I´m designing a 20 ft diam. and 18 ft. height water tank. I was wondering that the anchor bolt detail and results appears even that I´m specifying that the tank is unanchored. Perhaps because I put 0.3 siesmic coefficient. I need your help, thanks.

Even if your input indicates that the tank is unanchored, there could be reasons that anchors are required: high wind speed, seismic conditions, or the requirements of Section 3.12. If any of the checks fail, then anchors are required and the software will size the anchor bolts.

According to the result, the anchor bolt is required for Section 3.12, can you give me a clue to eliminate the anchor bolt, probably adding the thickness of the bottom, shell or roof, etc. or reduce the corrosion allowance. Thanks

Look at the bolting table. See which entries have nonzero values, and work backwards from there.

Can you please tell me where can I find the bolting table, is it included in the software or just having a bolt catalog. Thanks.

I meant the "bolt load/stress" output table produced by the software, in the Bolting Report.

Any line that has non-zero values means a positive load was computed from the equations in API-650 Section 3.12. Go to these equations and see what you may be able to change to drive the result to zero (or less than zero). This will avoid bolting.

I have intented several times to eliminate the anchor bolt, but I failed. Are you so kind to send me a benchmark without anchor bolt on the result. This is my e-mail..arivera@ciateq.mx..thank you very much.

You already have one. Run the B&Y example job.

Good morning,

I obtained this output report : "
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WIND OVERTURNING STABILITY CHECK
Overturning moment * (V/100)^2 (ft-lb) 0.31148E+07
Resisting (dead load) moment (ft-lb): 0.43386E+08
Anchors not required

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UNANCHORED TANK WL VALUES
Design Case 6263.3
Test Case 4734.6
Empty Case 0.00000

CASE : DESIGN
Moment & Wt : 0.10732E+09 1539.6
M /(D^2 *(Wt+Wl)): 0.51110

CASE : TEST
Moment & Wt : 0.61845E+08 1539.6
M /(D^2 *(Wt+Wl)): 0.36629

CASE : USER
Moment & Wt : 0.12121E+07 1539.6
M /(D^2 *(Wt+Wl)): 0.29257E-01

UNANCHORED TANK LONGITUDINAL COMPRESSIVE STRESSES
Design Case (psi) 398.81
Test Case (psi) 269.15
Empty Case (psi) 96.258

TANK ALLOWABLE COMPRESSIVE STRESSES
Design Case (psi) 8427.9
Test Case (psi) 7382.7
Empty Case (psi) 3371.2

TANK SEISMIC STRESS PASS/FAIL STATUS
Design Case Passed
Test Case Passed
Empty Case Passed "


 So a tank is not required to be anchored (per Section 3.11 and Appendix E).
According to 3.12.1 (API 650), The requirements of section 3.12 shall not be met.

However, I find the Anchor bolt table (section 3.12) designed in the output report and the Anchors are required :

" ANCHOR BOLT DETAILS - Section 3.12

Case Uplift Allowable Load/Bolt
(N. ) Bolt Stress (N. )
(KPa )
Design Pressure : 0.00000 103419. 0.00000
Test Pressure : 0.00000 137892. 0.00000
Failure Pressure : 0.00000 248206. 0.00000
Wind Loading : 0.00000 198564. 0.00000
Seismic OPE : 0.81106E+07 198564. 0.15597E+06
Seismic Test : 0.31784E+07 198564. 61124.
Design Press + Wind Load : 0.00000 137892. 0.00000
Design Press + Seismic OPE : 0.00000 198564. 0.00000
Design Press + Seismic Test: 0.00000 198564. 0.00000


ANCHOR BOLT RESULTS - Section 3.12

Case Number Bolt Bolt Stress
of Bolts Diameter (KPa )
(mm. )
Design Pressure : 52 38.100 0.
Test Pressure : 52 38.100 0.
Failure Pressure : 52 38.100 0.
Wind Loading : 52 38.100 0.
Seismic OPE : 52 38.100 172075.
Seismic Test : 52 38.100 67434.
Design Press + Wind Load : 52 38.100 0.
Design Press + Seismic OPE : 52 38.100 0.
Design Press + Seismic Test: 52 38.100 0.

Final Anchor Bolt Spacing .............. (m. ) 3.02 "


So, please, Can you clarify me this point?

TANK determines the uplift for the conditions defined in Section 3.11. If any uplift value is greater than zero, TANK designs anchor bolts. (So Section 3.11 appears to be inconsistent with the other Code Sections.)

Version 3.11 (which is in testing) will only implement Section 3.11 if one of the other Code Sections requires bolting.)