Unreinforced Masonry Structures 1

[ramzy77]

I am trying to figure out if unreinforced masonry stuctures in the IBC 2006/ACI 530-05 require minimum reinforcing steel no matter what.

I used to work in CA and we reinforced everything bearing and non-bearing walls. Now I work in a non-seismic area and there is this grey area between contractors and designers. I don't have access to the ACI code now.

Thank you,

 

[Lion06]

No, unreinforced masonry doesn't require minimum reinforcing.

 

[concretemasonry]

It is not required, but there are places where some steel may be used, but it is not structural.

The miscellaneous uses would be bent flat plates to anchor intersecting walls where the normal bond of the walls is not sufficient ("other than running bond"), to tie separate wythes together to get composite action (greater d) and for joint reinforcement (Dur-O-Wal, etc.) for crack control and continuity.

Take a look at the ACI 530 section on Empirical Design.

Just keep in mind that you generally design masonry using the wall as a structural element and not the minute, "nit-picking" concept of looking at the block and mortar as separate structural elements.

Also avoid arbitrarily fill all the cores of concrete masonry, since you could be creating problems.

Dick

 

[hokie66]

"Also avoid arbitrarilly fill all the cores of concrete masonry, since you could be creating problems."

But you will usually solve more problems than you create.

 

[civeng80]

Im doing a job right at this moment where Im doing 8" concrete blocks and insisted that all cores be filled. Why

"Also avoid arbitrarilly fill all the cores of concrete masonry, since you could be creating problems" ?

Although my walls have lots of reo (Im trying to achieve a concrete panel strength since I cannot erect concrete panels here !)

 

[hokie66]

civeng,

That's a funny idea they have in the US. I suggest you ignore it, and just keep on working in accordance with Australian practice.

 

[apsix]

Two problems I can think of due to filling all cores are additional cost and additional weight, are there any others?

 

[msquared48]

A CMU wall should also be designed laterally to resist its own weight from appropriate seismic forces. If the wall is marginally reinforced for that, adding additional infill material could structurally compromise the wall in a seismic event - increasing the weight by as much as 50% - and the required seismic reinforcing.

Mike McCann
MMC Engineering

 

[apsix]

Thanks Mike.
A good reminder for those of us who don't practise within a seismic zone.