Column to Footing Reinforcement 1

[Althalus]

I was just reading through some old standards from another company. It says that where the vertical reinforcement from the column meets the footing, the 90° bend shall be "near the bottom of the foundation with the free end of the bars oriented towards the center of the column"

Why would they not be oriented towards the outside of the footing?

 

[dik]

If you take a look at the moment diagram or compression diagram for the column, by bending the bars towards the column, you are putting the hooks into the compression zone and ending up with greater bond.

Dik

 

[asixth]

I remember reading somewhere that reinforcement with the cog radii facing inwards to the joints achieves better moment development than when the radii is facing outwards.

 

[Althalus]

Interesting. So, does this hold true for simple pedestals as well?

In addition to the ACI definitional difference, I'm also considering the conceptual difference between a high moment column vs a low moment pedestal.

 

[dik]

Yup... and retaining and foundation walls, too...

Dik

 

[JoshPlumSE]

If you're talking about seismic, then you get better "confinement" of the concrete at the joint when you turn the bars inwards.

 

[Hokie93]

The recommendation you cite is good advice if the detail in question is designed to transfer significant moment. This issue was discussed in some detail in the "Detailing Corner" article in the November 2009 issue of Concrete International magazine. It is also discussed in Chapter 11 of "Design of Concrete Structures" by Nilson, Darwin, and Dolan (14th edition and 11th edition, for sure) and the ACI Detailing Manual (ACI 315).

 

[slickdeals]

You can also refer to Page 15 of the document in the link below.

http://www.conveyinc.com/things/crsidesigner.pdf

 

[slickdeals]

The exact wording you mentioned is in ACI 318-05 Section 21.10.2.2

 

[hokie66]

As the reference slickdeals provided says, the direction is important where moment is present. If no moment, the column starters can be placed either way. They stand up better with the cogs outward.

 

[Archie264]

[Warning: potential thread high-jack.}

Regarding some of the structural elements in the reference that slickdeals' posted, are those things constructable? Particularly the forest of rebar shown in the pictures on pages 3 and 11?

And if that's what's required is it time to return to encasing hot-rolled steel shapes in concrete as was often done many years ago? That would seem to be easier to build than what's shown.

Any thoughts or comments?

 

[Archie264]

Whoops, never mind. I see the author addressed that topic in the article. Next time I'll try to read the article before commenting.

 

[hokie66]

Archie,
Carefully planned, congested beam-column joints (Page 3) and core coupling beams (Page 11) are constructable, but they require care and a bit of sophistication. They also require well qualified inspection. Coupling beams not being constructed correctly is the primary reason for the impending demolition of the partly completed Harmon Tower in Las Vegas.

http://www.reviewjournal.com/business/judge-oks-demolition-half-built-citycenter-hotel-tower

Not sure that there is a case to be made for concrete encased structural steel construction.

 

[dik]

Hokie... if the concrete is in compression or the steel is in tension, then it's likely better to have the bars bent towards the compression zone. Just a personal quirk... I agree that it is sometimes easier to stabilise the bars with the legs out...

Dik

 

[Archie264]

Wow, demolishing a 48 story building prior to occupancy...very interesting.

 

[hokie66]

Actually, they had "only" built 26 stories before an engineer who knew what he was looking at saw the problem. Pity the design engineers weren't engaged to monitor the construction.

 

[Qrs]

What an interesting bulletin, slick. Seems as CRSI puts out a series of them. Anyone know how to access the others? I looked on the CRSI website and ended up at a broken link..

I found the second one on progressive collapse...what else it out there?