Horizontal Shear reinforcing in Walls

[slickdeals]

Folks,
Are you required to develop the horizontal shear reinforcing bars at each end of the wall or is it sufficient for the bars to be straight without hooks or closure U bars.

 

[msquared48]

#7 seems awful large here. What's generating the load?

Mike McCann
MMC Engineering

 

[BAretired]

Perhaps #5 bars at half the spacing would be easier to accommodate in the wall. Alternatively, you may want to consider mechanical anchorage.

BA

 

[hokie66]

Slickdeals,

In a wall where you need #7 bars as the shear stirrups, I would not skimp on the anchorage. Shear walls are just cantilevered deep beams, and you wouldn't change the size for beam stirrups. Anchorage of shear reinforcement is critical. As to #7 bars being hard to bend, I don't think so. If there is not enough room to accommodate the bend, your wall is not thick enough. I imagine this shear wall is in a high rise building, so low rise thinking has no place.

 

[OldPaperMaker]

slickdeals,
I don't think that I understand your question. If you have a shearwall it can have two kinds of reinforcing:
1. The vertical flexural rebar, that is located on both ends of the shearwall.
2. The horizontal and vertical closed stirrups that are required when the shear is greater than phi times Vc/2. These closed stirrups are sized and spaced as called for in chapter 11 of the ACI.

I don't see how the vertical or horizontal closed stirrups need "development".

 

[hokie66]

The closure at the ends of the stirrups develops the horizontal bars. The vertical bars are developed by being continuous with the wall above.

 

[WillisV]

I generally put U-bars at the ends of the same size and spacing as the main horizontal reinforcing.

 

[kslee1000]

I still feel it is helpful to exam the stress on a plate model. Or, how about strut & tie method (truss analogy).

 

[Mixtli]

I think there are two different things here, as I understand, a shear wall is designed to take lateral forces, i.e. forces paralel to the plane of the wall; then if there is wind present, I would obviously assume it acts on the face of the wall, in which case we are talking about shear due to flexion.

Greetings

Tony

 

[BAretired]

antoniodelaconcha,

What we are talking about, if I understand the thread correctly, is a shear parallel to the shear wall under consideration. It arises from wind pressure acting on faces of the building normal to the shear wall. It does not act on the face of the wall in question. It is transferred through diaphragm action of the floors and roof to the shear wall whose reinforcement we are discussing.

BA

 

[slickdeals]

Folks,
The wind load is normal to a 24" thick wall which is about 26' long. The building is a stadium and I can't divulge more details. We are assuming certain portions of the building not contributing to the lateral system to build in a conservatism in design.

 

[hokie66]

slickdeals,

That is a completely different situation from the question posed in your OP. You talked about horizontal bars, which won't contribute to the shear resistance normal to the wall.

 

[kslee1000]

Slick:

That's the reason I was urging you to perform a plate model. It is suspecious that you have such high shear under the condition stated. I think the #7 is for flexural bending, not for shear. If this is correct, the development #7 is up to the location that requires it (ends, or middle). But no matter what, for 24" thick wall without column at wall ends, I would provide U bars to better protect the end faces. However, I would try to use smaller bars, such as #5, to reduce the unprotect space in between wall corners and the bar bents.

 

[BAretired]

If the wall spans 26' horizontally, I don't understand why there is a problem with shear. The wind reaction per foot of wall is 13w where 'w' is the wind pressure. Assuming an effective depth of 22" and a wind pressure of 40 psf, the maximum shear stress is 13*40/22*12 = 2 psi which is trifling.

Maybe I still don't understand the problem. Perhaps a sketch would be helpful.

BA

 

[slickdeals]

sorry, my mistake. It was early in the morning. The shear is in-plane, not out of plane.

 

[Mixtli]

So it is shear due to flexion, right? then you just figure it as a simple slab, and the shear is generaly taken by the concrete thicknes. It also depends on the boundary conditions. Kslee1000 was right from the very begining


Tony.

 

[kslee1000]

Slick:

Suggest to review ACI 11.10 (shear wall). Read commentary carefully, and try to understand it. You may need to get to other texts to have full grab on what it was talking about.

Please keep in mind, unlike typical cantilever beam, you have relatively high gravity load compared to the lateral load (due to wind), which would help alleviate the in plane shear stress. Double check your design with methods suggested.

 

[swivel63]

i do the same as Willis