Masonry arching

[woodman1967]

I appreciate the help I have received so far on this project.

I do have one more question:

There is an existing opening in an existing large CMU wall (its a theatre classroom). The lintel I am assuming is designed to carry the arch of CMUs above. This opening leads to a small foyer and the main door into the theatre.

Now, they want to expand the foyer by removing the rest of the CMU wall to one side of the opening (Its about 7' to the corner of the wall). There will be a concrete post and a concrete lintel installed to carry the load of the removed wall.

So, now that the wall on one side of the opening has been removed does that have an effect on the masonry arch above the existing lintel? Has the loading on that lintel changed? And should the new post and lintel be design to take the thrust?

Thanks again for your help.

 

[youngstructural]

Whether or not the existing arch has a thrust reaction depends on the geometry, but if it does (which it almost certainly does) you still need to have a load path for the thrust.

So what I am saying is that unless this is a semi-circular arch, the force applied along your new support beam has to g somewhere, and that somewhere sounds like it's going to be into your new column.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[woodman1967]

Thanks YS

But, what I meant by arch of CMUs above was the existing lintel is horizontal (not arched) but was carrying a triangle of CMUs above it not the entire wall above.

Thanks

 

[youngstructural]

Okay, well then you have an entirely new problem, and should treat it as such.

In case you don't have a great deal of masonry design experience, I'll explain how I would handle this: If you are going to be going past the length of the original lintel, you can only count on the arching action of the CMU wall above if the projected arch action of the new length of beam is still within the length of the wall. IE: If you are considering a 60 degree arch action (conservative, given that many argue 45 degrees is permissible), you need to have at least three courses of masonry block above this, and then only the area (approx 0.433L^2) of block above the lintel is carried by the lintel. The remainder of the force is carried as a load outside of this span, and if I am picturing your case correctly, will act as a load on your new end column. So you still have to design the column for this load, but it saves you a bit when sizing the beam.

Note that you can argue 45 degrees, which is commonly done, and what I have outlined above is conservatively based on 60 deg.

Does that help a bit more? Post some sketches if you need more help, they are worth their weight in gold when it comes to these discussions.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...