Probabilistic Seismic Fragility Analysis Of Reticulated Shells

As the major form of long-span spatial latticed structures,the reticulated shells are widely used in gymnasiums,conference and exhibition centers,airport terminal buildings,industrial buildings,etc.China is located in one of the most active earthquake regions in the world.This poses a severe threaten to the widely used reticulated shells.The statistics of recent earthquake disasters indicate that the damage or collapse of long-span spatial latticed structures usually leads to large amount of casualty,economy loss and great impact on society.The Chinese seismic code aims only at the performance level of life safety,which is not capable of satisfying the demands of users.On the background of performance-based design and performance-based seimic risk evaluation,the fragility analyses of single-layer reticulated domes and cylindrical shells are carried out in this dissertation,which will on the one hand provide theoretical support to the performance-based seismic design,on the other hand,it will lay the groundwork for the evaluation of seismic loss.More specifically,the main contents are as following:（1）The average modal strain energy ratio of each vibration mode is used to serve as the magnitude of contribution of each mode to the total seismic response,and the modes whose average modal strain energy ratios are larger than 0.01 are defined as the dominant vibration modes.The dominant vibration modes of single-layer reticulated domes and cylindrical shells are identified using the average modal strain energy ratios,for 20 ground motion records under four cases of seismic excitation:only X-directional seismic excitation,only Y-directional seismic excitation,only Z-directional seismic excitation and tri-directional seismic excitation.The mode superposition method and the CQC（Complete Quadratic Combination）rule are used to combine the modal maxima of the identified dominant vibration modes,the first 30 modes and the first 250 modes of the reticulated shells,the corresponding results are compared with the time history analysis results.（2）Based on the dominant vibration modes of the reticulated shells,a scalar ground motion intensity measure,i.e.,Sa,dom（T₁^d,T₂^d,...,T_i^d,...T_N^d,（ζ））,is proposed for use in evaluating the seismic response of single-layer reticulated shells,which is expressed as the weighted geometric mean of the spectral acceleration ordinates at the periods of the dominant vibration modes of the structure considered,and the average modal strain energy ratio of each mode is the corresponding weight.Its applicability and superiority to 11 other existing IMs are firstly investigated in terms of correlation with the nonlinear seismic response,efficiency and sufficiency.The hazard computability of this newly proposed ground motion intensity measure is also briefly discussed and illustrated.（3）The selection critiria and the minimum number of ground motion records used in seismic fragility analysis are firstly given,and 40 far-field ground motion records are selected from the "Next Generation Attenuation models”ground motion database of the Pacific Earthquake Engineering Research Center for the following seismic fragility analyses.The probability distribution models of the 13 random parameters in structural modeling are summarized.The local sensitivity analyses are carried out on these 13 parameters and the tornado diagrams are obtained.Based on these results,the global sensitivity analyses are performed on these 5 significant parameters,using the Sobol’ method and the Latin Hypercubic Sampling method,the contribution factors of each parameter to the seismic responses are obtained.（4）Based on the idea that the seismic input energy to structures are mainly dissipated via the hysteretic energy,a structural damage index on the basis of the seismic energy demand is introduced,in which the seismic energy demand can be obtained via the continuous wavelet transform on the acceleration time histories.The incremental dynamic analyses are performed on 18 reticulated shells with different rise-to-span ratios and roof weights,using 40 far-field ground motion records.Using the damage index proposed in this dissertation,the probabilistic seismic demand models,the probabilistic seismic capacity models and the probabilistic collapse capacity models are established based on the incremental dynamic analyses results,and the fragility curves are obtained.（5）40 near-fault pulse-like ground motions are chosen using the identification methods presented in the literature,and then the seismic responses including the displacements and axial forces of the reticulated domes and cylindrical shells are investigated.Incremental dynamic analyses are carried out and the probabilistic seismic demand and capacity models are developed based on the incremental dynamic analysis results.The results are compared with the outcomes for the far-field ground motions.