Modifications to an existing industrial facility required the removal of a 220 foot tall steel stack with a six-foot diameter. The challenge was that the stack had a gimble base and guy wires that attached to the stack 180 feet above grade. Once the top portion of the stack was removed to below the guy wire connections, there was nothing to prevent the remaining stack from falling over. There were no large structures nearby to temporarily attach to and due to plant expansions over the years around the stack, a large crane could not access the area immediately adjacent to the stack to remove the entire stack in one lift and lay it down.
An Innovative Staged Demolition Was Required
Engineering Specialties Used
Codes and Standards
A Temporary Structural Steel Frame to Fix the Base
A review of the design drawings for structures and foundations in the immediate vicinity revealed that a large mat foundation was under the stack and neighboring structure that contained heavy equipment. Wind loads were governing for the stack removal process. Because the guy wire-less stack would be temporary, the required wind loading was reduced. However, substantial temporary design loads still remained. A braced steel frame was designed and installed around the gimble base and attached to the mat foundation. This changed the stack base to a moment connection allowing shorter segments of the stack to be cut and removed.
Collaboration Produced the Best Solution
We enjoy challenging situations and looking for the best way to address a given issue. By working closely with the owner and contractor, we were able to develop a temporary design that satisfied the appropriate Codes and Building Officials. The approach developed also greatly reduced risk by providing a robust temporary solution.