ABSTRACT
Individual types of analysis have been carried out so far. However, the structural engineer is normally responsible for the building as a whole, not only for certain units or individual aspects of its behaviour. Before the building is constructed, all areas relating to structural behaviour have to be looked at. This chapter shows how such global analysis is carried out using a real building. The investigation normally starts with the stability analysis and then moves on to determine the fundamental frequency of the building. The maximum deflection of the building under horizontal load concludes the global analysis. Many stiffness characteristics needed for the individual investigations are identical, and they only have to be established once and then can be reused. Hence the resulting global analysis covering the three different areas requires much less work than three individual analyses separately. The case study is based on and uses a simplified version of the structure of the Sheffield Arts Tower, seen on the cover of the book. The twenty-three storey structure is braced by four reinforced concrete cores and four perimeter frames. The perimeter frames are replaced by 16 bulky columns on ground floor level making this region much stiffer than the superstructure. The simplified static model of the twenty-two storey superstructure is the subject of the analysis, whose layout is shown in Figure 11.1. The basic data of the superstructure is given below. Size of ground plan: L = 36.0 m and B = 20.0 m. Storey height: h = 3 m. Number of storeys: 22. Height of structure: 66 m. Modulus of elasticity: E = 23·103 MN/m2. Shear modulus: G = 9.583·103 MN/m2. Cross-sections of both the beams and the columns of the frames: 0.4 m/0.4 m. In addition to the eight bracing units, concrete columns are also part of the vertical load carrying system but their contribution to the lateral and torsional stiffness is small compared to that of the bracing units and is therefore ignored for the calculation. It is assumed for the analysis that the cores only develop bending deformation. The weight per unit volume of the building (for the dynamic analysis) is assumed to be γ = 3 kN/m3. A vertical load of Q = 10 kN/m2 is considered for the stability analysis and for the determination of the global critical load ratio. When the structure is subjected to lateral load and the top rotation and deflection are calculated, a uniformly distributed horizontal load of intensity 1.3 kN/m2 is considered in direction y, which results in a wind load of wy = 46.8 kN/m.
