Hawaii Wind - Kd Values

[PMR06]

In the Hawaii building code, tables 1609.3.4a... define the directionality factor Kd to be used for various buildings. Does anyone know of a commentary or an explicit definition for "Main Wind Force Resisting Systems with totally independent systems in each orthogonal direction"?

For our specific project, the interpretation of "totally independent" is in question. The building in question has moment frames in one direction, x-braces in the other, but no roof diaphragm (not one we will count on anyway). The x-braces share columns from the moment frames though. Are they "totally independent" then?

Thanks in advance.

 

[msquared48]

With no roof diaphragm, how is the force getting to the frames? X Bracing?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[PMR06]

Yes, x-bracing in the roof plane too.

 

[msquared48]

"Totally Independent" to me means no torsional forces from one direction affecting the members for the other. I do not know how that is possible though with the 5% accidental torsion stipulation.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

If your diaphragms are flexible and not rigid, the 5% rule does not apply and the lateral loads are transmitted only through tributary area, hence the orthoginal directions are independent.

The thought occurred to me an hour ago as I was driving 15 miles from here. And so it goes.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[PMR06]

That's funny, I too often do my best thinking on the road.

My thought was that "totally independent" would have something to do with a lack of rigid diaphragm that is able to distribute load to lateral systems in other directions. But I cannot find a commentary or definition explaining so?

Unless I can find otherwise, I think I'll go with the conservative interpretation. It means Kd=0.75 instead of 0.65.