Short Lintels?

[Redacted]

Hi there,

I have a project where the client will be putting in some holes for HVAC equipment in some exterior stone walls for an industrial building. The walls are 12" thick, in what I assume is limestone (I'll confirm).

The holes will be a 12"x12" square and a 24"x24" square.

For the 12"x12" square, are lintels normally used for such short spans? I can understand perhaps putting in a lintel for the 24" square but I've never had to design such a short lintel before.

I just want to know if it's standard practice.

I was thinking of using a reinforced concrete lintel. The hole location would be quite high up though, about 16' up, so wondering about the constructability.

My local building residential building code states that lintels should be used for all holes in walls greater than 12". This is an industrial building though and not residential, so I'm on the fence on whether it is standard to include them for 12" holes as well.

Is there a better choice of lintel for these short spans instead of reinforced concrete? We don't have pre-cast here so can't use that.

If I put a lintel in for the 12"x12" square it would most likely have an 8" bearing either side ending up with a 28" long lintel.

Any advice would be appreciated.

 

[psychedomination]

I guess it would depend on the arching action/load. I haven't seen a 1' lintel before, I think the shortest I've needed to design in the past was 3' long.

 

[phamENG]

Depends on the masonry as well. Is it rubble stone masonry? Ashlar? Etc. If you're depending on tension and/or shear in the mortar to keep any blocks from falling out, then I'd put in a lintel. If they are all sufficiently supported and can arch over, then I wouldn't worry about it as long as the wall is in good shape.

 

[dik]

A lintel may not be required... as a caution, in these environs stonework used a 1/4" mortar joint and not a 3/8" one.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Redacted]

@psychedomination thanks I assessed the arching action and loads and they are very small, see below

@phamENG thanks for your comments, after reviewing the as built's the wall is actually CMU block laid in running bond fashion. What do you mean by if they are all sufficiently supported (are you referring to the running bond layout or similar)? The wall is in good shape btw. See the below analysis. How would I go about calculating if an unsupported running bond CMU block can take that small calculated bending moment or not?

@dik thanks; yes I am thinking that the bending moment for the 1'x 1' hole is very small and most likely doesn't need a lintel. I would like to know how to go about proving that unsupported masonry can hold up the small bending moment though?

On another note just for my learning. If this was a solid concrete wall instead of masonry, would this arching mechanism still be the preferred way to analyse/design a lintel?

 

[dik]

If solid concrete it's easy... plain concrete strength would likely be lots. With masonry, you might want to use a bent plate lintel angle that spans the opening with vertical plate columns on each end that trim the sides of the opening and it just 'slides in'. Likely be less costly than designing for the opening. You can use a temporary channel to provide support for the opening until the hole is cut. Seems like a lot of work for a 'foolproof' method.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Something like:

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

can you tapcon a BAR 1/4 x 3 on each face of the opening taking it a tapcon distance past the opening. If fire rated then intumescent coating or whatever. The tapcons in the middle (span) pick up the masonry and the tapcons at the end look after the reactions.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Redacted]

Hi Dik,

Thanks for your comments.

I was considering using an angle. I haven't used one for a lintel before but at this stage, I am definitely looking for the easiest and cheapest option as this is for a temporary fit-out.

Originally I was thinking that they could just cut the opening and cut the space for the RC lintel at the same time as the loading zone is small(chance of block work falling out is low), form up for the lintel, lay two t12's or w/e the minimum reinforcement requirement is and then just pour.

I think what you have shown above can work as well. Although can't do bespoke plate bending (in my location unfortunately), it would need to be an off the shelf steel angle, which has leg lengths of 6". I guess for this approach(I haven't done this before so speculating), the contractor would saw cut the angle thickness the full width of the opening and 6" or 8" either side for the angle to bear on the existing wall and then just slide the angle in on both sides. Would this work as well, I'm just trying to understand your recommendation for having vertical plate columns, as I'm sure there's a good reason I'm not realising.

I'm not sure which would be easier from a construction point of view RC or steel. They both seem quite straight forward.

 

[dik]

or... this should be the least costly... and it looks after the temporary support... install the bar and then remove CB that isn't needed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

and improved... mind the edge distance can stagger fasteners... may only need two at each end... and there are two on the opposite side of the wall four should easily take care of the load. Load from block weight is going into the wall and not the free edge of the opening.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Redacted]

@Dik, that's an interesting concept, kind of reminds me of a pinch beam but not through bolted.

I think the main issue with doing something like that is I am unsure if the CMU is grouted or not. I assumed it as grouted as a worse case scenario when calculating the lintel loads but it is common to not grout above ground CMU in my location. I think I would need to assume it is not grouted for potential fixes, so supporting from the bottom may be the safest bet.

I think it would make sense to support the 2' opening but what are your thoughts on the 1' opening. Considering the load triangle would only be 6" deep when the height of a cmu block is 8", do these really need a lintel?

 

[dik]

It should't matter if it's grouted or isn't. You are relying on the BAR to support the CMUs... grouting has nothing to do with it other than increase the loading.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

You can use the same detail for either case... else leave the 1' opening as it is... only may be difficult to justify that. The loads in any event will likely be very small with any serious loads above arching over the opening. I'll see if I can dig up one of my classic lintels from the past where I cut out the flange and web of a W24 beam and used the infill masonry as load bearing. Found it, this was for a 6' opening. The beam was at the main floor, in about a 14 storey building and the owner wanted to have a stair going from grade to the basement.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

There's an interesting story behind that opening. The contractor Herman Rattai had no sense of humour, and was a little concerned about the detail. I explained how it worked, including the new strip underpinned foundation in the basement and he was finally satisfied. He was non-plussed as I walked away, telling him to make sure he wore a hard hat. I still haven't changed, much and that was nearly 50 years ago.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[phamENG]

Redacted - in a 12" wide opening with smaller stones or even standard sized bricks, there's a good chance that you'll have at least one on the bottom course over the opening that has nothing below it - it relies only on the shear in the head joints and the tension in the bed joint above. That's no good. I've seen where people have tried to do that - because arching action worked - and within a couple of years the masonry under the 'arch' was falling out. But if you have 16" blocks...I wouldn't be concerned. Though it's not a bad idea to use a piece of flat bar either in the head joint just above the opening or applied to the face as dik has shown - especially if you have a point load or if there's a good chance you'll get a crack at the new opening. Be sure to look at current joints/self created relief cracks and see if there's a risk for a new one forming at your new opening. If so, arching won't help.