There is a good book on offshore platforms edited by James Wilson
http://www.gulfpub.com/product.asp?PositionID=search&ProductID=5636
Contents:
?Structures in the Offshore Environment (J. Wilson).
?Structure-Environmental Force Interactions (J. Wilson).
?Deterministic Descriptions of...
This source isn't free but since the Rip Weaver books are out of print it is a pretty good substitue
http://www.gulfpub.com/product.asp?PositionID=search&ProductID=6901