Deep Beams Definition - ACI 318 Section 10.7

[wayniac3]

Can anyone clearly explain what ACI 318 section 10.7 means by a deep beam with regard to section depth and span length? I am getting differing opinions. The code section states:

"Deep beams are members loaded on one face and supported on the opposite face so that compression struts can develop between the loads and the supports, and have either: a)clear spans equal to or less than four times the overall member depth b) regions with concentrated loads within twice the member depth from the face of the support"

The way this reads is a continuous beam with a 36 inch depth would be considered a "deep beam" if it has a clearspan less than 144 inches between supports. Is this correct?

 

[frv]

It would depend on the loading, but more than likely, yes.

That's a 3' beam spanning 12'. Pretty classic definition of deep beam.

 

[hokie66]

Yes, seems clear enough to me. What is the other opinion?

 

[wayniac3]

For the example above, the party with the other opinion was initially telling me, that the beam with the 36 inch depth is considered deep if it has a clearspan OVER 144 inches - which contradicts ACI. They have since informed me they were mistaken. Thank you for your replies.

 

[cooperDBM]

Just to be clear, the clause is loading dependent.

The 12' limit in this case (3' deep beam) is applicable for beams with no significant concentrated loads within 6' of the support. If you have a significant (my addition) concentrated load within 6' of the support of longer spans the portion of the beam between the load and the support would be considered a "deep beam". Simple beam theory couldn't be assumed in that case and another analysis method, such as strut and tie, would be required. Actually the clause says the whole beam would be considered a deep beam in that case but I don't always look at it that way. So you have to be careful not to hang your hat on the 12'.

 

[rscassar]

The other party admitted they were mistaken. I use a length to depth ratio of 4 for spans and 2 for cantilevers. The concrete code which I use allows concrete compressive struts to be used at 30deg (2H:1V) so that being the reason why I use the ratio's I use for strut-tie analysis and design.