Consideration of Slab’s Bending Resistance to the Lateral Load Resistance of a Rigid Frame 1

[AshiqRumi]

Hi Everyone,

I would like to know about your opinion regarding consideration of a slab’s bending resistance (transverse bending stiffness) to the lateral load resistance of a column – beam rigid frame structure…………

In the “Tall Building Structure” – Stafford smith, Alex Coull, it is suggested to ignore the bending stiffness of slab. (5.2.4)
Can you give me anymore references???
According to this philosophy, we are modifying slab bending moment coefficient (m11, m22, m12) to a negligible value (Say 0.01) while modeling a structure in ETABS.

But can you give me any more specific guideline for this???

Thanks in Advance.

 

[hokie66]

For lateral resistance, I have never considered slab stiffness in a rigid frame or shear wall structure.

 

[PicoStruc]

Canadian code recommand to use 80% reduction in bending stiffness in modelling.

Slab Diaphragm act as membrane in the lateral load path.

 

[KootK]

I wouldn't normally attempt it but, in principle, I don't see why you couldn't include slab slab flexural capacity. You would need to assess it's contribution in a way that respects relative stiffness between slabs and beams however. And I'd expect the result to be that the beams still wind up doing most of the work.

In a seismic zone where you're looking to form plastic hinges in the floor framing, you'd need to consider if you then also need to form hinges in the slab as well. Although I suppose that's technically true whether or not we choose to ignore the slab's contribution.

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.

 

[bookowski]

Yes, this is done in my area for tall buildings by some firms - others don't agree. They call them 'slab frames' around here, or slab-column frames. It can really help control drifts. You need an effective width and a stiffness/cracking reduction. You also need to look into punching shear including the lateral moments. This is one of those things that exists whether you model it or not.

Google slab frames and grossman, they're always writing papers on it.

 

[AshiqRumi]

The interesting thing is as the beam and slab is usually monolithically casted in R.C.C frame structure, it will definitely have some stiffness on the beam column joints and which shall not be completely avoided.

bookowaski, the thing you describing is known as flat slab frames to me (which also known as flat plate slab frames i guess). But the main problem of that type of structure is the R value (response modification factor for equivalent static analysis of earthquake loading))of the system. for slab frames, the value of R is very questionable because the frame doesn't behaves like a complete intermediate moment frame. so, it is difficult to chose the actual value of R. i have read a paper on it. i will share the link on the next comment......

anybody has anything to add on this view ????

please do share your opinions ..........

 

[bookowski]

Have you looked at 'seismic design of reinforced concrete special moment frames: a guide for practicing engineers" by moehle, it's a nehrp document. They discuss it a bit in there. There's lots of info on this - but you probably won't find anything definitive/codified.

 

[AshiqRumi]

http://www.iitk.ac.in/nicee/wcee/article/WCEE2012_4902.pdf

Go through the link......and read the paper

Here, in the section 2.2 it is written that:

"The flat plate structure is an undefined seismic resistance system in the design code. If it is
demonstrated that the seismic performance of a flat plate structure is similar to that of the seismic
force–resisting systems defined in the design code, through analytical and experimental study, the
seismic performance factors(response modification factor ( ); system overstrength factor( 0 );
deflection amplification factor ( )) are applicable to design flat plate structure."

do anyone have anything to say about this ?? cause i am searching for more references ........

and we were discussing about "Consideration of Slab’s Bending Resistance". if anyone has found something more about the topic please do share........

Thanks

 

[BUGGAR]

I find it is easy to throw in a beam to model the base slab in a frame, as well as conventional fixed/pinned anchorages at the base of the columns. With today's analysis programs (I use Risa), it's easy to turn things on and off and see if there is any significance.
Also on important stuff we go through the geotechnical soil spring modeling routine.