Wind Case - Height Above Ground Level?

[Annonymous]

When specifiying wind loads, CAESAR asks for a "Height Above Ground Level". There's been some uncertainty as what this means, is this grade elevation or is this the HEIGHT ABOVE GROUND LEVEL?

i.e., if the first node of my pipe model is at 115'-0" and grade is at 110'-0". Is the input 110'-0"(grade elevation) or 5'-0"(the height above grade)?

CAESAR help says it is the height above local ground level, it goes on to reference ASCE and as clear as this sounds (as the height above ground), I've been advised that it is grade elevation.

Any input is appreciated. Thanks!

 

[Annonymous]

Anyone?

 

[ApC2Kp]

Height above ground level would be the correct usage.
Wind velocity profiles are based on height above ground.

 

[Annonymous]

...so I made a couple trial runs with different "Height Above Ground Level" inputs.
I have to say that in CAESAR version 4.50_****07 the results are exactly the same. Results are not affected AT ALL by this input.

The wind IS affected by the global coordinates you specify to the first point (i.e. node 10). I still have to determine whether CAESAR takes grade elevation to be at zero and builds the wind profile from there.

Any other knowledge/experience will be appreciated!

 

[richay]

CAESAR II assumes "grade" is at elevation 0.0. You have to set the coordinates of the first node point to correctly correspond to "grade"

Richard Ay
COADE, Inc.

 

[richay]

Further to my earlier post, the "Height above ground level", on the "Wind Load definition" dialog, is one of the "Topographic Factors", used by ASCE #7 to determine the velocity pressure. This height is used to determine the "Kzt" factor (Section 6.5.7 in ASCE #7 2002).

There are a number of criteria for the use of "Kzt", which if your input doesn't comply, Kzt is set to 1.0. This would explain how you can change the data and obtain the same results.

Additionally, ASCE #7 states that the minimum wind pressure is 10 psf, so if you're less than this, you can change data quite a bit and still get the same results.

I don't often visit this forum. Questions of this nature will be answered faster if you post directly on the CAESAR II Forum on the COADE website.

Richard Ay
COADE, Inc.

 

[StressGuy]

I have to bust new people often coding in their first element at the 110' that shows on the piping ISO instead of the 10' above grade that the point actually is.

I understand that using grade as 100' for modeling purposes is a hold over from a time when modeling packages couldn't handle negative numbers for undergound pipe.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.