Ellis Clamp 2

[slickdeals]

Would an ellis shore clamp have the same capacity if installed upside down?

Typically the fixed end is nailed to the bottom post and the clamp is wedged to the top post. What would happen if installed upside down.

The way I understand how the clamp works is that once the two shore try to slip against each other, the 2 rods that wrap around the shores go in tension and prevent slip.

 

[RHTPE]

An Ellis clamped lumber member is simply a compression member. Its orientation does not really after a load is applied.

That said, the initial contact of the free end of the clamp depends on gravity. If you put the bottom stick (the one that the clamps are nailed to) on top, the clamp's free end wants to fall down and loosen. It will not maintain any clamping force until the assembly is loaded.

Bottom line - keep the Ellis clamps nailed to the bottom stick.


Ralph
Structures Consulting
Northeast USA

 

[msquared48]

Never heard of this... Is this a holddown?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[slickdeals]

M^2

http://www.ellisok.com/ellisok/products_shores.html

 

[RHTPE]

slickdeals I have worked with these things for about 30 years. My employer sponsored a series of load tests done to develop an analytical method of designing Ellis shores based on the lumber properties. They can make some pretty resilient post shores, though I suspect that, if Ellis still publishes safe loading it would be a bit liberal.

Ralph
Structures Consulting
Northeast USA

 

[BAretired]

You cannot use them upside down or you will have a disaster.

http://www.masco.net/pdf/catalogs/formingandaccessories/page65.pdf

BA

 

[msquared48]

So you have to be rightside up when you install them?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

SD...if you're asking if the device itself can be installed with the castings on either piece (upper or lower), yes. The device is bi-directional and symmetric.

If you are asking if they will work with the load applied in either direction...No. If either of the two posts goes into tension, you have a problem.

 

[slickdeals]

Ron, my question was only pertaining to compression loads.

However, in the attachment BA sent, if I took the same post shore and flipped it upside down and subject it to compression loads, would it work?

The reason I ask is because I have always see these clamps installed such that the clamps are sloping down towards the top post (ie) higher on the bottom post and lower on the top post.

 

[RHTPE]

SD

The reason I ask is because I have always see these clamps installed such that the clamps are sloping down towards the top post (ie) higher on the bottom post and lower on the top post.

Take that picture and turn it upside down and what do you have? The exact same orientation of the clamps.

BTW, I'd bet that these clamps could function in tension, but the clamp angle would be opposite that angle used for compression.


Ralph
Structures Consulting
Northeast USA

 

[slickdeals]

duh!! You are right. The clamp orientation does not change.

What would happen if the clamp orientation was opposite (ie) sloping upwards and subject to compression loads? Would it still work?

 

[RHTPE]

SD

What would happen if the clamp orientation was opposite (ie) sloping upwards and subject to compression loads? Would it still work?

To be clear: Bottom stick on the left, top stick on the right, clamp rods slope upper left to lower right. Ellis shore works fine in compression (with some initial movement in the 2 pieces of lumber as the castings "bite" into the wood.
Reverse the angle of the clamp rods (i.e. lower left to upper right, same lumber orientation) and they will function in tension (assuming some initial "help" to get the castings to grip the wood), but NOT in compression.

Ralph
Structures Consulting
Northeast USA

 

[DTGT2002]

NO!!!

If the clamps are installed such that the castings on the top stick are above the castings on the bottom stick (I have seen it done - usually involving nails on the side members of the clamps), the shore would have no substantial compressive capacity until the point in which the castings on the top stick have rotated and dropped (about 4" or so) and are located below the castings on the bottom stick.

So no, you cannot support compressive loads in the orientation you suggest. You will have a substantial displacement with likely loss of stability of the formwork in question.

Whoever installed them upside down can be called creative, but alarmingly dangerous.


I have seen 2x4 blocking used to hold the top stick up with the clamps out of whack, 16d nails under the "clamp rods" and toe nailing used to get the castings inverted. All scary things and a bit baffling.


Then again, I've also had junior staff draw them upside down and at least one more senior person do the same.


Any insight as to why you are asking?


Daniel Toon

 

[RHTPE]

Daniel, It's about time that you sounded off on this one!


Ralph
Structures Consulting
Northeast USA

 

[slickdeals]

No specific reason, Dennis. I don't design shoring, but I was looking at these shores long and hard yesterday when at a job site (while waiting for concrete to show up).

Every shore was installed with the castings on the top stick below the castings on the bottom stick. The castings were nailed to the bottom stick (at the top) and a safety nail above the casting on the top stick.

I think I stared at it too long to start thinking what would happen if the clamps were upside down.

From the responses here, the clamps will have to slip into place and (top stick casting below bottom stick casting) to work in compression.