Height and Length of a Special Reinforced Masonry Shear Wall

[emothman]

ACI 530-11 Sec 1.18.3.2.6 specifies the minimum spacing of vertical and horizontal reinforcing in Special Reinforced Masonry Shear Walls as 1/3 the Length or Height of the wall.

With single story masonry warehouses the walls are long and are at times interrupted with overhead doors, man doors and windows. For sake of discussion say the wall is 80' long and 24' high. Pier dimensions being - 30' pier, 12'wx14'h opening, 6' pier, 12'wx14'h opening, 8' pier, 3'wx7'h opening, 4' pier, 3'wx3'h elevated opening, 2' pier. Note that masonry is continuous over the openings.

My question, is what should I use for the "Wall Length" and "Wall Height" to determine minimum spacing of horz and vert bars. Do I use the entire wall? Do I use individual pier widths and the total height? Do I use the pier width and opening height?

I would assume that the spacing applies only to the area bounded by the length and height used to determine it.

Any help is appreciated, especially if that help includes a reference.

Another related question - I see engineers ignore smaller piers in the analysis. I think that is usually okay for the stress analysis, but do these piers still have to meet the spacing requirements given in the section above? Again, references are appreciated.

Thanks, Eric

 

[JLNJ]

If the intent of the code provision is to make sure there is some shear reinforcement in each element, then maybe
you need to think about applying the provision locally rather than globally.

 

[JAE]

I would think that each individual shear wall along that 80 ft. length would have its own design based on that section.

Note that 1.18.3.2.6 says "smaller of" for the criteria.

So for your wall:
30 ft. pier the height and width would not control but the 48" or 24" requirement would control.
On the shorter 2 ft. pier - I'd probably ignore it for seismic as its aspect ratio is too much.
On a 4 ft. pier - then 4'/3 = 16" as a maximum spacing might control.
etc.



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[sandman21]

ACI 1.18.4.3.2.4 80% of lateral stiffness shall come from walls. If you are using an R of 1.5 piers and columns are permitted to provide support. We have a local change to the code that has you provide a min. of #3 ties at 8"o.c.. So without the local change the reinforcing would be based on the walls you have participating as lateral elements. If you are using pier or columns than you would need to apply the min to those.

 

[emothman]

sandman21, ACI 530-11 defines "piers" as isolated elements. I don't think the referenced section applies here. Note that ACI 530-13 has gotten rid of the old "pier" definition and now has piers defined as portions of walls between openings. The commentary says that piers are only used in strength design.

I am still not sure about what to do in this situation. How do you define the "Length" of the wall and why do you use a pier length vs a total length? NERHP has a design guide that has a picture of the typical reinforcing, and it tends to make me think that it is not piers, but an entire wall. Perhaps control joint spacing or something. I am interested in other thoughts, sources, or if you know a way I could get a definitive interpretation on this, I would appreciate it.

 

[emothman]

To make sure I am clear, I have attached a marked up version of NEHRP's provided elevation from their "Seismic Design of Special Reinforced Masonry Shear Walls: A Guide for Practicing Engineers".

Note that I am using ASD design.

So, if I were specifying reinforcing in this wall, which length and height would I use for the prescriptive spacing requirements? And where would that reinforcing be required?

 

[emothman]

Trying the upload again.

 

[emothman]

For whatever reason the regions aren't showing up right. Say Region 1 is the full wall heights, region 2 from the top of door to the base, and region 3 was just the height of the window.