Second Floor Concrete Slab Analysis
Second Floor Concrete Slab Analysis
(OP)
Attached is the first floor plan for an existing two story building. The second floor is 5.5" thick reinforced concrete. The building is around 40 years old. No drawings exist so we had the reinforcing located in the slab, then certain areas chipped out to reveal the rebar. The rebar is #3 @ 10" east to west and #5 @ 12" north to south. I've been trying to rationalize why someone would design a slab with #3 bars running parallel to the short span and #5 parallel to the long span, but since given up on that. Trying to come up with a justifiable live load capacity is stumping me. I've considered a one way slab in the short span direction and yield line theory, but neither one is giving me anything that I feel confident in. I'm now going back through some old references I have from Westergaard and Park/Gamble.
Does anyone have any suggestions regarding how they would approach this?
Does anyone have any suggestions regarding how they would approach this?






RE: Second Floor Concrete Slab Analysis
RE: Second Floor Concrete Slab Analysis
RE: Second Floor Concrete Slab Analysis
Could the #5's be in periodic beam strips within the slab to which the #3's span?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Second Floor Concrete Slab Analysis
I've thought of using FEM to evaluate the slab, but I'm trying to make some sense of the original design first so that I can check the computer output. Someone had to design the slab using hand calcs, so I'm trying to figure out the assumptions used. At least I hope someone designed the slab, although it's not looking that way.
Very good questions. Please keep them coming.
RE: Second Floor Concrete Slab Analysis
BA
RE: Second Floor Concrete Slab Analysis
When I did a quick check of slab with the #5 bars running the other direction it easily worked for residential loading...but for that pesky minimum slab thickness requirement.
If I had to guess how it came to be oriented the other direction I can all too easily envision a scenario wherein the field personnel took it upon themselves to "correct" the engineer's "obvious mistake" of calling for the large bars to run the short direction and the small bars to run the long direction. That's considering the slab as a whole, of course, not how it actually spans. I would give the field personnel more benefit of the doubt if I didn't have to experience that type of thing on a regular basis...
RE: Second Floor Concrete Slab Analysis
BA
RE: Second Floor Concrete Slab Analysis
RE: Second Floor Concrete Slab Analysis
RE: Second Floor Concrete Slab Analysis
Could that fit into what you have there?
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Second Floor Concrete Slab Analysis
concretemasonry-
That seems to fit what I have here.
RE: Second Floor Concrete Slab Analysis
gjc