Do you apply Kd to W when dealing with uplift effect?
Do you apply Kd to W when dealing with uplift effect?
(OP)
ASCE7-05 Table 6-4 says: Directionality Factor Kd shall only be applied when used in conjunction with load combinations specified in 2.3 and 2.4.
This Directionality Factor Kd basiclly reduces the wind load value. I can see its reasonablity by using reduced "W" when calculating combined downward load effect.
However, when calculating upward load effect in 2.3, equation 6: 0.9D+1.6W+1.6H, if still apply this Kd factor to "W", it will make the uplift value smaller and possibily make it underestimated.
Do you guys use Kd factor in uplift load combination calculation like in equation 6?
Thanks.
This Directionality Factor Kd basiclly reduces the wind load value. I can see its reasonablity by using reduced "W" when calculating combined downward load effect.
However, when calculating upward load effect in 2.3, equation 6: 0.9D+1.6W+1.6H, if still apply this Kd factor to "W", it will make the uplift value smaller and possibily make it underestimated.
Do you guys use Kd factor in uplift load combination calculation like in equation 6?
Thanks.






RE: Do you apply Kd to W when dealing with uplift effect?
RE: Do you apply Kd to W when dealing with uplift effect?
IMHO, you can use the Kd factor along with Equation 6.
See Miami-Dade county's position statement
http://ww
RE: Do you apply Kd to W when dealing with uplift effect?
RE: Do you apply Kd to W when dealing with uplift effect?
I raise this question because I have seen some structural engineering design reports in which when checking the anchor bolt pull out (or concrete breakout) strength, they neglect the structure dead load (either because it is unknown or it is minimal), and only wind uplift alone is considered, therefore it is no longer a load combination, so Kd is not applied.
I find the logic here is a little bit funny, with the dead load to help the anchorage, the wind uplift load is reduced by Kd, that makes resultant uplift double lower. while without considering the anchorage help from dead load, the wind uplift load stay high without reduction.
That's why I raise this question here.
RE: Do you apply Kd to W when dealing with uplift effect?
RE: Do you apply Kd to W when dealing with uplift effect?
Either way, their "design" seems very conservative. Now maybe that conservatism is costing money??