Study Of Seismic Performance Of Stairs In Fram Structures

Seismic survey in 2008 WENCHUAN showed that the damage of stairs in many kinds of structural types occurred before the main structure,which was particularly serious in the frame structures.These suggest that the traditional design method of the stairs only bear vertical load is debatable.In this paper,the main work includes:Establishing four models by using PKPM software.Model one is ten across frame structure considering stairs.Model 2 is ten across frame structure neglecting stairs.Model 3is six across frame structure considering stairs.Model 4 is six across frame structure neglecting stairs.Analyzing the models of natural vibration period,structure displacement,interlaminar shear force,floor shear force,seismic response force,bending moment and shear weight ratio and so on.Results showed that under the action of earthquake in vertical stair run direction,floor shear and seismic response force,bending moment and shear weight ratio,in the case of the stairs participating in the overall structure calculation compared with not participating in the overall structure calculation change is small;Under the action of earthquake in stair run direction,floor shear and seismic response force,bending moment and shear weight ratio,in the case of the stairs participating in the overall structure calculation compared with not participating in the overall structure calculation change is large.These suggest that when the staircase is involved in the calculation,the effect of the stair run direction is greater than the influence of vertical staircase run direction.Analyzing the change of the internal force of main components around the stair by comparing different models.Results show that the change of the internal force of the structure near the stair is obvious,however the internal force of the structure far away from the stairs is small,which can be ignored.Establishing a single stair by using the finite element software ANSYS and analyzing the force characteristics of the stair step plate,platform beam and plate.In the analysis and design of the bench plate,simple calculation according to the flexural part result to stair plate reinforcement insufficient.When the earthquake come,the stair will damage.The finite element analysis shows that resting flat pallet destroyed in the earthquake is less,so thetraditional design method can be retained.Under the action of earthquake,shear force and bending moment of the ladder beam increased sharply.According to the traditional design methods,shear damage occurs because of lacking reinforcement,which cannot guarantee the safety of the ladder beam,meanwhile the torsion and stress concentration appear in the middle of the cross between the two steps of the ladder beam.