Wind loads, envelope procedure

Pressures on the main wind force resisting system of a low-rise building by ASCE 7-22 Chapter 28, with flat or gable roofs. For the procedure of Chapter 27, components and cladding, or other roofs, use Wind loads. The two types share only the terrain data, so nothing links their results.

Inputs of the envelope procedure #

• Wind speed, exposure, Kd, Kzt, Ke: Chapter 26. Kd is applied in Eq. 28.3-1. Kzt is entered: the Wind loads type computes it where you need that.
• Enclosure: enclosed, partially enclosed or partially open, with both signs of GCpi. Open buildings use 27.4 and 28.3.7, which this type does not cover.
• Roof: flat or gable. The building is a rectangle in plan, with the ridge along L.
• Eave height, roof angle: h is the eave height for roofs up to 10 degrees, as the figures say, and the mean roof height above that.
• Parapet height, overhang: 28.3.4 and 28.3.5.
• Stories, light-frame, flexible diaphragms: only for the exceptions to the torsional load cases (28.3.2).
• Moment frames resist the wind: turns off the floor of 28.3.3 (the shear with the roof neglected).

Checks performed #

The type gives loads and reads Calculated. There is nothing to size.

The coefficients are pseudo loadings: each corner takes its turn as the windward corner, and frames and bracing take the zone pressures in their own calculations. The totals here are for one reference corner, to check the pressures and to size a system by hand, and do not replace those cases.

Limitations #

• Conditions of 28.1.2 are yours to confirm: a regular shape, no across-wind effects, no channeling or buffeting, no arched or unusual roof.
• Hip roofs are not here. Step 6 of Table 28.2-1 gives coefficients for flat and gable roofs, and Commentary Figure C28.3-3 only suggests how to adapt them, as a judgment of the committee.
• 28.3.7 (longitudinal loads on open or partially enclosed frames) and open buildings are not covered.
• Monoslope roofs, multiple ridges and non-rectangular plans are not covered.
• 28.3.2.1 is applied across the ridge. In Load Case 2 this type keeps Zone 2 for the whole depth along the ridge, the conservative reading for uplift. The text is not explicit there: the ASCE Wind Guide (not on hand) should confirm it.
• Torsion and shear totals add the wall and roof zones by area. In Load Case 4 only the end walls count, as the slopes run along the wind.
• Overturning is not reported: it depends on what resists it. Components and cladding are in Wind loads.

Verification examples #

Verification status: 46 values compared in 6 examples (6 published, 0 hand calculations from the cited equations): 46 within tolerance, 0 recorded deviations. Code basis: the provisions it uses were read in the target edition.

I found no free published worked example of Chapter 28. The ASCE guide to the wind provisions of ASCE 7-22 has them (Chapter 4), and it is on the list to buy after wave 7.

Everything else is a hand calculation from the code's equations, written in the tests: qh, the end zones, interpolation, the rule for Zone 2, shears, torsion, uplift, the floor of 28.3.3, the minimum loads, the torsion exceptions, parapets and overhangs. What the Wind Guide should confirm: the totals of Load Cases 1 to 4, and the reading of 28.3.2.1 along the ridge.