That depends on size and loading...If the diameter is less than 12m, self supporting cone roof with rafters is OK. Up to 40 m, you may use internal truss without column . Center supported roof with radial rafter is an option for diameters around 12 to 15 m.
That is usually an economic decision, including erection costs, and will vary depending on the constructor.
If an internal floater is used, it is desirable to limit the number of columns.
Available stock rafter and beam lengths may affect the decision. Available crane reach may affect the decision.
Note that taller tanks will have more expensive columns which will shift those roofs to use fewer columns.
I would like to throw in more details, The entire tank structure has been made up of stainless steel 304 and the diameter of the tank is 36m and roof plate thickness is 6mm. The standards followed was EN 14015. How to calculate the number of rafters with the details and is there any formula ?
Pls look EN 14015 10.3 Roof plating with supporting structure .(..... The spacing of roof plate supporting members for cone roofs shall be such that the span between them does not exceed 2,0 m...)
Regarding the design of supporting structure , you must look to Eurocode 3. Design of steel structures.
Dears,
Could you please advise whether Mn controlled(0.80% to 1.2%) material is compulsory for fabricating platforms and handrails for a fuel storage tanks or normal material with below 0.80% manganese is acceptable?.
Also pls let me know it has mentioned in API 650 standard, if Manganese controlled material required as said above.
Also pls let me know Grating and stir tread also to be MN controlled as per API650
I am expecting your valuable reply to my query. Thanks
