ASCE 7-16: Wind Adjustment Factor for Building Height and Exposure: MWFRS and C/C

[keen_mentee]

Has anyone noticed the wind adjustment factor for 25 ft is not present in the Component and Cladding but is present in Main Wind Force Resisting System? Not a big difference but I wanted to share this information and ask if you think there is a deeper logic behind it? or may be as simple as the page for C/C could not fit the extra line in ASCE 7-16 (as we have the value for 25ft height C/C adjustment factor in ASCE 7-10). I always thought the adjustment factor would be same for MWFRS and C/C but I got a little curious when ENERCALC showed two different values. What are your thoughts?

Thank you.

 

[structSU10]

C&C loading accounts for localized wind effects. Figure C28.3-1 give an illustration of what really happens and what C&C pressure is trying to capture - the peak loads that occur that are more critical for small tributary area elements.

 

[ProgrammingPE]

I think you're correct that the 25 ft table row was just not included in Figure 30.4-1 of ASCE 7-16 in order to get it to fit on the page since it was included in the identical figure in ASCE 7-10 (Figure 30.5-1).

The reason you get a different value in ENERCALC is because they are interpolating. Since the table is missing an entry it has to interpolate between different values so you get a slightly different result.

For MWFRS:

λ = 1.29 + (20.42ft-20ft) * (1.35-1.29) / (25ft-20ft) = 1.30​

For C&C:

λ = 1.29 + (20.42ft-20ft) * (1.40-1.29) / (30ft-20ft) = 1.29​

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[keen_mentee]

@structSU10: Thank you.

@ProgrammingPE : That is what I think too. Never thought a availability of a single line space would impact the code presentation.Thank you.

Thank you.