Making the Right Choice in Prefabricated Restrooms
Chris Reese
PHOTO COURTESY OF EASI-SET BUILDINGS
When planning for a new restroom facility, many questions come into play. Can it be combined with other functions, like a concession stand? What is more important—low initial investment or long-term value? How much maintenance will be required? Will it look good? Will it last? Let's go through some details that will hopefully bring you closer to making an informed decision on whether a precast concrete building is the right choice for you.
What are the risks for your location?
Wind Loads
In sustained winds or sudden thunderstorms, broken tree branches and loose debris can become lethal projectiles. Even 75 to 85 mph hurricanes can compromise weak structures like metal sheds and poorly constructed wooden buildings. Typical 3-inch steel-reinforced precast concrete walls can be designed to withstand wind speeds of 165 mph and more. Heavier walls, such as 4 inches, in combination with specialized doors, impact-resistant windows and hardware will meet Miami-Dade hurricane standards of 185 mph. Prefabricated concrete buildings can even be designed to meet ICC-500 and FEMA guidelines for Tornado and Hurricane Shelters (with wind speeds ranging from 130 to 250 mph). These shelters are designed to shield debris hazards, including wind-borne missile impact resistance. Prefabricated concrete restrooms offer flexibility in accommodating various wind speed design criteria.
Tree Fall (Impact Resistance)
Winds combined with torrential rainfall can cause catastrophic damage to buildings and the people who seek shelter in them. A 50-foot maple tree can easily weigh more than 10,000 pounds, and could completely destroy a typical site-built structure. All-precast concrete buildings have proven in real life and test scenarios to be a durable solution to impact loads, playing a large role in building resilient facilities.
Snow loads: One square foot of wet snow can weigh 12.5 lbs., meaning just 12 inches of snow on a 10-by-12-foot roof equates to 1,500 pounds. On a 20-by-50-foot building, that's more than 6 tons. Designing for snow loads varies by area, region and elevation. Depending on location, snow loads could be anywhere from negligible to exceeding 300 pounds-per-square foot. Pre-engineered, pre-fabricated structures offer flexibility to accommodate various different load requirements, eliminating the worry of structure collapse.
As required, prefabricated concrete buildings can be designed, constructed, connected and anchored to resist floatation, collapse and permanent lateral displacement due to flooding. Step-down floors, specialized seal-tight doors and caulking systems resist water infiltration. Concrete buildings also provide for less internal damage and easier cleanup if water and debris do enter.
Precast concrete buildings, including nonstructural components, can be designed and constructed to resist the effects of earthquake motions as prescribed by seismic mandated codes. Connections are designed between components to provide adequate strength to resist shears, axial forces and moments that permit rotational and/or translational movement without degradation of the buildings' performance in accordance with ASCE 7. Standard and modified designs are available to accommodate all seismic zone categories.
Brush fires, electrical fires, lightning strikes, mishaps or arson all present fatal dangers to structures. Fire ratings of precast concrete can far exceed those of wood, metal or thin wall masonry. Concrete components can be designed to meet any degree of fire resistance that may generally be required by building codes, insurance companies and other authorities. Fire resistance ratings of a building can be determined from AS™ E119 standard fire tests, code-approved empirical data, or by calculation procedures detailed in industry codes.
Vandals are a common problem for many facilities. Reinforced precast concrete panels resist damage through actual strength of material as well as a visual and psychological deterrent. Surfaces can be treated with anti-graffiti coatings for easier cleanup. Electrical conduit can be cast into the walls versus exposed on the interior walls or placed behind sheet rock. Standard and optional features like electric time locks, heavy-duty doors and frames, LEXAN polycarbonate windows, metal mirrors, vandal-resistant/kick-proof vents, stainless vs. porcelain fixtures, and tamperproof hardware all add an extra level of security.
Precast concrete structures can provide greater protection from gunfire than typical metal, wood, brick or concrete block. In tests, a 3-inch reinforced precast concrete panel met UL 752, Level 5 (NIJ Level 3) protection. This standard test uses military full metal copper jacketed ammunition fired from a hunting rifle, such as the 308 Winchester or a military rifle with muzzle energy of 2519-3048 foot-pounds.
In many facilities wear and tear is the number-one factor in limiting the useful life of a building. Restrooms made of all-concrete, including interior walls and partitions, not only stand up to abuse, but are also easily repaired when damage does occur. Long-life epoxy paints that combat mold and abuse are typically applied to interior walls. Exterior walls are normally impregnated with stain that long outlasts typical building finishes. Stainless-steel or powder-coated hardware, fixtures and trim that resist wear and corrosion provide years of service.
Precast concrete structures handle the stresses of all of these various risk factors using several means. Roofs and floors are post-tensioned for added strength—mechanically stressed to 30,000 pounds after assembly by using steel cables strung through conduit channels cast into the panels. This creates not only additional strength, but also increased water tightness of the exposed surfaces. Larger roof sections can be pre-stressed while being made in the factory. Pre-stressing or post-tensioning removes a number of design limitations associated with conventional poured-on-site concrete, allowing for the building of roofs and floors with longer unsupported spans and capable of carrying heavier loads. This allows for designing and building lighter and thinner concrete structures without sacrificing strength, and creates durable roof systems that last for the life of the building.
For more factors to consider when selecting prefabricated restroom structures, click here to read Part 2 of this column.
Multi-sectional (modular) buildings are designed using sectional roof (and floor) slabs with longitudinal post-tensioning. After building installation, the roof joints are fully grouted and transverse post-tensioning is applied across all roof sections along the entire length of the building. In addition to creating characteristics of a monolithic slab system across all sections, the post-tensioning process increases the average compressive strength of the roof diaphragm controlling and counteracting shrinkage and flexural cracks.
Chris Reese is the senior engineer for Easi-Set Worldwide, where he oversees research and development of new technologies within the precast concrete products industry, and manages the production of a wide range of Easi-Set Building engineering projects across North America. For more information, visit www.easiset.com.