The Earthquake Engineering Online Archive

Response of tension-leg platforms to vertical seismic excitations

Liou, Gin-Show; Penzien, Joseph; Yeung, Ronald W.

UCB/EERC-85/14, Earthquake Engineering Research Center, University of California, Berkeley, 1985-12, 149 pages (530/L56/1985)

A systematic approach is presented for analyzing the vertical platform motion, tendon force, and foundation uplift when subsea soil is excited by vertical seismic waves. The problem, involving multiple interactions among soil, foundations, fluid, and platform, is mathematically modeled using a substructure technique. A set of frequency-dependent impedance functions is obtained for each structure and the total system is solved in the frequency domain. A specific tension leg platform is analyzed to show the application of the procedures developed and the importance of response to vertical seismic excitation. The hydrodynamic added mass and damping coefficients induced by vertical, translational, and rocking motions of the cylinder resting on the sea bed are obtained by dividing the entire fluid domain into an exterior region outside the cylinder and its vertical projection and an interior region inside the cylinder projection. The potential function in Laplace's equation is solved by matching eigenfunctions at the interface of the exterior and interior regions. Finally, a model simulating flexural waves propagating in the tendons, as would be produced by horizontal earthquake motions, is formulated and analyzed to determine the maximum tendon slope at the base connection point with the foundation. This maximum slope is required to design the connection details.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-85-14.pdf (7 MB)