I'm still back in the ASCE 7-05 code for this project. They haven't adopted the new IBC yet.
I've read through the commentary and I understand the reasoning behind using the 1.9 multiplier on buildings less than 60ft. It accounts for the actual gust factor being more like 1.6 and not .85 typically used. I guess it assumes that you assumed the roof top structure was rigid (1.6/.85 = 1.9 approximately).
So back to h > 60ft. I know I use Figure 6-21 to get my Cf. But to get my gust factor I need to use section 6.5.8. Would you assume it is rigid and use .85 in this case since it appears they assumed it for less than 60ft. Has there been any testing done with h > 60ft? I guess the gust factor should be somewhere between .85 and 1.6 but not sure what exactly. Being at 75' my Kz is pretty big 1.19 and my Cf is 1.3. I just don't want to overkill this unit support design.
Any thoughts?
I've read through the commentary and I understand the reasoning behind using the 1.9 multiplier on buildings less than 60ft. It accounts for the actual gust factor being more like 1.6 and not .85 typically used. I guess it assumes that you assumed the roof top structure was rigid (1.6/.85 = 1.9 approximately).
So back to h > 60ft. I know I use Figure 6-21 to get my Cf. But to get my gust factor I need to use section 6.5.8. Would you assume it is rigid and use .85 in this case since it appears they assumed it for less than 60ft. Has there been any testing done with h > 60ft? I guess the gust factor should be somewhere between .85 and 1.6 but not sure what exactly. Being at 75' my Kz is pretty big 1.19 and my Cf is 1.3. I just don't want to overkill this unit support design.
Any thoughts?
