Simple for DL but contionous for LL - negative moment 1

[mar2805]

Hello!
Can you please look at the picture attached.
I have and series of T beam over wich an RC slab will be poured.

When designing for an negative moment over the support, wich of the 3 geometry cases is valid for design:

1) TOP one, the whole structure is behaving as one body - T beam and decks act as one body. reinforcement will be placed in the top layer of the slab

2.) MIDDLE one, using only T section for determining flexural reinforcement wich will be placed in RC slab in top layer

3.) BOTTOM one, using only slab portion of the geometry for determinng flexural reinforcement wich will be placed in top layer of the slab

Basicly first two statements are the same since the neutral axis is always going to be under the flange BUT there is an difference in height of the section!

 

[mar2805]

adequate reinforcing crossing the interface between the T sections and the slab
I think that this is the most important aspect of this problem. If this isnt designed properly there cant be any continuity over the support. Beam and saba will act as 2 bodies and not as 1.

But one thing that has crossed my mind.
Please look at the picture attached.
Its an sketch of the support where two T beams rest and the RC slab poured above them.
What if I use RC bars in U form shape that spans into RC diaphragma wich will be cast later.
Basicly the bars are coming from the bottom of the beam, going a 90 degress up and then back into beams top part.
The top reinfrocement would be design as I have an beam over the middle support (covering negative moment and then anchorage at the proper distance form the support)
Could this alone, without RC slab, using only diaphragma, work as an continous beam?

Just an theoretical question.....

 

[mar2805]

So, the whole thing would look like this....

 

[mar2805]

...and lets say that the beams are rectangular couse I see detailing issues if using T beams for this last idea....

 

[BridgeSmith]

The details as you have shown them would provide a continuous beam, so long as the reinforcing in the top is developed properly. Only a small amount of reinforcing is required in the bottom, since it's in compression. The reinforcing in the flange of the T section will be less effective than in the slab, however.