Tools › User guides › Intze Tank Designer
The Intze Water Tank Designer designs a complete Intze-type elevated tank — top dome, cylindrical wall, ring beams, conical slab, bottom dome, circular girder, staging columns and bracings, and the foundation — to IS 3370, IS 456, IS 875 (Part 3) and IS 1893 (Part 2). Everything is free on screen; the A4 design booklet PDF is ₹49 per design.
Open the Intze Tank Designer › Design guide (theory)
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Project / work name, client, location, sheet no., revision, designed / checked by, firm, date Enter your value | These go on the cover and the title block of your PDF booklet. They do not change the design at all. | Copy the name of work, client and location from the work order or estimate. | fill in “Designed by” and “Checked by” before you download — they print in the sign-off panel. |
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Net storage capacity Enter your value | How much water the tank must hold when full, in kilolitres. 1 kL = 1,000 litres = 1 m³. Source: The water-supply design of the scheme. Daily demand = population × litres per person per day (CPHEEO Manual: 135 L for towns with sewerage, 70 L without; 55 L under Jal Jeevan Mission for rural supply). An overhead tank usually stores about a quarter to a third of the daily demand; the exact figure comes from the pumping hours and the mass-curve method. | 100 to 1,000 kL for most village and town schemes. Common sizes: 150, 200, 250, 300, 450, 500, 1,000 kL. | Example: 10,000 people × 135 L = 1,350 kL a day → a tank of about 450 kL. An Intze tank is the economical shape from roughly 200 kL upward; below that a plain cylindrical tank is often cheaper. |
| Freeboard above top water level Check after the run | The empty gap between the highest water level and the roof. It stops the water hitting the roof when it sloshes in an earthquake. Source: IS 1893 (Part 2):2014 requires the freeboard to be at least the sloshing wave height. The calculator works that height out and flags it if your freeboard is too small. | 0.3 to 0.6 m. 0.5 m suits most tanks in Zone III. | start with 0.5 m, run the design, and raise it only if the “sloshing” check fails. |
| How to fix the tank diameter Usually keep default | Auto finds the diameter that gives your capacity with the proportions below. Manual lets you fix the diameter yourself. | Auto, unless a drawing or the site already fixes the diameter. | use Manual to check an existing drawing — enter its diameter and compare the results. |
| Internal diameter of the cylinder, D Enter your value | The inside diameter of the cylindrical part of the tank. Source: The drawing you are checking, or the space available on site. | 8 to 16 m for 250–1,000 kL. | choose below whether the cylinder height comes from H₁/D (the capacity then follows) or is solved to give exactly your capacity. |
| How to fix the cylinder height Usually keep default | With the diameter fixed, the height can come straight from the H₁/D ratio (the tank then holds whatever that gives, and it is checked against your capacity), or it can be worked out so that the tank holds exactly your capacity. | From H₁/D, to check a drawing: enter its diameter and its H₁/D. Exactly the capacity, for a new design with a fixed diameter. | when the height is worked out from the capacity, the H₁/D box shows the ratio that results. Typing in it switches back to “From H₁/D”. |
| Cylinder height ÷ diameter (H₁/D) Usually keep default | How tall the straight cylindrical wall is compared with the tank diameter. Source: Standard Intze proportions (RDSO type designs; textbooks by Punmia, Krishna Raju, Jain). | 0.30 to 0.50. RDSO type drawings use about 0.32. | a taller wall gives a narrower tank with more water pressure at the bottom of the wall; a shorter wall gives a wider, heavier roof. In manual diameter mode, typing a ratio here switches the height to “from H₁/D”. |
| Bottom ring radius ÷ tank radius (r/R) Usually keep default | The size of the ring at the bottom of the cone, compared with the tank. This ring sits on the columns, so it also fixes the column circle (diameter 2r). Source: Standard Intze proportions. | 0.60 to 0.70. The classic Intze proportion is 5/8 = 0.625; RDSO uses about 0.66. | a smaller ring means a tighter column circle, which is cheaper to brace but more sensitive to overturning. |
