Yield-Line Software for RC slabs

[MacGruber22]

Recently read this Structure magazine article: [URL unfurl="true"]http://www.structuremag.org/?p=9007[/url]

Any thoughts about this type of analysis software? It seems like [in the near future] it could be much cheaper and practical for complicated RC slab design than trying to perform plastic analysis with ANSYS and the like.



"It is imperative Cunth doesn't get his hands on those codes."

 

[KootK]

My main issue with plastic limit design methods, and any software automating them, is that they have little to say about deflection. Modern concrete slab design seems to be mostly the story of deflection rather than strength. I pretty much only use the plastic limit methods when I'm desperate to prove that some existing structure isn't a safety hazard. I have a hard time visualizing a scenario where I'd want to use yield line etc for the production design of a suspended slab.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Trenno]

I tend to agree with KootK. I rarely find strength governing slab design, but usually LT deflections and vibrations (to a lesser extent) governing.

However in saying that... it could be useful for getting the column mushroom reo down.

 

[Trenno]

Anyone else have an opinion?

 

[MacGruber22]

Makes sense, for sure. To be practical, it seems the software would have to be able to provide FEM elastic analysis as well.

"It is imperative Cunth doesn't get his hands on those codes."

 

[KootK]

As the article mentions, limit methods would likely result in substantially less top steel at columns. I wonder what effect that would have on punching shear where some parity between shear and flexural reinforcement is assumed.

If software could do all of the following, I'd be on board:

1) use limit analysis to establish reinforcing demand.
2) allow the user to lay out a rationalized reinforcing scheme.
3) perform some kind of valid deflection check on the rebar as set out.

Another issue that I'm not clear on is how one would efficiently determine bar cut offs coming out of a two way slab limit analysis where the yield lines are somewhat randomly oriented. The problem studied in the article conveniently used a uniform mat top and bottom. That wouldn't be so well received off campus.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dcarr82775]

Very useful if looking at collapse prevention where say in a 2 way slab big ugly cracks everywhere can be tolerated. I would think yield line would yield unacceptable crack widths and other serviceability/lifespan issues.

Whenever I see a slab without enough steel over a column, it just has big ugly cracks that nobody will accept. It hasn't been the reason for a collapse.

 

[cliff234]

"As the article mentions, limit methods would likely result in substantially less top steel at columns."

I don't like the sound of that. The top bars over the columns are the most important reinforcing bars in the slab - and when you look at the tonnage of steel in the slab, the top bars over the columns constitute a fairly small percentage of the overall. To reduce that steel further makes me nervous. But I'm an old dinosaur - so don't pay me no nevermind...