Wind Kd Factor and Drift

[VTPE]

I have a question on the wind load provisions of ASCE 7-05 that I thought I would pass around.

Article 6.5.4.4 – Wind Directionality Factor says that Kd (=0.85 for MWFRS and C&C) , “Shall only be used with the combinations specified in section 2.3 and 2.4”. Those (2) sections are the LRFD and ASD load combinations for strength

Commentary CC1.2 says that the strength combinations are not applicable for drift determination. For checking short term deflections use D+0.5L+0.7W.

I think this says that tehre should be separate wind loads for Strength (utilizing Kd=0.85) and Serviceability (not using Kd).

I am interested to hear what people think and how they have been doing their work:
1.) Do you figure your velocity pressure once and then use it for both strength and serviceability
2.) Do you use (2) different velocity pressures?

Thanks in advance for your input.

 

[WillisV]

Use Kd = 0.85 even with drift combinations. The intent of the sentence you quote in article 6.5.4.4 was to differentiate between the previous load combinations that used a 1.3 factor on W with no Kd (they split it out several cycles ago - 1.6 * 0.85 approx = 1.3)