Author: Brad Bartilson, Product Manager
Design for wind can help your structures withstand the elements and enhance the safety of its occupants.
It’s no secret that wind affects doors. We’ve all experienced a door being caught by the wind and quickly appreciating the potential of Mother Nature to do some serious damage. And with the intensity of storms increasing in recent years, knowing how to design for wind is an important skill set for designing and selecting door solutions that can withstand the elements and enhance the safety of your structure and its occupants.
Considering that wind speed and direction can vary greatly and change quickly, what’s the maximum speed to be considered for design? And how do building size, location and orientation affect the requirements? While the final details of design are best left to licensed experts, knowledge of the basics can inform the dialog between experts, building architects and door suppliers during the design and selection process. Here’s a glimpse into the process.
Design for Wind
The key factor we’re considering in door selection is the pressure that will be placed on the door under maximum conditions. Wind pressure (expressed in units of psi or N/m2) on a door results from wind velocity and its relative direction. To determine this loading at a specific door location requires the collection of building geometry, location, orientation and other site-specific information. Experts have condensed the determination of the pressure that imparts on buildings, expressed as ASCE 7-10. The process breaks down into pressure on the Main Wind-Force Resisting System and secondly, the components and cladding of the building, calculated from the following variables:
- Basic Wind Speed (V)
- Wind Directionality Factor (Kd)
- Exposure Category
- Topographic Factor (Kzt)
- Gust Factor (G)
- Enclosure Classification
- Internal Pressure Coefficient (GCpi)
Each of the variables above requires gathering information for entry into tables and/or formulas. Risk category determination is the first step in the process. It examines the use, occupancy and potential effect of environmental hazards. Fig. 1 (Table 1.5-1) lays out the category determination:
The Need to Determine Speed
With the category determined, the basic wind speed is then selected by the site’s location on the appropriate map; example Fig. 2 (26.5-1-D) below. Basic wind speed from this map represents a three-second gust at 10m height above the ground:
It should be noted there are special consideration zones that increase the Risk Category due to special wind conditions, including hurricanes (Fig. 3).
Once the basic wind speed is determined the other factors listed above are required for entry into the velocity pressure equation.
Velocity pressure exposure coefficient is provided by formula or by Fig. 5 (Table 27.3-1):
Figure 5: Topographic Factor Kzt, is drawn from Figure 26.8 which has geometric factors of the surrounding landscape as inputs.
Figure 6 (Table 26.8)
Wind pressure is then arrived at by:
G is the gust effect factor (for a rigid building is 0.85)
CP are wall pressure coefficients, related to wind direction on the wall in question:
For the case of the Gable and Hip Roof:
Example results of velocity pressure calculations of specific building design, location, orientation and surroundings are shown in the following table:
Again, the above results are calculated for a specific set of design, location and surrounding conditions. Assuming we have those results from an expert, door selection can begin.
Door Selection for High Wind
Horton Automatics provides a wide range of high wind protecting doors. Rated from 45-55 psf, Horton’s Profiler® Storm Series sliding doors address all but the most extreme examples from the above table and provide premier performance at an affordable price. For the most extreme wind velocity pressure levels, you can look at the Miami examples in the table above. Addressing those conditions (71.3 and 62.9 psf) Horton’s HD-Storm™ Sliding Door System is able to withstand wind pressure from 70 to 85 psf (as per Dade County, Miami testing and certification – regarded as the highest standards in the U.S.).
Rugged Corner Block Construction
Heavy-duty rails with integral corner blocks add structural integrity that is far superior to mass produced through-bolt panels.
3-Point Locking System
HD-Storm’s 3-point locking system ensures the entrance is secure and anchored when the door’s not in operation. The doors are approved for single and bi-parting configurations with full breakout option.
Steel Reinformced Rails
High strength tubes are integrated into rails to reinforce holding power during severe weather.
But Pressure is not the Only Consideration
Wind not only exerts pressure on doors, but can drive debris right into them. Wind-borne Debris Regions have been established with location-specific requirements and certifications. Fig. 10 shows these regions in Florida.
Horton’s HD-Storm Level E addresses wind-borne debris requirements. Employing the same rugged, patented corner block, steel reinforcement and 3-point locking system, HD-Storm Level E adds further design enhancements to meet the small and large missile impact requirements of Level E hurricane testing (January 20, 2022 HD-Storm Level E door was granted its Notice of Acceptance by Miami-Dade County for Risk Category IV).
For more information about selecting the right door for your application, you can read more about Hurricane Rated Sliding Door Systems here, or you can contact your local Horton distributor by clicking here.