Wind Speed-Up Topographic Factor

[BPA827]

My question to all is regarding the Wind Speed-Up Topographic Factor Kzt in the ASCE/SEI 7-05 6.5.7.1 & 6.5.7.2

Is there are simplified way to address this factor? Is this ever just equal to 1 (K1, K2, K3=0)? Is this just applied in specific isolated conditions?

I'm a little confused by how I get the H, Lh, x & z values in Figure 6-4

Thanks for any help!

 

[csd72]

BPA827,

These apply to significant geographical features e.g. sea cliffs, escarpements, steep hills, mountains and deep valleys. If you dont have any of these features nearby then just take it as 1.

If you do, then you will need a topographical map to assess some of the factors.

Check out

http://www.topozone.com/

 

[BPA827]

csd72: would a hillside lot qualify as significant geographical features? It sounds like we're talking about some severe topographic changes for this factor to apply.

 

[sennafan]

BPA827

ASCE 7-05 section 6.5.7.1 has a list of conditions that determine when you need to use the speed-up factor. No. 3 in particular might answer your question. You need a little bit of topographic information to apply the rules.

 

[BPA827]

Thanks for the help!

 

[UcfSE]

You can play with the factors a bit to help you get a feel for when you can assume it's 1. It doesn't hurt to just study it and see what goes on when you change the inputs.

 

[BPA827]

UcfSE: Is there a maximum Kzt when you go through all the possible combinations of K1, K2 & K3? I think I heard someone say it was 1.8. This is if someone didn't want to go through all the specific details.

 

[UcfSE]

You should just use your case. It doesn't make sense to assume you're on top of Mt. Everest and go from there. That isn't fair to your client and makes your job harder in the end. You have to make everything work.

You probably could do all the substitutions and come up with your equation and then maximize it (take derivatives, set = 0, substitute results and so on, do parametric study). Sounds like a lot of work to me. You would be better off calculating them max than to go on hearsay of what someone said. Then you'll learn something