×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

ASCE 7 velocity pressure numerical constant

ASCE 7 velocity pressure numerical constant

ASCE 7 velocity pressure numerical constant

(OP)
Refer to Chapter C27 (Commentary) page 550 in ASCE 7-10

"The constant 0.00256 reflects the mass density of air for the standard atmosphere, that is, temp of 59 F and sea level pressure of 29.92 in Hg, and dimensions associated with wind speed in mi/h."

When deriving the constant, ASCE has chosen to take an average value for the mass density (0.0765 lbm/ft^3) opposed to the apparent maximum of 0.0822 lbm/ft^3. Any idea which reference on pgs 555-556 get into that detail? I would think the oldest reference would be most likely.


In Russia building design you!

RE: ASCE 7 velocity pressure numerical constant

The formula appears to be a derivation of ½mv² for velocity head or kinetic energy. A basic fluids or physics text should include a discussion on Bernoulli Equation and the conservation of energy.

RE: ASCE 7 velocity pressure numerical constant

(OP)
wannabe: I understand the use of the relationship, and agree with you on its use. Do you really think a basic physics text would explain (or even address) the use of average air density for wind pressure computations? That seems like a decision that ASCE has made based on empirical evaluations, opposed to some universal accepted norm - that is why I suspect it is in one of the references indicated in that chapter.

In Russia building design you!

RE: ASCE 7 velocity pressure numerical constant

I missed the part in our post about using the average density of air at sea level rather than the maximum. It seems like a reasonable and perhaps conservative number. The maximum density is only 7% greater than the average used. At 1000 ft elevation, the maximum pressure is 4% greater than the average used. I would sure hate to see ASCE start requiring temperature, altitude and barometric pressure data to calculate the basic velocity pressure.

If you want to reduce the wind pressure because the project is located at high altitude (high temperature), the commentary does state this is possible. I never tried to sharpen the pencil that much.

RE: ASCE 7 velocity pressure numerical constant

(OP)
Good Lord. I would never want to do that. Maybe one day when we are building skyscrapers in a more literal meaning - to the sky. Besides, pressure varies linearly with the density, unlike varying to the square of the velocity. Further, the velocity is a function of elevation. I would guess that it may not do much good to reduce the density, as the loading pressure at high altitudes would be dominated by the velocity component.

Maybe I will tabulate something to see how it varies to some high elevations...maybe...

In Russia building design you!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources