Collar Joint Question

[maxwolf]

I'm working on a parapet that's 48" high. It's 3 wythes thick with the inner two wythes acting compositely. The outer wythe is a veneer separated by a cavity.

ACI 530-02 and UBC say a 2" min collar joint for 5' height for the 2 grouted wythes. I don't think we can go much less than that. Also, the #4's @ 32 o.c. need at least 1-1/2 practically. The architect wants 3/4" so he can put in headers. With a 2" collar the headers don't span. And says he can cut out around the vert. #4's to provide grout space around them.

Thanks for any suggestions.

 

[bjb]

how thick are your wythe's? does a 48" tall parapet really need composite behavior? Can one wythe be thick enough to get some rebar in it without using composite action?

 

[concretemasonry]

A 4" thick brick wythe cannot be effectively reinforced, considering the small "d" dimension.

A 6" block could easily be reinforced and still provide the cavity with a thinner wall section than the doule brick plus cavity, plus veneer.

Dick

 

[maxwolf]

The bricks are 3-5/8" wide. So the two inner wythes with a two inch collar joint between them net out 9-1/4."

I suggested cmu before as you mentioned, Dick, but the archtiect said no. He wants a parapet of only clay brick.

Thanks very much for the comments.