Can I design the shear reinforcement spacing to exceed the maximum spacing?

[AzzA16]

Hello Everyone,

I have a beam with dimensions of 200mm x 300mm, with a maximum spacing of 60mm. The nominal shear value with a spacing of 100mm is still more than enough to resist the occurring Vu. Can I use that spacing?

 

[cliff234]

No.

First of all, that's a really small beam (8" wide x 12" deep). Trying to fit shear reinforcing in such a narrow beam will be nearly impossible. ACI 318 requires 1.5" of cover on all sides to the shear reinforcing.

But to answer your question, the maximum permitted spacing of the shear reinforcing is d/2, which for this beam is about 5". The only way you can avoid that maximum permitted shear reinforcing spacing requirement is if the required shear strength Vu is less than 0.5 x phi Vc, in which case you don't need any shear reinforcing.

 

[Larryhd2]

following up on cliff234.... if you exceed the d/2 spacing then the shear reinforcing doesn't do anything at all... the shear plane is 45 degrees and if the ties don't cross that plane then they do nothing.