New Floor at mid height - wall to floor connection

[PROFR]

I have an old buried concrete structure in which it is required to introduced a new floor at mid height as shown. I used steel beams and metal composite deck to create the new floor. This floor will be supported by the external wall which also supports earth pressure and an internal wall on the other side. I am planning on using steel dowels to tie the slab to the wall. My only concern here is the new slab might transfer some lateral loads to the internal wall which might not be designed for. On the other hand, a crack is expected to form between the wall the slab if the slab is not doweled. In general, is it a good idea NOT to dowel the slab to the internal wall?

 

[phamENG]

Two things come to mind for me here:

1) Slabs on composite deck tend to be pretty thin. Much of their strength comes from the composite action with the deck and any reinforcing is usually welded wire and is there more for temp/shrinkage than strength. So clearance and development of dowels could be a challenge. Failure to properly develop the bars could give you a nice tension crack several feet away from the wall.

2) You'll need edge support for your deck - maybe running steel angles along the walls? Bolt these to the walls and fasten your deck to them and don't worry about the dowels. You can calculate rotation of your framing at the support - using that angle, calculate the gap formed at the top surface of the slab. You'll probably find that it isn't much. Even with a 1/2" PEJ or similar along the wall in addition to the rotation, the baseboard will probably cover it.

Unless this is going to be a dance floor for synchronized dancers, the lateral load being transferred to the side walls probably won't be too dramatic.

 

[azcats]

How common are dowels from a concrete over metal deck (composite or not) slab into concrete walls? I don't know that I've ever come across that.

Is the wall against soil already loaded? Any reason to consider location of reinforcement in that wall and potential for negative moments?

 

[phamENG]

azcats - I think it depends on the design assumptions for the slab in flexure and as a diaphragm. If you assume the boundaries to be fixed, you need to develop that into the wall (and you also need a pretty thick slab). If your just looking at the metal deck as disposable form work then you'd have to use dowels to transfer shear from any diaphragm forces. If it's assumed that the boundary is pinned and the metal deck is considered permanent (paint spec or galv) and designed to act as the diaphragm (stiffened with concrete), then it's easier to just anchor a boundary support angle and transfer the shear that way.

 

[PROFR]

Azcats,
The soil already loaded. The concrete thickness is 5.0 in. The floor will be supporting a blower machine. The wall has steel on both sides.

 

[RPMG]

 

[KootK]

The wall has steel on both sides.

1) If the interior wall is reinforced and not containing liquids, I'd not worry about lateral load transfer to it via the new floor deck. The wall can handle a little minor cracking if need be and the floor can likely serve as mid-height bracing for the walls.

2) If the new floor will attach to solid walls on all sides, then it will likely be the perpendicular side walls that resist most of the future lateral loads via diaphragm force transfer. And that's probably good news for your interior wall. You'd just have to tend to the deck / side wall shear connections etc.

 

[PROFR]

KootK,
The new floor will indeed attach to solid wall on all sides. So, you do not see a problem having dowels between the 5.0 in deck slab and the walls on all four sides, correct? I personally like to do that as the machine might produce some floor vibrations. At the same time I would like not to have any major effect on the existing walls.

 

[KootK]

So, you do not see a problem having dowels between the 5.0 in deck slab and the walls on all four sides, correct?

I don't but my default choice would be the deck edge bearing angles that the other folks here have mentioned.

I personally like to do that as the machine might produce some floor vibrations.

My gut feel is that this would do fairly little to alleviate any vibration issues and is unnecessary on this basis alone.

At the same time I would like not to have any major effect on the existing walls.

Baring some unusual detailing, I feel that your beams will axially connect your interior and exterior walls regardless of what you do with the slab. So I'd simply assume axial connection between the walls and reconcile myself with that being acceptable. Or not.

 

[r13]

Unless the beam was designed as fixed end, it is better not to dowel the slab into the walls, as beam ends will need to under go minor rotation that would cause cracks in the slab. Rather, at the support ends, you should use filler material to form a gap, that can be sealed with sealant later. But do dowel the slab edges that run parallel to the beams to ensure the edge slab panels are adequately supported. For slab supporting vibratory machines, you need to check the frequencies to avoid resonance to occur, you can add mass (thicken the slab), or use damper, if it is a problem.

What is the nature of the existing structure? As ventilation usually a problem of underground facilities, if the environment is damp and humid, I would seriously consider, for the long run, whether steel deck is the correct material or not. I usually avoid steel deck in industrial slabs, as frequent change in loading conditions that may cause problems at bottom side of the slab, which almost impossible to detect shall anything gets wrong. Just a word of warning.