×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

4" CMU with 4" Brick Composite Wall

4" CMU with 4" Brick Composite Wall

4" CMU with 4" Brick Composite Wall

(OP)
A few questions about 4" CMU and brick composite wall.

In general I'm not so comfortable with this. Probably because I would normally not use 4" CMU for anything. However in this case if it is a composite wall, I might feel OK if the wall works as unreinforced fully grouted. However even if it does work as fully grouted/unreinforced, I would still be inclined to add #3 rebar. However, from reading other threads it sounds like the rebar makes grouting difficult, so I may infact be making things worse by adding the rebar.

Thoughts on 4" block/brick composite load bearing walls?
Thoughts on adding reinforcement?

EIT
www.HowToEngineer.com

RE: 4" CMU with 4" Brick Composite Wall

If the two wythes are interlocked together then conceivably they could be considered as an 8" wall, with slightly different stiffnesses and stress capacities of course.

However, brick over time will expand while concrete masonry will contract causing some possible distress and loss of interlock between the wythes, which then would imply that you loose that composite action that you need.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: 4" CMU with 4" Brick Composite Wall

I believe there are different ways to create a composite wall. I don't think just grouting the collar is sufficient, although I could be mistaken. BIA or NCMA are probably your best bets for resources. I've done it in the distant past, but I think I added bars to the collar as it was large enough and this gets it in the middle of the wall.

RE: 4" CMU with 4" Brick Composite Wall

(OP)
JAE -> Interesting, I don't doubt you but I'm surprised I can't find more on this being a problem (meaning brick / cmu composite with grouted collar joint). Although maybe it is not done often and that is why.

PUEEng -> Yes you are right you must be able to transfer shear forces. However if the wall works as unreinforced then I'm not sure it is required. Although I would still have joint reinforcement that extended across the collar joint.

EIT
www.HowToEngineer.com

RE: 4" CMU with 4" Brick Composite Wall

I never have designed those as composite. I alway use a 6" or 8" CMU as the backup and consider the brick non-structural. The architects hate me.
On one screenwall job, we did 8" CMU with bonded thin brick. It kept it pretty svelte.

RE: 4" CMU with 4" Brick Composite Wall

(OP)
It's good to hear that I'm not crazy for being hesitant to use this. I'm going to push for 6".

Some follow up info from MSJC's ACI 530-11

Multiwythe composite walls must be connected by either headers or filled with mortar/grout and connected by wall ties. With a grouted collar joint being the recommended method.
Limiting shear stress:
Mortar = 7psi
Collar joint = 13psi
Headers 1.3xsqrt(compressive unit strength) / net area of header
Tests indicates a vary sporadic range of allowable shear stress values. From 5-100 psi.
Type S Mortar had better shear bond characteristics than Type N.
Joint thickness / unit absorption and reinforcement had negligible effect on shear bond strength.
The show a diagram Fig CC-2.1-1, which to me is a bit misleading. They show a tension / compression stress diagram which is a normal stress diagram. The stresses you would want to know are the shear stresses, which would be VQ/I. Or am I missing something here?

Thanks again for the input!

EIT
www.HowToEngineer.com

RE: 4" CMU with 4" Brick Composite Wall

(OP)
Not that I was doubting JAE, but just to reinforce his point:

NCMA Tek 16-1A states:
"While not prohibited by the code(ref. 2), wythes of composite masonry walls should not be constructed with dissimilar materials, such as clay and concrete masonry, as rigidly bonding such materials together does not permit differential movement between wythes."

So I guess if you are using concrete brick and concrete block you would be OK.

EIT
www.HowToEngineer.com

RE: 4" CMU with 4" Brick Composite Wall

In my view, Full grout and properly spaced wall ties take care of differential. I have seen quite a few older buildings mixing these types of masonry without any problems. Maybe its just a commonplace myth.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources