Design cone roofs with clear inputs and checks. See geometry, loads, and rafter sizing instantly. Download tidy summaries for teams, clients, and inspectors now.
| Scenario | Diameter | Slope | Plate thickness | Total load | Required section modulus |
|---|---|---|---|---|---|
| Water tank roof | 60 ft | 0.25 | 0.1875 in | ~58 psf | ~7.1 in³ |
| Fuel tank roof | 18 m | 0.20 | 6 mm | ~3.0 kPa | ~160 cm³ |
| Maintenance heavy | 40 ft | 0.30 | 0.25 in | ~72 psf | ~9.0 in³ |
1) Cone roof geometry
Radius: R = D ÷ 2
Rise: h = R × slope
Slant length: L = √(R² + h²)
Area: A = π × R × L
2) Load build-up
Dead load from plate: q_dead = density × thickness
Total downward load: q_total = q_dead + q_ins + q_live + q_snow
3) Rafter demand (simple beam)
Line load: w = q_total × spacing
Max moment: M = w × span² ÷ 8
Allowable stress: σ_allow = 0.6 × Fy
Section modulus: S_req = M ÷ σ_allow
Accurate tank roof planning starts with geometry. Diameter and slope ratio define the rise, slant length, and roof area. Area drives plate quantity, coatings, insulation coverage, and access costs. The calculator converts slope to an angle for easier review. Use shell centerline diameter to match drawings.
Loads should reflect service conditions and construction needs. Plate dead load is derived from thickness and steel density. Add insulation, coating, walkway, and attachments as an allowance. Live load represents maintenance activity and temporary equipment. Snow load should use governing project criteria and drift considerations. Use conservative values early, then refine later.
Rafter sizing here is a screening check, not a final design. The tool converts total area load into a line load using rafter spacing. A simple beam assumption produces maximum moment and a required section modulus. Material strength is reduced with an allowable stress factor. Compare the required section modulus to candidate shapes from catalogs.
Wind uplift can control attachment and stability. The calculator compares a reference uplift pressure to the roof dead load. If the result indicates net uplift, review roof-to-shell connections, clips, and bracing. Consider internal pressure, openings, and local suction zones. Field conditions and temporary states may be critical.
Use the report outputs to support fast decisions. Start with a few roof concepts and compare area, rise, and framing demand. Document assumptions for loads and support type for later checking. Share CSV for estimating and PDF for reviews. For final design, verify rings, compression members, and detailing.
Also review drainage and corrosion protection. Slope affects water ponding risk and ice buildup. Confirm that nozzles, vents, and manways do not conflict with rafters. For supported roofs, check the compression ring and any intermediate columns. For self-supported roofs, consider plate buckling and meridional stresses. Always coordinate with fabrication limits, plate sizes, weld details, and erection sequencing. Small changes in slope or spacing can shift material and labor significantly. Record design temperatures and inspection access requirements before issuing drawings to the field.
1) What roof shape does this calculator cover?
It estimates cone roofs using diameter and slope ratio. The outputs include rise, slant length, and area. Other roof types need different geometry and stress checks.
2) Does the rafter section modulus equal the final member size?
No. It is a planning requirement from a simple beam model. Final sizing should include connection details, continuity, buckling, lateral bracing, and any openings or concentrated loads.
3) How should I choose the insulation allowance?
Combine insulation weight, cladding, coatings, and attachments into one area load. If you are unsure, use a conservative allowance and refine once vendor data and thicknesses are confirmed.
4) What does the uplift note mean?
It compares a reference uplift pressure to dead load from plate weight. If net uplift is possible, review anchorage, clips, ring members, and temporary construction conditions with your engineer.
5) Which span is used for the rafter moment?
The calculator uses radius for the self-supported option and slant length for the supported option. Treat this as a conservative screening assumption and confirm the actual framing layout.
6) Can I use metric or imperial inputs?
Yes. Select the unit system first, then enter values consistently. The tool keeps calculations in the selected system and formats outputs for reporting and coordination.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.