Concrete Reinforcing Detail at Depression and Mat Slab

[marinaman]

I have designed a mat slab for a machine. I would appreciate some input on two reinforcing details.

I have designed a mat slab for a machine foundation. I have two questions regarding detailing of the bars in the mat slab. I've attached two details.

Detail 1 - This mat slab is 58' long and 12' wide and 2' thick. Top transverse bars are there for temp and shrinkage. Bottom transverse bars are there for both temp and shrinkage and for bending. I want to terminate both the top transverse bars and bottom transverse bars in a positive manner (not just stop them at the edge of footing). They need to be terminated in some sort of hook to develope the bars. How is this best detailed? Bottom bars with 180 hooks and top with 90 degree hooks? Bottom bars with 180 hooks, top bars straight but lapped with 90 degree additional corner bars? Both top and bottom bars terminated in 90 degree hooks?

Detail 2 - The mat slab requires a 2 5/8" depression for machine parts. I have shown the top bars with a 45 degree bend to allow the depression, keeping 2" clear of the bottom corner of the depression. Is this the best way to detail this? Will the corner of the depression crack off? Is there a better way to detail the top reinforcing to accomodate the depression?

I know I need to extend the end of the mat slab to accomodate more reinforcing on the other end of the depression.

I've checked CRSI and ACI and cant find any recommendations on these two detailing questions.

Thank You guys!

 

[ToadJones]

I haven't read this PDF thoroughly but it might help...

 

[dik]

If not for flexure, then I would use straight bars ea way for the top reinforcing. If reasonably high moment in the bottom, I'd use alternate hooked bars for the 12' direction, hook one end of a single bar and alternate (ie, flip around). For the 58' length, the bars can be in two lengths with one bar hooked one end. and these alternated so each second bar has a hook at the exterior of the pad.

Dik

 

[marinaman]

ToadJones - My mat is 24" thick with #6 bars each way top and bottom. At the edge around the permeter of the slab, I'm wondering if I ought to simply require the top and bottom bars to terminate in a 90 degree bar at both ends. The hairpin on the perimeter doesn't make sense because a #6 bar will require a 46" lap on the top bars and a 36" lap on the bottom bars.

dik - If I only use a staight bar on top for temp and shrink, its not developed. The bar will be in tension, as when the concrete shrinks, a crack starts, thus putting the bar in tension. The way I read ACI, all bars would need to be developed, either by slicing to a hairpin or by terminating in a 90 degree hook.

I was thinking about ToadJones reference said and was wondering if a hairpin could be used with a lap with the top and bottom bars less than that needed for full flexural development?.....Since these bars are really just for Temp and Shrink. The bars running the long way need full lap lengths and full development, but the shorter transverse bars just need to be terminated in a positive manner. I dont think I feel good about using a straight bar with no positive end termination for the transverse bars.

 

[JAE]

Detail 2 - if there is significant tension in the top bent bars they will try to straighten out and spall off the concrete above.

 

[hokie66]

Detail 1, provide 90 degree hooks on all bars at the edges.

Detail 2, use all straight bars, with the bars under the depression lapped with the bars outside the depression. But if the top bars are truly only for T&S, just use a complete mat at the level below the depression. As JAE said, the 45 degree bends represent inacceptable detailing.