Research On Failure Mechanism And Seismic Evaluation Method Of Reticulated Domes Under Sequenced Ground Motions

Because of their rational strength distribution,economical material adoption,beautiful shapes,various forms and other advantages,reticulated domes have been developed rapidly during the last thirty years of engineering construction in our country and widely applied to public infrastructures such as exhibition centers,large gymnasia,airport terminals and large opera houses,commonly used as the structural forms of important and landmark buildings.Our country is located between the Pacific seismic belt and the Mediterranean-Himalaya seismic belt,with frequent earthquakes and a wide range of seismic areas,and reticulated domes and other large span space structures constructed in our country are severely threatened by earthquakes.Historical earthquake disasters indicate that in most cases,an earthquake process contains main shock,aftershock and other swarm sequences.After main shocks,aftershocks often cause additional structural damage,even make structures collapse.However,the existing researches of seismic performance of reticulated domes are all based on single earthquake,and the related researches considering sequenced ground motions are still on blank stage,so that the existing seismic design method can not guarantee the safety of reticulated domes under aftershocks.Furthermore,reticulated domes are often used as temporary emergency shelters in earthquake-stricken areas with their large space to solve the personal aftercare problem,so it has great social significance that reticulated domes can still function under sequenced ground motions.Based on the above background,in this paper,reticulated domes,typical large span space grid structures are studied.Structural response regularity and failure mechanism are investigated under sequenced ground motions.Then,sensitivity and fragility analysis of reticulated domes considering sequenced ground motion effect are performed,and seismic design method and rapid evaluation method of seismic damage are proposed for reticulated domes considering sequenced ground motion effect.The main research contents are as follows.(1)Collection and correlation analysis of main shock-aftershock ground motions are conducted.According to the selection criteria,338 pairs of main shock-aftershock magnitude records and 342 groups of main shock-aftershock acceleration time histories,dated from 1961 to 2016 are selected.In terms of magnitudes,frequency spectra,durations and energies,correlations between main shocks and aftershocks are investigated,and duration ratio is proposed to describe the concentration of seismic energy release.Based on the above correlation research results,an aftershock synthesis method is proposed considering the correlation of magnitudes,frequency spectra,durations and duration ratios of main shock-aftershock sequences,and artificial aftershock ground motion records are compared with actual aftershock ground motion records to verify the rationality and applicability of this method.(2)Seismic response analysis of reticulated domes under sequenced ground motions is conducted.Finite element models of single-layer and double-layer reticulated domes with different spans are established by the finite element software ABAQUS.The input method of ground motions is linking the displacement time history of main shock and aftershock end to end with a zero-amplitude interval.Through incremental dynamic analysis,aftershock influence on ultimate bearing capacity of reticulated domes is investigated.Through dynamic analysis in full process domain,response regularity and failure mechanism of reticulated domes under main shock-aftershock sequences are discussed,and four aftershock influence levels of seismic responses of reticulated domes are proposed.(3)A shaking-table test of a single-layer reticulated dome under sequenced ground motions is conducted.Based on the design principle of similarity ratio,the test model is designed and produced on the shaking table.Before the formal test,noise acquisition test and dynamic performance test are conducted.The excitation signal is the seismic sequence recorded by the CHY081 station in Chi-Chi during the Taiwan earthquake in 1999.The formal test contains test at elastic stage,test at plastic stage and test of collapse.By observing the test phenomena and data analysis,the above four aftershock influence levels of seismic responses of reticulated domes are verified and the failure history of reticulated domes under sequenced ground motions is obtained.Using the finite element software ABAQUS,the test model is established in detail and the process of formal test is shown.Through the comparison of test phenomena and numerical results,the reliability of ABAQUS in the research of sequenced ground motion effects of reticulated domes is verified.(4)Sensitivity analysis of reticulated domes considering sequenced ground motion effect is conducted.Based on the relevant suggestions of transfer standard about site classification in seismic codes of China and America in existing researches,according to the site classification conditions in China,from the above 342 groups of main shock-aftershock acceleration time histories,10 ground motion records with the site classification of I,II and III are selected respectively.Through dynamic time history analysis,plenty of numerical examples for single-layer and double-layer reticulated domes with different spans are performed.Then,aftershock collapse sensitivity of reticulated domes with different characteristic responses at the end of main shocks is discussed,and the related characteristic response indexes and the corresponding threshold values are obtained.Moreover,the seismic design method of reticulated domes considering aftershock effect is proposed.(5)Fragility analysis of reticulated domes considering sequenced ground motion effect is conducted.Correlation analysis between additional damage of reticulated domes with different initial damage levels and ground motion intensity measures is conducted.Correlation and efficiency of 11 common ground motion intensity measures are compared,and PGA is chosen as the appropriate ground motion intensity measure for sequenced ground motion effect research of reticulated domes.Through incremental dynamic analysis,main shock-aftershock sequence fragility curves(matrixes)for seismic design and aftershock fragility curves(matrixes)for seismic evaluation of reticulated domes are established respectively,and aftershock collapse fragility curves of reticulated domes with different initial damage levels are obtained.Based on the above fragility analysis results,rapid evaluation models of seismic damage for reticulated domes under main shock-aftershock sequences are proposed with PGA of main shock and PGA ratio of main shock-aftershock sequence as independent variables,and rapid evaluation models of seismic damage for reticulated domes with known and unknown initial damage levels under aftershocks are established respectively,which expands the application scope of traditional rapid evaluation models of seismic damage for reticulated domes.