Seismic Performance Research And Parameter Analysis Of Isolation Stair

As the vertical channel of multi-storey concrete frame structure,stairwell not only plays a role in traffic dispersion at normal times,but also serves as an escape route when earthquake comes.However,due to the diagonal bracing of cast-in-place stair components,the lateral stiffness of the stairwell is generally large and the staircase components often lost efficacy before the structure of the main body has been destroyed,losing the function as a safe passage.There are two main types of staircase components design methods in China after Wenchuan and Yushu earthquake: the whole cast-in-place practice,in which the staircase components are not involved in the overall calculation of the structure and are only strengthened in the structure;the arrangement of sliding support at the lower end of the ladder slab to release the diagonal bracing effect.Since both of the two design methods are inappropriate,in this paper,based on the staircase sliding support,a new kind of rubber isolation bearing is proposed,which can release the horizontal seismic force of the staircase while making up for its shortcomings.Meanwhile,through the shaking table test of the scale model and the contrastive analysis of the finite element model,the influence of the new type of rubber isolation bearing on the seismic performance of the stair structure and frame structure is being researched on.The main content and achievements are as follows:(1)By using the SAP2000 software to build seven reinforced concrete frame structure models with different ladder forms,the modal analysis,response spectrum analysis and static pushover analysis were carried out to study the effect of different staircase support forms on the overall structure and the seismic performance of the staircase components.The calculation results shows that different stair column form has impact on the stiffness and internal force distribution of the main structure,thus the impact should be fully considered in the design of frame structures.Considering the influence of earthquake,the four stair columns stairwell should be adopted for general stairwell in order to separate the stairwell from main structure and reduce the interaction between staircase and the main structure.Otherwise,we suggest setting slide bearings or rubber isolation bearings under the stair slab to release horizontal seismic force of the stairwells,making sure the stair not been destroyed or fail later than the overall structural,guaranteeing the safety island function of the stairwell.(2)In order to verify the influence of rubber isolation bearing at the lower end of the stair slabs on the seismic performance of the cranked slab stair of cast-in-place reinforced concrete(RC),a two-storey and two-span stair model with a similarity ratio of 1: 3 is designed according to the similarity principle.Rubber isolation bearing and PTFE(Polytetrafluoroethylene)sliding bearing are respectively arranged at the lower end of the ladder slab of the two-span stair for comparing and analyzing.By observing the process of destruction under seismic waves of different intensity and analyzing the natural vibration frequency,acceleration and the displacement response,the mechanism of fracture is studied.The results show that the stair unit with the rubber bearing and the sliding bearing being arranged at the lower end of the ladder has good seismic performance.Under the rare earthquake,the damage is mainly concentrated on the frame structure,which effectively releases the diagonal bracing of the stair slab,thus making the damage of the stair’s substructure posterior to the damage of the major structure.When the sliding bearing is adopted,the ladder slab in the resonant failure test has a sharp vertical tilt and a left and right shaking phenomenon;when the rubber isolation bearing is adopted,the vertical acceleration of the stair slab is reduced,and the rocking phenomenon does not appear in the resonance failure test.