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wind analysis that I need help identifying

  • 1.  wind analysis that I need help identifying

    Posted 03-08-2022 08:05 AM
      |   view attached
    I have been asked to review a calculation by an engineer that they could not identify its origin. The Engineer is stating that the wind speed impacting a house will speed up over the ridge and the speed will increase in the example by a factor of 1.64. After spending a long time researching by old dynamics books and on-line; no source of any formula such as this could be found. Need opinions on this and any help identifying it if possible.
    Thanks for any help

    ------------------------------
    George Miles P.E., M.ASCE
    President
    Alligator Engineering Inc
    Edgewater FL
    ------------------------------

    Attachment(s)

    pdf
    Ex C - Notes.pdf   1.23 MB 1 version


  • 2.  RE: wind analysis that I need help identifying

    Posted 03-08-2022 09:37 PM
    George

    I cannot identify the calculation in the attachment to your message.  However, I presume you are familiar with the topographic effects factor Kzt in ASCE 7 Chapter 26.  Depending on the geometry of the terrain, and the location of the house relative to the slope, it is possible to see wind speeds increase by as much as 1.64.   I suggest you do a check using the procedure of ASCE 7-22, Section 26.8.

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    Ronald Hamburger P.E., F.SEI
    Principal
    Simpson Gumpertz & Heger
    Oakland CA
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  • 3.  RE: wind analysis that I need help identifying

    Posted 03-09-2022 01:04 PM
    the terrain is flat and Kzt for single story would not do that even for multi story. The jump is outside of the Kzt increase value for elevation while it does increase at higher altitudes over 33 feet. No one has come up with a good source other than this is not a valid equation. I figured I would see what the populus knows on this one. I have come up blank on it.

    ------------------------------
    George Miles P.E., M.ASCE
    President
    Alligator Engineering Inc
    Edgewater FL
    [Phone]
    ------------------------------



  • 4.  RE: wind analysis that I need help identifying

    Posted 03-14-2022 11:02 PM
    file:///C:/Users/rbowm/Downloads/N%20Hann_CEM_how%20to%20calculate%20wind%20speeds_Panel%201%20and%202_20190703_20190708.PDF

    There are at least some factors in here that appear to align with what you're review.  Just be careful that you're not conducting a peer review without notice.

    ------------------------------
    Rebecca Bowman P.E., M.ASCE
    Sole proprietor
    Rebecca A. Bowman, Esq., P.E.
    Mc Murray PA
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  • 5.  RE: wind analysis that I need help identifying

    Posted 03-21-2022 11:24 AM
    Its a legal case involving insurance fraud so he has been notified. At this point the Engineer using the formula that is not approved is going to have to answer to the State Engineering Board.

    ------------------------------
    George Miles P.E., M.ASCE
    President
    Alligator Engineering Inc
    Edgewater FL
    [Phone]
    ------------------------------



  • 6.  RE: wind analysis that I need help identifying

    Posted 03-28-2022 03:27 PM
    George,
    I agree with James Williams as to doing your own calculations.  As long as his result is greater than the minimum required code value, whether his formula is " approved" then he is only being conservative.  The code defines itself as a "minimum" set of standards and have been accused of "over design many times in the last 50 years.  I maintain there are only varying degrees of conservatism.
    Don Lee, SE

    ------------------------------
    Donald Lee M.ASCE
    Struct Engr
    Don Lee Engineering
    Lakewood CA
    ------------------------------



  • 7.  RE: wind analysis that I need help identifying

    Posted 03-15-2022 07:49 AM

    George, I am not aware of any discussion of this in any manual on engineering. But intuitively as a Certified Flight Instructor and semi-retired engineer, I'd say this could be valid. Consider two factors: 1) the compressibility of air (wind) against the ridge and, 2) the aerodynamic effect of the air going over the ridge has to travel faster than the air well above the ridge. Distance from the ridge, other topographic features and vegetation all come into play for obvious reasons.

    As a pilot in New England, I have experienced significant wind velocity increases between two small mountains (1,500 AGL) enough to put my plane into a wings vertical attitude (Venturi effect). And, downslope winds can be faster than those on the upslope side similar to what has been described and calculated. In any event, these empirical examples should be considered to at least help validate the calculations. 

    Paul T. Carroccio, P.E., L.S., CFI, F.ASCE



    ------------------------------
    Paul Carroccio P.E., L.S., F.ASCE
    Owner/Consulting
    PTC Consulting LLC
    Manchester VT
    ------------------------------



  • 8.  RE: wind analysis that I need help identifying

    Posted 03-15-2022 10:36 AM
    Hi Paul

    What you experienced is a consideration on large mountains  and will cause changes in fires. As for the speed up over a wing, that is different, that air flow is different and has minimal resistance, reynolds number, with the fact that air has to be split over a thin surface with air on both sides. When treating like a building, the volume comes into play.
    I spent a week looking through every text book and on line with no proven or approved formula that looks anything like it. It all has to do with roof tiles. I have now written a paper on how to perform wind analysis of tiles for damage that I will be trying to get published after my research. This is the last thing though I need to disprove for a court case.

    ------------------------------
    George Miles P.E., M.ASCE
    President
    Alligator Engineering Inc
    Edgewater FL
    [Phone]
    ------------------------------



  • 9.  RE: wind analysis that I need help identifying

    Posted 03-25-2022 12:49 PM

    George, if not done so, perhaps you can consult the following two references to further your effort:

    • Emil Simiu and DongHun Yeo, 2019. Wind Effects on Structures: Modern Structural Design for Wind (4th Ed). Wiley Blackwell, ISBN: 978-1-119-37588-3.

