Performance Evaluation Methods For Existing Spatial Latticed Structures

With the gradual improvement of structural seismic performance evaluation theory,the research on structural seismic performance-based design method has achieved many results,which are widely used in engineering design,but at present,the research on the seismic performance-based evaluation method of existing structures is still few and not in-depth.Due to natural disasters(earthquake,flood,snow and wind,etc.),artificial accidental accidents(explosion,impact),design errors,unqualified construction quality or untimely maintenance in service,the existing spatial latticed structures may occur different types and degrees of defects and damages,resulting in the degradation of the overall seismic performance of the structure.Therefore,it is of great theoretical significance and engineering practical value to study and propose an approach to seismic response calculation of spatial latticed structures with high calculation efficiency and accuracy,evaluate the current overall damage degree and seismic performance level on the basis of accurately obtaining the damage information,and gradually form and improve the performance-based seismic evaluation and appraisal method for existing spatial latticed structure.Based on the mechanical and vibration characteristics of typical spatial latticed structures such as single-layer reticulated shells and lattice arches,this thesis studies the practical method suitable for the seismic performance evaluation and appraisal of existing spatial latticed structures.To improve the seismic response calculation efficiency of spatial latticed structures on the basis of ensuring the calculation accuracy,this thesis proposes an improved Marshall model based on the hysteretic energy equivalent criterion.Based on parameter analysis and theoretical derivation,an approximate formula for calculating the bending amplitude of compression members and tension members in the process of reciprocating loading is proposed.Then,combined with the modification of model control parameters and the change of axial compression stability bearing capacity of members with large bending amplitude,an improved parametric hysteretic model is proposed in this thesis.Compared with the simulation results based on the shell element theory of single reciprocating loading,multiple reciprocating loading and the test results of multiple groups of members,it is proved that the proposed model can accurately simulate the complex inelastic force displacement hysteretic characteristics of axially loaded members on the basis of balancing the calculation efficiency and accuracy.Given that the long time-consuming and low computational efficiency in the traditional seismic response calculation process based on nonlinear time history analysis method,with the comprehensive analysis of the limitations in existing modal pushover analysis method,the modal pushover load expression considering the current state of the structure is derived by using the theoretical derivation method according to the nonlinear mechanical characteristics of spatial latticed structures.By appropriate simplification,the basic form of adaptive modal pushover load is then obtained,and the calculation equation of capacity curve of adaptive equivalent single degree of freedom system is constructed.Then,the basic framework of adaptive modal pushover method is formed in this thesis,and the calculation flows of this method are also given.Two different types of single large-span latticed arch structures are applied as numerical examples to verify the accuracy and applicability of proposed method.In view of the limitations of the traditional static pushover analysis method considering the contribution of multiple modes and the characteristics of spatial latticed structures,a two-stage pushover analysis method is proposed in this thesis to predict the vibration mode response characteristics of structures in the nonlinear stage.This method includes the trial calculation of modal combination coefficient in the first stage and the recombining of equivalent static load in the second stage,so as to form the basic calculation framework of two-stage modal combination coefficient method considering the contribution of multiple modes,which can be used for the seismic response evaluation of single-layer reticulated shells,and the calculation flows are also given.Numerical examples of three different types of reticulated shells are built to investigate the applicability and effectiveness of the proposed method.Results indicate that the proposed method can predict the nodal displacement,the member stress,the number of yield members and base shear response accurately.There are still some problems in the existing damage member detection index used for spatial latticed structures,such as poor anti-noise interference ability,insufficient detection accuracy of multiple damage members,insufficient sensitivity of damage index and so on.According to the mechanical characteristics of spatial latticed structures and the influence law of member damage on modal parameters,a modal matching-combination method is proposed to construct the combined mode,which includes the modal matching between the original mode and the damaged mode based on the mode confidence criterion and the modal combination based on Kriging interpolation.According to the modal strain energy difference between the constructed combined mode and the target original mode,the calculation formula of the variation index of the combined modal strain energy is deduced and proposed.The detection results of the numerical examples of single-layer spherical reticulated shell indicate that the damage index proposed in this thesis has good damage identification accuracy and noise robustness.To propose an overall damage index which can reflect the mechanical characteristics and actual damage development characteristics of spatial latticed structures,based on the theory of modal pushover analysis,the equivalent static displacement expression considering the contribution of multi-order modes under the action of unit seismic force is derived,and the multi-modal equivalent static model of spatial grid structure is then constructed.According to the difference degree of equivalent static displacement of the structure before and after the earthquake,the overall damage index is constructed,and the seismic damage evaluation method suitable for spatial latticed structures is proposed.The numerical examples results indicate that the damage assessment method proposed in this thesis can evaluate the current overall damage state and performance level of the structure more effectively.To quantitatively evaluate the collapse resistance of structures under rare earthquakes,according to the characteristics of spatial latticed structures and based on the existing research,this thesis studies and determines the ground motion intensity measure,the collapse performance measure and corresponding collapse judgment criteria used for spatial latticed structures.According to the collapse vulnerability analysis results,the basic processes of collapse resistance performance evaluation of spatial latticed structures are given based on the collapse safety reserve coefficient and consistent collapse probability.To improve the evaluation efficiency of structural collapse resistance performance evaluation and collapse resistance design,a collapse resistance performance evaluation method of spatial latticed structures based on static pushover method is proposed in this thesis.By the comparison with the performancebased seismic design method,the improvement suggestions for the performance-based seismic appraisal of existing structures are put forward.