Wind-induced dynamic response of tall buildings with coupled 3D modes of vibration by David Yun Nin Yip.

Abstract

This thesis presents the results of a very thorough study of the wind-induced dynamic response of buildings of complex shape with coupled 3D modes. Tall buildings with coupled 3D modes are not uncommon in modern building design, and therefore there is a real need to further the understanding of the wind-induced response of these types of buildings. The thesis starts with an extensive literature survey of the subject. Results obtained from the survey show that there is only partial understanding of the wind-induced coupled building response at present. There are a number of areas which still require further study when dealing with real buildings in a city wind environment. To clarify some of these areas, a complete matrix formulation of the wind-induced coupled 3D building motion is presented and discussed. With this formulation, the complexity of the interaction between statistical correlation of the wind forces and structural coupling of mode shapes is demonstrated. In addition, the importance of consistency in the formulation of the equations of motion using the same set of reference axes for structural mode shapes, wind forces and response is stressed. The first part of the thesis also details a general mathematical 3D wind force model developed by the author. The model is not restricted to the case of normally incident wind and regular rectangular building plan. It offers a comparatively economical means of conducting detailed parametric wind model studies, before resorting to expensive wind tunnel model tests. The wind-induced coupled building response has been extensively examined by the author using numerically simulated wind forces, as well as wind tunnel model test results. In the later part of this thesis, the experimental results obtained from the wind tunnel model tests are presented. The experiments carried out for this study included pressure model tests ( using an electronic pressure scanner), force balance tests and multi-degree-of-freedom aeroelastic model tests of a 275m high hypothetical building. Actual building properties of a similar real building were adopted for the hypothetical building. The wind forces measured with the pressure model were used to investigate the characteristics of the wind-induced coupled building responses. The aeroelastic tests provided additional information on the aerodynamic damping and probability distributions of the responses. Results obtained from the wind tunnel model studies indicate that the dynamic response of a building with coupled 3D modes may be significantly different from those of the same building with uncoupled modes. Within the range of wind speeds tested, the aerodynamic damping was found to be positive in sway and negligible in torsional motions. It was also found that aerodynamic damping became relatively insignificant in built-up city environments compared with homogeneous terrain. Another important and major part of this study was the development of an improved balance data analysis method for routine wind tunnel force balance rigid model tests of general building types, including those with coupled 3D modes. Details of the new method are presented. The new method does not require explicit mode shape correction factors and is applicable to buildings with or without coupled modes. The findings of an extensive validation study of the new method are also presented in the thesis. The validation study demonstrated clearly the improved accuracy of the method in predicting wind-induced dynamic response, and loads.