Special Masonry Shear Wall Reinforcement Requirements

[mbozzo]

I have an 8" special masonry shear wall with long, short windows (see attachment for specifics), and I'm not sure the proper way to interpret the code requirements for the reinforcement. TMS 402-13/ACI 530-13, section 7.3.2.6 states that

(a) "the maximum spacing of vertical reinforcement shall be the smallest of one-third the length of the shear wall, one-third the height of the shear wall, and 48 in." and (b) "the maximum spacing of horizontal reinforcement...shall be the smaller of one-third the length of the shear wall, one-third the height of the shear wall, and shall be embedded in grout."

I can read this code provision in one of three ways:
[ol 1]
[li]The way I interpret this code provision means I would have to reinforce my wall with bars at 8" on center each way. The commentary states that the intent is to provide a minimum level of in-plane shear reinforcement to improve ductility. This seems perfectly fine for normal-sized piers, but seems to result in over-reinforced walls when short openings are involved. What if the window was only 12" tall? Bars at 4" seems absurd.[/li]

[li]Perhaps the height of the windows need not be taken into account for the purposes of this code provision? This seems implausible.[/li]

[li]Finally, perhaps the intent is to reinforce only the piers (i.e. the 3'-4" band that contains the windows) per that section and the rest of the wall can be reinforced according to its dimensions. Maybe a 'happy medium' of sorts, but does it make sense to have a single band of highly reinforced wall with much lighter reinforcement above and, particularly, below?[/li]
[/ol]

How would you interpret this code provision?

 

[JAE]

I don't see your horizontal band between windows as your shear wall. Your center shear wall is 16'-8" wide x 22 ft. tall.

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[mbozzo]

For analysis, though, wouldn't you assume the pier dimensions as the height of the windows x each pier length? If so, wouldn't those then be your shear wall dimensions as well?

 

[KootK]

I believe that JAE is correct here. Of course it's a trickier thing to try to explain why you are incorrect.

I suspect that the 1/3 spacing limitations are about ensuring that a minimum number of bars are crossing any potential shear crack in the wall. Viewed that way, I think that you'd have a hard time envisioning a potential shear crack that only crosses your 3'-4" dimension and extends no further.

 

[EDub24]

In my mind the shear wall is the entire length of the wall (or length between control joints if that controls) as well as the total height of the wall for maximum spacing of rebar disregarding the windows. You have to check the the pier obviously for the forces though.