Structural Magnets 1

[msquared48]

Anyone ever heard of or used a high strength magnet in a structural application, such as attaching ta bracket to the metal skin of a water tank?

Our in-house Archiitect has a web site he is sending me to look at, but I am skeptical at the moment. This would have to be a use that is tested and rated under the IBC, for, currently, there is no mention of using this type of force in the IBC.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[OHIOMatt]

I experimented with the idea 10 years ago. I purchased samples of "rare earth" magnets. Really amazing force that can be excerted. The thought process that we used was to calculate the normal force excerted on the suface of the base metal and then determine a coeficient of friction between the two materials. Once that was done, we assumed that this could be scaled to larger magnents. The application that we were looking at would have been for shear.

The project got to complex and expensive so we went a more conventional route. I still wish that we could have continued.

 

[IRstuff]

I would advise against that. While magnet pull strengths are what everyone touts, bracketry, and even refrigerator items are held by friction. Friction is not something to be relied upon for structural integrity.

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[dhengr]

Mike:
What’s a “ta bracket?” Theoretically it should be possible. But, the question will always be, what are the consequences if it lets go (fails by any means) or slips in a frictional/shearing way, as Matt suggests, since it is not a permanent connection? Although, bolted and welded connections fail too. We use magnets now for lifting steel plates and the like, and use them as the bases for portable drills, etc. But, failure means a dropped plate or drill, or broken drill bit. I wouldn’t have any qualms about using magnets to fix a cloth banner (light banner) to a water tank for a short period of time, for example. Who guarantees that the magnet will never fail or slip, your in house Arch., not you.

 

[Ron]

What is the "permanence" of a "permanent" magnet?

 

[msquared48]

dhenger:

I meant "a bracket". Sorry.

Ron:

I know, and that's one aspect of the design that I'm worried about. The Architect claims that they do not lose their magnetism, but that seems odd unless this is new technology.

The other thing is, will the magnetism be negatively afffected if it is hit by lightning? After all, the structure is a lightning magnet, not to be punny here.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MikeHalloran]

There is such a thing as a magnetic 'circuit', even in and around a permanent magnet.
The analogue to current is extraordinarily sensitive to 'gaps' in the circuit. Even gage block surfaces are rough enough to be a magnetic gap.

Since magnet poles are typically planar, the curvature of the tank surface will interfere with the magnetic circuit, effectively producing a gap of variable dimension.
... unless one inserts a soft iron 'pole shoe' with one planar face and one face of curvature matching the tank. ... which introduces two smaller, but still finite, gaps in the magnetic circuit.
The paint on the tank also introduces a gap in the magnetic circuit.
The tank skin is likely too thin to not act as a restriction in the magnetic circuit.

Even if you get all of that right, the random huge currents and fields associated with a lightning strike can make it all go to hell.

I wouldn't consider a magnet mount anything on a water tank.
Magmount CB antennas barely work on a clean steel automobile roof.



Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

http://www.kjmagnetics.com/

has some FAQ's one of which talks about the permanency of Neodymium magnets

http://www.kjmagnetics.com/FAQ.asp#time.

They also give a lift of uses, not sure any exactly match with yours.

http://www.kjmagnetics.com/uses.asp

As others mention I'd be as if not more concerned by the friction as by the magnets - unless there are some kinds of rips or similar physical features to pick up on.

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[MJB315]

Ha, I was joking around with an Architect today saying that a correction for a field issue could be a "structural magnet."

Little did I know...

"We shape our buildings, thereafter they shape us." -WSC

 

[hokie66]

Architects would jump at the use of structural magnets...after all, for years they have been advocating the use of skyhooks.

 

[JAE]

What happens if lightning strikes the water tank? Dead magnet? Bracket fall down go boom?

 

[TheoreticalHope]

Another consideration; Heat. I don't know whether there is zero chance of fire near your tank, but I wouldn't want all your brackets to fail as soon as the temperature rises.

 

[JStephen]

I can see using something like that for a line of conduit clamps up the side of a tank or something like that, where the main point is to keep things from blowing in the wind, as opposed to keeping them from falling off the tank.

Corrosion of exposed metal surfaces, accumulation of ferrous dust/crap around the magnets, and staining would be some concerns.

If it was placed where somebody COULD grab it, assume somebody will.

 

[handleman]

My knowledge is admittedly fairly limited in this area, however, I haven't seen mention of saturation yet. I do know that the magnetic strengths that manufacturers use are for attraction force to a pretty massive ferrous target. I have a super-strong magnet stuck to the side of my filing cabinet. I can easily pull the magnet off with one hand. However, if I go out and stick it to a 2" thick steel machine base it's a struggle to get it separated. As if the other negatives mentioned above weren't enough... be sure to consider saturation on your thin(?) walled tank!

-handleman, CSWP (The new, easy test)

 

[apsix]

Magnets are used inside some wind turbine towers for the attachment of ladders.

http://www.vestas.com/Files/Filer/EN/Brochures/Vestas_V_90LOW.PDF

see page 10.

 

[TomDOT]

You know, I wasn't sure if I should thank/star KENAT for his links, or curse at him. It's hard to resist buying nice magnets, but I already have too many toys.

Went with starring the post anyway.

 

[msquared48]

Can beer be considered a structural magnet?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[btrueblood]

Mike,

In addition to the other problems noted above, the newer high-strength magnets are made from powder metallurgy (pressed and sintered powders). This means the materials are porous, which means there is a high probability that water and air will enter the part, regardless of anything you can do to seal/encapsulate the magnet. If the surface gets wet and the temperature can vary, you can guarantee that some moisture will penetrate. The magnet as a result slowly oxidizes internally, and loses strength over time.

 

[MikeHalloran]

It will lose strength more quickly if the permeated water freezes.


Mike Halloran
Pembroke Pines, FL, USA