document updated 13 years ago, on Sep 22, 2011

I'm looking for a quick and flexible way to clamp onto the bottom of I-beams, for the purpose of buildering.

I'm looking for something akin to the American death triangle anchor, since in this case, I actually desire the lateral forces, since that helps secure the anchor.

McMaster-Carr

Go their website, and look under the I-Beam clamps section:

"Double-Grip Adjustable I-Beam Clamps"
"Double-Grip Adjustable I-Beam Clamps for Threaded Rod"
"I-Beam Clamps for Strut Channel"
"I-Beam Clamps for Pipe and Conduit"
- These aren't weight-rated, while the strut-channel ones are. Why??

Look under plate lifting clamps:

"Horizontal Plate-Lifting Clamps"
- perfect. But $225. :|
"Beam Tongs"
- wow, that's... nearly perfect. But $400??? Though you can get them cheaper elsewhere.

Failure modes of the "grab hook" / American death triangle design

Lateral swinging could cause one of the hooks to yaw. The fatal downside of grab-hooks, compared to all other anchor methods, is that they aren't yaw-stabilized. If one of the hooks yaws enough, it can come completely off. Once one hook fails, the other one will almost certainly fail.

Desired behavior under lateral loads

The anchor should either:

stay in place, if lateral loads are low, or:
slide along the I-beam if lateral loads are high

In all circumstances, it should RESIST ROTATING. Linear motion is acceptable; rotational motion is not.