The Source Civil Engineering Magazine Sidebar: Secure structures
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Sidebar: Secure structures

By Thomas Lanzer, P.E., M.ASCE, and Eric Hollman, P.E.

The Nixon Forensic Center is an interesting combination of a health facility and detention center. The state of Missouri and WSP worked together to provide an environment in which patients would not feel as though they were in a typical incarceration environment. This had to be combined with consideration for the security and safety of patients and staff.

Each of the six main living units was divided into two sides off a central spine. One of the main structural design challenges involved the need for clear lines of sight to the living units. To achieve this, each side consists of a central area with corridors extending out radially in plan. This main area was to remain column free; different levels of framing at the roof provided upper windows and daylighting in this common area. Long-span roof girders—spanning up to 50 ft—were designed to support multiple roof levels while maintaining the open space below. Steel framing was supported on concrete masonry unit (CMU) walls. These walls also functioned as shear walls for resistance to lateral loading. One corridor on each side was designed as a tornado-safe zone and featured additional wall reinforcing and precast-concrete ceilings. An early concept that would have allowed an entire corridor to be closed off had to be abandoned for security reasons, but the hardened structure remained in the design and thus this reinforced corridor could be used in the future if local safe zones are required.

Common areas within the complex are generally steel-framed structures with CMU exterior walls. Attics or partial attics are provided for utility distribution. The attic floors feature concrete slabs over steel decking; the roofs are steel framed with decking and roofing material specified by the architect. Interior columns are either structural tubes or wide-flange sections with full concrete encasement, providing fire protection and smooth, hard surfaces for durability.

A system of corridors connects the living units with the administration building on the western side of the complex, central common spaces, and the new central plant building, known as the energy and control center (ECC), to the east. Corridors consist of 8 in. thick precast concrete walls approximately 24 ft high, a 12 in. cast-in-place ceiling/mechanical floor at the approximate midpoint of the height of the walls, and steel-framed roofs. The mechanical floor, called an attic, serves as the distribution corridor for all utilities originating at the ECC and used throughout the complex. Attic spaces are also located above the living units and other areas within the complex and serve to house and distribute utility services locally. Lateral wind and seismic loads are resisted by moment frames consisting of the concrete walls and the mechanical floor slab; special connectors within the walls and doweled into slabs provide continuity for the moment connections. The walls cantilever above these mechanical floors and extend to the roof; the walls, roof, and floor are all designed to support loads from distribution piping and wiring conduits and duct banks.

Before designing the overall hospital complex, WSP designed the ECC. One side of this facility houses mechanical and electrical equipment serving the entire facility; the other side houses staff and equipment providing food service to patients. Early in the final design, the decision was made to construct this building using a preengineered metal structure for the main structural frame. WSP designed the foundations and floors as well as secondary roof framing, which included support for solar panels and support and screening for rooftop heating, ventilation, and air-conditioning  systems, as well as interior structural work. The floor and foundation systems included special supports for an 11,000 gal. hot water storage tank, generators, and chillers. These foundations were proportioned to accommodate local bearing pressures generally on the order of 1,500 psf.

This article first appeared in the September 2020 issue of Civil Engineering.

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