CMU Wall inside Preengineered MB - Brace or Cantilever 1

[markmartinfan]

Interior non bearing walls inside pre engineered metal buildings.

Realitvely tall - 20 feet.

Is it better to design as free standing cantilever for seismic loads or

brace the top of wall with slotted connections for vertical loads and design for all in plane and out of plane loads?

Thank you.

 

[ChipB]

Brace the wall. But...you have to let the MB mfr know your seismic loads and deflection criteria (L/600).

 

[markmartinfan]

I have been stuggling to justify the L(H)/600 vs .007H.

I have searched the codes - am I missing this?

No one here to talk with.

Thank you.

 

[shobroco]

Sorry, I don't know L/600 either. I use L/360 for no cracking in rigid materials (concrete, masonry, plaster)& this is typical in Canadian codes. The standard MB deflections could be much larger though, typically L/180 vert & hor unless you ask for less.

 

[ChipB]

That .007H is including your deflection amplification factor. If you've reduced your seismic load by R, you need to increase the calculated deflection by multiplying it by your deflection amplification factor, and compare it to .007H.

L/600 is what I've always used for deflection of masonry. I use it b/c I was told to a long time ago, to avoid cracking, and have heard it multiple times from multiple people since.

Guess I should investigate further as well. :-(

 

[markmartinfan]

Thank you all for the help

I have been told L/600 in a previous employment as a rule of thumb - but the MBM do not want to cooperate and can usually convince the architects to lessen the requirement.

Again Thank you.

 

[JAE]

I doubt you will get a MB mfr. to limit the overall building drift to L/600.

Keep in mind that the L/600 is codified for vertical deflections (ACI 530). For out-of-plane deflections I agree that L/600 is a good idea for exterior walls. For interior walls that don't have to remain water resistant, perhaps a lessor out-of-plane deflection can occur with adequate servicability.

L/360 perhaps?

 

[msquared48]

Very true as JAE says, since most metal buildings are laterally designed to somewhere between L/180 and L/240. In hooking the wall to the building, depending on the orientation of the wall and your bracing, it could start functioning as a shearwall. Be careful with the connection.

The design of the metal building manufacturer must coincide with your design. Coordination is essential here.

Mike McCann
MMC Engineering

 

[markmartinfan]

I have walls both parallel and perpendicular to the roof purlins, thus I am trying to allow vertical deflection and designing as a shear wall for the inplane loads.

I had detailed a totally free system with fluorogold bearings (a tip I found at this site) but it just seemed to be too complicated.

Thank you

 

[SteveGregory]

L/600 is for vertical deflection or out-of-plane simple span bending. H/360 is for story drift or a cantilever condition in masonry walls.