Regarding Overhead Beam Capacity Tag 1

[kaffy]

Good Morning Fellow Engineers,

For the overhead beam, I’ve been asked to provide a rated load tag. I plan to base the rating on CMAA guidelines, as using a beam trolley or clamp attached to the bottom flange and concentrated load on the middle likely represents the worst-case loading scenario. Any thoughts or additional considerations?

Thank You

 

[Maslov]

Loading the very end of the beam is also worth checking, as that will maximize loading at the beam connection there. Personally, I would check the crane at the start, middle, and end of the beam. If things are broadly symmetric then checking at only one end and at the middle should suffice.

Check CISC's Crane-Supporting Steel Structures Guide if you haven't already. You should account for lateral side thrusts from swinging loads and partially non-vertical lifts, along with longitudinal loads from acceleration/braking and bumper impacts. NBCC only requires 20% of total weight distributed laterally on each side, and 10% of the max wheel/clamp load applied longitudinally at the wheels/clamp, but you may find these non-conservative depending on what you're lifting.

Lastly, a few random thoughts:

- Check the capacity of the clamps/trolley. They could be limiting.

- Lifting can jam, and if there's no load limiting device you could exceed capacity. Should be part of operator training to halt a lift upon jamming, but it's something to think about.

- Supporting structures (and foundation) should be checked under NBCC load combinations with crane loads.

 

[EngDM]

Check CISC's Crane-Supporting Steel Structures Guide if you haven't already. You should account for lateral side thrusts from swinging loads and partially non-vertical lifts, along with longitudinal loads from acceleration/braking and bumper impacts. NBCC only requires 20% of total weight distributed laterally on each side, and 10% of the max wheel/clamp load applied longitudinally at the wheels/clamp, but you may find these non-conservative depending on what you're lifting.

The crane guide also has instruction for the load being applied at the top rails compared to most equations where the load is taken about the shear center.

 

[TLHS]

I wouldn't say that you should assume the worst case condition. The rating should be for something specific. Why do they want the rating? The flange local bending stuff tends to govern in the modern CMAA style formulations, so having clear requirements for wheel or clamp locations is pretty important.

If it's just going to be a rigging point, then the way the rigging is attached should be clearly described.