Concrete I beam 1

[hessamcivileng]

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

 

[mike20793]

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.

 

[hessamcivileng]

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

 

[mike20793]

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.

 

[KootK]

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.

 

[UcfSE]

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

 

[hessamcivileng]

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.

 

[KootK]

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.

 

[hessamcivileng]

Thanks dear KootK for your help again