Measuring lintel sag 2

[WARose]

I have a existing masonry lintel that I suspect is sagging more with time. I don't know how to measure it. And I worry that even something as precise as a laser or whatever may not detect what I want since this appears to be so minimal. Ergo, I am looking for ideas. I have a few Wile E. Coyote type ideas in mind.....but I wanted to ask here: any suggestions?

And before you ask: there is not enough masonry above this to see those tell-tale stair like cracks. So that one is out.

 

[dik]

Is that temperature sensitive and likely barometric pressure... this thread reminds me of the razorblades...

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

-Dik

 

[IRstuff]

Another option, this laser rangefinder does have 1-mm resolution and pretty decent repeatability, so you can just place it in the same spot and ping the lintel as often as you like.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[EdStainless]

Sorry War, that was a few lives ago and I don't have any of that stuff any longer.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[WARose]

Sorry War, that was a few lives ago and I don't have any of that stuff any longer.

Ok. Still appreciate the suggestion.

 

[Tomfh]

Take a good straight edge and mark at the lintel supports and the lintel at midspan. A needle point permanent marker should do.

Come back later with the same straight edge and see it if still aligns with the marks. That will be better than 1mm accuracy.

 

[WARose]

Take a good straight edge and mark at the lintel supports and the lintel at midspan. A needle point permanent marker should do.

Come back later with the same straight edge and see it if still aligns with the marks. That will be better than 1mm accuracy.

I doubt you could get that within that type of accuracy. (Especially using a straight edge & a level.) We are talking a 14' span here.

 

[Celt83]

..And I worry that even something as precise as a laser or whatever may not detect what I want since this appears to be so minimal...

If your movement is anticipated to be so small a laser won't pick it up you may want to look into mounting a strain gauge or a couple of strain gauges along the bottom surface of the lintel.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[Ron]

A nail set on each side of the header. Piano wire attached to one nail and extending across the other nail with a weight attached to the second end (takes out temperature changes). Put a precision scale behind the wire attached to the header at the midpoint (glued). Attaching the scale on a mirror helps with reading. Take readings periodically.

 

[Tomfh]

We are talking a 14' span here.

If it’s that long then shoot a laser line onto it, mark the ends and midspan, and compare again later.

Or some nails and a string line, as mentioned by others.

 

[dik]

What magnitude of deflection are you looking at... generally no need for a Swiss watch...

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

-Dik

 

[HouseBoy]

Many good suggestions here but I'm curious about a few things:
What is the length of the span? That might give some perspective on solutions. For example, a straightedge might be useful if the span is not too great.
What is it about the lintel that make you think the sag is going to increase? Very long span? Very short lintel? Just wondering about the scale of things.
Hoe old is the lintel/opening? I'm wondering about the "rate of change" that you anticipate.
Pics are always nice!

 

[JLNJ]

Shooting elevations with a traditional level is not accurate enough? The “rod” you choose can be marked as fine a scale as you like.

 

[dik]

I've used a steel rule with my theodolite... OK to 1/64 or thereabouts...

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

-Dik

 

[PEinc]

As long as the lintel is not too long (no length was mentioned), why not just hold a +2' long spirit level under and against the bottom of the lintel at midspan with the end of the level also touching the side of the window frame. Make a thin pencil mark on the side frame at the bottom of the level. As the lintel sags over time, you should be able to measure how much the lintel has sagged by measuring how much the pencil mark has moved down. Very cheap, easy, fast, non-destructive, and certainly accurate enough as long as the vertical side of the window frame is not also settling.

http://www.PeirceEngineering.com

 

[phamENG]

We are talking a 14' span here.

Probably tough to make that work with a 2' level...or any level with any sort of accuracy.

I'm guessing the concerns with the lasers, etc. is 1) tolerances in consumer laser measuring products (they aren't great...) and 2) variations introduced in setting up and taking down. I think the nails with a thin wire and a suspended weight on one side is going to be the most accurate to get a relatively consistent datum from which to measure.

 

[Brad805]

We would use our 3D laser scanner. Barring having one of those, I think the string line option makes the most sense.

 

[EdStainless]

Or instead of using a physical level use a laser level (even a cheap home one) and line it up with the center (marked spot) of the lintel and then make marks on the sides. This should give a good indication of movement.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[PEinc]

I missed the 14' width. That leaves out the spirit level. The wire method is good unless the vertical sides of the opening are also settling or compressing.

http://www.PeirceEngineering.com

 

[WARose]

I'm guessing the concerns with the lasers, etc. is 1) tolerances in consumer laser measuring products (they aren't great...) and 2) variations introduced in setting up and taking down. I think the nails with a thin wire and a suspended weight on one side is going to be the most accurate to get a relatively consistent datum from which to measure.

It's very much #2. Even with a pretty level floor....you'd better set it up at the same spot every time (if we are talking monitoring something like this).