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Horizontal Shear reinforcing in Walls

Horizontal Shear reinforcing in Walls

Horizontal Shear reinforcing in Walls

(OP)
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.

RE: Horizontal Shear reinforcing in Walls

If you need to develope the steel for yield, follow development length requirement. Otherwise, straight (most likely in walls).

RE: Horizontal Shear reinforcing in Walls

(OP)
Is it sufficient if the horizontal steel gets developed within the boundary steel (in non-seismic applications, I guess this would be the T/C steel at the ends of walls).

RE: Horizontal Shear reinforcing in Walls

If you need shear reinforcing, it has to be developed.  This is best done by using U-bars at the ends/corners, lapped with the straight bars.

RE: Horizontal Shear reinforcing in Walls

What is the load causing high shear in wall, if not seismic effect? Like two way slab, flexural shear rarely a problem, since stress tends to distributed out except at openings, and at around high concentrate loads.

RE: Horizontal Shear reinforcing in Walls

(OP)
Wind is causing high shear in these walls. I am using # 7 shear reinforcing bars

RE: Horizontal Shear reinforcing in Walls

Check your design uplate model. Your concern does not seem real.

RE: Horizontal Shear reinforcing in Walls

Check your design by plate model with proper boundary conditions. Your concern (shear force)does not seem real.

RE: Horizontal Shear reinforcing in Walls

kslee,

I don't know how you can possibly know whether slickdeals needs shear reinforcing in his walls, or how much, without knowing anything about his building.  Shear walls in buildings often do require shear reinforcing.  I don't find his question unusual at all.

RE: Horizontal Shear reinforcing in Walls

Hokie:

I don't know either, so that's why I suggested to double check analysis using FE to utilize two way action. Many times, it goes away, or might stick, but worth a try if he hasn't done so. We both know shear reinf is not desirable in wall unless there is no way out.

RE: Horizontal Shear reinforcing in Walls

(OP)
Assuming my model is right and I require shear reinforcing, would you please answer my original question.

RE: Horizontal Shear reinforcing in Walls

slickdeals,

If it is kslee that you are asking to answer your question, I doubt that he understands the question.  Otherwise, why would he say that SHEAR reinforcement in a SHEAR wall is not desirable?  That's like saying that compression reinforcement in a column is not desirable.  

For my answer to your original question, refer to my first post.  

RE: Horizontal Shear reinforcing in Walls

kslee,

What does "two way action" have to do with the design of shear walls?

RE: Horizontal Shear reinforcing in Walls

For concrete shear wall with boundary elements, the shear is distributed all around its perimeter, thus the stress is two way in nature. Assumption based on one way shear distribution vs two way leads to different results. Similar to one way vs 2 way slabs. Though, often times the later assumption was made to simplify the design process, and be on the conservative side.
 

RE: Horizontal Shear reinforcing in Walls

In the 97 UBC there was a revision to section 21.6.2.2 of the ACI 318 that required hooks or "U" bars at the ends of horizontal reinforcement when Vu exceeded one sq-root of f`c, which is approximately ½ the concrete shear strength.  This revision was not carried into the IBC.  ACI requires all continuous reinforcement in walls to be developed (19.9.2.3) if required to meet the provisions of chapter 21.  
I typically still apply the hook requirement to non-seismic walls with Vc over 1 sq-root.    

RE: Horizontal Shear reinforcing in Walls

Should have said "former (one way)", not "latter (two way)".

RE: Horizontal Shear reinforcing in Walls

I have always been under the impression that stirrups in a deep beam do not need to be closed, i.e. that straight bars will develop adequately by bond at each end to resist diagonal tension.  On the other hand, I have never used #7 stirrups.

In a wall, both horizontal and vertical bars will contribute to shear strength.  

 

BA

RE: Horizontal Shear reinforcing in Walls

(OP)
@Hokie66,
Does the U bar size need to be the same size as that of the horizontal shear reinforcing bar or is the U bar only a better detail? For example, can I use a #5 U bar lapped with a # 7 bar about 24"?

RE: Horizontal Shear reinforcing in Walls

Please disregard my last comment.  It is only true for the compression side of the beam.  In the case of a shear wall, either side can be the compression side, so shear reinforcement must be developed at each end.

 

BA

RE: Horizontal Shear reinforcing in Walls

Slick:

Are you designing facility for nuclear power plant? How thick is the wall, how you bend #7 into U, have you check the bendind radius, does the required bond can develop, would the enclosed concrete crash before the yield of steel??????

RE: Horizontal Shear reinforcing in Walls

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

Mike McCann
MMC Engineering

RE: Horizontal Shear reinforcing in Walls

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

BA

RE: Horizontal Shear reinforcing in Walls

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.

RE: Horizontal Shear reinforcing in Walls

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".  

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

(OP)
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.

RE: Horizontal Shear reinforcing in Walls

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.

RE: Horizontal Shear reinforcing in Walls

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.  

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

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

RE: Horizontal Shear reinforcing in Walls

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.

RE: Horizontal Shear reinforcing in Walls

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.  

RE: Horizontal Shear reinforcing in Walls

i do the same as Willis

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