Masonry Rebar Positioners 2

[abusementpark]

Do you require that rebar positioners be provided for all masonry construction? If so, at what frequency do you require them?

I believe they not required per any code as far as I can tell. Is this correct?

 

[csd72]

This is a means and methods item that I doubt would form part of any code. I would say it is a specification requirement, like load indicating washers, that is there to make life easier for the engineer.

 

[rscassar]

I have never seen it in a specification. What I do regulary see on drawings and specifications is that all CMU reinforcement to be in place and fixed prior to calling for an inspection by the engineer. Of which, they never have the vertical reinforcement fixed because the use the reo to help them compact the grout.

I find it strange that engineers are prepared to design and detail reinforcement hard against the shell of the CMU even though in reality the bar is never placed there and if it were, it would be difficult to get good compaction between the reinforcement and the shell of the CMU.

 

[abusementpark]

ACI clearly states that all rebar must be set and tied prior to pouring. I would think that the masonry code would have a similar requirement, but I don't see anything. I believe that the UBC used to have a requirement of masonry rebar positioners at a certain frequency, but I do not believe the IBC carried that requirement over.

 

[csd72]

You american engineers are always looking for a code clause. Whatever happened to engineering judgement and good practice?

 

[steellion]

@abusementpark: We put it into our specs.

@csd: That's because American contractors will try to get away with anything, and refuse to do proper work unless you can refer them to a requirement in the code or specs.

 

[looslib]

Engineering judgement went away when lawyers started sueing and winning for things like "getting burned because I put my coffee cup between my legs while driving, hit a bump in the road and burned my leg because the coffee was hot and splashed on my leg."

If there isn't a code/booklet/procedure specifying something then something is missing and one will be written.

Too much paperwork kills a lot of projects.



"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[concretemasonry]

amusementpark

The code writers finally realized that the requiring of direct location of reinforcement could be detrimental to the quality of design, construction and performance.

Between the light use of reinforcement and the course by course construction, much of the steel location is covered, so no blanket "well meaning" code requirement is prudent, but you always have the opportunity to make a specific requirement for certain walls in your plans and specs.

ACI 530, which is the most recent consensus code and the basis for the IBC and IRC model codes did a good job of handling the subject.

If you have a vertical wall with the some cores reinforced, the location of reinforcement is not that critical (except for masonry columns) since the critical loads put everything into compression. For vertical walls with controlling loads making flexure critical, horizontal reinforcement (if required to be placed close enough can retain the steel away from the center of the core and steel wire spacers can be used/specified in critical walls.

If you actually look at a modern masonry unit, you will find it has a top and bottom. The top (as used) is the bottom (as manufactured), but they can be delivered in any orientation. The mason will lay the widest surface as the top because this provides a wider mortar bed (and a hand hold) and less droppings into the open cores. For a block with a 1 1/4" or 1 1/2" minimum face shell, the top face shell width could be 2", which prevents the reinforcement from laying against the interior of the face shell and provides room for grout to surround the reinforcement, where required. On 6" CMUs the extra width is not that great, but they are normally not used in flexural walls.

There are also specific units engineered/designed to locate reinforcement in the block core. The advent of modern design with less full wall grouting has lead to these hidden/unknown advances. - most come from some good engineers and from foreign applications where masonry engineering, design and construction is more advanced than the U.S.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[archeng59]

I specify rebar positioners for load bearing walls.

 

[concretemasonry]

Nothing wrong, but not always necessary but it can obstruct the grouting. A pair of suspenders and a belt always seem to work even if they get in the way of performance.

Just do not over-grout the wall or have too high of grout strength allowed.

After looking at the Northridge, CA seismic damage the effects were obvious. It was interesting to see the damage and them come back a day later (and after shocks) and see the more final effects.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[structuresguy]

Virtually all the masonry walls we design here in Florida are limited by flexural tension. As such, bar position is critical IMO. We specify bar positioners on all our jobs for exterior walls. But that's not to say that they get used on all jobs.

As Steelion said above, the contractors will try to cut every corner they can, and the more they get away with, the more corners they keep trying to cut. Personally, I try to be very sticky while reviewing shop drawings, setting the tone as early as possible that I expect to see what I specified. Then I like to visit a site as soon as they are starting foundation work. I hammer them hard on every little thing on my first visit, just to keep them honest. I find I have fewer problems latter on, once they see that I am serious. Of course, this various a little with some contractors, especially those we have worked with before.

 

[structuresguy]

concretemasonry: Can you clarify why I would not want to over-grout the wall (assuming you mean spacing of grouted cells close together), or have high strength grout. Ungrouted cells will be a weak point in a wall, leading to extreme cracking at those locations, I would think. When I have done heavily loaded masonry shear walls, they were almost always fully grouted, with 3000 psi grout and horizontal bond beams at 24" oc.

 

[abusementpark]

@csd: That's because American contractors will try to get away with anything, and refuse to do proper work unless you can refer them to a requirement in the code or specs.

Bingo.

When contractors complain about something you are requiring or question the necessity, it is a lot easier to simply say, "It is the code. We can't violate the code.", than to break out the engineering mumbo jumbo and give them the real explanation.