Discussion on irregular classification of high-rise steel structure

The irregular shape of high-rise steel structures is not conducive to earthquake resistance and may even suffer serious damage or collapse. Therefore, the design of high-rise steel structure in Shandong should be regular and symmetrical. The irregular shape of high-rise steel structure can be divided into two types, one is the irregular plane of high-rise steel structure, the other is the irregular vertical section and elevation of high-rise steel structure, the latter is more harmful.

I. Irregular plane of high-rise steel structure

Irregular plane and corresponding design measures, seismic fortification of high-rise steel structure, in the plane layout of one of the following situations, also belong to the irregular structure, and corresponding design and calculation measures can be taken: the eccentricity of any layer is greater than 0.15. Such irregular structures should be modeled by taking torsion effect into account. The concave angles of the plane shape of the structure and the protrusions of the concave angles in one direction are longer than 25% of the dimensions of the building in that direction. Corresponding seismic structural measures should be taken for the concave and convex parts of such irregular structures. The floor is not connected or has sudden stiffness, including openings that exceed 50% of the total area of the floor. This irregular structure should be calculated by a model which considers the elastic deformation of the floor slab. The components resisting the horizontal force are neither parallel nor asymmetrical to the two mutually perpendicular main axes of the lateral force resisting structure. Such irregular structures should be calculated by a computational model considering torsion effect.

The vertical section of high-rise steel structure is irregular

The transverse stiffness of high-rise steel structure should be uniformly changed along the vertical direction to avoid the sudden change of transverse stiffness. The section size and material strength grade of the main lateral force resistant members should be gradually reduced from the bottom to avoid sudden changes in bearing capacity. A high-rise steel structure with seismic fortification shall be an irregular structure if one of the following situations occurs in the vertical arrangement: the transverse stiffness of the floor slab is less than 70% of the transverse stiffness of the adjacent upper floor, and the total transverse stiffness of the three consecutive floors is reduced by more than 50%. The mass ratio of adjacent floors exceeds 1.5(except the top floor when the building has a light roof). Discontinuities of vertical lateral force resistant members (e.g. structures with conversion beams or trusses supporting upper columns). The total shear capacity of lateral force members of any floor is less than 80% of that of adjacent upper floors. For the vertical irregular structure, in addition to the reinforcement measures for the weak parts of the structure, the structural calculation model which conforms to the actual situation and considers the torsion effect should also be used for calculation. For particularly irregular structures, the elastic time-history analysis method should be used for supplementary calculation. In addition, for the internal forces of the beams and columns supporting the non-floor columns or non-floor seismic walls, the internal forces generated by the earthquake should be multiplied by the increasing coefficient according to the provisions.