API 650 11 th Edition Appendix R

[dharmeshajoshi]

Appendix R of API 650 gives the load combinations to be considered for combined stress analysis for the shell.

I assume that we have to calculate the stress induced due to various loads like:
Dead load : DL
Design External pressure : Pe
Design Internal Pressure : Pi
Live Load : Lr
Seismic Load : E
Wind Load : W
Stored Liquid : F
Snow : S
Test Pressure : Pt
Hydrostatic Test : Ht
Then based on the load combinations given in App. R we have to add up the stresses due to the loads and check that the combined stresses are within allowable values.

But what should be the allowable compressive stress?
How do we calculate the induced longitudinal stress due to internal pressure and external pressure?
There is no formula given in API 650 regarding induced longitudinal stress due to internal and external pressure.

Does someone have any idea how calculation as per Appendix R is to be done?

I thank you in advance for any help.

Regards,
Dharmesh Joshi

 

[JStephen]

Under normal circumstances, the only significant compressive loading would be under seismic loading, and App. E gives the allowable seismic compressive stress. If for some reason you needed allowable compressive stress while empty, you could use the allowables from API-620 or AWWA D100. Longitudinal stress under liquid load only is zero. Longitudinal stress from internal pressure would just be P/A, assuming the roof is all supported from the shell, but it is not normally a significant stress.

Generally, you'd add up the loads as indicated and then calculate the stresses, rather than calculating separate stresses and then adding. The stresses are not always proportional to the load.