The guyed tower is an offshore platform that rests on a spud can or bearing foundation and is held upright by multiple guylines. A simplified procedure for calculating the wave-induced dynamic response of this compliant tower is presented. Also, the dynamic characteristics that allow the structure to safely resist large ocean waves is discussed. A large scale test model of the tower has been installed in 300 feet of water in the Gulf of Mexico to verify the validity of the conclusions drawn.

INTRODUCTION

A new compliant offshore structure, the guyed tower, has been proposed as a deep water production and drilling platform. The concept as proposed has two major advantages over other pr0posed schemes; first, the structure can be fabricated and installed using presently available equipment and technology; second, this production platform is anticipated to be less expensive to build, and maintain than present alternatives proposed for water depths from 600 to 2000 feet. This paper describes the basic guyed tower concept and illustrates the design procedures used to insure that the compliant structure will safely withstand severe environmental forces and yet be slender, lightweight and economical.

Prototype Guyed Tower

The guyed tower is a trussed structure that rests on the ocean floor, extends upward to a deck supported above the waves, and is held upright by multiple guylines (Fig. 1). The base of the tower is supported on a truss reinforced shell foundation called a spud can. During installation the spud can is forced into the ocean bottom until the desired load carrying capability is attained. The amount of design penetration is of course dependent on the load to be carried and the site soil parameters.

The main truss of the tower as currently proposed would have four equally spaced legs connected primarily with x-bracing. However, other geometric configurations could be used.

For a structure supporting 24 wells in 1500 feet of water, the legs would be spaced 100 feet apart and range in size from 5 to 8 feet in diameter. Ideally the deck would be designed to support all the equipment to drill and produce a large number (20 to 40) of wells. The deck for the 24 well 1500 ft structure would have two levels 150 feet on a side and would support 7500 tons deck payload, which is adequate for many areas of the world. To carry larger payloads, the support capacity of the tower truss, spud can, and guying system would have to be increased proportionally.