point load on a beam

[frank999]

Hi,

I wish to run a hoist trolley along a steel beam (say 1.0 mt long) to support a 300kg weight (variable load).

Assuming the hoist is 30kg's itself (permanent load).

I have used the 'www.steelbeamcalculator.co.uk' to experiment with a 1mt beam using a 178x102x19kg beam.

I selected:
Variable: 2.7kN, Permanent: 0.294kN
Distance to point ('A' in diagram): 0.5m

The report produced 'Therefore OK' on the 'results of analysis' section.

Could anyone tell me if that sounds about right (not fully understanding structural engineering myself), ie its telling me its OK to support that weight on that particular beam.

I can upload images of the report in the morning if that will help.

 

[tony1851]

Hi Frank. As its only a 1m span, you could use a much smaller beam. A 152x 89 or 125 x78 would be fine.

Your load of approx 3kn is very low, so the bending moment on that span
will also be very low, even allowing for the self-weight of the beam.

Looking in the published tables, a 178 x 102 over a span of 1m has a buckling resistance moment of 46kNm; your beam has an applied bending moment of less than 2kNm.

 

[^woody^]

That program calculation is probably based on a stationary load to the top of the beam, whereas your trolley hoist may be loading the bottom flange only, or even just the edges of either flange at variable points

 

[tony1851]

That program calculation is probably based on a stationary load to the top of the beam, whereas your trolley hoist may be loading the bottom flange only, or even just the edges of either flange at variable points

Yes, the tables will be based on stationary rather than moving loads. A moving load will cause a higher stress than an equivalent static load. however, that is applied principally for bridges and long gantries, and the OP is unlikely to get up much speed on a 1m span.

If the load is suspended off the bottom flange, it will be beneficial; an equivalent load applied on the top flange is destabilizing and the allowable stress must be slightly lower.

(just hair-splitting).

 

[^woody^]

The point is, the OP should not rely on a calculation for a completely different scenario

 

[frank999]

Thank you for the replies.

Interesting, didn't know a moving load will cause a higher stress than an equivalent static load, question for another day.

Ahh yes of course, the forces will be acting on the bottom flange only, so I guess www.steelbeamcalculator.co.uk is not applicable for this calculation.

I see you mention tables, is that manufacturers specs, I assume you gleen the Knm value from those ? could you enlighten me ?

Assuming the beam can support 46 Knm, and my load is only 2 knm, if the beam was 1.5-2.0mts long - do you think it would be strong enough, I'm well out of my depth here - a 300kg weight (a steel beam) on the end of a chained hoist connected to a trolley is a lot of weight.

How do you arrive at 2 knm for a 300 kilo weight.

Spoke to a manufacturer and hoped he would suggest beam sizes - but sadly not.

Here is the output from steelbeamcalculator, if of interest:

View media item 49248 View media item 49249 View media item 49250

 

[tony1851]

Frank; It would be possible to post some figures for your beam/loading, but they wouldn't mean much because of the factors and constants involved, for which you need the tables and texts.

Back here on planet earth, your beam will be more than OK with that load trundling up and down all day , and on a 2m span as well. My advice is to stop worrying and just do it

 

[frank999]

Thanks for your opinion Tony, its a brain ache knowing you should know some basics to get the job done - but then feeling like a fish out of water.

A little knowledge ...