The Research About The Effects Of The Arrangement Form Of Stairs To The Mechanic Properties Of Reinforced Concrete Frame-core Tube Structure

The stairs is an important part of the building with the function of vertical transportation.The stairs is the only "lifeline" for people to evacuate and an important channel for rescuers to save the people when the earthquake occurs.After the Wenchuan earthquake,experts and scholars investigated the disaster area and found out that the stairs were so severely damaged in the earthquake that they didn't play their “lifeline” role in earthquake damage.The stairs exerted great influences on the seismic performance of structures,which have attracted wide attention around the world.Domestic and foreign scholars have already done a lot of research on the stairs' impact to the seismic performance of frame structure,frame shear wall structure and shear wall structure,but there are few researches about the stairs' influence to the seismic performance of frame-core tube structure.The effects of the stairs to the seismic performance of the frame-core tube structure are studied in this paper.Taking a 100-meter-high frame-core tube structure as an example,by using PMSAP software ETABS software and SAUSAGE finite element analysis software,the influence of stairs to the seismic performance of frame-core tube structure is systematically studied through response spectrum analysis and dynamic elastic-plastic time history analysis.In the structure integral analysis,the following variables are considered.Firstly,whether to set up stairs in the frame-core tube structure.Secondly,whether the stairs are set up in a symmetrical way in the frame-core tube structure.In the model analysis,whether the stair and frame-core tube structure are set up in the frame-core tube structure as a variable.Through the comparison between the models,the important parameters affecting the seismic performance of the whole structure(such as period,floor shear,floor displacement,interlayer displacement angle)and internal force of beam and column members are analyzed.The influence of staircase member on the overall seismic behavior of frame shear wall structure and the influence on internal force of members such as beam,column and wall during the frequent earthquakes and rare earthquakes are mainly studied.The results of small earthquake elasticity calculation showed that:Firstly,the lateral stiffness in both the X direction and the Y direction are increased in the frame-core tube structure when the effect of stairs is considered.And correspondingly,the displacement angle in both X direction and Y direction are decreased when the effect of stairs is considered.From the above analysis,it can be concluded that the stairs work as a component which resists lateral force,and they increased not only the structural stiffness in parallel with stairs(Y-direction),but also the stiffness of the vertical stair direction(X-direction).Secondly,the earthquake shearing force increased in both directions of the framecore tube structure when the effect of stairs is considered,so the structural design is not safe when the effect of stairs is considered in the frame-core tube structure.Thirdly,the cycle ratio and torsion displacement ratio increased significantly when the stairs are arranged in a decentered way in the frame-core tube structure,and they are bigger than the circumstance under which the effect of stairs is considered.Those findings indicated that the decentered arrangement of the stairs can increase the torsional effect of the structure and impose negative effect on the structure,which should be taken into account in the structural design.Fourthly,the frame-core tube structure in the consideration of stair action,the column shear force increase is not obvious,.The wall shearing force is increased obviously.The results of elastic-plastic calculation under large earthquakes showed that:Firstly,the base shear force increased in both directions of the frame-core tube structure when the effect of stairs is considered,and correspondingly,the displacement angle between stories decreased in the direction of paralleling with the stairs.It shows that the structural design is not safe when the effect of stairs is not considered in the frame-core tube structure.Secondly,the bottom columns and the shear wall limbs are slightly damaged under the 7 degree earthquake,and the beams are subjected to different degrees of compressive damage.The beams have fully exerted the function of energy dissipation,which effectively protected the main wall limbs;To further research the failure law of the structure under larger earthquakes,the loading states of the structure under 8 degree earthquake are calculated.The bottom shear wall and the connecting beam have been damaged seriously.The shear wall of the frame-core tube structure model is damaged more seriously when the effect of stairs is considered.The damage of the frame column was smaller.The stairs provided major horizontal lateral movement stiffness for the core barrel of the structure as the inclined brace member,which shared the shear force of the frame column and reduced the frame columns' damage,simultaneously increased the damage of the core barrel.