ASCE Wind Components and Cladding

[xkcstructural]

When using chp 30 in ASCE 7 and the components and cladding tables I believe figure 30-1 for calculating pnet are you allowed to use elevation reduction factor Ke, even if it is not in the equation for calculating your wind pressure using pnet?

 

[Aesur]

What version of ASCE 7 are you using, 7-16 Table 30.3-1 has Ke listed in the calculation, typically I have included this factor as it basically is a conversion accounting for density of air based on elevation.

 

[ProgrammingPE]

This must be for ASCE 7-16 (or later) since that's when the Ground Elevation Factor, Ke, was introduced.

There should be no problem including Ke in Equation 30.4-1 (pnet = λ*Kzt*pnet30). Part 2 of Chapter 30 (Low-Rise Buildings Simplified) will give the exact same results as Part 1 of Chapter 30. They just compiled the pressures into a table to simplify things for enclosed buildings.

For example, Figure 30.4-1 lists a pnet30 of 16.2 psf for Zone 4 walls, A = 10 ft², V = 95 mph, Exposure B, h = 30 ft. You get the same results if you calculate this using the Part 1 or Part 2 procedure, except Ke is included when you use Part 1.

Part 1
qh = 0.00256*Kz*Kzt*Kd*Ke*V² = 0.00256*0.70*Kzt*0.85*Ke*95² = Kzt*Ke*(13.7 psf)
p = qh*(GCp - GCpi) = Kzt*Ke*(13.7 psf)*(1.0 + 0.18) = Kzt*Ke*(16.2 psf)

Part 2
p = λ*Kzt*pnet30 = 1.0*Kzt*(16.2 psf) = Kzt*(16.2 psf)


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[Aesur]

Not a lot of people realize this, but the older version of ASCE had air density adjustments to the constant in the commentary based on ground elevation. These were in the commentary and not "code" therefore rarely if ever actually used. See C27.3.2 of ASCE7-10 for example.