Analysis Of The Mechanical Properties Of A Complex And Irregular Box-type Steel Spiral Staircas

Steel structure spiral stairs have the characteristics of light weight,large span,high bearing capacity,good overall stiffness,etc.Compared with concrete stairs,steel structure stairs are widely used in various commercial and office buildings because of their convenient installation and low cost.However,the design methods of some large span and irregular shape spiral stairs are not specified in the existing standard drawing set in China.In this thesis,the complex calculation problems caused by irregular shape and large span in the design process of a steel spiral staircase in a sinking square of a business center in Jinan are studied.The main research contents are as follows:1.Four different structural design schemes of the whole box girder plate type,side beam type,side beam type with bottom sealing plate(map style)and box step type are proposed.The finite element analysis software SAP2000 is used to establish the overall model of steel spiral staircase.The static analysis of the four schemes is carried out,and the advantages and disadvantages of each structural design scheme are obtained according to the analysis results.2.The existing evaluation methods of comfort level are introduced.At present,the main evaluation methods of comfort level are avoiding sensitive frequency method and braking force response value method.There is no clear description of comfort level evaluation of steel spiral staircase in China.An experimental comfort test results show that the comfort level of complex special-shaped steel staircase can not only be evaluated by avoiding the sensitive frequency method,but also by selecting the appropriate load to stimulate the structure,combined with their acceleration in the stable state.The modal analysis of steel staircase with four schemes was carried out,and the human walking excitation load model and the crowd excitation load model were respectively adopted to apply the excitation load to the structure,and the acceleration response time history curve under the action of load excitation was obtained,and the comfort level of the staircase was evaluated.Finally,it is concluded that the complex special-shaped steel spiral staircase preferentially selects the walking excitation load to check the comfort level of the staircase.3.Through the response spectrum analysis and elastic time history analysis of steel spiral staircase,it is found that the difference between the results obtained by the mode decomposition response spectrum method and the time history analysis method is small,indicating that the mode decomposition response spectrum method is accurate enough,and the response spectrum method is more simple than the time history analysis method.Therefore,the mode decomposition response spectrum method can be directly used for seismic calculation in the design work.When the seismic fortification intensity is 7 degrees(0.10g),7degrees(0.15g)and 8 degrees(0.20g),it is found that the stress of the upper bearing of the stair under the vertical seismic fortification intensity is 8 degrees(0.20g)is greater than that without the earthquake.Therefore,in the area of seismic fortification intensity of more than 8degrees,the complex special-shaped box step-type steel spiral staircase needs to carry out the seismic checking calculation under the vertical earthquake action.The seismic action can be ignored in the area of 7 degrees and below 7 degrees.4.Because of its complex structure and irregular shape,the precise modeling work is large.Through simplifying the steps and bolts of the analysis model of the complex special-shaped box step steel spiral staircase,it is found that the simplification has little influence on the mechanical performance and comfort of the box step steel spiral staircase.Therefore,the simplified model can be used to replace the accurate box step model in the actual project to reduce the workload.The results show that increasing the number of longitudinal ribs and the height of box girders on both sides has little influence on the strength,deformation and comfort of box girders.In design,it is preferred to increase the thickness of box girders on both sides to improve the strength and reduce the deformation of the staircase.