Suporting the Top Bar Mat in a Deep Concrete Slab 3

[YSINC]

Slab dimensions: 144' (trans.) x 72' (long.)x 8' (deep)
Top Bar Mat: 3 layers: #11 (trans) @ 8" oc
#10 (trans) @8" oc
#9 (long) @8" oc

The top mat of bar will deform out of tolerance, therefore it must be supported. In order to support the mat plus 100psf LL during construction some type of internal or external bracing must be designed. Tie wire, Dobie's and standard bar chairs are out of the question since the slab is so deep. I have a priliminary plan to use warren trusses with verticals made out of double angle (top and bottom), #11 bars (vert.) and #7 bars (diag.)(member size will change pending further analysis). Does anyone have a solution that would be more efficient than using the trusses to support the top mat?
Thank you,
John

 

[Focht3]

That brings back fond memories of walking mats the night before the pour!

I've always seen the supports composed of bent rebar, tied to the 'actual' reinforcement. Lots of ties! Particularly with double steel layers. Most of these mats were 6 to 14 feet thick -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[YSINC]

Thank you,
I proposed a similar idea. Since, we have #5 hairpins 24" OC EW. I thought that we could use those to absorb the vertical load or increase the size of the hair pins. However, our steel sub. does not think that is a stable approach. I will look into that option and if it is $$$ efficient I am sure it will be more enticing.
John

 

[Taro]

On the only 8-foot thick mat I have designed, we used #8 or #9 vertical bars spaced at several feet to support the top mats. The vertical bars are also good in case the mat cannot be completed in a single pour, which can easily happen for such a large mat.