Masonry lintel question

Well masonry walls do arch over and around openings. But only if there is adequate wall length on each side of the opening to resist the arching lateral thrust each way.

So if there's adequate lateral resistance from wall lengths on each side, you can assume that the upper floors dead and live loads get transferred to the adjacent walls and footings.
You'd have to check that these adjacent walls and footings can carry the load without overstress.
Note that the transference of load can induce new settlements in the footings now taking additional force so that could create differential movements that induce cracking in your wall. Not necessarily a structural capacity issue but mostly an aesthetic issue.

I believe that NCMA (in the US) has information on arching over openings. Try this:
As far as means and methods, this depends on the actual project conditions and geometry. Many times, if the opening width is small enough, the opening can be made without temporary shoring as the wall naturally arches - you may lose some blocks "under" the natural arch but these can be replaced by a mason once the new lintel is placed.

Otherwise we've used needle beams located just above the opening to shore up the wall above - again possibly losing some blocks below the needle beams.

Thank you for the response. This won’t be an arch. I guess I was mostly concerned with load path. Do I take the section directly above the lintel and call it conservative? Or is it not that simple? Also do I have to “start from scratch” with a new beam and reinforcement or can I take credit for some of the block above for depth purposes?

I guess I have used the triangle method before. It’s a very tall wall, but no windows or openings directly above it so I guess I just have masonry dead weight and I do not consider floor loads from above (considering they are further away vertically than half my lintel span)

JAE was using 'arch' as a verb. Take a look at the section called 'arching action' in the document linked.

How much of the existing wall to consider as part of your beam? I'd say zero, but the specific reinforcing and opening width in your case might suggest otherwise.

Yes, there's always some arching action in masonry and your description certainly suggests that A) there plenty of masonry above the new opening and B) there some degree of wall on either side of the opening.

The main problem is usually some minor amounts of wall on either side not adequate to complete the equalization of forces (lateral) of the arching behavior.

But to answer your question - yes you can conservatively take ALL the masonry above the opening as the load, but this is very conservative for the lintel design.

Also - you could conceivably use multiple courses above the "lintel course" as part of the lintel beam/flexure strength but I'd be careful there as hollow masonry above a solid single course lintel is more difficult to analyze its true strength. We have simply fully grouted multiple courses above the lintel course to add to the lintel flexural depth in the calcs.

Look for control joints. You don't get that arching action through a vertical control joint.

Thanks guys. I guess my only variable is the clear space on the side of the opening to the edge of wall. I know there is plenty of block above. Doesn’t seem like much load. Do you guys just specify a basic bond beam with xx reinforcement fully grouted?

For the lintel? Bond beam, precast concrete beam, steel beam/ angles, they all work. Depends on situation. I use a lot of double channels sandwiching the masonry to create new lintels. Saves on having to worry about the shoring/ needle beams aspect because they install the steel first then knock out the block/ brick below.

jerseyshore said:

I use a lot of double channels sandwiching the masonry to create new lintels.

Click to expand...

How do you deal with the force at the last bolt? Are you using thru bolts in hollow masonry?

I’d be curious to see that detail (channels)

I have done the double channel. What I do is put what I call 'needle plates' below the channels through a bed joint. They can be installed in a few foot sections at a time. Same thing at the ends to get bearing. I through bolt to wall to tie it all together. It has worked well for me on some fairly large openings.

So you basically “chisel” for lack of a better word the mortar out on each side of the wall far enough to stick the channel flanges in? And then through bolt the whole thing?

Don't try to push channel flanges into the joints. The channels are best left with flanges outward and either plates or small angles welded to the back side of the channels to fit into small slots in the mortar. This puts the load near the shear center of the channels.

The forces at the ends of the channel (end shear reactions of the channels) are either taken into the wall via a group of through bolts or by using vertical channels as end columns extending down the floor.

Anyone know why they don't make or rent needle beam rigs or strongboys in the United States?

Flanges in or out, depends on if it's going to be exposed or not. Put end bearing plates first, chase one side and put channel, put thru-bolts with pipe spacers, chase the other side and put 2nd channel. Use steel shims and non-shrink grout to make everything tight. Once the masonry is knocked out below they weld on a bottom plate. Channels usually 12" longer than opening on each side with a long weld to bottom plate at the ends. Pretty easy for smaller to mid size openings.

Just sayin - putting the flanges into cut slots in the masonry is a lot of work and only perhaps adds a bit to the aesthetics.
And channels of some sizes don't always align with the masonry coursing.

Flanges-in is less popular for sure, usually not worth the extra work. I've done a bunch of flanges-out, but with the entire channel set into the masonry. Usually easier to cut a giant chunk of masonry out on each side then little slots that align with the flanges.