Maintenance stairs in semisub legs should ideally be easy to instal, maintenance free and lightweight.
We were asked to design and manufacture a modular spiral stair system by KeppelFels for Petrobras on such a project. The final design was lightweight (about 25% of a steel equivalent), quickly assembled (1 week for a 55m high stair) and completely maintenance free. The system components were produced in the factory and trial assembled before being shipped to site for re-assembly. Needless to say, the overall cost of the system was cheaper than a steel equivalent. All system parts are customized extrusions which means that they stairs are easily reproduced to exact detail on future, similar projects without much trouble.