connection between steel column and concrete slab and beam system? 1

[juandavidguzman]

Hello to all,
This is the analysis of the connection between metal columns (2x U channel filled with concrete) with concrete slab and inverted beams in a one-storey house.

The problem is that I have little space to carry out any gadgets in the slab interspace, as you can see in the attached screenshot.

I think the problem is a load transfer problem because the resistance calculations give me good results.

On the other hand, is it OK to worry about this? on the one hand I want to weld irons to the inside of the column so that they can be attached to the top reinforcement of the beam. But as it is a two-way slab system supported on inverted beams and these on columns, should I worry about the load transmission or is this taken care of by the beam itself?

 

[hetgen]

Consider providing a column end-plate with sufficient stiffness to transfer axial load. The endplate could be fixed to the soffit of the slab.

 

[KootK]

I vote for the column end plate as well. It's conventional, easy to construct, and provides a better mechanism for shear transfer from the beam into the column. Studs or deformed bar anchors on top of the cap plate.

 

[juandavidguzman]

I vote for the column end plate as well. It's conventional, easy to construct, and provides a better mechanism for shear transfer from the beam into the column. Studs or deformed bar anchors on top of the cap plate.

Yes, I would have gone for that solution too, but due to architectural requirements the plate should not be visible as the slab is visible.

 

[KootK]

Yes, I would have gone for that solution too, but due to architectural requirements the plate should not be visible as the slab is visible.

So go with a cap plate that does not overhang the steel column.

 

[juandavidguzman]

@KootK Could you tell me if I am reasoning correctly?

If the plate serves to transfer the axial forces that reach the column, in the case that the column is filled with concrete, would the plate be necessary? is it not transmitted through the monolithism of the concrete?

 

[KootK]

If the plate serves to transfer the axial forces that reach the column, in the case that the column is filled with concrete, would the plate be necessary? is it not transmitted through the monolithism of the concrete?

Yes, if the column will be concrete filled, I do believe that you can transfer the axial load through that concrete. For simplicity, I'd still be inclined to assume that the steel alone is providing buckling stability to the combined assembly. You may also need to take care that the concrete / grout within the column is properly consolidated etc.

Your original scheme with the dowels and no concrete fill could work too. You'd just have to consider some extra things in your stirrup detailing near the columns.

 

[le99]

I would consider bringing the column to the slab top bar level without the dowels, which will not be developed properly in the column due to the inadequate concrete cover that is required to develop the strength.

 

[juandavidguzman]

@le99 so let me get this straight, you would do this?

 

[KootK]

The original plan was for the rebar dowels to be welded to the channels, correct?

 

[juandavidguzman]

The original plan was for the rebar dowels to be welded to the channels, correct?

Yes, and after this im thinking about doing this:

The column is still filled with concrete to achieve a watertight seal and thus make the column more durable.

 

[KootK]

Nice. I wouldn't bother with the 180 hooks -- or any hooks -- on the dowels:

1) They add no real structural benefit.

2) They create unnecessary congestion.

3) They will prevent the bars from being gun welded to the plate.

I feel that it is important to keep the top of the column below the beam bottom bars as you have done. My reasoning:

4) Running the column up higher compromises the shear capacity at both interior supports and end supports without special detailing.

5) Running the column up higher compromises the anchorage of bottom steel at end supports without special detailing.

6) Running the column up higher compromises the integrity steel at interior and end supports without special detailing.

That said, folks in my area do this all the time for grade beam and helical pile setups. There have been no problems that I'm aware of.

 

[le99]

Yes, it is exactly what I meant, watch out for punching shear though.