| Slope of the conical slab Usually keep default | How steeply the conical slab rises from the columns up to the wall, measured from the horizontal. Source: Standard practice. A 45° cone gives equal horizontal and vertical thrust, which is what lets the cone and bottom dome balance. | 45° in almost every Intze tank. | Leave it at 45° unless you are matching a drawing. Steeper cones push harder sideways on the girder and upset the balance. |
| Top dome rise ÷ D Usually keep default | How high the roof dome rises, compared with the tank diameter. Source: Standard dome proportions. | 1/8 to 1/6 of D (0.125 to 0.167). RDSO uses about 0.165. | a flatter dome is lighter but pushes harder outward on the top ring beam. |
| Bottom dome rise ÷ r (the dome arches upward) Check after the run | How high the bottom dome arches up into the tank, compared with the bottom ring radius r. This rise decides whether the dome’s outward push cancels the cone’s inward push — the “Intze balance”. Source: Worked out by the design. After you run it, section 8 of the results tells you the exact rise that balances your tank. | 0.22r to 0.30r. RDSO B-1235 uses 0.245r. Many textbooks quote 0.3–0.45r; for the arrangement drawn here the balance usually lands lower. | run once, read the “to balance exactly” line in section 8, type that value here and run again. |
| Shell thicknesses Usually keep default | Thickness of the four shells. In Auto the calculator increases the wall and cone until concrete stays uncracked under water pressure (IS 3370), and uses your top and bottom dome values as minimums. Source: IS 3370 (Part 2):2009 crack check decides the wall and cone. 100 mm is the practical minimum for a dome, 150 mm for a water-retaining wall. | Top dome 100–125 mm · wall 150–300 mm · cone 200–400 mm · bottom dome 150–250 mm. | Use Auto for a new design. Use Manual to check an existing drawing. |
| Top ring beam B₁ (width × depth) Usually keep default | The ring beam round the top of the wall. The roof dome pushes outward on it, so it works in tension like the hoop of a barrel. Source: Sized by the tension check. Type the size as “width x depth”, e.g. 320 x 210. | 250–350 mm wide × 200–300 mm deep. | If it fails, the results tell you the concrete area needed — make the beam a little wider. |
| Ring beam B₂ where the wall meets the cone Usually keep default | The ring beam where the cylindrical wall meets the cone. The cone and the water both push it outward, so it is usually the most heavily stretched ring in the tank. Source: Sized by the tension check (IS 3370). | 500–800 mm wide × 350–600 mm deep. | If it fails, increase the width first; its area is what resists the pull. |
| Circular girder B₃ on the columns Check after the run | The circular beam at the bottom of the cone that sits directly on the columns. It carries the whole tank and bends and twists between the columns. Source: IS 456:2000 limit state design for bending, shear and torsion. | Width 450–650 mm (at least the column width). Depth about one-sixth to one-eighth of the distance between columns, usually 700–1,200 mm. | If the girder fails in shear or bending, make it deeper before making it wider. |
| Live load on the roof dome Usually keep default | The load of people and equipment on the roof dome during maintenance. Source: IS 875 (Part 2):1987, imposed loads on roofs. | 1.5 kN/m² if there is a ladder and people walk on the roof; 0.75 kN/m² if there is no access. | Water tanks normally have roof access, so keep 1.5. |
| Allowance for finishes and fittings Usually keep default | An extra percentage added to the concrete weight for plaster, waterproofing, ladder, railing, manhole, pipes and fittings. Source: Engineering practice; there is no single code figure. | 5–10%. 8% is a sensible middle. | Raise it if the roof carries heavy equipment or a thick screed. |
