After enduring a record-breaking year of storms and natural disasters in 2011, today’s owners, architects, and builders are working diligently to design and construct buildings to withstand the punishment of the elements. Building a structure that will endure the beatings from the wind and weather takes more than just brawn and heavy-duty materials: it also takes brains and careful planning.
Wind and live loads are two of the most important considerations to think about when designing a wall and roof system, no matter what part of the country you’re in. Many people think of direct wind forces as being the primary concern for buildings, but in most cases, it’s the negative loads, which are outward or suction forces, that are more powerful and require greater attention from the designer.
While manufacturers of metal-roof and -wall systems constantly test their products and work with designers and installers to make sure the correct gauge, profile, and fasteners are used, calculating the correct direct wind and negative loads is vital to ensuring proper long-term performance of any system. Building codes require two sets of wind loads to be determined. The first is for the main wind-force resisting system (MWFRS), which refers to the major structural elements of a building. The second set is for components and cladding. This set is more stringent and is what is needed when designing metal-wall and -roof systems.
The ever-changing landscape of building codes has developed stiffer requirements for wind mitigation over the years. “I’ve seen everything from building codes that were pretty lax in the 1960s and 1970s to codes today that have gone the other way,” says Denny Koska, senior product engineer for Moon Township, Pa.–based Centria. “There have been many significant changes to the building codes in the 45 years that I have been in the metal construction business. I’m sure a lot of it comes from insurance companies because of the payouts they’ve had to make with storms like Hurricane Katrina, as well as recent damage from strong tornadoes.”
Understanding the stresses that wind creates on a building has evolved over the decades, and codes have adapted along the way. “In the late 1970s and early 1980s, codes really started to consider negative wind loads as controlling factors and started to identify that the corners of buildings and perimeters of roofs have higher wind-load requirements than the rest of the building,” Koska recalls. “That’s when codes first started to print wind-speed maps for the U.S.”