Design Concrete Ring Beam for Storage Tank_PDF

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Design of Concrete Ring Beam for Storage Tank

In this page I will talk about the design philosophy of ring beam for storage water tank. The granular fill foundation of

the tank shall be designed per project design criteria / specification. This type of foundation is mostly common to all

project site. However, sometimes we design concrete ring beam around the tank foundation. Following are some

reasons for design of concrete ring beam, though this is more costly and take longer to construct than granular fill rin

Sometimes clients ask to provide concrete ring beam around tank foundation.

Prevent uplift of the tank due to wind or earthquake

Prevent edge failure of the soil at the tank shell

Prevent local uplift of the tank due to internal pressure.

Now you will follow the following steps to start the foundation load calculation and design:

Step-1 : Review of Tank detail drawing (Vendor Drawing)

You need to review tank drawings from foundation design point of view and check whether you have all the following

information:

Tank Dimension, Diameter and Height

Type of Roof (Floating or fixed roof), weight of roof

Detail of tank shell and weight of tank shell

Detail of tank base plate, location of base sump, annular plate and total weight of base plateDetail of anchor bolt (BCD, no of bolt and dia of bolt) and anchor bolt fixing detail

Location and detai l of man-hole at bottom portion of tank

Product density and and maximum height of product

Maximum height of water inside the tank for the hydrotest* Internal pressure or suction

Live load

Wind Shear and moment on tank shell

Seismic shear and moment on tank shell

Step-2 : Verification of foundation location, elevation and external fittings loads

You need to review Plot plan, Equipment location drawings and 3 -D Models and check whether you have all the

following information:

Verify the area available for foundation.

Verify Foundation location and ElevationPipe supports and Nozzle loads on tank (Dp)

Location and size of Platforms around the tank

Locations of underground pipes

Electrical and Instrument duct banks

Locations and extent of adjacent foundations

Verify the location and extent of new/existing foundations not shown in 3D model or plot plan.

Step-3 : Loads on concrete ring beam and on the confined compacted granular fill in-side the ring:

You need to place concrete ring beam in such a way that outer surface of the tank shell should be the center of ring

beam. Consider the following loads on ring beam and on granular compacted fill inside the concrete ring.

Geotechnical Data:

Before starting the design, you need to collect the following information about soil:

Allowable Bearing Pressure

Density of Soil

Co-efficient of earth pressure at rest (Ko)

Loads on Ring beam:

Total weight of tank shell (vertical load), kN / m (DL)

Total weight of roof , for fixed roof case. For floating roof, part of the roof weight will come on the ring beam, kN

m (DL)

Total live load on roof , for fixed roof case. For floating roof, part of the live load will come on the ring beam, kN

m (LL)

Part of annular base weight on ring beam, kN / m2 (DL)
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Part of product / test water load on ring beam, kN / m2(PL)

Seismic shear and wind shear on ring beam, kN / m

Part of internal pressure / suction load on ring beam, kN / m2(IP)

Loads on compacted granular fill inside the ring beam:

Floating roof weight on compacted granular fill, kN / m2(DL)

Annular base weight on compacted granular fill, kN / m2 (DL)

Live load on floated roof, kN / m2 (LL)

Product / test water load on compacted granular fill, kN / m2(PL)

Internal pressure / suction load on compacted granular fill, kN / m2(IP)

Following load combimations can be used for soil bearing pressure check (at bottom of ring beam level) :

Load Combination: LC1 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure

Load Combination: LC2 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal Pressure

+ Live Load


Wind Load


Seismic Load


Live Load + Wind Load


Live Load + Seismic LoadLoad Combination: LC7 - Self weight of soil / Beam + Self weight of tank + Test water weight

Load combinations for Ring beam design for Hoop tension:

Load Combination: UC1 - 1.7 x (Surcharge load of confined soil) + 1.7 x Surcharge load of (Self weight of tan

+ Product weight + Internal pressure)


+ Product weight + Internal pressure)+ 1.4 x surcharge of Live Load


+ test water weight)

Step-4 : Determination of concrete ring beam size:

The ring wall should be a minimum 300 mm thick and extend to a suitable bearing stratum, whch may be natural

ground or built-up compacted granular material. It should be 500 mm below ground level and extend below frost line.

The bearing capacity of the soil below the ringwall should be calculated using a strip foundation analysis loaded with

vertical load as mentioned in step-3.

API 650, appendix-B, clause B.4.2.2 states that it is desireable that the ringwall width be such that the average unit

soil loading under the ring wall will be approximately equal to the earth pressure under the confined earth at the sam

depth (in maximum liquid level condition).

Once, the ringwall thickness is determined from above condition, it should be reviewed to ensure that excessive

quantities of concrete are not used for tanks with low liquid levels and that the permissible ground pressure for the

width of the wall is not exceeded.

Please note that, soil bearing pressure under the ring beam and under the confined earth at same depth should not

exceed the allowable soil bearing pressure for any of the above described load and any load combinations.

Step-5 : Determination of Hoop Tension on concrete ring beam and reinforcement calculation:

The concrete ring beam shall be designed for hoop tension. This hoop tension will be generated from surcharge loa

due to confined soil and loads on confined soil.

Load calculation:

Surcharge due to confined soil: Sursoil = 0.5 x (height of ringwall)2x soil density x Co-efficient of earth pressure at

rest (Ko)

Surcharge due to uniform load on confined soil: Surudl = (Load on confined soil) x (height of ringwall) x Co-efficient

earth pressure at rest (Ko)


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o a oop ens on = urso uru x . x cen er ne ame er o r ng eam

Factored Hoop Tension load can be calculated as per step-3.

Required area of Hoop reinforcement is, Ast = (Factored Hoop tension) / (0.9 x yeild stress of rebar---fy)

The ringwall must also be designed to take care circumferential bending moments due to the vertical load being

applied eccentrically to the ringwall center line.

The ringwall should be reinforced on both faces, with vertical reinforcement (stirrups) closest to the concrete surface

Not more than 50% of the hoop reinforcement should be lapped at any one position.

Step-6 : Anchor Bolt Design:

Anchor bolt shall be checked per design criteria and Tenssion & Shear load supplied by vendor. If wind and shear

forces are not supllied by vendor, you need to calculate the anchorage load from API 650. Anchor bolt shall be

designed for ductility failure. If required, addi tional reinforcement to be provided around the anchor bolt.

For a typical concrete ring beam detail click here.

I hope this page will be very helpful to you to understand the basic design of a concrete ring beam for storage tan

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Copyright 2009. All rights reserved. Please do not print or copy of this page or any part of this page without written

permission from Subhro Roy.

Disclaimer: This page is prepared based on experience on Civil Engineering Design. All definitions and most of the

explanations are taken from different text books and international design codes, which are referenced in the contents. Any

similarity of the content or part of with any company document is simply a coincidence. Subhro Roy is not responsible for

that.
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Design Concrete Ring Beam for Storage Tank_PDF