Considering Floor Stiffness Of Tall Steel Frame Structure With Overall Stability Study

Multi-storied or high-rise steel framed structures are in the ascendant as an important structural system. Stability of structures is one of the main contents of the analysis and design of steel structures. The in-plane flexural rigidity of floor slabs is usually assumed to be infinite and the out-plane flexural rigidity is usually assumed to be zero for simplifying analysis. The effects of the variety of actual flexural rigidity of slabs on the global stability of structures are mainly researched in this paper, which isn't given enough attention in existing researches.Development of steel framed structures, current research of global stability of steel framed structures, existing problems and structural stability theory are introduced. The finite element method for stability analysis of structures is deduced emphatically.Based on the feasibility verification about using the finite element program of ANSYS to analyse the global elasto-plastic stability of spacial steel framed structures, multi-storied and high-rise steel frames are modeled, in which the thicknesses of floor slabs and cross-sectional heights of members assumed numerous values. In most of these structures, a slab may have one or more openings with various types and size. The ultimate loading capability of theses structures is calculated. The effect of thickness of slabs, openings and beams in openings on stability of structures is analyzed.Results indicate that the stability of steel framed structures is influenced deeply by thickness of slabs, location and size of openings in the slabs, the beams in openings, and inconsiderably by edge-beams of openings. In this paper It is proposed that the thickness of slabs should be more than 150mm, and the ratio of the length of openings to that of the floor plan should be less than 30% for the stability of structures. The optimal location of openings and the way of disposition of the beams in openings are also proposed. The problems existing in technical specification for steel structure of tall buildings (JGJ99-98) are pointed and some advice to promote them to be solved are given in this paper.