Location of Primary Wind Girder

[Anand23404]

Somebody please explain how to select the location of a primary wind girder.

regards

 

[bimr]

Wind girders are usually formed by welding an angle or a channel around the top edge of the shell. At the top of an open tank (or one with a floating roof), circumferential stiffening is needed to maintain the roundness of the tank when it is subject to wind load. This stiffening is particularly necessary when the tank is empty.

 

[IFRs]

One determines a transformed shell using API 650 or other guides, this gives you an equivalent shell of uniform thickness and a new height of each course. Then, you determine the maximum height of this transformed shell, again using API 650, etc. You would want the wind girder to be equi-distant from the top and bottom of the unstiffened transformed shell. You could also locate the girder so the distance above and below the girder is less than the maximum, there may be a range of locations that are suitable. Then, you find the distance on the actual shell by reversing the transformation process.

 

[bimr]

primary wind girder:

stiffening assembly ring located near the top of the shell course of open top floating roof tanks. Maintains roundness when the tank is subjected to wind loads.

secondary wind girder:

increased tank height, resulting in specific portions of unstiffened shell may require adding of a small annular ring at some lower elevation than the primary wind girder

 

[Anand23404]

API 650 provides loacation of Secondary wind girder not primary wind girders. It is calculated based on transposed height. That is documented.Primary wind girder can be located near the top shell course but do we have any range?

i want to alter the location of PWG because of change in fire hydrant position.
What may be the range of locating Primary Wind Girder in a tank. The Tank is Cone Roof Tank, not internal floating.

 

[IFRs]

I apologize for not answering the question you asked. In section 5.9, API 650 says the top windgirder "shall be located at or near the top of the top course". There is no more specific location. If located more than 2 feet down from the top, a top angle is required. It may be used as a walkways if 42" down from the top and 28" wide. However, for a cone roof tank, the fixed roof acts as a top wind girder and no top wind girder is needed.

 

[Anand23404]

okay.
So should i consider providing only secondary Wind Girder in Cone roof tanks?
And what about Internal Floating Roof Vertical Tanks (IFRVT)?

 

[IFRs]

API 650 says that "An open-top tank shall be provided with stiffening rings to maintain roundness when the tank is subjected to wind loads"

Cone roof tanks are not open-top and do not need a top wind girder.

You need to consider intermediate wind girders for all tanks.

By definition, internal floating roof tanks have a fixed roof. If the fixed roof is a cone roof, no top wind girder is needed (see above). If the fixed roof does not add stiffness to the top of the tank ( ie an aluminum dome roof, see G.1.3.1 ) then treat the tank as an open-top tank and evaluate for a top wind girder.

 

[Syahar1975]

Usually top wind girder also could be used as a walkway. In my past experience is about 1 M from the top angle.

For fixed roof tank (Cone or Dome) the shell stiffener requirement is determined by the wind speed and tank diameter.

 

[bimr]

The secondary wind girder may be necessary depending on the height of the tank and thickness of the steel.

 

[Syahar1975]

Yes BIMR,

These are 2 factors that need to be considered as well for shell stiffener.

 

[Anand23404]

thank you everybody

 

[bimr]

Couple more pictures of a tank that I observed today that show the primary and secondary wind girders.