Concrete Deep Beam to Shallow Beam Connection

[Jay618]

Hi everyone,

I have a situation where I have to frame a 48” deep beam to a 24” deep beam. I’m not sure what to do with the 48” beam’s bottom bars. Since there is only negative moment at the interface, should I just develop the top bars of the 48” beam into the 24” beam? For the bottom bars of the 48” beam, do I also need to develop them to the 24” beam or they can just have a standard hook end?

Thanks in advance.

Jay

 

[KootK]

1) Weird... with the potential to be dangerous if not handled carefully.

2) I'd be calling your 48" beam pinned at this end and take whatever negative moment you might get as bonus.

3) If possible, I'd like to see the 48" run clear through the 24" with a gaggle of stirrups at the end of the 48" dragging the beam reaction up to the top of the 24". This arrangement might make for ugly formwork though.

4) My second choice would be detailing the 48" like a precast dapped end connection with hanger bars in the 24" to drag the reaction up to the top.

5) In days gone by you'd probably see this handled by sloping the bottom bars up into the 24" beam and anchoring them as best you can. This might still have legs but I'd want to find some way to quantify capacity (not sure how off of the top of my head).

 

[KootK]

Share your beam widths, bottom bar sizes and quantities, and your supported reaction. We'll have some fun with this.

 

[Lomarandil]

My first take would be to either bend the bottom bars up to midheight at the ends, or provide some midheight bars in the beam that are adequate for -M and whatever +M develops before your 48" beam bottom bars develop.

(With a little attention to shear detailing as KootK alluded to).

----
just call me Lo.

 

[r13]

I assume you have considered the torsion produced by the 48" beam on 24" beam, then treat the 48" beam as beam with notched bearing, and pay attention to details for shears near the interface. You need to develop top bars from the 48" beam into 24" beam to maintain the connectivity, you also need a middle layer bars extend from the former into the later, and develop these bars as well. I'll either bend the bottom bars of the 48" beam at the interface, or provide U bars to assist in preventing diagonal shear to occur near the interface.