Dynamic impedances and load carrying mechanism for skirted foundations |
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| Institution: | 1. College of Urban Construction, Zhejiang Shuren University, Hangzhou 310015, China;2. Dept. of Civil Engineering and Dept. of Mathematics, University of Akron, USA;1. School of Civil Engineering, Anhui Jianzhu University, Hefei, China;2. Key Laboratory of Intelligent Underground Detection Technology, Anhui Jianzhu University, Hefei, China;3. Chongqing Chengtou Road and Bridge Administration Co., Ltd, Chongqing, China;4. Department of Civil Engineering, Sichuan University, Chengdu, China;5. Geological Exploration Technology Institute of Jiangsu Province, Nanjing, China;6. Chongqing Nengke Engineering Investigation Co. Ltd., Chongqing, China;8. School of Civil Engineering, Chongqing University, Chongqing, China;1. Fujian Provincial Key Laboratory of Advanced Technology and Informatization in Civil Engineering, School of Civil Engineering, Fujian University of Technology, Fuzhou 350118, China;2. Priority Research Centre for Geotechnical Science and Engineering, Faculty of Engineering and Built Environment, The University of Newcastle, Callaghan, NSW 2308, Australia;3. College of Engineering, Ocean University of China, Qingdao 266100, China |
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| Abstract: | Dynamic impedances of foundations include dynamic stiffness and damping which have important effect on the internal forces in the structure. In some cases, such as offshore wind turbines, the influence of the foundation impedances on the system's natural frequency and overall damping could potentially have a significant effect on the fatigue life of the structure. The vertical, horizontal and rocking impedances of a skirted foundation (also termed bucket foundation in offshore wind industry) embedded in a fully saturated poroelastic seabed are addressed in this paper. The vertical impedance is most relevant for jacket foundations supported on three or four bucket foundations, while horizontal and rocking impedances are applicable for mono-bucket foundations. The dynamic vibration problems are solved semi-analytically with the help of dual integral equations and Green's functions. Numerical results for dynamic impedances are obtained; damping ratio are also obtained to show the importance of radiation damping for bucket foundations, even at very small excitation frequencies. The influence of length-to-radius ratio, Poisson's ratio, permeability of soil, excitation frequency and thickness-to-radius ratio on the impedances are also studied. Besides, the dynamic load sharing among the top plate, bucket shaft and bucket tip is obtained for vertical load, horizontal load and moment to shed light on the carrying mechanism of bucket foundation at dynamic working loads. It is found that for a rigid bucket foundation, even when the length-to-radius ratio is small (e.g. l/a = 1.0), most of the loads are carried by the shaft, while the top plate and tip of the bucket take only a small portion of the loads. The results of this study will be helpful for understanding the load-carrying mechanism of offshore bucket foundations for normal operation conditions. |
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| Keywords: | Bucket foundation Poroelastic soil Dynamic stiffness Damping ratio Load sharing ratio |
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