Wind Loading of Silos

[CRQUT]

Hi all,

I have a question regarding AS1170.2 Appendix E.

We have been asked to provide an incremental base wind pressure for a rectangular steel silo supported on a steel frame. The overall height is 25m and in plan 11 x 4 m.

Can I utilise the aspect ratio correction factor (Kar) in T.E1 to reduce my base pressure? In this case possibly by upto 30%.

Undergrad@work.

 

[handex]

Someone please correct me if im wrong, but I was under the impression that Appendix E of AS1170.2 only applies to individual members in frames etc whos aspect ratio is greater than 8, which in this case will not apply to the silo. You can obviously utilise it for the steel frame members though.

 

[handex]

and before someone else posts it, I will add that as an undergrad you should be going through the problem with an experienced engineer

 

[sdz]

I agree with handex. I would use
Section 5.4 EXTERNAL PRESSURES FOR ENCLOSED RECTANGULAR BUILDINGS.

This should give pressure coeff someting like +0.8 on the windward face and -0.5 on th eleeward face.

 

[CRQUT]

Handex

Thanks for your input and you are right, it is used for individual exposed steel members whose aspect ratio is greater than 8 and I should be going through it with an experienced engineer.

It was an experienced engineer who adopted this method of analysis using the code and I have been asked to work out the base pressures. I have discussed it with other engineers here and have also been told to consider it as an enclosed rectangular building. I believe a silo undergoes vastly different loading to an enclosed building and therefore that part of the code might not be as applicable as it first seems. The structure is also in a cyclonic region.

Using Appendix E gives me results that are nearly twice as large as using the section for enclosed rectangular buildings. If I utilise the Kar factor I am somewhere in between.

I guess i wanted to get an idea of how best to apply the code to a situation that isnt explicitly covered within it and see if I can get a few opinions of experienced engineers along the way.

 

[hokie66]

A silo of a different shape than rectangular would see different loading, but a rectangular silo is just an enclosed building. Not sure why you think otherwise. Use Section 5.4 as sdz and some of your experienced engineers suggest. The fellow who is using Appendix E is off base.

 

[SAIL3]

As suggested, I would also use a drag coeff. or form factor of
+0.8 windward and -0.5 leeward for the silo.
However, I believe there is a difference between an enclosed bldg.
and this silo supported on an open frame structure.
On an enclosed bldg one would evaluate the leeward press. using
an exposure coeff. Kh evauluated at the eve height.
Where on this setup with the silo, one would use Kz evaluated
at different heights both for the windward and leeward.
The reason for this, on the silo setup, is that wind press. can escape thru the open support stl at the base of the silo and
influence the press. on the leeward side.

 

[CRQUT]

Thanks everyone for your responses.