Wind Load on Building "Wing" Wall

[WillisV]

I have a condition where a large wall cantilevers horizontally about 15 feet beyond the envelope of a building along the full height of the building.

It does not seem like the solid wall/sign provisions really apply due to the orientation and the fact that this is not a freestanding structure independant of the large building next to it.

It is not really a regular C&C element in that the internal pressure coefficients do not really apply and the wall will have combined windward and leeward forces.

It appears like the most rational method would be to take both positive and negative C&C wall pressures and add them together which is similiar to what is done in the new ASCE 7-02 parapet provisions (6.5.12.4.4).

Any thoughts?

 

[WillisV]

Oops..I meant ASCE 7-05 parapet provisions...ASCE 7-02 method was revised.

 

[scottiesei]

Just because the wall is connected to the building does not mean that it does not need to be designed independently of the structure (is that a run on sentence or what?!?). Is the wall going to be designed to transfer the load to the building? Is the building going to be designed to take care of this extra load? Probably not and it would probably be impractical. Typically I design screen and privacy walls as cantilevered walls using the wind load from ASCE 7-02 for solid free standing walls. Be sure to watch the load combos when considering over turning!

 

[JAE]

For your overall main wind force resisting analysis, the wing wall adds lateral thrust to the system and I would agree that using windward/leeward primary wind loads added together would be appropriate. (assuming that the wall is attached and supported by the main building).

For the wall itself, I would check the greater of the
1. MWFRS windward + leeward pressure, or
2. the Component and cladding pressure from ASCE which you refer to.

Not sure which would control but I would say that both need to be checked.

 

[WillisV]

Yes the wall is going to transfer the load to the building - as I said in my original post it is a horizontal cantilever off of the main building.

For the MWFRS, which is already designed, I just extended the envelope of the building used to calculate the forces out to the edge of the walls (essentially adding MWFRS windward plus leeward as JAE noted in point 1).

My question was really concerning the local design of the tubes which are cantilevered out from the building - looks like I'll just add the + - C&C together.

 

[scottiesei]

Ooops, I did not realize that the wall was a cantilever. I think I was thrown off by the "full height of the building" comment. I assumed that it had a footing. With that being said, I would agree with your approach. Maybe also consider the projection as a "sign" type structure and see how that compares with the combined CC calcs. Good luck and sorry for the misunderstanding.

 

[BSE05]

I was involved recently with a 45' high free standing (vertical cantilever) precast fire wall that extended out beyond the building) It was designed for IBC-2003 wind load, however to make it work, a concrete column (up about half the full height of the wall) was added to the outer edge.

 

[csd72]

Be careful of the deflection differential between the wall and the building.

I designed some 12m (about 40foot) tall signs adjacent a shopping mall. These cantilevered from the ground and therefore had quite high deflections at the top. Where these butted in the building these had to be either isolated or fixed in to prevent differential deflection.

In one case we cantilevered a beam horizontally to support the signs. beware of the high reaction.

When the wind blows at 45 degrees to the wall you can get high local pressures at the end of the cantilever as well as overall pressures 15% higher than the overall external pressure on a building. This is reflected in the Australian code, but I have no idea where to find it in the US codes.