Concrete deep beams

[tonycampos88]

Hello,
I am designing the lintels of a load bearing wall as deep beams as the ratio of span over lintel height is waaay below 4. My question is related to shear. I am using strut and tie models to obtain by flexural reinforcement but all I have found on books about shear is a 10*sqrt(f'c) limitation and some vertical and horizontal minimum steel, but I just want to confirm that I still need to design stirrups like a normal beam, is this correct? (taking into account the provided vertical steel).
Thanks

 

[asixth]

Depends on where you are. Some places required diagonal x struts detailed thru this zone but when looking at the shear transfer across these lintels (headers/link beams) to couple the walls together I design them using the beam shear provisions. Depending on how you model it as well I reduce the stiffness to 40%. Be careful with the analysis program as well, I assign spandrels in ETAB's and it is pretty good at converting the shell stresses to beam forces but moments can be a bit hit or miss.

 

[asixth]

And the max shear limit still applies for beam shear applications. It is not relevant if it can be designed by strut tie and a properly detailed concrete strut is provided.

 

[aaronPTeng]

Also just a note check the applications of your codes and texts, The assumption of plane sections remaining plane (Bernoulli's principle) means that strains above and below the neutral axis NA are proportional to the distance from the neutral axis. This is not the case in deep beams!

I have been caught out designing a deep beam to transfer, I designed the shear reinforcement incorrectly. And had cracking which indicated a shear failure. Further stress analysis showed the reinforcement provided was OK for strength, however cracking did occur in the concrete.

 

[Lion06]

My understanding for deep beams is that diagonal cracking occurs at stress levels well below ultimate strength and very often in the service level load range. I did much more research on this than I ever thought I would.

I have a few very deep concrete beams (with flanges) on a project now and I'm expecting some diagonal cracking. I'm within the (10 sq rt f'c)bd for the shear strength and the reinforcement is provided per the strut and tie provisions, but the beam is very heavily reinforced and I am fully expecting diagonal cracking.

 

[hokie66]

Diagonal cracking in deep beams (and walls) is often not due to gravity loading. Rather, it can be restraint shrinkage cracking. Depends on the geometry.