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Staging height Enter your value | The height from the top of the foundation to the top of the columns, i.e. to the circular girder at the bottom of the cone. The container sits above this. Source: The hydraulic design. The lowest water level must give enough pressure at the farthest tap. CPHEEO suggests a residual head of about 7 m for single-storey, 12 m for two-storey and 17 m for three-storey buildings, plus the pipe friction losses and any rise in ground level. | 12 to 25 m. | Example: 12 m residual head at the farthest tap + 7 m of pipe friction loss − 1 m because the tank site is higher → about 18 m of staging. The outlet is at the bottom of the tank, which is at the top of the columns. |
| Number of columns Check after the run | How many columns carry the tank, equally spaced round a circle. Source: Practice: keep the distance between neighbouring columns to about 3–5 m so the girder spans stay reasonable. | 6 for up to about 200 kL, 8 for 200–600 kL, 10 or 12 for larger tanks. | More columns reduce the girder bending and the load on each column, but cost more formwork. |
| Column circle Usually keep default | Where the columns stand. In an Intze tank they sit under the bottom of the cone, on a circle of diameter 2r — not under the tank wall. Source: RDSO standard arrangement (drawing B-1235). | Auto. | Use Manual only to check a drawing with a different column circle. |
| Column circle diameter Enter your value | The diameter of the circle through the centres of the columns. Source: The drawing you are checking. | About 0.6 to 0.7 times the tank diameter. | |
| Column shape Check after the run | The cross-section of the staging columns: square (side a), rectangular (width b along the ring by depth d radially) or circular (diameter D). Source: The drawing or specification for the tank. | Square is simplest to shutter. Circular columns are common in railway and public-health tanks and give less wind area per column. | Auto sizing picks a circular column of the same area as the square one, so the two shapes can be compared fairly. A circular column also gets the circular-section wind coefficient and ring ties. A rectangular column is checked about both axes for every wind or earthquake direction, so if it is much slimmer one way it needs more steel than a square column of the same area. |
| Column size Usually keep default | Auto picks a column of about 27 mm (square side) per metre of staging height, at least 450 mm. A circular column gets the diameter with the same area. Source: Practice; the design then works out the steel it needs. | Auto for a first design. | If the results show more than 4% steel in the column, switch to Manual and try a bigger size. |
| Column side (square) Enter your value | The side of the square column, the diameter of the circular one, or the width b of a rectangular column, measured along the ring. Source: Your drawing, or trial and error: aim for 0.8–2.5% steel in the results. | 400–700 mm for 12–25 m staging. | |
| Column depth d (radial) Enter your value | The depth d of a rectangular column, measured radially (in and out from the centre of the tank). Source: Your drawing, or trial and error: aim for 0.8–2.5% steel in the results. | A little larger than b, for example 450 × 650 mm on 20 m staging. | Only used when the column shape is Rectangular. The direction of the wind or earthquake is not known, so both axes are checked. |
| Bracing levels Usually keep default | Bracing beams tie the columns together at intervals up the height, so each column only bends over a short length. Source: Common practice for frame staging. | Auto places a level about every 3.6–4 m. | |
| Number of bracing levels Enter your value | Number of bracing levels between the foundation and the girder. Source: Your drawing. | Staging height ÷ 4, rounded, minus one. | |
| Bracing beam size (width × depth) Usually keep default | The size of each bracing beam, as width x depth. Source: Designed for earthquake and wind in section 9 of the results. | 300–450 mm wide × 600–750 mm deep. | Keep the width at most the column width so the bars can pass. |
| Bracing flexibility factor β Usually keep default | A correction for the fact that real bracings bend a little. It makes the staging slightly softer in the earthquake calculation. Source: Engineering judgement; a full frame analysis would replace it. | 0.80 to 0.90. Use 1.0 only to see the upper limit. | Leave at 0.85. |
