Concrete needed for prison security but poses weighty problems

M.A. Mortenson Company

Security concerns alone make building a federal detention center challenging. Building a secure, radius-shaped concrete facility on a very steep, terraced, compact site in only 20 months is an even greater challenge.

How M.A. Mortenson Company responded to the challenges of building this facility may serve as an outline for more effectively managing the construction of large concrete projects with special needs.


Located on a seven-acre site, the $54.5 million Federal Detention Center at SeaTac is a 355,000-square-foot, 11-story structure. Construction began in January 1995 and is scheduled for completion in August 1996. When finished, the facility will provide 563 cells for detainees awaiting trial in Seattle; support facilities such as medical and dental service areas; laundry, kitchen and loading docks; an administrative area; and a marshall sally port for the receipt, transfer and administration of detainees.

Concrete was chosen for this specialized facility because of the security it provides and because it is extremely durable. The unique properties of special types of concrete designed, however, required an exceptional level of preplanning and technical expertise.

Radius-shaped concrete walls at the Federal Detention Center are one of the many challenges of the $54.5 million project. (Photo by Soundview Aerial)


Mortenson's goal is to work with the owner, architects and its subcontractors to build every project safely, on-time, on-budget and in a manner that exceeds the expectations of the client. From the start, the Federal Detention Center has required ongoing communications and thorough planning by all parties involved. In addition to working with the construction team members, special attention was given to the community's concerns and communications with the general public.

Only through constant communications have we been able to address the special needs of this facility, which include a 20-month timeline, security requirements, radius configuration and building with 25,000 cubic yards of concrete on stepped or tiered earth.

Security requirements

The special security needs provided Mortenson with the opportunity to more thoroughly review the facility's design and evaluate solutions prior to beginning construction. We studied a wide range of floor slab formwork systems to balance material cost, manpower and schedule at the most efficient level. Extensive preplanning required us to pour the 25,000 cubic yards of concrete and coordinate the locations of more than 30,000 metal imbeds and additional items, such as rebar, post-tensioning cable and special conduit needs.

The project's security needs required special construction components, such as:

Building with concrete

To address the extreme weight of the heavily reinforced concrete floor slabs, plinths and columns were built within the walls of the prison to support the loads of the solid concrete frame. Post-tensioned decks were used with the shear wall moment frame systems because they allow for the placement of thinner concrete slabs.

Throughout the extensive coordination and planning efforts, one of the greatest challenges was addressing the interaction of the building's radius shape with the shear wall moment frame structure.

Since the moment frame is not round, Mortenson had to determine how to cast support columns so that they were integral with the radius walls. As with the floor slabs, Mortenson analyzed several wall-forming systems and selected one based on the efficiency, cycle time, economics and safety it provided.

The complex forming systems are working very well. The Federal Detention Center is on track for its scheduled completion. The forming system was a result of intense evaluation, interactive communication and exceptional planning.

Christopher Augustine is the Federal Detention Center project manager for Mortenson.

Return to Building with Concrete top page