Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Load Case Subarea: Original Author: Bentley Technical Support Group Comments Questions and Answers about Wind loads Item #1, Comment: The Load Wind command enables the user to define static wind load cases (W1 - W10) by generating wind pressure vs. (system) height profiles, or according to ASCE 7, or Uniform Building Code (UBC) requirements. The wind force is applied as uniform loads in the local coordinate system of the straight pipe or bend element. The equivalent wind force is assumed to act through the centroid of the element. Iten #2, Comment: Beam members are not subjected to wind loads, enhancement has been logged, CAE-CR-8199. Item #3, Commment: In order to exclude piping inside a building from wind loads, the piping inside should be entered as a separate segment(s) from the piping outside the building. With the model Input grid opened select the Segment Tab, see column labled "Apply Wind", Applies wind load cases to the segment corresponding with the selected row. Enable (check ON) / Disable (check OFF) check boxes a required for segments listed in the model. Itme #4, Comment: When specifying elevations wind load profile remember to check that ground is correctly defined on the main Wind screen. This applies also to wind loadings per ASCE-7 and UBC. Opening older models a warning message "negative elevations found" may indicate an incorrect wind loading across this model. If the Ground elevation for wind is entered with a value greater than the vertical coordinates of the model (i.e. the whole model is below ground) it will result in zero forces. Item #5, Queston: The "negative value" used for wind ground elevation is confusing. Is there a simple explanation? Answer : AutoPIPE allows the user to create a piping system anywhere within the coordinate system constraints, how does the program know where the Ground level is unless you tell it! Ground level could be anywhere on the vertical axis: -4000 mm, -125 ft, 0 ft, +30 ft, +86645mm, anywhere, etc…. Just identify where it is and anything below that vertical level is considered underground. Item #6 Question: I would like to know if the wind profile can be input with Wind Velocity and Height data. It seems that, in the user interface in autopipe, Height and pressure has to be input in the wind profile. Answer : AutoPIPE does not accept velocity profile input at this time. AutopIPE does show the pressure profile and how it is calculated in load summary of the input listing. ASCE 7 defines wind speed as the nominal design 3-second gust wind speed at 33 ft (10 m) above ground for Exposure C category. Note that Kz value is 1.0 at 33 ft. So Kz gives the velocity profile per ASCE-7. You may use a similar procedure, entering your own velocity profile, to compute the pressure profile in Excel and then input in AutoPIPE. Refer to ASCE-7 for actual tables or equations. Item #7 Question: Do we need to specify the vector as -1 to specify the wind direction in -X direction. I understand that I need to make two cases for wind loading in east and west direction. similarly for earthquake cases we need to make a separate case? Answer : A. Please see the following AutoPIPE help section: Help Contents Contents Tab Bentley AutoPIPE FAQ FAQ #24. In order to account for a negative wind direction: add an additional wind load case specifying the Inclined direction to be opposite of the initial wind direction. For instance: +X axis only : Wind direction = Global X -X axis only : Wind direction = inclined, Dx = -1, Dy = 0, DZ = 0 Item #8, Question: I am assuming the wind direction of "Inclined" in combination with the DX, DY, and DZ should take care of any user required eccentric, torsional, or pitched loadings. Do you agree? Answer : Inclined wind will typically not give a eccentric loading since wind method (force or projected area) methods are applied uniformly at center of pipe An offset weight loading will give eccentric type loading or some offset force or moment loading. Item #9, Question: When setting up wind loading in Autopipe, should the Wind Shape Factor Multiplier be 1 or 0.7 when using the ASCE wind specification type. If you choose the ASCE wind specification type, this type has a force coefficient factor. I think this force coefficient factor may take the place of the wind shape factor multiplier when the ASCE wind specification type is used. Are we "double dipping" by using 0.7 for the Wind Shape Factor Multiplier and 0.7 for the Force Coefficient when using the ASCE wind specification type? Answer : The intent of Wind shape factor multiplier on the 1st screen of the Wind load case dialogs is to provide a uniform factor that is applied to ALL wind load cases. However, AutoPIPE provides another more flexible method of applying this factor to the individual wind load cases; ASCE refers to this shape factor as "Force Coefficient Cf" and the UBC refers to it as "Pressure Coefficient Cq". Using these coefficient values on the individual load case dialogs enables the user to create a more accurate wind load based on the objects shape by providing different values for different wind directions (i.e. W1: Cf or Cq.