Main bar bundles in an RC beam 1

[nivoo_boss]

Hey everyone!

Perhaps you can give some advice. I have a heavily loaded RC beam with a 5,6 m span with a design moment of around 1000 kNm. I calculated I need to use 8 D25 B500B main bars in the bottom. I want to place them in the mid-section of the cross-section because I use Peikko's PC beam shoes in the ends and want to concentrate the bars around the bars the shoes have for anchorage.

Now, the problem is space - it's hard to fit these bars in the mid-section. What's your experience, is this kind of two-bar vertical bundling okay as you can see in the picture?

 

[Lomarandil]

Sure, this can be OK. The challenge of bundling bars like this will be development and lap lengths. Presuming that your bundled bars are needed primarily at midspan, and that you can potentially curtail one from each bundle before the supports, it should be very achievable with just a little extra attention.

(There's also a small constructibility hurdle to tie the top row middle bars into place -- but a few short pieces of 6mm or 8mm fixing bar will solve it).

 

[MotorCity]

It will be difficult to tie the two middle bundles so they stay vertical. If they roll over into a horizontal position during concrete placement, it could be difficult to get concrete consolidated around the bars. Detailer may need supplemental bars or chairs to hold them in position.

 

[BridgeSmith]

Any reason you can't move a couple of the bars out on each side, inside the wider tie?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[nivoo_boss]

Any reason you can't move a couple of the bars out on each side, inside the wider tie?

I'm a bit worried about this because of the Peikko beam shoes I mentioned - they have their welded bars concentrated in the middle and for development I want to place the beam's main bars close to these as well. Below is a screenshot from Peikko's manual:

 

[BridgeSmith]

I guess that makes sense, assuming the capacity of anchorage bars for the beam shoes exceeds the capacity of 4 of your main reinforcing bars.

In that case, if it doesn't compromise the capacity too much, you could do what we do in those situations - separate them into 2nd row, an inch or so above, supported by small 'cross ties' across the main stirrups.

We space them fairly wide for bigger bars; if I understand your bar designations correctly, your main steel is 25mm diameter bars. For that size, we'd space the supports up to 1000mm apart.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[nivoo_boss]

Thanks for the answers anyway. It seems this arrangement is generally fine, apart from some potential troubles when casting the beams. I'll look more into the anchorage problem, perhaps I can place some of the bars to the flanges of the beam.

 

[HTURKAK]

...And a pink star for this comment..

My points are,

- Try large dia reinf. Φ32, 40 mm .. if available instead of bundle,

- Choose middle bundles at horizontal position..

The following figure from Manual for Detailing Reinforced Concrete Structures to EC2 ( by JOSE CALAVERA)

Not to know is bad;
not to wish to know is worse.

NIGERIAN PROVERB

 

[BridgeSmith]

We always just do as shown in the diagram for "N=12" for individual bars, to avoid all the restrictions and checks associated with using bundled bars. I guess we're just lazy that way.

Rod Smith, P.E., The artist formerly known as HotRod10