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Basic wind speed Vb Enter your value | The 3-second gust speed for your district. Source: IS 875 (Part 3):2015 — the basic wind speed map, and the list of cities in its annex. | Kolkata 50 · most of West Bengal 47–50 · Delhi 47 · Mumbai 44 · Chennai 50 · Bengaluru 33 m/s. | Look up your nearest listed city. If you are between two map contours, use the higher value. |
| Terrain around the site Check after the run | How rough the ground around the tank is. Open ground lets wind build up speed; buildings slow it down. Source: IS 875 (Part 3):2015, terrain categories. | Category 2 for most village and small-town sites. | When in doubt, choose the lower number — it is the safer side. |
| k₁ — design life (risk) factor Usually keep default | Adjusts wind for how long the structure is meant to last. Source: IS 875 (Part 3):2015, risk coefficient table. | 1.00 for a normal 50-year tank. | |
| k₃ — ground slope (topography) Check after the run | Wind speeds up over hills and ridges. Source: IS 875 (Part 3):2015, topography factor. | 1.00 on flat ground. | Only change it if the tank stands on or near the top of a slope steeper than about 3°. |
| k₄ — cyclone importance Check after the run | An extra safety factor for tanks near the east and west coasts where cyclones strike. Source: IS 875 (Part 3):2015, importance factor for cyclonic regions. | 1.00 inland. 1.30 for a water-supply tank within about 60 km of a cyclone-prone coast (for example coastal West Bengal and Odisha). | |
| Shielding factor η for the rear frame Usually keep default | The columns at the back are partly hidden from the wind by the ones in front. This factor says how much wind the back row still gets. Source: IS 875 (Part 3):2015, shielding factors for multiple frames (depends on solidity and spacing). | 0.4 to 0.6. | Leave at 0.45. |
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Seismic zone Enter your value | How strong an earthquake the site must be designed for. Source: IS 1893 (Part 1):2016, seismic zone map and the list of towns in its annex (zone factor Z). | Kolkata and most of southern West Bengal: III · North Bengal hills and Sikkim: IV · Delhi: IV · Guwahati: V · Mumbai, Chennai: III · Bengaluru: II. | Check which edition of the zone map your department follows. |
| Type of soil at the site Check after the run | Soft soil shakes more, and for longer, than rock. Source: IS 1893 (Part 1):2016, classification of soil by SPT value. Read N from the soil investigation report. | I: rock, or dense sand / gravel with SPT N above 30 · II: medium soil, N 10–30 · III: soft soil, N below 10. | Most alluvial plains of Bengal are type II or III. |
| Importance factor I Usually keep default | Tanks that must keep working after an earthquake are designed for bigger forces. Source: IS 1893 (Part 2):2014, importance factor table. | 1.5 for drinking water and fire-fighting tanks. | Almost every public water tank uses 1.5. |
| Response reduction factor R Usually keep default | How much the staging can safely deform beyond its elastic limit. A higher R means smaller design forces, but only if the bars are detailed for ductility. Source: IS 1893 (Part 2):2014, response reduction factor table. | 2.5 for RC frame staging detailed to IS 13920. | Use 2.5 only if the columns and bracings will be detailed to IS 13920 (closely spaced ties at the joints). Otherwise ask the checking engineer. |
| Damping multiplier for the sloshing water Usually keep default | The sloshing water has very little damping (0.5%), so its spectrum is raised by this factor. Source: IS 1893 (Part 2):2014, clause on the convective mode. | 1.75. | Do not change it. |
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Concrete grade Usually keep default | The strength class of concrete. Source: IS 3370 (Part 1):2009 — M30 is the minimum grade for reinforced concrete that holds water. | M30 for the tank and staging. | M35 helps if the girder or columns come out very heavy. |
| Steel grade Usually keep default | The grade of reinforcing bars. Source: IS 1786. In the water-retaining parts the allowed stress is capped at 130 N/mm² whatever the grade, so the grade mainly matters for the girder, columns and foundation. | Fe 500 (or Fe 500D). | |
