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T.T
10-16-2008, 04:37 PM
can any one tel how to calculate the tonnage the crane wil lift.
the span of the crane is 23 metres
it runs on 2 box section beams 23 metres long by 1175 mm x 500mm constructed of 12 mm plate on the top and bottom and 6mm plate on the sides it also has sections of 6mm plate welded every 2metres inside the box section

MoonRise
10-16-2008, 05:14 PM
Find the answer from the engineer or company (with their engineers) that designed it.

A couple of guys (or gals) welding some 1/2 inch (12 mm) plate together does not a crane make.

And an industrial use crane (and I don't think there's any way a crane spanning 70 feet long would fit into a 'hobby' exemption) has to meet industrial criteria.

A_DAB_will_do
10-16-2008, 10:06 PM
2nd that notion...consult with the manufacturer or a licensed structural engineer. anything else is insufficient due diligence.

T.T
10-17-2008, 03:26 PM
the problem is that the beams have to be extended by 3m.the S.W.L of the beam at the minute is 16 tonne.but what wil it be when it is extended.the engineer said that the weight it wil lift when it is extended wil decrease by 20%,he also said that its not allowed to flex more than 1mm over a length ot 700mm.was curious to see if it could be worked out mathmatically.will post some pictures wen its ready to go up.

MoonRise
10-17-2008, 03:32 PM
If the engineer already said that the SWL will decrease by 20% once the crane is modified, why are you asking us??

Yes it can be calculated mathematically, that's what the engineer most likely did (somehow).

ElGuapo
10-17-2008, 07:03 PM
Is there any history on the crane?
If it's an old abused dog which has not had it's inspections and on which has been fiddled with overload safety's, then better leave it alone. You'll never know how much of it's fatigue strength has been used already.

If it's a neatly kept, inspected and maintained unit, it's probably never been above maximum fatigue load, the welds are ok then it can have a second life. