How to go about determining the maximum opening you can make in a load-bearing masonry wall?

[J.K.]

Hey all, I was tasked with figuring out for our client how big of an opening they can make in an existing load-bearing masonry wall. The building is a large warehouse that is built around an existing smaller warehouse, and they would like to open up the interior, existing warehouse walls to the rest of the larger warehouse. The wall has a triangular top section (looks like a section cut of a classic house with triangular roof) and the actual roof is supported by wooden rafters going across. The rectangular section of the wall is ~12' tall, the triangular section ~9'-6" tall, and the span 56'. I've attached a sketch below of what it looks like.

I know that you can create these openings in masonry walls given proper shoring during construction and an adequate lintel going across, but I haven't encountered a project where you need to determine the maximum possible size opening you can make. I'm not sure how the load path would follow down the wall from the roof if there's a large opening in the middle of it as a result. Would you simply take the two sections of masonry on either side of the opening and treat them as columns? And if so, does there need to be extra reinforcement in the corners besides the lintel since they'd experience the most stress?

Any tips on how to approach the analysis of a wall like this with the condition of having the maximum possible opening size would be immensely helpful, so thank you for your time!

 

[BAretired]

There is no hard and fast rule, but the width of opening would likely be limited by economic factors.

The wall is load bearing, so the lintel must span across the opening and be stiff enough so that deflection is limited to L/600 or thereabouts, to prevent excessive cracking in the masonry above. You may need new columns forming the door jambs, which in turn may require new foundations.

The existing wall is acting as a shear wall, so the wall section remaining each side of the new opening will need to be adequate to resist lateral loads.

The opening could be made 56' wide by removing all masonry and installing a rigid frame, but that would be a costly plan.



BA

 

[SlideRuleEra]

J.K.- As BAretired stated, there are no "rules", but there are ways to get an informed idea of what is reasonable and what is not. I'll assume you want to create an opening that will not require a total rebuild.

I worked as an employee in heavy industry (not for clients). It was my job to address problems like this one and come up with solutions. They had to be "right" the first time since there was no one to technically "approve" or even "review" my work.

This is how I would address the problem:

1) Make a scaled drawing (pencil/paper or software) similar to your sketch; reasonable accuracy (say each dimension within 3"+ is good).

2) Download the "Brick Industry Association Technical Note 31B Revised, Structural Steel Lintels". After reading it carefully, make use of this image:

Note that as opening width increases, so does the height of masonry bearing on the lintel. From the scaled sketch, you can see that the building is "wide", but "low"... the opening is not going to be very "wide" compared to the 56' building width.

3) Create an approximate graphical "solution", that is actually draw some openings, including arching action above the lintel. Won't take many tries to get an idea of what may be reasonable. On my drawing, what I consider a reasonable maximum opening scales off to 16' wide and 10' high.

Is this an answer... No.
It is a reasonable place to start making calcs to see what will or will not work along with what has to be done to make it so.