When Canadian Forces Base (CFB) and the British Army Training Unit Suffield (BATUS) needed more space to store ammunition, Defence Construction Canada’s first call wasn’t to the local hardware store to purchase an off the shelf product. What they needed was an Explosive Storehouse or ESH which is a unique special purpose building. In fact, to safely store enough ammunition they were going to need four of them. Defence Construction Canada (DCC) sent out a request for a design build proposal based on strict performance criteria to a select list of Contractors.
Design Requirements
The ESH buildings were designed as medium walled buildings in accordance with performance specification JSP 482s. These specifications require the walls and roof to have a minimum thickness of 6” of reinforced concrete combined with a design live load of 250 psf on the roof to provide a reasonable level of protection from fragments, lobbed munitions and fire from explosives.
Since a medium walled building will not resist penetration of certain high velocity fragments, the possibility of internal blast overpressure was also to be considered. It is not possible to design a medium walled storehouse to resist blast overpressures considering the large volume of ammunition stored. Therefore, the walls were required to relieve overpressure and columns and beams were required to support the roof and prevent progressive collapse of the building in this event.
The exterior walls were designed for wind loads in the Suffield area and increased to 15 pounds per square foot to account for pressure and gust coefficients. In accordance with specification JSP 482, these medium walled ESH’s were surrounded by traverses (berms) that are high enough to intercept all missiles projected at 40 degrees or less which could result if the walls failed.
Construction
The design team reviewed the performance criteria and evaluated various available material options. Obviously the use of wood was totally out of the question, however, a steel option was considered. Prestressed concrete was considered an obvious choice of material to achieve minimum thickness and the required clear spans for the roof structure. Steel fireproofing and its lack of mass lead the team to choose a concrete solution. Structural steel, cast-in-place concrete and precast concrete were considered for the building frame. Combinations of cast-in-place and precast were considered, however, the aggressive schedule andrequired winter construction which tilted the scales in the favour of a single sourcetotal precast design for the roof and frame.
The minimum thickness for the roof structure was achieved with prestressed double tees with a 6 inch thick flange. The double tee roof structure was supported by a precast column and beam frame with the columns fixed at the base to provide stability for the roof diaphragm.
Early concepts for the walls were based on existing facilities, using masonry infill panels between columns. However, the team made the decision to use prestressed precast, insulated concrete sandwich panels which were located in front of the column line.This provided an uninterrupted building envelope as well as ensuring the columns would not attract unplanned loads in the event of a blast overpressure. This decision resulted in a total precast concrete solution for the building superstructure.
An attached mechanical equipment room was framed with precast panels and a hollow core roof. The hollow core roof was covered by a concrete topping to achieve the minimum required concrete thickness. Isolation from the storage area was provided by the precast wall system.
WINNER
ACI Awards of Excellence 2007
Concrete Design & Construction
Conclusion
The strength and mass provided by the precast concrete made it an excellent material choice to meet the owner’s needs. The roof structure provides protection from lobbed munitions and falling debris as well as protection from fire.
The prestressed precast wall system will relieve blast pressure without fragmenting, while at the same time, serve as the building envelope. Architecturally, when combined with the red accent trim, the consistent color and texture of the concrete finish eliminated the need for any further treatment. No other construction material could match the simplicity of design and efficiency in meeting the owner’s unique needs for these structures.
The successful design-team consisted of:
Contractor: Graham Construction & Engineering Inc.
Prime Consultant: Genivar (formerly Cochrane Engineering Ltd.)
Architect: Kindrachuk Agrey Architecture
Precast Engineer: Gratec Engineering
Precast Supplier: Lafarge Precast Division
