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 Question relates to Section 30.10.2 (External Walls of Isolated Circular Bins, Silos, and Tanks)

  • ASCE Standards
  • ASCE7-22
Meg Dalton's profile image
Meg Dalton posted 06-21-2023 04:29 PM

On behalf of colleague, Scott Hampton.

These question relates to ASCE7-22 (the information related to the question below is displayed the same in ASCE7-16, except the Section, figure, and equation numbers have changed).

These question relates to Section 30.10.2 (External Walls of Isolated Circular Bins, Silos, and Tanks)

1)     Confirm that Equation 30.10-4 for C(a) is written incorrectly?

a.      By comparison to AS/NZS 1170.2:2011, the second line of Equation 30.10-4 as given in ASCE7 [ 1 − 0.1cos4α − 0.05cos5α ] should be a continuation of the first line of the equation [ C(α) = − 0.5 + 0.4cos α + 0.8cos2α + 0.3cos3α ], but the number 1 should be deleted.  That is, C(α) = − 0.5 + 0.4cos α + 0.8cos2α + 0.3cos3α − 0.1cos4α − 0.05cos5α.

2)     There is also a formatting issue with Equation 30.10.3, including the equation number itself, which should likely be 30.10-3.

3)     When a = 0, C(a) = -0.5 + 0.4 + 0.8 + 0.3 -0.1 – 0.05 = 0.85, and Kb = 1.0.  Therefore by Equation 30.10-2, GCp(a) = Kb*C(a) = 1.0*0.85 = 0.85.  And notice that this is independent of H/D.

a.      So why, in Figure 30.10-1, for angle a = 0, are all the GCp(a) values listed as 1.00, instead of 0.85?

b.      The GCp(a) values for all other angles (a) listed in Figure 30.10-1, when H/D = 1, are zero to 0.05 off from what is calculated using the presumably correct equation for C(a) given above.  This variance of precision might not otherwise appear to be an issue, but the values in Table 30.10-1 are written to two significant figures after the decimal, with all the second digits being zero.  If two significant digits after the decimal are shown, why not use the actual value as calculated from the C(a) equation above in the table?

4)     In the Commentary for Chapter 30, in Table C30.10-1, the combined external and internal pressure coefficients are shown (GCp – GCpi).

a.      If the equation for C(a) as given above is correct, then this table also appears to have issues with pressure coefficients for a = 0, and significant figure issues for all the other pressure coefficient values.