There is no part of the country that remains free of high wind events, from powerful nor'easters and hurricanes to blizzard conditions and high-speed straight-line winds often seen in the plains. Every structure that rises above ground level must be able to handle extreme wind and weather events.
While nothing will survive a direct hit from an F5 tornado, there are design options that can protect your building from destructive winds.
Wind Resistance Factors
There are several factors to consider when designing a metal building for wind resistance.
- Exposure ratings indicate the threat level of the wind in various regions of the country, including the impact of urbanization.
- Exposure B denotes the low wind threat generally found in urban, suburban, or wooded areas with plenty of windbreaks such as buildings that sit close together. Exposure B is used as the default absent other characteristics for a different exposure rating.
- Exposure C includes open, rural areas with few buildings or hills below 30 feet high. With the lack of windbreaks, appropriate wind load design is required.
- Exposure D ratings are assigned to flat expanses of land with no obstructions.
Wind forces break down into shear load, lateral load and uplift load. Shear load is caused by horizontal wind pressure and can force a structure to tilt and sway. Lateral load includes horizontal wind forces that push or pull and can move a building off the foundation. Uplift load is the lifting pressure exerted by wind over a surface, damaging roofs and walls.
The impact of wind forces depends on the building’s orientation to the wind direction, the method of construction, and the strength of the wind.
Finally, building designers must take the prevailing wind of a region into account. While the wind can blow from any direction, most regions of the country experience prevailing winds, which regularly arrive from a single direction. In Texas and Oklahoma, strong southern winds prevail. Building design must take this into account to ensure the durability of the structure over the decades.
Steel frame buildings offer the best protection against wind loads. Steel has the highest strength to weight ratio of any construction material, so you have a lightweight material that remains strong in the face of wind loading.
- Rigid frame (I-beam) is used in commercial and industrial construction. Paired with a shallow roof, rigid frame buildings can survive extreme wind events.
- Open web truss is found in residential areas. The buildings are heavier and of greater strength than those constructed of other materials, and are durable in the face of high wind conditions.
Engineers have developed better methods of construction through years of experience, analysis, and innovation. For example, designers have found that wall junctures and roof edges are the weakest points in the building. Additional reinforcement is added to reduce the risk of damage.
There is always more to learn, but a steel building constructed today stands a better chance of survival than one built 50 years ago.
Nails and staples typically used in wood-frame construction are no match for gale-force winds. They tend to pull out and allow the roof to separate from the structure.
High strength bolts, screws, and anchors are more wind resistant and distribute the uplift forces evenly. For example, columns attached to the foundation with steel J-bolts embedded in the concrete are less likely to fail. The appropriate anchors depend on the style of structure, the building site, and the location.
Height and Roof Pitch
There is no getting around the fact that the taller a structure is built, the more wind forces act upon it. Lower, wider buildings are inherently more stable than taller structures. Also, a single tall building will experience higher wind forces than a group of closely placed structures of similar height.
- Flat roofs are at higher risk of uplift forces.
- Like the wing of a plane, when wind passes over a level surface, it exerts an uplifting force that can suck the roof panels off a building.
- A high pitched roof, on the other hand, is less likely to tear off and expose the interior of the building to the elements.
One advantage of a steel roof is that the panels are installed as a continuous piece of material extending from the peak to the eave of the roof. There are fewer places where the wind can penetrate to tear away the covering.
Skin and Doors
The thickness and design of the envelope have a direct bearing on a structure's wind resistance.
- Thicker steel, such as heavy-duty 26 gauge exterior panels, withstand higher pressures as flying debris than lighter gauge steel.
- Purlin bearing rib panels have higher tensile strength than panels with shallower-depth designs.
- A greater overlap between panels increases durability and wind resistance.
Wind-rated doors contain reinforcements to prevent damage from strong winds. In hurricane-prone areas, wind-rated exterior doors are a primary building code requirement.
Your best protection against high wind speeds is the strength and durability of steel.
Wind loads can change, and a steel building is easily adjusted to new loads, reducing the need to demolish and rebuild. Steel has a high strength-to-weight ratio meaning it adds strength without excessive weight.
Steel has low maintenance requirements and can be repaired quickly when damaged. Durability increases safety; there is less chance of failure due to wear and tear. Keep the roof clean and clear of debris as well as inspect and replace fasteners to keep the roof panels intact. Repair scratches in the finish quickly to prevent the entry of moisture that promotes rust and corrosion.
Steel is a versatile material that can be adapted to any design or shape. Color and texture options are practically infinite, allowing the installation of a strong roof with high curb-appeal. You can meet design requirements while installing a durable roof that meets or exceeds local building codes.
Steel Is Sustainable
- It is made of a significant proportion of recycled material and is, itself, 100% recyclable with no loss of strength.
- A steel building can be disassembled and reassembled in a new location if needed or desired.
- Steel buildings are easy to insulate, saving energy costs and helping reduce heat island effects with cool roof technology and metal that quickly sheds heat during the night.
Steel is the only building material that can offer sustainability paired with strength in the face of strong winds. Consider building low structures that are spread out to decrease wind forces and provide the best anchors your budget allows to keep the structure on its foundation.
Over time, you will realize a better return on your investment through lower total cost of ownership along with a safer structure than if you built with other construction materials.