Shell to Roof junction verification according to API 650 for Roof Weight.

[Alessandro87]

Dear All,

I design storage roof tanks according to API 650 appendix F.
My question is : according to section F.5.1 we can calculate the resisting Area required at the junction when we have established the internal pressure.
But,Does API 650 prescribe how to verify if the junction is able to resist to the weight of the roof itself when the internal pressure is 0 ?
How could I take into account this verification to be sure that the roof isn't too heavy for my last shell course?
It seems to me that the appendix F doesn't match this point
Thanks all for your help!

Regards

 

[chicopee]

Wrong location to post. Question s/b posted under API code issues.

 

[fegenbush]

Appendix F is applicable to tanks designed with small internal pressures, although Figure F-2 is referenced in the main standard. The general requirements for minimum top angle size are listed in 5.1.5.9. Additional criteria exist for tanks with frangible roofs. For the area requirements to resist the roof load, use section 5.10.5.2 for self supported cone roofs and use section 5.10.6.2 for self supported dome or umbrella roofs.

 

[Alessandro87]

Dear Fegenbush,
thank for your suggestion,but sections 5.10.5.2 and 5.10.6.2 are for self supported roof, Do these sections work also for rafter supported cone?
Which section should I consider for this kind of roof?
Thank you

 

[fegenbush]

5.1.5.9(e) specifies the minimum top angle required for an internal pressure of zero. If the roof is rafter supported, the rafters will take the weight of the roof plate and snow/live load. 5.10.4.6 specifies that the rafters will connect to the shell by rafter clips. So, the top angle will only see a small amount of load due to the weight of the roof plates.

 

[Alessandro87]

Dear fegenbush,
thanks again,but,maybe my question is a bit different,I'll try to explain better.
My tank D=22.5m H=15.2m, last shell course is 6mm, the top angle ring is 120x120x10,the weight of roof plates is 20000kg and rafter weight is 12000kg.
The roof is rafter supportd roof. P=0.
How could I understand if the last course and its junction would last to the weight of the roof plates and its rafter?
Thanks all!

 

[JStephen]

If you are assuming the top angle acts as a tension ring to restrain the thrust of rafters (as in some grain silos), refer to Roark's Formulas for Stress and Strain, specifically, the formulas dealing with radial loads in a circular ring.

If it is a conventional roof with low slope and center column, the assumption is that there is no thrust and the minimum top angle size specified by API should be adequate.

 

[Alessandro87]

Dear JStephen,
Thank you for your post.
My case is the first one that you have mentioned. So,as I have thought,API doesn't face this problem and I should check on the Roark's Formulas for Stress and Strain.
Thank you for you suggestion!