Study On Performance Of RC Frame Structure With Self-centering Braces Under Main And Aftershocks

Existing seismic observations show that strong earthquakes are often accompanied by strong aftershocks.The occurrence of aftershocks may aggravate the cumulative damage of the structure,and the structure is more seriously damaged or even collapsed,seriously endangering the safety of people’s lives and property.In order to study the seismic performance of the pre-pressed spring self-centering energy dissipation(PSSCED)braced structure under the action of the main and aftershock sequences,based on the magnitude,peak ground acceleration(PGA)and frequency spectrum of ground motion,this paper first proposes a method for constructing main and aftershock sequences with a simple process suitable for the field of seismic engineering.The seismic performance of a 12-story PS-SCED braced reinforced concrete(RC)frame structure is studied under the main and aftershock and compared with that of the buckling restrained braced(BRB)structure.Based on the equivalent principle of structural damage,a design approach for self-centering braced frame structure considering the main and aftershock effect is proposed,and the seismic performance comparison of the improved design structure and the original one is conducted.The main contents and achievements are summarized as follows:(1)By modifying Bath’s law to determine the aftershock magnitude,and combining Bath’s law and the ground vibration attenuation formula,three methods for calculating the PGA of aftershocks are proposed,and the main and aftershock sequences are constructed based on the magnitude,PGA and frequency spectrum.Through the comparison with the real main and aftershock sequence,it is found that when the PGA of mainshock is less than 0.2g,it is recommended to use the third method in which the PGA ratio of the mainshock to the aftershock is a fixed value.When the PGA of the mainshock is from 0.2g to 0.6g,it is recommended to use the first or second method in which the PGA of aftershock is determined by the magnitude of earthquake or the epicenter distance.The second method is recommended when the PGA of the mainshock is greater than 0.6g.The magnitude,PGA and frequency spectrum of the constructed main and aftershock sequences agree well with the real ones.(2)A 12-story PS-SCED braced RC frame structure is designed based on the current specifications.Five artificial main and aftershock sequences are constructed,and two real main and aftershock sequences are selected.The dynamic responses and energy dissipation characteristics of the PS-SCED braced structure under frequent,basis and rare earthquake level main and aftershock sequences are analyzed and compared with those of BRB structure.The results show that the inter-story drift ratio and the maximum roof acceleration of the PS-SCED braced structure are slightly greater than those of the BRB structure,and the largest increases are 20.1% and 10.3% respectively.Under the action of the rare earthquake level main and aftershock sequences,the BRB structure has a larger residual displacement,and the maximum displacement of the PS-SCED braced structure is less than that of the BRB structure.The PS-SCED braced structure has almost no residual displacement after the earthquake,and the average value is only 0.091%,which fully reflects the excellent re-centering performance of the PS-SCED braces.The PSSCED brace has a better control effect on the residual deformation growth under aftershocks.Aftershocks increase the residual displacement and energy dissipation of the structure.When the residual displacement of the structure after main earthquake is large,the residual displacement of the structure may be significantly increased and the damage will be aggravated by the aftershock,and the maximum increase in the residual drift ratio is 35.3%,and the increase in energy dissipation is 19.6%.(3)Based on the study on the structural response of the braced RC frame structure under the main and aftershock sequences,a design approach for the self-centering braced RC frame structure considering the main and aftershock effects is proposed.Based on the equivalent principle of structural damage,the correction coefficient ?α of the seismic impact coefficient is introduced,and its recommended value is given.Considering the effect of main and aftershocks,the PS-SCED braced RC frame structure is improved and designed,and the seismic performances of the improved structure and the original one are compared to validate the feasibility and rationality of the design approach.The results show that the improved structure has a better control effect on the residual displacement with the average value of only 0.05%,and its displacement and inter-story drift ratio are significantly reduced compared with the initial structure.The energy dissipation of PSSCED brace is greatly increased.During the aftershock period,the acceleration of the improved structure is reduced by 12.7%,21.7% and 29.4% under the action of frequent,basis and rare earthquake levels compared with the initial structure.With the increase of seismic intensity,the main energy dissipation of structure changes from damping energy dissipation to bracing energy dissipation,indicating that under the strong aftershocks,the PS-SCED brace can give a full play to the energy dissipation capacity,thereby effectively protecting the structure and reducing structural damage.