| Clear cover to the bars Usually keep default | The concrete between the bars and the surface. It keeps water away from the steel. Source: IS 3370 (Part 1):2009. | 45 mm on faces in contact with water. | |
| Allowed steel stress, direct tension σst Usually keep default | The highest stress allowed in the bars that resist water pressure. Keeping it low keeps cracks too fine to leak. Source: IS 3370 (Part 2):2009, clause 4.4.3.1. The old 1965 code allowed 150; some departments still use it. | 130 N/mm² for deformed (HYSD) bars; 115 for plain bars. | Use 150 only if your department asks you to follow IS 3370:1965. |
| Allowed steel stress, bending on the water face Usually keep default | The same limit for bars resisting bending on the face in contact with water. Source: IS 3370 (Part 2):2009, clause 4.4.3.1. | 130 N/mm². | |
| Unit weight of reinforced concrete Usually keep default | Weight of one cubic metre of reinforced concrete. Source: IS 875 (Part 1):1987. | 25 kN/m³. |
| Box | What it means | Typical value | Tip |
|---|---|---|---|
| Net safe bearing capacity of the soil Enter your value | How much pressure the soil at founding level can carry safely, after taking away the soil that was dug out. Source: The soil investigation report for the site (IS 1892 for the investigation, IS 6403 for bearing capacity). Never guess this for real construction. | Soft clay 50–100 · medium clay or loose sand 100–150 · stiff clay or dense sand 150–250 · gravel / soft rock 250+ kN/m². Indicative only. | Important: an elevated tank is heavy and tall. A soil test at the actual founding depth is essential. |
| Founding depth below ground Check after the run | How deep below ground the bottom of the foundation sits. Source: The soil report: go below topsoil, filled-up ground and any swelling clay layer. | 1.5 to 3 m. | |
| Foundation type Check after the run | A ring raft joins all the columns in one wide slab. Separate footings are cheaper but each one takes its column’s load alone. Source: Practice; IS 11682 for staging of elevated tanks. | Ring raft for most Intze tanks, and always on soft soil. | If you choose separate footings, tie them together with plinth beams. |
| Allowed increase in bearing for wind or earthquake Usually keep default | Soil can carry a short-lived extra load during wind or an earthquake, so the allowed pressure is increased for those cases only. Source: IS 1893 (Part 1):2016, table on the increase in allowable bearing pressure; IS 1904. | 25% for most soils; 0% for loose sand or soft clay that could liquefy. | |
| Raft width each side of the column line Check after the run | How far the raft extends inside and outside the column line. Wider means lower soil pressure. Source: Trial: increase it until the bearing check in section 10 passes. | Start at about 0.3 × the column circle diameter. | If the bearing check fails, this is the input to increase. |
| Raft / footing thickness Check after the run | The thickness of the raft or footing. Source: Bending and punching shear under the columns. | About one-third of the raft width each side; 600–1,000 mm usually. | |
| Unit weight of soil Usually keep default | Weight of one cubic metre of the soil filled back over the raft. Source: The soil report; 16–20 is normal. | 18 kN/m³. |
Use Save / Save as new to keep several tanks in your browser, Export file to download a project file and Import file to open it on another computer. Reset to defaults loads the 450 kL example again.
Every member is shown with its sketch, forces, thickness, reinforcement and a PASS / REVIEW / FAIL check, followed by the summary bar bending schedule. To print or save the A4 design booklet (title block, sketches, every calculation, BBS and sign-off panel) press Download PDF and pay ₹49 for that design — no sign-in needed. Keep the receipt code to unlock the same design on another device.
Capacity, staging height, basic wind speed, seismic zone and soil type, and the safe bearing capacity of the soil. The rest are standard Intze proportions and code values.
Raise the freeboard in steps of 0.1 m and run the design again.
No. The whole design is free on screen. The ₹49 PDF is the printable booklet with title block and sign-off panel.