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.

 

[XR250]

Chalk line?

 

[WARose]

Good idea....but I think that still creates a issue as far as measurement accuracy. I don't think a lot of movement is happening.

 

[phamENG]

This might fall in the Wile E. Coyote category, but what about stretching a guitar string (or something similar since your opening is likely wider than a guitar string is long) between two fixed points and using a crack gauge to measure the difference between bottom of lintel and wire? Make sure one end is attached to an adjustment screw (like a string on the neck of a guitar) so you can ensure it's pulled tight before you measure.

Not super precise, but unless this lintel is supporting a floor that, in turn, supports some high precision balancing equipment in a lab, I'm not sure how important more precision would be?

 

[WARose]

This might fall in the Wile E. Coyote category, but what about stretching a guitar string (or something similar since your opening is likely wider than a guitar string is long) between two fixed points and using a crack gauge to measure the difference between bottom of lintel and wire? Make sure one end is attached to an adjustment screw (like a string on the neck of a guitar) so you can ensure it's pulled tight before you measure.

I am thinking about something along those lines: I was going to set up a string/rope system with it attached to the lintel and to a hanging fruit scale.....with it pretensioned, any change in sag will alter the measured level of pretension. But I have to think some more about that.

 

[XR250]

Put a nail in the masonry on either side of the opening. Stretch a string line across to measure the sag periodically.

 

[GC_Hopi]

How much precision are you needing here. On the order of a 1/16 of an inch? Masonry is pretty forgiving when it comes to movement so I am a little surprise that a laser and tape measure is not precise enough.

 

[IRstuff]

You can use GPS in real-time kinematic (RTK) mode; detection of millimeter motions. Most total station suppliers have RTK operational modes. The Sparkfun option is mainly dirt cheap, relatively speaking, although it does require post processing on separate hardware. The

https://en.wikipedia.org/wiki/Real-...enhancements up,position of the base station.

https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all.

The big question is HOW MUCH sag change are you trying to detect? Strings and whatnot are prone to stretching, etc.
Sparkfun has a bunch of other sensors:

https://www.sparkfun.com/distance_sensor_comparison_guide

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

 

[WARose]

How much precision are you needing here. On the order of a 1/16 of an inch?

Possibly. But I'm not sure. I don't know how much it will sag from this point forward. (Or even if it has.)

 

[IRstuff]

Commercial ultrasonic solution

https://senix.com/ultrasonic-sensors/general-purpose-sensors/toughsonic-3/

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

 

[phamENG]

any change in sag will alter the measured level of pretension.

What about relaxation? That could skew your results a bit.

 

[EdStainless]

I would look to set nails just outboard of the lintel and string a piece of fine music wire (0.005" maybe). The wire needs to be strung the same way each time (over the nails for example) and needs to be tensioned with a weight (same each time) so that it sags the same amount. Make a small mark in the lintel at the measurement point. I have a machinists ruler with one side marked in 64ths and other side in 1/100ths of an inch, that should work fine.
We used to do this with equipment in the plant, we had a written procedure for setting up and recording.

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

 

[phamENG]

Another option. Bolt a flat steel bar (or angle, or channel as needed based on span) over the opening. Mark it in several places where you're going to measure. Then use the depth probe on the end of a caliper to measure the distance from the lintel up to the bar. The bar may not be perfectly straight, but since you're just trying get relative measurements to track movement it should be good enough.

 

[dik]

really thin chalk line?

Depends on the accuracy... I've used a couple of 'concrete nails' set into 1/8" drilled holes and mounted an L2x2x1/8 to span below the opening and a digital vernier calipre to measure up from it. I've also used my 5sec theodolite to optically measure from a datum benchmark... in this case, the outside edge of the head of another concrete nail. Neither are really rocket science precise, but more than adequate.

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

-Dik

 

[phamENG]

tensioned with a weight

Seems a bit more foolproof than my adjustment screw idea...nice.

 

[WARose]

What about relaxation? That could skew your results a bit.

I know. It may need some settling time. (For a lack of a better way to put it.)

Maybe I modified version of what you suggested is to run a string between the end and the mid-point of the span....and if it gets broken, you know it's sagging. Only problem with that is: finding a "string" that won't stretch to accommodate it.

 

[dik]

I should have added that if measurements to within 1/81/16" are OK, I'd use my Hilti distance measuring Laser... never done this for deflections before, but if you have a fixed base and a target on the lintel to maintain the same reference points this should give you a fairly good idea.

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

-Dik

 

[EdStainless]

Every string or wire has sag in it, regardless of how tight you have it. The old Machinist Handbook had tables for this in it. We were doing this on 120' long pieces of equipment so it mattered if it sagged 0.010" in the middle.

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

 

[WARose]

Good idea EDStainless. You wouldn't happen to have a pic of this would you? (Or be willing to share that "written procedure"?)

 

[RWW0002]

@ pham - the advantage if your "guitar string" method would be that you could tighten down and then record the note of the string when plucked each time and measure the change in tension as the note changes.. talk about detecting slight variation. "The lintel appears to have sagged by at least an octave.." ha.

(obviously change in temperature, etc would likely play in too much for this to be reliable, but an interesting idea..)