WIND LOAD ON ROOF STRUCTURE

[LAZAR90]

Do we need to take into consideration wind load when design roof structure for tank?

 

[Dhurjati Sen]

https://www.eng-tips.com/viewthread.cfm?qid=159697

https://www.eng-tips.com/viewthread.cfm?qid=150765

DHURJATI SEN
Kolkata, India

 

[Jay_]

Dear Sir,
Yes, uplifting on the tank does affect the design of the roof structure and wether to to anchor down the tank or not.
Refer to ASCE 7-16 and API 650 ed13.

Detailing is a hobby,

 

[IFRs]

API 650 has an exception for standard cone roofs.

 

[HTURKAK]

API 650 does not allow the attaching of the roof plates to the roof support members
and explicitly forbidden for frangible roofs and allow for For Appendix F tanks.

Is this an Appendix F tank ?

When you look to the ( Figure F-1—Appendix F Decision Tree ) where is your position ?

If there is no internal pressure, you will follow basic design requirements.
If the roof plates are not attached to the supporting rafters ( in your case ), The wind uplift will not affect the design of rafters..

 

[HTURKAK]

Let me explicitly explain = if the roof plates are not attached to the supporting rafters, the wind suction pressure will not affect the design of rafters.

I do not know your wind code, and cone roof angle . If positive pressure develops (may be one side of the roof ), the positive pressure shall be accounted for the design of rafters.

You did not answer the questions (Is this an Appendix F tank ? When you look to the ( Figure F-1—Appendix F Decision Tree ) where is your position ? Is there internal pressure? )

 

[HTURKAK]

O.K. this is Appendix F tank with frangible roof ..What is the internal pressure ? what is your position at Figure F-1—Appendix F Decision Tree ?


Are you sure with this speed ? that means 280 kph. (i could not see )??


I could not get your point for using the dome roof tank coeff.. If this is a frangible roof, the rules are mentioned at ( 5.10.2.6 Frangible Roof).

Regarding wind suction , (the roof plating supported freely on rafters , this also mandatory req. for frangible roof ) , the wind suction pressure will be resisted by roof plates weight, shell wt, and (if applicable ) anchors. Not by rafters and supporting columns.

What is duopith roof ?

 

[HTURKAK]

This snap from EC 1-4, Figure 7.12 - Recommended values of external pressure coefficients cpe,10 for domes with circular
base.

For your case, d=7.0 m , h= 11.5 m and f =3.5*TAN 6= 0.37 m. and h/d=1.64 , f/d=0.05

Cpe values for zone A = -1.4 , B=-0.5 and C =- 0.5

The roof having 6 degr slope, which is essentially flat. And... the full roof is subject to suction.

If you average the values proportional with the related areas, Cp value will be around -0.8

We= 0.8* 3.70 = 2.96 kN/m2 (suction pressure for the full roof area )

and API 650 proposes We= 1.44 kPa *(V/190)**2 = 3.12 kN /m2

Again asking, If this is an API 650 tank , When you look to the ( Figure F-1—Appendix F Decision Tree ) where is your position ?

 

[HTURKAK]

If the answer to "does internal pressure exceed 18kpa ?" is no, you may apply the App. F or alternatively API 620.

I will suggest you, attach the roof plates to the supporting rafters and forget the frangible roof , otherwise the roof plate thk . will be an issue.

The roof structure could be supported cone roof without interior column.

 

[HTURKAK]

Lejkhraj (Petroleum), you have deleted most of your posts..

I just want to remind one of the forum rules ;

One can see your original post just by clicking on [Post Deleted] .
... and I will not delete my posts ..