    • The National Institute of Standards and Technology (NIST) website for: (1) Standardized extreme wind speed database for the United States; (2) Extreme Winds and Wind Effects on Structures.

    -----

    Dr. Dilip K Barua, Ph.D, P.Eng, M.ASCE

    Website

    Google Scholar




  • 10.  RE: wind analysis that I need help identifying

    Posted 03-27-2022 10:08 AM
    In my professional opinion, I would perform my own calculations based on criteria I could define in accordance with ASCE 7 and compare the results.  ASCE 7 represents a minimum design standard. Making the definitive statement as to whether or not the values exceed or do not meet an applicable minimum standard vs. hours locating a formula may be the way to go. There are just too many potential sources. I have used technical research papers (I do list my technical references) when things seem a bit outside the basics of ASCE 7.

    ------------------------------
    James Williams P.E., M.ASCE
    Principal/Owner
    POA&M Structural Engineering, PLC
    Yorktown, VA
    ------------------------------



  • 11.  RE: wind analysis that I need help identifying

    Posted 03-28-2022 10:14 AM
    That's a solid approach, going at it from scratch.  The original engineer may have his own short cut to getting to an acceptable (greater than minimum required) wind pressure.  Looking at the calculation sheet I wonder if he or she was converting  from a measured wind speed, a sustained wind speed or fastest mile wind speed to 3 second gust for ASCE 7.

    ------------------------------
    Jan Harris P.E., F.ASCE
    President
    Liberty Engineering, PC
    Virginia Beach VA
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  • 12.  RE: wind analysis that I need help identifying

    Posted 03-28-2022 03:27 PM
    That is the challenge when technical sources are not identified. The two minutes to list a reference & page number can save hours of searching. May have used data from NOAA for wind speeds and an equation from any number to legitimate technical resources and authorities. Finding one or two equations (that may also be derived from a basic formula) in a known technical source is like finding a needle on a carpeted floor. You only find it when you are doing something else & not looking, bare foot and purely by accident. LOL!!!

    ------------------------------
    James Williams P.E., M.ASCE
    Principal/Owner
    POA&M Structural Engineering, PLC
    Yorktown, VA
    ------------------------------



  • 13.  RE: wind analysis that I need help identifying

    Posted 03-27-2022 10:08 AM
    In the ATC Design Guide 2 "Basic Wind Engineering for Low-Rise Buildings" pg 9-10 there is a mention that
    "There are two approaches to modeling the effects of terrain roughness on mean wind-speed profiles. They are the power-law and log-law models of atmospheric wind profiles. The first model used for engineering purposes is the power law. It is represented by the equation:

    U(z1)/U(zg) = (z1/zg)ā
    (Note: I am substituting an "a" for the "α" given my inability to find the "α" with the line over it)
    where U(z1) is the wind velocity profile, zg is the gradient height, z1 is any other height in the same terrain exposure with a height lower than zg and ā is the power law exponent dependent on terrain roughness. The basic assumption used to calculate mean velocities at various heights in different terrain exposures is that the mean wind speed at gradient height is the same for all terrain exposures. However, the gradient height and the power law exponent ā, vary from one terrain exposure to another. This equation is the basis for the variation in mean wind speed with height shown in figure 2-5. Table 2-2 lists values of zg and ā that have historically been used in ASCE 7 to represent the variation in mean wind speed with height."


    I am uncertain as to whether you can extrapolate ... Working with the inverse ... . I will stop here. What often seems to follow a logical path in my mind may not make any sense. The pg 10 has the following.

    "Meteorologists and atmospheric scientists prefer the log law as a mathematical model for the variation of mean wind speed with height. The derivation of the log-law equation has a more constant theoretical basis than the empirically-based power law. Consequently, the log law is frequently used as the basis for developing gust response relationships (gust factors). The expression for the log law is: U(z) = (1/k)u* ln(z/zo) where U(z) is the mean wind speed, k is Karman's constant generally taken as ∼ 0.4, z is the height above the surface, zo is the roughness length, u* is the shear velocity of flow, which is a relationship between shear stress and air density, and ln is the natural log."

    "Engineers should be aware that wind speeds measured by NOAA during hurricanes as they advance toward a landfalling location, are frequently obtained at flight levels between .. ."
    [A extremely loose and reaching connection to NOAA.]

    One reference from the section
    SEAW/ATC, 2004a, SEAW Commentary on Wind Code Provisions, Volumes 1 and 2, SEAW/ATC 60 Report, prepared by the Structural Engineers Association of Washington, published by the Applied Technology Council, Redwood City, California.

    ------------------------------
    James Williams P.E., M.ASCE
    Principal/Owner
    POA&M Structural Engineering, PLC
    Yorktown, VA
    ------------------------------



  • 14.  RE: wind analysis that I need help identifying

    Posted 04-02-2022 09:28 AM
    estimado Señor George;

    I would like to say that I have not seen the approach demonstrated in the Notes.  If you are judging it based on the Dynamics theory, then I think it is very noble.  However our Engineering discipline provides us to examine the Winds on buildings according to the theories of the ASCE 7 standard.  The ASCE 7 Standard has promoted several methods of approaching wind theories.  For any rationale assessment, nothing is worse than a hurricane.  If you have any questions on topics in the ASCE 7 Wind Design Chapters, I am of the mind that the rationale of the separate sections of the 7-16 code and the 7-22 code are playing new roles that were not involved in earlier portions of the code.

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    Refugio Rochin P.E., M.ASCE
    Civil Engineer V
    NAXUTL, Inc.
    Jacksonville FL
    ------------------------------