Brian Smith, M.SAME, George Rogers, M.SAME, and Steven H. Miller, M.SAME | Published in The Military Engineer
Consider this scenario: You must build a town of more than 50 permanent buildings from the ground up in just seven months. The remote desert location is seismically active and experiences temperatures ranging from below freezing to 120°F. There is no electricity or water on the jobsite. The buildings must withstand combat. and the budget it tight.
Though this may sound like a situation in the Middle East, it is actually a project constructed in the California desert in 2007. The “town” was a simulated Iraqi village, a Military Operations in Urban Terrain (MOUT) live-fire training facility.
A crucial element in bringing the project in quickly and cost effectively was a prefabricated studcast building system manufactured by Ecolite Concrete USA. Studcast is a hybrid of panelized, coldformed steel stud framing structurally married to lightweight cellular concrete to achieve composite strength. Comprising both frame and skin, units come off the casting bed as complete and ready-to-erect walls suitable for use as load-bearing walls in low- or mid-rise construction or curtain wall for high-rise buildings. It is structurally robust, durable and offers a range of high-performance properties.
The Test Case – Ft. Irwin
The first phase of the MOUT facility at the U.S. Army National Training Center (NTC) at Fort Irwin, Calif., consists of 54 buildings ranging in height from one to four stories. The U.S. Army Corps of Engineers’ (USACE) original plan called for cast-in-place concrete and traditional masonry, and was projected for one year of construction.
When the original plan was deemed too costly, RQ Construction of Bonsall, Calif., proposed substituting walls made of studcast, cutting the budget by 30 percent and accelerating construction 50 percent.
When the contract was let, however, there was no studcast factory in the area. Installation of a factory in a vacant building in Barstow, Calif., began in March 2007. Simultaneously, site work began 45-mi away at Fort Irwin. The factory was brought on line in less than 30 days; the first walls were erected in early April and erection of walls, steel floor and roof decks was completed by August. After interior finishing, the complex was turned over to NTC on Oct. 1, 2007.
The experience of building the MOUT – the first project constructed with this technology – has refined the system and proven its potential for rapid construction and emergency response. The new technology’s learning curve undoubtedly lengthened the construction process. It is estimated that a similarly-sized project could now be completed in two months instead of four.
The project was deemed a sucess, and USACE has listed the Ecolite studcast system as an acceptable material for the second phase of the MOUT.
The studcast process is fast in both manufacture and construction, lending itself to rapid deployment.
The building design is converted into a Building Information Model (BIM) that identifies the components required for each wall. The BIM instructs a numerically-controlled roll-forming machine that cuts and forms flat steel into precise studs and rails. The machine punches fastener holes to simplify panelization. It notches C-shaped rails and swages stud ends so components fit together more precisely and provide greater strength, and it pre-punches utility access holes and fabricates special components for doors and window openings. The machine also numbers all pieces for accurate assembly.
Framing is panelized by small teams using simple tools. Expandid metal mesh is attached over one side of the panel to reinforce the concrete and connect to to the studs. The panel is placed on the casting table with mesh facing downwards. An edge strip acts as a form for the concrete and suspends the frame at the proper height so that one inch of the stud thickness will be embedded into the concrete facing.
Next, a self-consolidating cementitious slurry containing billions of microscopic air bubbles is pumped in. The slurry cures into a lightweight cellular concrete that is 50 percent air by volume and half the weight of standard concrete. The closed cells contribute to the concrete’s thermal insulating and fire resistance properties. Using up to 50 percent fly ash 0 a pozzolanic byproduct of coal-fired power plants – improves the performance of the concrete and contributes to environmental sustainability.
The entire process, from sttel fabrication to casting, takes about one hour.
Walls can be removed from the casting tables after curing overnight, keeping production rates high. Three days after casting, the wall is ready to ship and erect. The light weight enables wall sections up to 20-ft long to be lifted with a forklift or light-duty crane, and to be transported on a light-duty trailer pulled by a pickup truck.
Erection involves lowering the wall into position, bolting it to the foundation or to the story beneath it and screwing together the vertical steel members of adjacent walls. At Fort Irwin, four-man construction teams were able to erect, temporarily brace and bolt down a wall in seven minutes. While one man continued attaching one wall to adjoining walls, the other three men could start loading and erecting the next unit. To demonstrate the speed of the system, a five-man crew erected one 2,000-ft², two-story building, including floor and roof decks, in a single day.
Unlike many rapid-construction alternatives, studcast buildings can be permanent assets. In the aftermath of a disaster, they may be more durable than the structures they are replacing. However, for temporary usage, the construction process is also easily reversible: walls can be disassembled, stored and reused later.
A nationwide network of studcast factories is being planned, and the second factory is already being equipped. Walls produced at these facilities will be within one day’s shipping distance of virtually anywhere in the continental U.S.
For emergency response, standardized, off-the-shelf building kits can be manufactured and stockpiled in disassembled form, ready to ship and erect. Kits for barracks, dining facilities, classrooms, hospitals, offices and other facilities can consist of walls, partitions, floors, ceilings and roods. Wiring, plumbing, doors and windows can also be factory-installed in the walls.
A disassembled kit requires far less storage and shipping space than a conventional prefabricated building, yet can be erected and ready to occupy quickly. Exterior and interior walls for a 1,000-ft² residential unit, for instance, fit into the 160-ft² footprint of a standard shipping container and weigh less than 15-T.
Pre-fab kits can be pre-positioned in strategically located depots and shipped while construction sites and still being prepared. This approach would enable building replacement in a matter of days instead of months.
If onsite manufacturing is needed, factory elements, all of which are either portable or quickly constructable, can be brought to project areas anywhere on the globe.
Moreover, relatively unskilled local labor can be quickly trained for production and erection, as was proved during the Fort Irwin project. With effective supervision, construction crews need little or no construction experience. In the aftermath of disaster, a portable factory could provide buildings, as well as “back to work” jobs for some of the population, lightening the burden on military responders and allowing a limited number of trained personnel to produce large quantities of work.
Originally published in The Military Engineer, March-April 2008 Edition. Visit their website here.