T-BEAM - support moment - best reinforcement arrangement?

[BauTomTom]

Hi

there are different possibilities to position and arrange the reinforcement by a continues beam over a support. this is the case where you get the support moments into the beam with the tension forces in the slab.

I just wanted to find out the best solution for a case where the bars are actually quite heavy.

I prepared a sketch with four different solutions, would appreciate your comments or recommendations for it

BauTomTom

 

[rowingengineer]

I would lap some of the bottom bars over the column, makes for a more solid structure. As for best detail, A-A1 looks good for me, you need enough in the ligs to ensure you ligs are working for shear, but some outside the beam to allow for placing. Really all those details could be the best solution on any gven day. I don't really like A-A2, but that is just me.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”

 

[hokie66]

Generally, I would use the A-I placing.

 

[ishvaaag]

Any of the details, all within and some outside rebars, must ensure adequate reinforcement in shear, not only in the vertical plane but also for the horizontal shear lag when some rebars are outside the stirrup.

So if you place some rebars outside the stirrup, you need to check if the concrete alone has enough capacity to transfer the force to such rebars. In short, is it acceptable the shear in vertical cut sections parallel to the lateral faces of the beam when the section leaves such thick bars outside the stirrups and studied cut section? If not, a shear-friction scheme is usually employed to determine the amount of transverse rebar required to meet such shear at such sections.

The determined capacity must be then anchored beyond the last bar where it is deemed necessary, and is usually considered additional to any other transverse rebar present that has its own whole capacity in use to meet another solicitation, such transversal bending.

 

[keenaseng]

I believe it is good detailing in concrete T-beams to put the reinforcement in the top of the flange region in negative moment zones. This maximises internal leverarm, ensures access for good compaction of concrete in the web and provides good crack control in slab surface.
But like ishvaaag has suggested - If too much of the reinforcement is placed in the flange and outside the web stirrups, then you would need to rely on shear flow only to ensure the force gets into the reinforcement steel.
A-A1 or A-A3 for me.

 

[slickdeals]

ACI 318-05 Section 10.6.6 requires that when flanges of T-beams are in tension, part of the flexural tension reinforcing shall be distributed over the effective flange width or width equal to span/10, whichever is smaller. There is some information in the commentary R10.6.6

 

[Teguci]

A1 (sort of like PT banding) and A3 are valid for typical situations. A2 would be a good solution for crack control in exposed environments. I would only use A4 for a plastic hinge situation (high seismic) in which case your reinforcement would all be continuous.

 

[BauTomTom]

--- to rowingenieur ---
I agree A1 is also my favorite. For example 20mm diameter. Would you placed them like every 100mm gap between? My DIN code actually allows to use at the top the half width of the efficient width of the T beam. So for example when you see the T beam with a efficient 2m TOP member then you could distribute the bars in a 1m width.

---to ishvaaag ---
Of course the shear bars can be only considered inside the stirrup.

--- to keenaseng ---
Agree 100%

--- to slickdeals ---
You see the ACI says the whole effective flange width. The DIN says only the half


--- to all ---
So I see you definitely don’t recommend two layers on top. Rather split the bars to the flinch. Of course the shear forces in the beam must be checked.
In which distance would you split the top bars?




BauTomTom

 

[BauTomTom]

sorry I mean flunch not flinch

one other engineer is keep on telling me rather to put on top of the beam two layers of the 20mm bars, but I think it is really better to move them into the flunch.

It seams people are scarred to to untypical things which differ to the usuall and traditional way althought they are often more efficient

BauTomTom

 

[hokie66]

Flunch? That's a new one on me. Maybe you mean flange.

 

[BauTomTom]

oouu ja sorry flange, oohh my english :-(

BauTomTom