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Concrete I beam

Concrete I beam

Concrete I beam

(OP)
Hi everyone,

Could someone help me with this problem:
Consider 2 concrete sections; First one is an I beam as a unit cross section, and the other one is an I section again but this time with 2 parts in which the bottom part of the section is not connected to the upper part (so in this case we have a T beam and the bottom part). How can you explain the structural behavior of these two different sections when they act as beams?
Many thanks

RE: Concrete I beam

The solid section acts as one unit. The two separate beams don't unless they are connected and that connection is designed for the proper forces (shear flow). I believe there are some good threads that discuss this topic in relation to wood stud wall top plates in bending. The material is different, but the concept is the same.

RE: Concrete I beam

(OP)
Thank you dear Mike
Could you tell me how shear flow affects the behavior of the separate beams?

RE: Concrete I beam

It doesn't affect the individual beams. Shear flow is a function of shear stress and it's what you design for to ensure composite action between the separate members, if intended. There are a bunch of threads that discuss this topic in much more detail.

RE: Concrete I beam

When the two piece section flexes, it will deflect according to I_tee + I_bottom flange. When the combined, composite section flexes, it will deflect much less and in accordance with I_combined. Which model makes sense will depend on whether or not the required horizontal shear connection (VQ/I) can be achieved at the interface as mike20793 has described.

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.

RE: Concrete I beam

hessam, did you try asking a senior engineer at your job? This sounds like a homework problem the way it is written.

RE: Concrete I beam

(OP)
Dear KootK, Thank you. I liked the concept you explained about deflection. I think it's reasonable.
Anyway, I need much more evidential details about this problem. Could you guys recommend me some pages of a book on this special subject?
This is not a homework, it's just a question appeared in my mind.

RE: Concrete I beam

Here's a decent summary: Link

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.

RE: Concrete I beam

(OP)
Thanks dear KootK for your help again thanks2

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