Seismic Performance Of Step-Terrace Frame-Rocking Wall Structure

The non-uniform vertical stiffness is a prominent feature of the step-terrace frame structure.The dynamic response characteristics of this structure under seismic excitation are quite different from those of the ordinary frame structure.The the step-terrace frame structure's failure mechanism of story yielding is easy to occur in the upper ground stories.In order to improve the seismic performance of this kind of structure,this paper adds articulated bottom of ground floor and rocking wall with certain rotational ability to form a step-terrace frame-rocking wall structrue.The addition of rocking wall can effectively improve the seismic performance of step-terrace frame structure,and the centralized breakage of grounding layer on the original weak stories can be effectively improved,thus forming an overall seismic mode.Based on the dynamic elastic-plastic time-history analysis method and Abaqus,a series of structural models of mountain falling stories and corresponding rocking walls in 7 degree(0.15g)area designed according to current codes are established.Firstly,the influence of setting position of rocking wall on seismic performance of step-terrace frame-rocking wall structrue is explored.Then,aiming at the step-terrace frame-rocking wall structrue with rocking walls on the upper ground floor,the seismic performance of step-terrace frame structure before and after additional rocking walls is compared and analyzed,and the influence of stiffness ratio on the seismic performance of step-terrace frame-rocking wall structrue and the influence of the number of falling-story spans on the seismic performance of step-terrace frame-rocking wall structrue are explored.The main work and research results are as follows:(1)By simulating the quasi-static test of the step-terrace frame structure area completed by Chongqing University Structural Laboratory,the correctness and reliability of the beam-column fiber model and the constitutive parameters used in this paper are verified by comparing the total thrust-lateral hysteresis curves of the test results with those of the simulation results.(2)Five groups of finite element analysis models are established,each group includes the step-terrace frame structure and the corresponding step-terrace frame-rocking wall structrue with the rocking wall on the upper ground layer,the lower ground layer and both of them.Through dynamic elastic-plastic analysis,it is found that the dynamic response characteristics of the frame swing wall structure with falling stories in mountainous areas with swing walls at different locations are different.When the rocking walls are set on the upper grounding layer,the displacement of the upper grounding layer decreases,the top displacement increases,and the deformation of each layer tends to be uniform.The DCF value is close to 1,but the displacement of the falling layer decreases slightly and the displacement difference between layers is large.When the rocking walls are set on the lower grounding layer,the displacement of the upper and lower grounding side layers are inclined straight lines,but the displacement of the upper grounding side increases significantly,which leads to the increase of DCF value of the upper grounding side compared with the original structure,and further aggravates the displacement concentration phenomenon of the step-terrace frame structure.When both the upper and lower grounding layers are equipped with swing walls,the displacement of the upper grounding layer decreases slightly,and the top displacement increses slightly.Compared with the structure with swing walls in the upper grounding layer,the DCF value of the upper grounding side is larger than it,while the DCF value of the lower grounding side is smaller than it.(3)Comparing and analyzing the mechanical characteristics and seismic performance of five step-terrace frame structures before and after additional rocking walls,it is found that the basic period of the structure with additional rocking walls is not significantly different from that of the original structure,and the seismic effect of the structure will not be significantly increased.The maximum floor displacement,shear force,hysteretic dissipation energy ratio and acceleration amplification coefficient of the ground floor are all reduced.The displacement angle of each floor tends to be the same.The energy consumption ratio of beam to column increases significantly.The structure forms an overall seismic mode,which realizes the transformation from the layer yield mechanism to the whole yield mechanism.The displacement response,shear force and hysteretic energy dissipation of the story-falling frame structure with roking walls are slightly reduced compared with those of the original step-terrace frame structure.Therefore,the step-terrace frame-rocking wall structrue is a structural system with good seismic performance and wide application prospects.(4)The stiffness ratio of swaying wall to step-terrace frame structure area is related to the failure mechanism of step-terrace frame-rocking wall structure.A series of rocking walls with gradient section heights are set outside the three step-terrace frame-rocking wall structures.It is found that when the stiffness ratio is less than 1.5%,it has little effect on the seismic performance of the structure,and does not change the failure mechanism of the structure.When the stiffness ratio is more than 2.7%,the impact on the seismic performance of the structure increases gradually with the increase of the stiffness ratio,and the structure gradually changes from the original layer yield failure mechanism to the overall failure mechanism.When the stiffness ratio is more than 10.2%,the seismic performance of the structure is no longer evident with the increase of the stiffness ratio.Obviously,the structure has a stable destruction mechanism.Therefore,it is advisable to control the stiffness ratio at about 10.2% in the design of step-terrace frame-rocking wall structure.(5)The change of the number of stories and the span of stories of the step-terrace frame-rocking wall structure has different effects on the quality and stiffness of the structure.Through the analysis of the basic period,maximum floor displacement,maximum interlayer displacement angle,story shear force and energy dissipation capacity of the structure,it is found that the change of story number has much greater influence on the dynamic characteristics of the structure than the number of story dropping span.When the number of story dropping and span dropping are large,such as C3K3 YB in this paper,the index of story displacement angle and story shear force have sudden changes.