CMU ties

[reverbz]

Hey guys,

I was wondering when you require ties in CMU piers/pilasters/columns . Is it anytime you're using any type of built up CMU column? I've seen pilasters with no ties called out but not sure how the line is being drawn. Is there a good rule of thumb for this? I have a client asking if they can avoid it for some small 16" square piers experiencing bearing only.

Thank you!

 

[XR250]

I have never needed them by the numbers nor have I ever seen them.
I am now also curious.

 

[TRAK.Structural]

For commercial work I have always used them as a standard practice, #3's in the bed joints at regular spacing.

For residential I don't require any. If it's a pilaster as part of a wall I would make them course it in or provide wire type joint reinforcing just to hold it all together, but not rebar.

 

[reverbz]

For commercial work I have always used them as a standard practice, #3's in the bed joints at regular spacing.

For residential I don't require any. If it's a pilaster as part of a wall I would make them course it in or provide wire type joint reinforcing just to hold it all together, but not rebar.

Thanks for the reply. When you say you make them course it in could you explain that a bit please?

 

[bIockhead]

I think no ties are fine if the bars are there for tension (bending) and not required to not buckle in compression. There are many cases where a pilaster (thicker built up section) does the job with bars and no ties, simply from the increase in effective cross section depth (moving the steel further away from the compression face).

If you are using the masonry, grout, AND bars for your axial load carrying capacity then you need to tie them.

Only the designer knows whether they need that steel or not. If you are counting on those bars in compression, then it needs to be tied.

 

[bIockhead]

Thanks for the reply. When you say you make them course it in could you explain that a bit please?

I'm guessing they are referring to ties that line up with the mortar joints between full units. Can interfere with unit placement if the bars are too big, and ideally (not always practically) are under half the thickness of the specified joint.

 

[TRAK.Structural]

Thanks for the reply. When you say you make them course it in could you explain that a bit please?

See below. Basically building the pilaster integrally with the wall by the way you stack the blocks.

 

[bIockhead]

Good call, that makes more sense than just the reinforcement. I think building them up with regular units is much more common nowadays based on what I've seen, where the ties cross the mortar joints. Source: Canadian Drysdale book, 2nd edition

 

[RWW0002]

Mason's seem to hate tied columns, and in their defense I am sure they are a huge pain, especially with regular units. The line between a "wall" element and a "column" element can sometimes be a bit blurry. My understanding is that all "columns" are required to be reinforced with vertical reinf and ties. However I have justified masonry pilasters or small compression elements placed along a wall length as part of the wall itself, and avoided the ties for low to moderate loads. I have seen similar justification when pilasters are primarily bending elements.

I think no ties are fine if the bars are there for tension (bending) and not required to not buckle in compression.

What about a case where there is only axial load (and the required minimum eccentricity), the reinforcement itself does not necessarily have a huge affect on column axial capacity - Would you say that ties would be required for say a 16x16 masonry column (lets say 12' tall) with 20 kips? how about one with 70kips?

@concretemasonry - waiting for you to weigh in. - any code justification for omitting ties in a 16x16 masonry compression element placed integrally with an 8" wall??

 

[Ron247]

First, masonry is not my strong suit, but I am curious why you would do something for commercial but not residential. Is it a code requirement?

Also when some say put them in the mortar joint, do they mean aligned with the block shell or at the same elevation as the mortar joint but some distance inside the block shell profile?