Asce 07-10 Pdf

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Nerio Cintron

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Aug 3, 2024, 5:08:45 PM8/3/24

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Building design risk and exposure categories
There are many factors an engineer must consider when calculating wind uplift pressures per ASCE 07-10. One of these concerns is identifying what type of risk to human life the building is protecting, as classified into four categories:

Engineers must also consider where a building is positioned in relation to other structures around it. This will affect the ultimate design wind speed used in their calculation. There are three different Exposure Categories:

For each of the building design risk categories, the ultimate design wind speeds vary (Figure 3). For example, a Risk Category I building in the central part of the United States would be designed to withstand a three-second wind gust of 170 km/h (105 mph) at 10 m (33 ft) above ground. This applies to an Exposure Category C building.

Standing-seam metal roof panels (Figure 5) are attached to a purlin or substrate with clips designed specifically to allow the roof to move, and change dimensionally to accommodate thermal movement. This type of roof panel changes its shape under load and needs to be designed based on specific uplift tests, such as ASTM E1592, Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference, which was developed for this roof type.

As wind uplift acts on a standing-seam metal roof panel, the suction pressure distorts the panel upward, bowing it in the center (Figure 6). This action can cause a failure in the panel by shifting the seam sideways and splitting the seam. This distorting action could also allow the seam to unhook itself from the mounting hardware. Splitting seams open and unhooking the seams from the mounting hardware are the two most common modes of failure of this type of roof.

All these measures add varying amounts of cost increase to the metal roof. The manufacturer will work with the engineer to provide the best combination of the methods to minimize the cost impact while meeting required design pressures. Of the methods above, the newest innovation is the external seam clamp.