Tank Anchorage (API 650 5.12)

Mechanical anchorage of a flat-bottom tank to API 650 5.12: the net uplift for every load case of Table 5.20 (design and test pressure, wind, seismic, their combinations and frangibility), the load per anchor, bolt or strap stresses against their allowables, the number and spacing of anchors, eccentricity, minimum sizes, the embedment design load and the counterbalancing weight

New here? Read the User Manual — the load cases, the weights W₁, W₂, W₃, bolts and straps, worked example and how to read the results.

◉ API 650 14TH ED. (AUGUST 2025) 5.12 · TABLES 5.20a/b · FIGURES 5.28 – 5.30 · NOT A REGULATORY SUBMISSION TOOL

⚠ Indicative tool only. Follows API 650, 14th edition (August 2025), 5.12 with Tables 5.20a and 5.20b, checked against that text. The units also choose the rule set: SI uses Table 5.20a (pressures in kPa, the 785 factor, bolt F_y not over 380 MPa), US customary Table 5.20b (inches of water, 4.08, 55,000 lbf/in²), each as printed. The wind and seismic loads come from the Wind Design and Seismic tools: enter P_WR, P_WS, M_rw and A_v from them. The anchor chair itself (5.12.7: AISI Steel Plate Engineering Data, Vol. 2, Part 5) and the local shell stress at the attachment (5.12.8, 5.12.10) are not calculated: their allowables are listed and the design is a record item. Overturning stability and soil bearing of the foundation are evaluated per Annex B (5.12.14.1).

Identification

Company

Tank ID

Location

Record Type

Units and rule set

Switching converts what is typed in and the rule set (Table 5.20a or 5.20b). Saved records stay in SI.

Summary of checks

Enter the tank, its weights and at least one load to see the uplift cases.

1. Tank and Shell

Tank diameter, D m

Tank (shell) height, H m

Bottom shell course thickness mm

Bottom shell course material (F_ty)

Bottom course minimum yield, F_ty MPa

2. Resisting Weights W₁, W₂, W₃ (Table 5.20)

From the nominal weights and corrosion allowances, or enter W₁ – W₃ directly to override. The Shell Design and Roof Design tools give the shell and roof weights.

Shell, nominal kN

Shell corrosion allowance mm · average

Roof plates, nominal kN

Roof plate thickness / its CA mm

Other permanent attachments on the shell kN

Roof plates and framing carried by the shell, corroded kN · for W₂

W₁ override kN

W₂ override kN

W₃ override kN

3. Uplift Loads (Table 5.20)

A case applies when its loads are entered. Wind and seismic need not be combined (5.12.9).

Design internal pressure, P_i kPa

Test pressure, P_t kPa

Pressure combination factor, F_p 5.2.2 · at least 0.4

Frangible roof designed to 5.10.2.6 d

Failure pressure, P_f kPa · Annex F

Wind uplift pressure on the roof, P_WR kPa

Wind pressure on the shell, P_WS Pa

Supported cone roof meeting 5.10.4: P_WR = 0

Seismic ringwall moment, M_rw kN·m · Annex E

Vertical acceleration, A_v fraction of g

4. Anchors (5.12.2 – 5.12.6, 5.12.13)

Anchor type

Number of anchors, N equally spaced

Anchor material

F_y MPa

F_y at the maximum design temperature MPa · insulated anchors, welded straps (5.12.5)

Anchor corrosion allowance mm · Purchaser (5.12.6)

Bolt size

Bolt eccentricity from the shell, e mm

Bottom expansion coefficient, E_t /°C

Maximum design temperature − ambient °C

Strap width mm

Strap thickness mm

Reduced (contoured) width mm · blank = none

Slope from vertical degrees

5. Anchor Chair (5.12.7, 5.12.10)

AISI Steel Plate Engineering Data Vol. 2, Part V (Figure 5-1 c): top plate (5-1), height, side plates and welds (5-5 – 5-8); the shell at the attachment by separate-chair local stress (5-3), a continuous top ring (Figure 5-3), or a 5.12.8 analysis you enter. Leave a and h blank to keep the chair as a record item.

Shell at the attachment (5.12.10)

Top plate width along the shell, a mm

Top plate thickness, c mm

Distance between side plates, g mm · preferred d + 25

Outside of top plate to edge of hole, f mm

Chair height, h mm

Side plate thickness, j mm

Side plate average width, k mm

Bottom plate under the chair, m mm · blank: Z = 1

Chair-to-shell fillet weld leg, w mm

Design wind speed over 160 km/h (100 mph): 300 mm (12 in.) minimum chair height on a thin bottom

Ring radial width mm · from the shell

Ring thickness mm · blank = c

Enter the stress intensities (or equivalent stresses) at the attachment from the analysis (finite element, WRC 107 / 537, or equal) for the load case it was run for. S_m is that case’s Table 5.20 shell allowable (5.12.8). From a WRC 107 / 537 summary (PV Elite, Compress, CodeCalc): P_m → P_m, P_m + P_l → P_L, P_m + P_l + Q → P_L + P_b + Q; P_L + P_b may be left blank, as WRC 107 does not separate primary bending. Convert kgf/cm² (× 0.0981) or psi first.

Load case analysed

P_m MPa · general membrane

P_L MPa · local membrane

P_L + P_b MPa

P_L + P_b + Q MPa · with secondary

Analysis reference report no., method, by

6. Counterbalancing Weight (5.12.14)

Ringwall width m

Ringwall depth m

Concrete unit weight kN/m³ · blank = 23.5

Soil above the footing kN · 5.12.14.2

7. Anchorage Record (5.12)

Tick each item once it is confirmed. Items that don’t apply are hidden.

Save & Report

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