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C ivil Desi g n Hel p
Design of Concrete Ring Beam for Storage Tank Home Vertical Vessel/Tower Horizontal Vessel Tube & Shell Exchanger Rotating Equipment Storage Tank on Ring Beam Equipment on Skid Pipe Rack Transformer Pit Anchor Anchor Bolt Bolt Stack Foundation Help & More Help Feed Back About me Site Link
In this page I will talk about the design desi gn philosophy of ring beam bea m for storag e water tank. The granular fill foundation foundation of the tank tank shall be desi gned per project desi gn criteria / specifi cation. This This type of foundation is mostly common to all project site. si te. However, sometimes we des ign concrete ring be am around the the tank foundation. foundation. Following are some reasons for desi gn of concrete ring beam, though this this i s more costly c ostly and take longer to construct than than granular granular fill ring: Sometimes clients c lients ask to provide concrete ring beam around tank foundation. 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 i nternal nternal pressure. Now you will follow the following following steps to start the foundation load calculation and des ign: 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 Type of Roof (F loating or fixed roo f), weight of roof Detail of tank shell and weight of tank tank shell Detail of tank base plate, location of base sump, annular annular plate and and total weight of base plate Detail of o f anchor 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* hydrotest* Internal Internal pressure or s uction Live load Wind Shear and moment on tank shell Seismi c shear and moment on tank shell Step-2 : Verification Verifi cation of foundation foundation location, elevation and and external external fittings loads You need to review Plot plan, Equipment location drawi ngs and 3 -D Models and check whether you you have have all the following information: Verify the area available for foundation. foundation. Verify Foundation location and Elevation Pipe supports and Nozzle Nozzle loads on o n tank (Dp) Location and si ze of Platforms around the the tank Locations of underground underground pipes pip es Electrical and Instrument duct banks Locations and extent of adjacent foundations Verify the location a nd extent extent of new/existing foundations not shown in 3D model or plot plan. Step-3 : Loads on concrete ring beam and on the the confined 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 Conside r the following following loads on ring beam and a nd on granular granular compacted fill inside the concrete ring. Geotechnical Geotechnical Data: D ata: Before starti ng the design, you n need eed to collect c ollect the following information about soil: Allowable Allowable Bearing Bearing Pressur Pressure e Density of Soil Co-efficient of earth pressure at rest (Ko) Loads on Ring beam: Total weight of tank shell (vertical (vertical load), kN / m (DL) (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 annular base weight on ring beam, kN / m 2 (DL)
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Part of product / test water load on ring beam, kN / m 2 (PL) Seismi c shear and wind shear on ring beam, kN / m Part of i nternal pressure / suction load on ring beam, kN / m 2(IP) Loads on compacted granular fill inside the ring beam: Floating roof weight on compacted granular fill, kN / m 2(DL) Annular base weight on compacted granular fill, kN / m 2 (DL) Live load on floated roof, kN / m 2 (LL) Product / test water load on compacted granular fill, kN / m 2(PL) Internal pressure / suction load on compacted granular fill, kN / m 2 (IP) Following load combimations can be used for soil bearing pressure check (at bottom of ring beam level) : Load Combination: LC1 Load Combination: LC2 + Live Load Load Combination: LC3 Wind Load Load Combination: LC4 Seismic Load Load Combination: LC5 -
Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure Self weight of soil / Beam + Self weight of tank + Product weight + Internal Pressure Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure +
Live Load + Wind Load Load Combination: LC6 - Self weight of soil / Beam + Self weight of tank + Product weight + Internal pressure + Live Load + Seismic Load Load 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 tank + Product weight + Internal pressure) Load Combination: UC2 - 1.7 x (Surcharge load of confined soil) + 1.7 x Surcharge load of (Self weight of tank + Product weight + Internal pressure)+ 1.4 x surcharge of Live Load Load Combination: UC3 - 1.7 x (Surcharge load of confined soil) + 1.7 x Surcharge load of (Self weight of tank + test water weight) Step-4 : Determination of concrete ring beam size: The ri ng wall should be a minimum 300 mm thick and extend to a suitable bearing stratum, whch may be natural ground or built-up compacted g ranular material. It should be 500 mm below ground level and extend below frost line. The beari ng 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 b e approximately equal to the earth pressure under the confined earth at the same 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 wi th 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 beari ng 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 load due to confined soil and loads on confined soil. Load calculation: Surcharge due to confined soil: Sursoil = 0.5 x (height of ringwall) 2 x soil density x Co-effici ent 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 of earth pressure at rest (Ko) http://civildesignhelp.info/tf.html
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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 bei ng applied eccentrically to the ringwall center line. The ringwall should be reinforced on both faces, with vertical reinforcement (stirrups) closest to the concrete surfaces. Not more than 50% of the hoop reinforcement should be lapped at any one positi on. 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 tank.
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Copyright 2009. All rights reserved. Please do not print or copy of t his page or any part of this page without w ritten 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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