Design and Analysis of Complex Special-Shaped Steel Spiral Stairs

Compared with concrete stairs, steel stairs with light deadweight, large span, high bearing capacity, good overall stiffness and other characteristics are easy to install and low cost, and are widely used in various commercial and office buildings. However, the design methods of some structures with large span and irregular shape are not specified in the existing domestic standard drawings. Aiming at the complicated calculation problems caused by the irregular shape and large span of the steel structure spiral staircase at the sunken square of a business center in Jinan, this paper proposes four different structural design schemes of box girder, beam, atlas plate and box step. The finite element analysis software SAP 2000 is used to establish the overall model of the steel spiral staircase, and the static analysis and modal analysis are carried out for the four schemes. The cross-section design of the spiral staircase component is compeleted, and the comfort degree of each scheme is analyzed by using three different pedestrian excitation load cases. The four schemes are compared from the aspects of structural stiffness, component strength and overall comfort of stairs. The mechanical properties of stairs with different structural forms and the same shape are studied. The advantages and disadvantages of each structural design scheme are obtained, and the final design scheme is determined. The analysis results show that the four schemes can meet the design requirements in terms of deformation, strength and comfort. The maximum displacement of the four schemes occurs in the middle of the spiral staircase, and the deflection of scheme 2 is the largest, which indicates that sealing the bottom of the staircase to form a box shaped closed section of the stair treads can effectively increase the stiffness of the stairs. There is a large stress concentration at the turning point where the rest platform is connected to the ladder. By considering the nonlinearity of the material, the nonlinear analysis of the staircase shows that the stress concentration has little influence on the strength of the staircase. For the area of stress concentration, the steel box girder can be thickened from 16 mm to 20 mm thick.The focus of comfort research is to control the structural acceleration under dynamic load. When the natural frequency meets the requirements, the acceleration response will still be too large. Therefore, for comfort problems of complex structure, time history analysis should be adopted, combined with their accelerations in stable state for comprehensive evaluation. The design results of the four schemes are compared, and the box step stair is determined as the final design scheme after comprehensive consideration of the mechanical characteristics, overall aesthetic degree, construction convenience, stair cost, etc.