Ringwall Foundation (API 650 Annex B)

Concrete Ringwall Foundation (API 650 Annex B)

Concrete ringwall foundation for a flat-bottom tank to API 650 Annex B: proportions, depth and projection, soil bearing under the ringwall for the empty, operating, hydrotest, wind and seismic cases, hoop tension from the lateral pressure of the confined fill and product, the ring moment from the eccentric loads, hoop and vertical steel against the Annex B minimums, and the counterbalancing weight and overturning stability of an anchored tank

New here? Read the User Manual — filling from your saved calculations, the load cases, the hoop steel, a worked example and how to read the results.

◉ API 650 14TH ED. (AUGUST 2025) ANNEX B · B.4.2 CONCRETE RINGWALL · 5.12.14 · E.6.2.3 · NOT A REGULATORY SUBMISSION TOOL

⚠ Indicative tool only. Annex B is informative and gives no design equations: the tool applies the statics its text describes (B.4.2.2, B.4.2.3) with the seismic and uplift loads of E.6.2.3 and 5.12.14, and ACI 318 strength design for the hoop steel. The allowable soil bearing comes from the geotechnical engineer (B.2). Bending and torsion from wind or seismic loads applied eccentrically (B.4.2.3 c) need a rational analysis and are a record item here. Crushed-stone ringwalls (B.4.3) and slabs (B.4.4) are not covered.

Identification

Company

Tank ID

Location

Record Type

Units

Switching converts what is typed in. The calculation and saved records are in SI.

Summary of checks

Enter the tank, its loads at the shell and the ringwall.

1. Tank and Loads at the Shell

Nominal diameter, D m

Design liquid level, H m

Design specific gravity, G

Hydrotest water level m · blank = H

Shell, roof and attachments at the shell, w_s kN/m

Roof live or snow load at the shell kN/m

Design internal pressure kPa · blank = 0

Bottom plate thickness mm

Line loads are per unit length of the shell circumference: total weight ÷ π D. For a column-supported roof, only the share carried by the shell.

2. Ringwall (B.4.2.2, Figure B.1)

Ringwall width, b m · at least 0.3

Total depth from the top, h m

Top of ringwall above the lowest adjacent finished grade m

Shell outward of the ringwall centreline, e m · blank = 0

Footing width, B_f m · blank = no footing

Footing thickness, t_f m

Frost penetration depth m · blank = none

Concrete unit weight, γ_c kN/m³ · blank = 23.5 kN/m³ (150 lbf/ft³)

Concrete strength, f′_c (28 days) MPa

Fill and soil unit weight, γ_s kN/m³ · blank = 18 kN/m³ (115 lbf/ft³)

Lateral pressure coefficient, K (B.4.2.3 a)

K from the geotechnical analysis

3. Soil Bearing (B.2.2, B.4.2.2)

Allowable bearing, operating, q_a kPa

Allowable bearing, hydrotest kPa · blank = q_a

Allowable bearing, with wind or seismic kPa · blank = q_a

Gross pressure under the base of the ringwall or footing. B.2.2 suggests factors of safety against ultimate bearing failure of 2.0 to 3.0 in operation and 1.5 to 2.25 for the hydrotest and with wind or seismic, so the last two allowables can be higher.

4. Hoop Tension and Reinforcement (B.4.2.3)

Reinforcement yield, f_y MPa · blank = 420 MPa (60,000 lbf/in²)

Load factor on hoop tension and ring moment blank = 1.6 (ACI 318, lateral earth and fluid pressure)

Cover to the vertical bars mm · blank = 75 mm (3 in.)

Hoop bars in the section, number

Hoop bar diameter mm

Vertical bar (stirrup) diameter mm

Vertical legs per set

Spacing of the vertical sets along the ring mm

5. Wind, Seismic and Uplift (5.12.14, E.6.2.3)

Wind overturning moment, M_w kN·m

Seismic ringwall moment, M_rw kN·m

Seismic slab moment, M_s kN·m · for E.64

Vertical acceleration, A_v fraction of g

Anchorage

Largest net uplift, wind and pressure cases (Table 5.20) kN

Largest net uplift, seismic cases kN

Product over the ringwall and footing resists seismic uplift, × (1 − 0.4A_v) (E.6.2.3)

6. Design Record (Annex B)

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