= .7 for global X wind direction but W2: Cf or Cq = .9 for global Z wind direction). Using both Factor and coefficient values would reduce the wind load by the product of both values, which is incorrect. Therefore, either the Wind shape factor is modified and the coefficients are set to 1 or the Wind shape factor is set to 1 and the coefficients are modified. Item #10, Question: How to aply the same wind speed over the entire model? Answer : Specify a wind value using wind Profile command, and enter pressure which is calculated in the ASME 7. (example: 150mph = 41.706 psf) Item #11, Qu estion: In a model point A04 have a guide with 0.2" gap. I found that x-direction movement of GRTW1(GR+T1+W1, operating case) is 0.213". It means displacement exceeds gap allowance. Is it possible? Answer : Please see the following file " Nonlinear_wind_load_analysis.pdf ". It all depends on the specified load sequence or initial state. Defining nonlinear wind loads is much easier in AutoPIPE as all combinations are created for you automatically. Item #12, Question: I have been asked if the pressure used in a wind profile is the basic pressure i.e. acting on a plate is required in the input to allow AutoPIPE to adjust, or do I have to adjust the pressure for a pipe when inputting the figure? Answer : Yes for the wind profile you should calculate the pressure acting on a pipe or cylindrical shape including the shape factor. This pressure will be calculated and entered at different heights. Also enter the wind shape factor multiplier = 1.0. Note: Using UBC and ASCE-7 wind methods, the wind profile is automatically calculated. It is common practice to analyze at a minimum, wind loading for two non-concurrent directions typically X and Z (assuming Y vertical). However the wind could be acting in positive or negative directions like seismic so you may wish to analyze a minimum of four cases +/- X and +/- Z. If you have no gaps or non-linear features like friction then only two cases +X and +Z may only be necessary then create load combinations to include +/-X and +/-Z e.g. Gr+T1+W1 and Gr+T1-W1. Item #13, Question: What is the importance of annual probability of exceedancce for Wind Calculation (say 1/500)?...What is the interpretation for this value and its relevance for determining wind load? Answer : The annual probability for exceedance of a 1/500 storm event is a 0.2% chance of getting or exceeding that storm event...this basically saying it's a 500 year storm which is only supposed to happen once every 500 years, but what it really means is there's a 1 in 500 chance, or 0.2%, of getting that storm event every year. But then you get a situation as seen in southern United States a few years ago where you get three 100-year storms in less than five years. AutoPIPE is not concerend with the frequency of a 1 in 500 year storm, what needs to be determine is what's the minimum design requirements to be modeled? Are the Wind loads entered into the model based on a 1, 10, 50, 100, 500 and etc. event? Refer to governing regulation, building code, or project documentation for wind loads to be applied in a model. Apply the respective wind loads as desired into the AutoPIPE model. Item #14, Q uestion: Prefer not to consider friction in any occasional case (i.e. Wind, Siesmic, stc..). Is there any way to consider friction only the expansion case but not in any occasional Wind loads? Answer : Consider defining wind load cases in a separate analysis set and set the friction scale factor to zero in that analysis set. (Load Static Analysis Sets Enable "Gaps/Friction/Soil", with other load cases, press OK button, on the "Non-Linear Analysis settings, Friction scale factor = 0.0, press OK button). Item #15, Question: If an insulation thickness is provided for a member, does AutoPIPE adjust the effective diameter for wind/wave force calculations? Answer : Yes, Force coefficients (Cf) are given in Tables 6-10 for "Chimneys, Tanks and Similar Structures" in the ASCE 7-98 code. In Table 6-10, the force coefficient is a function of the h/D (= height/diameter) ratio and D*sqrt(qz). The default value "Automatic" will calculate Cf for each point based on D*sqrt(qz) as per Table 6-10 assuming round smooth pipes and a conservative h/D value of 25. The outside diameter D includes the pipe insulation thickness. The height h of chimneys and tanks in Table 6-10 would correspond to the pipe length facing the wind, not the pipe height. The pipe length is not considered in determining the Cf factor in AutoPIPE and instead a conservative value of h/D=25 is assumed. For most common pipe sizes, the shape factor is typically 0.7 when using "Automatic" option. Only very small diameters will have a shape factor of 1.2. The load summary will list calculated Kz, Cf and qz values as a function of height h. The Cf values in the load summary assume D = 1 ft. Item #16, Question: ASCE 7-10 Wind speeds Now Available on Web Answer : The wind speed site, www.atcouncil.org/windspeed , will be free for users. Users are encouraged to provide ATC with feedback about the site, using the Contact Us page, so that enhancements can be planned. Item #17, Commment: The following only affects AutoPIPE V8i 09.06.00.15 and will be fixed in the next new version 09.06.01.xx and higher: The Ground Elevation for Wind is always entered in Feet, regardless of the model units file specified on Tools Model Options General dialog . This can be confirmed with the Loads Summary Data Listing report using any metric units file (CAE-TR-11097). . See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? 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