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Wind Loads per PIP STC01015 2017 / ASCE 7-2010

For vertical vessels, wind load generation is calculated per the April 2017 edition of the PIP STC01015 code which in turn references the Wind load generation chapters of the ASCE 7-2010 code as mentioned in section 4.1.4.1 of the PIP document.

  1. Computation of the wind pressure from equation 29.3-1 of ASCE 7-10.

    The equations mentioned in that section of the code, for the English unit system (foot, pound) are used:

    qz = 0.00256×Kz×Kzt×Kd×V2 lb/ ft2

    as well as the SI unit system (meter, kNs),

    qz= 0.00613×Kz×Kzt×Kd×V2 N/m2

    The input that the engineer needs to provide are:

    • V = Basic Wind Speed in mph or meter per second (Section 26.5 has guidelines for this)
    • Kd = wind directionality factor defined in Section 26.6 of ASCE 7-2010
    • Exposure category – B, C or D – as per Section 26.7.3 of ASCE 7-2010
    • Kz = Based on the exposure category, program selects the value of velocity pressure exposure coefficient evaluated at height "z" from the table provided in Section 29.3.1
      Note: STAAD Foundation Advanced does not take the values from the table directly. Instead, it calculates Kz from the formulae provided in Note 1 of Table 29.3-1.
    • Kzt = Topographic factor defined in Section 26.8.2.
      Note: If site conditions and locations of structures do not meet all the conditions specified in section 26.8.1 of the code, you may set Kzt to 1.0. Since there are no provisions in STAAD Foundation Advanced to specify site conditions (ridge, escarpment or hills), a value of 1.0 is used for Kzt.
    • G = gust-effect factor from Section 26.9
    • Cf = Net force coefficient from Fig 29.4-1
  2. Computation of the force at various heights above the ground, and the resulting shear and moment at the top of pedestal.

    The force due to wind acting at various levels along the height of the pedestal and vessel is calculated using the guidelines provided in Chapter 29 of ASCE 7-2010. Specifically, equation 29.5-1 is used to determine the force at various heights "z" above the ground.

    F = qz × G × Cf × Af

    where
    Af
    		=
    Height segment × Width or diameter

    Table 29.3-1 on page 310 of ASCE 7-10 is used to find the exposure coefficient Kz and the height ranges for which it is applicable.

    The region spanning the distance between the ground level up to the top of the vessel is divided into various height segments as explained in Table 29.3-1 and the wind force is calculated for each segment. The force is considered to act at the mid-height of the respective segments, which provides the level arm for calculating the moment at the bottom of the pedestal.

Parent topic: Wind Load Generation