Methodology for preliminary design of high-rise buildings

Abstract: The construction of high-rise buildings has previously been limited in Sweden. Changes in society in recent years, related to urbanisation, economics and architectural standards have however resulted in a greater interest for the construction of high-rise buildings. When designing high-rise buildings, challenges are faced which often can be disregarded when designing lower buildings. In this dissertation, a methodology which can be used in the preliminary design process of high-rise buildings is developed. The methodology is based on idealised calculation models and idealised finite element models, especially focused on the dynamical properties, natural frequencies and accelerations of the building. The report will describe how these calculations can be used to make the preliminary design of high-rise building and still obtain reasonable results. The work is focused on buildings with a structural system consisting of a concrete core with the possibility of adding outriggers. The dissertation also highlights the different phenomena related to high-rise buildings that needs to be considered in the preliminary stage, or later, in the design process. This includes, among other things, comfort requirements and wind induced accelerations. The stiffness is of great importance when designing high-rise buildings. For this reason, different ways to change the stiffness of the building are also analysed. To evaluate how reliable the idealised calculations and models are, a case study on an ongoing project is performed. The calculations are performed on Gothenburg City Gate, a 120 meter tall building that is intended to be built in Gothenburg. The case study follows the methodology developed, in order to show an example of how the idealised models can be used in the preliminary design. The results of the idealised calculations are compared with the results of the finite element analysis to evaluate the accuracy of the calculations. The analysis shows that an idealised beam model of the building with varying stiffness will give sufficient results for the preliminary design. Also the shape function provided by Eurocode can be used with good results. The idealised calculations of the natural frequencies gives results that correspond with the more advanced FE-models, the results differed 3-13% in the first modes. This is however only true for translation modes and torsional modes are not accurate. Adding an outrigger to the building drastically increased the first natural frequencies of the building, by up to 50% for Gothenburg City Gate.