Curved Masonry Wall?

[SteelPE]

I am beginning the design process of a good size church. The back side of the sanctuary requires a curved fire wall (between the sanctuary and the lobby/offices). Since the fire wall is suppose to remain in place in case one of the buildings collapses during a fire it is planned on being a double masonry wall. Since we have a large masonry wall, there is a desire from the architect to make it a load bearing element (don’t know how this effects the fire rating). There is also a desire to make the wall part of the LFRS. The radius of the wall is approx 136’. Are there any references as to how to drive lateral forces through a curved segment of wall like I would have here (Code would be IBC 2003)?

 

[csd72]

I would treat it as an equivalent area of straight wall, say 2/3rds, similar to how a circular pipe is treated for shear.

 

[SteveGregory]

Since the radius is large, could you consider the wall as a collection of straight segments tied together?

 

[ishvaaag]

You can model it in finite element model as wall elements or plates. E is usually taken 500 times f'm (the crushing compression capacity of a segment of non-slender wall), and modulus of Poisson 0.15 or 0.2; some like use modulus of Poisson 0.

http://www.ndt.net/article/SimNDT2010/papers/15_Fuente.pdf

 

[SteelPE]

csd/Steve,

Designing the wall as a bunch of straight line elements was my fall back plan. It just gets a little confusing because the wall is 180' long on the 136' radius so some of the wall is out of line with my planned axis of the building.

ishvaag,

While I believe FEM would be good for this instance. I have only played with FEM, I do not feel comfortable enough in interpreting the results and applying these results to properly design my building.

 

[a2mfk]

I agree with Steve Gregory, I would do shear analysis as if it was a collection of straight elements. From a pure CMU shear analysis standpoint, a 16" block will not know if its part of a really long curved wall... But seems you may have some out-of-plane component you may have to analyze and detail.

 

[msquared48]

I agree with csd72 here. I use the same methodology for SW that are inclined to the force. Just take the length component of the wall that is parallel to the force in the solution process.

For a curved surface though, I would neglect any wall length contribution in the direction of analysis that is outside a 45 degree (90 degree total) arc to either side of the direction of application of the force. 2/3 seems reasonable.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[a2mfk]

How much shear is this wall taking? Does it have a lot of openings?

Also I assume this is a flexible diaphragm...

At 180 ft long I cannot imagine a plan of a church where the actual shear stress in the CMU would ever be a problem. In long walls with few openings shear stress in my experience (5 stories or less) is usually an afterthought.

I guess another question would be is do you have other lateral systems that can resist the shear forces from your diaphgram that do not align with the axis of your wall... If not then it seems like you are in the home stretch.

Though, the little I know about fire walls, etc. this is going to be your biggest headache...