Distribution of cladding moments

[ericjacques]

Hello everyone,
I am designing a two way flat plate slab using the direct design method. The perimeter of my structure has a cladding line load. I would like to consider the effects of these moments in my column and middle strips of my exterior panel although I cannot seem to find any guidance on this.

I am thinking about distributing the moment caused by cladding to the CS/MS according to their widths and adding top bars to the slab accordingly (with a few extra for safety).

Any advice on how to proceed would be greatly appreciated.

 

[Lion06]

I don't believe the ACI direct design method is set up for line loads. There are several specific criteria that must be met to use this method. Try looking at the equivalent frame method.

 

[asixth]

My understanding is that the direct design method derives moment co-efficients based on the results obtainable from an elastic analysis. If this is the case, then I do not see any problem with calculating the moments in your slab based on your udl loads and superimposing the moments in your slab that are caused by your cladding loads (assumming this is some kind of masonry vaneer).

If these loads are located around the perimeter of your slab, then the only way the line loads can get to the supports is by the edge column strip or edge beam if they are existant.

As for transverse moment in the perpendicular direction, depending on the eccentricity of the cladding load with the column centreline, additional "out-of-position" moment will be transferred into your column and possibly, additional negative moment in your slab over the supports if your slab cantilevers past the exterior columns.

Best bet is you ditch the direct design approach and analyse this problem by the equivalent frame method, modelling the cladding loads as line loads in the parallel edge strips and points loads in the perpendicular frame runs. You can use the direct desgin method and general structural analysis formulae to backcheck your results.

 

[ericjacques]

Excellent advice. I figured that the DDM would not be applicable in this case and am not comfortable enough with the results to superimpose the effects of cladding on the moments obtained by the DDM. Equivalent frame method is the way to go. Thank you again!
-EJ

 

[csd72]

What would happen if the cladding were partially removed in future.

In this situation if the moment from the floor loads is more than the column then I would conservatively ignore the cladding loads in analysis and then just add additional reinforcement to take care of the cladding loads.