Monorail Trolley

[hungrydinosaur]

Hi,

We have a 12 ft W Beam running in our workshop, with a 2 ton trolley running in it. Everything is rated for a WLL 2 ton. The W Beam is welded across to the transverse beams above it. All the transverse beams make up the roof of the structure, and all the transverse beams are placed at a distance of 3 ft apart. We are planning to lift a load of 2 ton, but now planning to use 2 trolleys, instead of one.
Will this arrangement (lift by 2 trolleys), have any effect or increase in the loading on the W-beam or on the roof structure/transverse beams above it? Now the point load on the beams is halved, in this scenario with the use of 2 trolleys. Do we need to have some minimum spacing between the 2 trolleys?

Thanks in advance.

HD

 

[JStephen]

If the beam is designed for 2 tons from a single trolley, it should be good for a total of 2 tons (not 2 tons each) from two separate trolleys with no minimum distance between them.

 

[TehMightyEngineer]

Assuming that 2 tons is correct, there will be no minimum spacing as the original engineer should have considered the worst case loading which is usually single trolleys. Thus, multiple trollies will only help. However, the 2 tons will include the weight of the trolleys and all lifting hardware, make sure to include those when you calculate the weight lifted.

Likely, by using two trollies with a minimum spacing you could increase the load rating for that lifting condition, but that would require reanalysis by a structural engineer.

Maine EIT, Civil/Structural.

 

[3DDave]

Does this beam also support the roof or apply a load to the roof beams to carry?

It is also worth considering the load that was included for the roof as well - ice, snow, extra layer of roofing material - can affect/be affected by things that are lifted. The analysis certainly made sure the connection to the roof was sturdy enough not to fail and should include a factor of safety for what they don't entirely expect. But, like the (Wisconson?) bridge that collapsed during remodeling, they can't include every mod made afterwards.

Also emphasis on what TME wrote - it's not what the trolleys lift, it is the entire lifting system - load, chain, cable, hooks, and trolleys.

 

[racookpe1978]

You appear to be within the "nameplate" safety limits of the trolley (at 2 tons - as pointed out above, make this is "total" weight, not just "below the hook" weight). But is your building and roof and roof truss still "per assumed original design" that allowed that original 2 ton load to be allowed?

Verify also that the roof outside is not overloaded with many layers of extra shingles, new air conditioners or solar panels or other "new" items.
Verify that the "ceiling" inside is not carrying extra HVAC ducts, massive new lights or doubled or tripled up cable trays.
Also: no other added crane railings (trolley or gantry rails) or equipment hooked on the same roof truss matrix. Widely separated new loads may not cause a problem, but new loads on the same truss will need careful re-calculation.