Traverse Spacing of Shear Reinf. in Wide Beams

[MPHenry]

In ACI 318 I cannot find any direct provision for the traverse spacing of shear stirrups in wide reinforced concrete beams (1m +). The code only seems to refer to the standard longitudinal spacing of stirrups using 2 legs. Can anyone give me some guidelines on this topic?

Regards

Mike B-)

 

[ishvaaag]

Spanish EH-91 articles 39.1.3 and 39.1.4 distinguished betweem beam or joists and plate and slabs. The difference was small, and the presently vigent EHE code for both RC and PC uses a unified formulation.

Maximum distances of
0.8d and no more than 300 mm
0.6d and no more than 300 mm0
0.3d and no more than 200 mm

are established for design shears exceeding less than 1/5, bigger than 1/5 and less than 2/3 and more than 2/3 of the crushing concrete strut capacity in the modeled strut as per the code (for which there is an evaluation therein).

(d is effective depth to center tensile reinforcement)

A sheet for design according to the present code you can download from the Mathcad Collaboratory site under the civil engineering folder.

 

[JAE]

Mike: I don't believe that there is anything DIRECT in ACI, but indirectly ACI requires a minimum amount of steel in beams where Vu exceeds phiVc/2. Now this usually amounts to only some nominal steel and when I've designed very wide beams (i.e. width > 30" or so) I've opted to use four vertical legs instead of two. We use simply a double U shaped stirrup that creates four equally spaced legs across the beam width. The stirrups actually overlap halfway to form the equal spacing. Your As for shear is 4 x stirrup bar area and you proceed the same as if you had only two or one leg.

 

[MPHenry]

Thanks guys for your comments.

On further investigation, it is also possible that the criteria for ties in columns as set out in ACI 318 ref: 7.10.5.3 could be adopted for traverse shear legs in wide beams.
This approach is similar to the requirements set out for wide beams in BS:8110 where it states that the maximum spacing of shear link vertical legs, at right angles to the span, should not exceed 'd' and all tension bars should be within 150mm of a vertical leg.

Regards

Mike B-)

 

[LPPE]

If you have a wide beam, I assume you have many top and/or bottom bars. ACI 7.10.5.3 says you have to tie every other longitudinal bar. These ties may provide the additional stirrups you're looking for.

 

[visitor]

The british standard BS8110 - Part 1 gives the transverse spacing requirement for
shear reinforcement.