Research On Seismic Performance Analysis Of Metal Dampers Applied To RC Step-terrace Frame Structure

As the most common form of mountain building structures,step-terrace structure is characterized by the unequal height of the bottom restraining end.This feature makes it natural to have "defects" such as vertical irregularities and torsion irregularities,and its seismic performance is weaker than that of ordinary structures.Therefore,in the actual design and construction,how to effectively improve the seismic performance of the stepterrace structure has always been the concern of the majority of researchers and designers.In this paper,the use of metal dampers to improve the seismic performance of stepterrace frame structures has been studied in depth.The damping design method based on the damping performance curve was selected as the main method of arranging the metal dampers in this paper,and combined with the characteristics of the step-terrace structure it was adjusted.Reasonable models were established with SAP2000 software,and through elastoplastic time-history analysis,the difference in damping effects of different dampers arrangements was compared,which verified the scientificity and rationality of the method selected in this paper.After that,six models of the step-terrace structure with different number of story-drops and span-drops was established and the damping design based on the damping performance curve was carried out.Through dynamic elastoplastic analysis,the damping effect of the metal damper acting on the structures with different story-drop numbers and span-drop numbers was evaluated,and the rule between the damping effect and the number of story-drop and span-drop was explored.Finally,based on the frame structure that drops 3 storys and 3 spans,IDA analysis and fragility analysis of the uncontrolled structure and the damping structure with seismic design were carried out to make a more comprehensive evaluation of the damping effect of the metal dampers.The main conclusions were summarized as follow:(1)Based on the Japanese code,the calculation formula of the floor shear force of the step-terrace frame structure is put forward,which is used to calculate the shear force of each floor and the shear force distribution of the story on the slope between the ground part and the part connected to the drop-story,and it is proved that the shear force distribution at the bottom of the step-terrace structure is directly related to its stiffness distribution and mass distribution.(2)The damping effects of three different damping arrangements are compared and the three damping arrangements are: arrangement based on damping performance curve,uniform arrangement of layers,arrangement based on displacement.According to the analysis results of the structure’s interstory displacement angle,interstory column shear force,and interstory torsion angle,the seismic performance of the structure based on the damping performance curve is better than that of the displacement based structure,and the seismic performance of the structure based on displacement is slightly better than that of the structure with uniform arrangement.When using the design method based on the damping performance curve for the damping design of the step-terrace structure,attention should be paid to slightly strengthening the story on the slope.(3)For the step-terrace structures with different number of story-drops and spandrops,reasonable arrangement of dampers can significantly enhance their seismic performance and achieve the expected seismic effect.Compared with the uncontrolled structure,the interstory displacement angle of the damping structure is reduced by30%～40% under the action of frequent and rare earthquakes.The shear force of the interstory column is reduced by 30%～40% under the action of frequent earthquakes and reduced by 10%～20% under the action of rare earthquakes;the interstory torsion angle is reduced by 40%～80% under the action of frequent earthquakes,and reduced by 40%～60%under the action of rare earthquakes;The damping effect is slightly enhanced with the increase in the number of story-drops and span-drops.(4)The reasonable arrangement of metal dampers can significantly enhance the ability of the step-terrace structure to withstand strong earthquakes,and the increase of ground motion PGA is about 60% when the structure is close to collapse.Compared with the uncontrolled structure,the deformation ability and ductility of the damping structure are also significantly improved.(5)The arrangement of metal dampers will slightly increase the shear force of the structural base,but the main reason for the increase is that the placement of metal dampers delays the rate of structural stiffness degradation.Under the premise that the two types of structural stiffness degradation are similar,using base-shear/PGA to evaluate their acceleration responses,the acceleration response of damping structure is less than that of uncontrolled structure when the earthquake intensity is greater than the rare earthquake.(6)Through the fragility analysis of uncontrolled structures and damping structures,according to the American codes FEMA273 and ATC63,it can be considered that though the uncontrolled structures in this paper are designed at 7 degrees(0.15g),under the action of 8 degrees(0.2g)earthquakes It is still approximately able to achieve the performance level of OP by frequent earthquakes,IO by fortification earthquakes,and LS by rare earthquakes;and the damping structure can be approximated to reach the performance level of OP by fortification earthquakes,IO by rare earthquakes under the action of 8degrees(0.2g)earthquakes.