Chemistry to the Rescue
Article originally from American Chemistry magazine.
When it comes to protecting buildings from natural disasters, today’s engineers have a wide range of construction materials to choose from. The cost of cleanup after a disaster can reach billions of dollars, once the price of home and public infrastructure repairs, debris removal, and temporary housing is included. Millions more are spent on less obvious items, such as medical/dental care, small business loans, water, and ice. However, with the use of some innovative building materials, the construction industry is taking the wind out of Mother Nature’s sails.
Spray Polyurethane Foam:
Florida’s Answer to High Winds
One assembly noted for its durability in storms is the spray polyurethane foam (SPF) roofing system. Many such roofs were able to survive the Florida storms of 2004 unscathed or with minor surface damage. Steep sloped roofs where asphalt shingles or ceramic tiles had been covered with SPF also fared well. In many cases where roofs were partially repaired with SPF after Hurricane Frances, the foam was the only product remaining after Jean, a few weeks later. Generally speaking, SPF failures were limited to buildings’ decks and substrates and while surface damage occurred, it was not a cause of failure or leakage.
Spray-applied as a liquid, SPF reacts and expands in place to form a firmly adhered, rigid, seamless mass of closed-cell foam. Roofing systems made of this material are frequently installed over existing membranes such as built-up roof (BUR) or modified bitumen (mod-bit). Due to the adhesive, compressive, and tensile strength of SPF, the typical mode of failure in small-scale wind uplift testing is the fastening of the deck (i.e. screw pullout).
Cellular Polycarbonate Glazing:
The Record Shows It Takes the Blows
When a building needs light, glass has long been the constructor’s glazing material of choice. Still, glass can be heavy and prone to breakage during high winds, so engineers often look to other materials, including plastic. Most designers are familiar with acrylic plastic, with the material’s virtues lying in its clarity and ultraviolet-resistant (UV-resistant) attributes. Another way to bring soft, diffused natural sunlight into a structure is through translucent panels — ‘sandwiches’ made of an aluminum grid core onto which fiberglass-reinforced polyester (FRP) facings are glued.
Polycarbonate was among the first window glazing materials certified under Florida’s Miami-Dade County building codes. In one test of the plastic’s strength, a polycarbonate barrel-vault skylight was tested to 412 psf (19,727 Pa) — the equivalent to 355-mph (571-km/h) winds. Successfully hurricane-tested polycarbonate windows consistently resist the impact of an 8-ft (2.4-m) long 2x4 fired from an air cannon at 34 mph (55 km/h).
Plastic and Concrete:
The Perfect Marriage
Integrally insulated concrete wall systems have insulation embedded within the wall, sandwiched between two facing concrete slabs. The core insulation not only offers a consistently high level of insulation, but also resists moisture movement through the wall. Usually, a connector ties both concrete slabs together so the wall works as a structural panel.
Integrally insulated concrete walls offer many design possibilities to combat high hurricane winds and wind-driven rain forces. The 2-in. (50.8-mm) outer concrete slab of an integrally insulated wall can provide excellent protection from any flying debris during high winds. Plates, designed to withstand high uplift forces, are cast into the upper and lower portions of the concrete panel, which allow the panels to be connected to the foundation and roof. Additional hurricane straps can be installed on-site for further security. Provided there is proper detailing at the panel joints and around windows/doors, the concrete panels can be impenetrable to wind-driven rain. Even when the roof blows away, the exterior building walls typically remain standing.