Seismic Response Analysis Of A Tall Frame-tube Structure Beyond The Code-specification With Energy-dissipated Outriggers Under Long-period Ground Motions

Relatively low peak acceleration and long duration are the significant characteristics of the long-period ground motion which are different from the ordinary ground motion. Historical earthquake disaster investigation shows that the long-period structure is subjected to long-period ground motion relatively large and severe damage occurred under long-period ground motion. On the other hand, with the development of the society, more and more complex high-rise buildings beyond the code-specification as city landmarks, whose fundmental natural periods are a few seconds. Therefore, how to ensure the safety of long-period structures under earthquake disaster are the main issues for civil engineers to solve. Outriggers with energy-dissipation mechanism are paid more attention due to its good seismic mitigation effect, novel design method and low cost. Tall buildings with energy-dissipation ouetriggers have been successfully constructed around the world. In this paper, seismic responses of a tall frame-tube structure beyond the code-specification with energy-dissipated outriggers are mainly investigated and the following researches are completed:In order to investigate the difference between long period ground motion and normal ground motion, ground motion records at61CAT station during2008Wenchuan earthquake are chosen as representative of long period ground motion records. Comparing with the normal ground motion records such as EL Centro records, low frequency content is more predominant and energy distributed in the long-period range is more abundant for long-period ground motion record. Furthermore, comparison of absolute acceleration amplification factor spectra and relative displacement spectra shows that spectral values in the long period range of long period ground motion are obviously larger than the corresponding values of normal ground motion. This result indicate that long period ground motion has much more unfavorable effects on the long-period structures such as tall building and long-span structure.In order to investigate the effect of long period ground motion on tall frame-tube with outriggers beyond the code-specification, Lanzhou Honglou Times Square was taken as example. And Elastic and elasticplastic dynamic time history analysis under frequently-occurred and rarely-occurred level long period ground motion input were conductd on the structure model. Comparison with analytical results under the corresponding level EL Centro input shows that the maximum horizontal displacement and maximum interstory drift ratios under long period ground motion records are obviously larger than the corresponding results under normal ground motion records. Furthermore, in order to investigate the seismic mitigation effects of energy dissipation devices on the long-period tall buildings, viscous dampers were introduced in the different components of outriggers such as horizontal chord, vertical chord and inclining brace to form the different energy-dissipated outrigger, that is horizontal, vertical and inclining-braced outrigger. The structure models with different energy-dissipated outriggers were further analyzed under long period ground motion inputs. Analytical results show that the maximum horizontal displacement and maximum interstory drift ratios of the structure with energy-dissipated outriggers are decreased significantly. This indicates that energy-dissipation outriggers are efficient to control the seismic responses of the structure under long period ground motion input. Among3types of energy-dissipation outriggers, vertical one has the best control effect. In addition, comparison with the results under normal ground motion record, EL Centro records, control effects of energy-dissipated outrigger are more obvious.Finally, the results of the study were summarized and further research direction and improvement were proposed.