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.

 

[kslee1000]

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

 

[slickdeals]

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).

 

[hokie66]

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.

 

[kslee1000]

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.

 

[slickdeals]

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

 

[kslee1000]

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

 

[kslee1000]

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

 

[hokie66]

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.

 

[kslee1000]

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.

 

[slickdeals]

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

 

[hokie66]

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.

 

[hokie66]

kslee,

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

 

[kslee1000]

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.

 

[Prestressed Guy]

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.

 

[kslee1000]

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

 

[BAretired]

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

 

[slickdeals]

@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"?

 

[BAretired]

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

 

[kslee1000]

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??????