steel frame to support 50 tons 4

[tartanss]

Hi this is my first post but have read many very interesting and helpful replies to posts made here. I am trying to design a frame for a platform to carry 50 tonnes(50,000kgs). The platform is 20mts long and 8mts wide. I cannot find computations for a spread load over a few of the beams. Also the beams supported at each end are really a cut (I) beam to creat a 1 degree fall to the centre. For safety concerns it would be necessary to allow for a concentrated loading over 2 to 3 beams. Initially I have used 250x300x10 (I) beams which have an excess strength but what about the rewelded joint. Any help would be greatly appreciated. Cheers, Rob

 

[Teguci]

I suggest calling a steel fabricator and asking them if they can bend the beams to your liking. As a minimum, they can put a reverse camber on the beams to provide a curved slope to the center. The full penetration welds at the center of the beam spans is a good thing to avoid.

As for the loading layout, I'd have to know how the beams are being loaded.

 

[MiketheEngineer]

Are 50 tonnes and 50,000 kgs the same or just close enough?? Make sure your loads are right.

Then go hire a structural engineer. You are fooling around with a quite a large load with many implications.

 

[hokie66]

Mike,
A tonne is 1000 kg.

 

[msquared48]

...Especially the special reinforcing needed for the drainage hole at the center of the beam.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MiketheEngineer]

Oh - a metric tonne?? We don't use those around here... Sorry.

 

[msquared48]

Kips, Kips, Kips... Think Kips man!

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

I'll never be able to educate you old guys. I've used both, for years each, and the SI system is much more logical.

 

[Ron]

hokie66...I just had to add a star...mostly for the "old guy" comment! In the US, the metric system was adopted as official by congress in 1875 or so.....interesting that it has never caught on here....yes, it is much more logical. It would probably simplify our little analytical minds a bit if we would adopt it in practice...I'm not holding my breath.....Yes, Mike...I think "kips".

 

[msquared48]

Slugs are good too! Yum!

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[tartanss]

Thanks guys yep Its a tricky one. Am in Thailand and hard to find a structural engineer but have some leeds to follow. I grew up with imperial but man metric is so much simpler and accurate. 1mm or lets talk 1/24"<> Cheers

 

[tartanss]

This is the structure. The load will be concentrated towards the middle. The spacing of beams and the design of drain facility was earlier option. ends of beams welded to solid structure. Rob

 

[hokie66]

It is difficult for me to imagine why you would want to slope the beams such a small amount for drainage. You may as well leave them flat and make up slope in whatever deck you have.

It also seems improbable to me that you would need to run the drainage channel through the beams. Why can't you go below?

This would seem to be some type of industrial platform, in which case you should have latitude to improve the design. Perhaps if you can tell us what it is for, maybe we could give better advice.

 

[tartanss]

Your probably right hokie that would eliminate a lot of problems. So I can go away and re-design. Is there a table anywhere to give me load bearings on multiple frames as opposed to only one beam, but for safety maybe I should calculate weight on one. The Platform is for holding a 50tonne boat.
Cheers, Rob

 

[bigmig]

The first thing I'm asking is why in the heck do you have to span so far? Your diagrams and sketches don't show what is supporting your "Frame". Footings? Piers? More steel? I would be adding about 5 columns down the center beam and reduce your structure weight (and price) by around 40%.

I disagree with Hokie about slope. We slope steel every day. You need the deck to attach to the steel to form a diaphragm. NOT doing this will give you problems with lateral stability. Don't even think about raising your deck off the steel and sloping it with shims or however you would do it. They attach and have to be in contact.

 

[hokie66]

bigmig,
You are drawing a long bow. Just because you do it that way for the type structures you design doesn't mean there are not other types of structures requiring different solutions.

The OP is identified as being a marine/ocean guy, so I would think there may be water below...no place to put additional columns. The span is not great.

 

[hokie66]

tartanss,

The way the load distributes onto the beams will depend on the stiffness of the boat. I don't think you will have to assume the load is only on one beam, as the boat won't deflect like that. For example, if the boat is a flat bottomed barge with stiff sides, the beams would all have to deflect together. If the boat is supported on cradles, then those beams under the cradles would take the load. You will have to assess how the loads are applied to the beams. Don't depend on a table which may not be applicable to your situation.

 

[pilesmakesmiles]

Does a 1 degree fall give enough slope for the water to run off quickly enough?
It might be easier to have it flat and let people brush the water to the drainage point if needed?

What is below the structure? Would it be easier to drill holes in the decking to allow water to drain straight through rather than using collecting channels?

 

[StructDave]

tartanss - the variety of questions back to you should be a clear indicator that more info is needed, both on your objectives and on the limitatons of your situation. That is, of course, ignoring all the quips about kips, and fun about tonnes.
BTW the designations of your proposed beams seem to indicate 250 wide, 300 deep, 10 thick - is that correct? Now, 300 doesn't seem very deep with nearly 8m span; have you checked beam deflection?
If the beams can't be bent for you (as suggested above), another way to get the welded splices away from mid-span would be to use two splices per beam, at the third-points (out of the high moment area) but this gives a different config and might not suit you at all, besides using 2x the welding.
If a concrete deck is a possibility, you could build the slope into the concrete, and keep the beams straight.
How are the beams supported - on walls, girders, or a lift system? Are the ends of beams securely supported and prevented from rotating?
Will salt water be present on the structure?
Can you get the boat stiffness and load distribution info from the naval architect or other party, or do you have to guess?
Lastly, if the waste-drainage channel can be stiff enough to work as a strut, maybe the all-important lateral stability matter can be solved using X-bracing in a horizontal plane.

 

[tartanss]

Thanks.