Deep Beam Maximum Height criteria.

[serrojo]

Hello Everyone!

I am working on a 31 story building and my boss insists to use deep beams as solution for the transition from walls to columns (it is a common practice in the office) but not for a 105 meters high rise.
today I am trying to prove his theory configuring a deep beam with 8.4 meters span and the program I usually use says to me that 10 meters height maximum.

As I understand the height of a deep beam may be relative to it´s span, and it has different behaviors when the relation Height/Span is in low ranges of 0.5 to 1 and an other when that ratio increases from 1.5 to 2.

I can preform a manual revision using struts and ties method, but I will have to design more then 10 different options by hand.

Please if you have any suggestions to my situation, will be appreciated.

Regards

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[JAE]

Concrete beams, correct?

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[Teguci]

Per PCA's "Design of Deep Girders" article, the analysis covers a height to span ratio of 1/2, 2/3 1 and infinity. Per the charts provided, designing to a ratio of 1 is about equal to designing to a ratio of infinity except for a slight elongation of the compression zone at the top (the top for the infinity case being at a height = to the span and not heaven).

In reality, I'd think construction phasing would eliminate any deep beam concerns over the first pour. I would design the first pour of concrete as the beam and design anything above that as a wall. I'd be way more concerned with the "soft story" that is being created and the detailing of the column to wall reinforcement.

 

[KootK]

I am working on a 31 story building and my boss insists to use deep beams as solution for the transition from walls to columns

You mean where the beam IS the wall for a certain height, right? If so, the bottle neck usually is not so much the wall but:

a) the joint between the wall and the column and;
b) the joint between the wall and the slab if substantial shear will be transferred.

For both purposes, it can be handy to have a conventional, probably not deep beam at the transition.

I can preform a manual revision using struts and ties method, but I will have to design more then 10 different options by hand.

At those proportions, it's almost certainly a strut and tie thing. Why so many options?

Per PCA's "Design of Deep Girders" article

You can find that here if you're interested: Link

This was an excellent thread on a similar topic that may interest you: 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.

 

[serrojo]

Thanks for the replies,

JAE: Yes, Reinforced Concrete Deep Beams.
Teguci: Thank you for your suggestion, but My model gives back that the higher the deep beam better it can handle the efforts (2000kN/m Dead + 450kN/m Live) I might need that height after all!

Regards.

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[MotorCity]

I am not aware of any criteria that limits the maximum height of a deep beam, although depending on the ratio of height to span at some point it ceases to act like a deep beam and more like a shear wall.

 

[serrojo]

KootK:

Thank you for your suggestions,

Let me clear myself a little:

This is the view of my issue.

The options are due to the different span lengths and continuous changes in architecture that I have to face, usually I do a couple of hand solutions and check similar using software tools.

The article Is great I had a similar info from a book called "Reinforced Concrete Deep Beams"

http://files.engineering.com/getfil...reinforcedconcretedeepbeams-prof.f.k.kong.pdf

If you got any automation suggestion for this design purpose, I will be very grateful.

Best Regards.




MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[KootK]

Are you only interested in gravity load effects at the moment? Or are we considering shear wall behaviour as well? Your stress diagram kinda suggests the latter. As Teguci intimated, there is rather a lot to consider in a shear wall application, particularly in a high seismic locale. No doubt you'll eventlly be considering shear wall behaviour as it would be quite unavoidable.

For gravity load considerations, my automation suggestion would be not to automate. An elastic computer model isn't going to be particularly helpful where you're dealing with strut and tie proportions and a non-linear, cracked material. Research suggests strut and tie models like those presented in the other thread that I linked are appropriate. Under concentric load, that will effectively make your "beam" depth about L/2.



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.

 

[rapt]

In the time you have messed around creating and looking at FEM models of your deep beams, you could have designed all of them by hand calculation by strut tie methods from your design code.

Even calculating the column loads using FEM will not be accurate as it does not account for construction sequence and normally leads to an un-conservative result (possibly not so much for deep beams as for flexural transfer beams).

 

[serrojo]

Thank you for your tips, I have created a Mathcad sheet to check the deep beams... I took me the whole weekend but it worth it! Now I can make fast depositions according to the correct theories.

Regards,

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.