Steel Floor Framing over Concrete Columns and Walls

[8thStreet]

Hi All,

I recently engineered two schematic for a two story over podium project. The owner wanted two designs for the podium: 1) concrete PT with conc columns and shear walls and 2) all steel with pan deck with steel columns and bracing.

Now they want us to look at hybrid version - Concrete columns and walls supporting Steel Framing and pan deck.

I haven't done that type of system, dont like it, and already told the owners that it will be more complicated due to more trades and coordination, but they still want to persue.

I am looking for some pros and cons of the steel framing over concrete columns and shear walls.

 

[phamENG]

Is this a single story podium for parking?

If so, concrete columns/walls will be more robust and, if hit by a car at low speed, is less likely to be seriously damaged (though you could pick a steel section that would win that fight, too). So I could see some logic there - nice, fat, resilient concrete columns are cast, and when they reach sufficient strength, you have a floor system that requires zero temporary form work and zero shoring.

 

[8thStreet]

Yes. This is for a single story podium with parking below.

One of main concerns is the connection at the top of the column and how to drag the shear load into the shear walls.

No shoring is definitely good.

 

[jayrod12]

Cast a weld plate into the top of the walls and weld the deck directly to the wall.

If the deck alone isn't adequate, put reinforcing in the wall that goes up into the slab.

If there's not enough wall and you need the beam to act like a collector, then design the beam connection to the wall for the tension/compression force of the collector.

This type of thing is super common where I'm from.

 

[phamENG]

I've done the cast in plate as jayrod12 suggests, but some contractors in my area seem to prefer angles bolted the wall. If the shear loads are light enough, you can get away with post installed. Otherwise you have to cast them in. Either way, it avoids a bunch of field welding, much of it is likely overhead. In this kind system, the diaphragm is actually the deck - the concrete just stiffens it and prevents buckling, etc.

Alternatively, design the deck as sacrificial form work. Concrete slab does everything, and you can transfer shear from the slab to the top of wall just as you would if the deck wasn't there.

 

[KootK]

1) Another connection option below. It kinda depends on whether or not your wall continues above and in what form.

2) I don't love the use of steel deck form slabs as transfer slabs regardless of the column type. That said, my concerns are related to engineering and would likely be of little concern to most clients as long as they can get a stamp on whatever system they wind up with.

3) With respect to the pricing exercise, obviously ensure that the client is cognizant of the costs associated with fireproofing and, quite possibly, reduced durability.

4) I can't supply supporting evidence but have heard some folks complain that there is rather a lot of noise transfer from steel framing over parking levels into the occupied spaces above.

 

[phamENG]

If noise is a concern, you can always take a look at AISC's Design Guide 30, Sound Isolation and Noise Control in Steel Buildings.

 

[r13]

All system works, but the cost and length/speed of the construction. My personal opinion will preclude the all steel solution, long term performance out weigh its advantages.

 

[8thStreet]

Thanks for the great suggestions and insight.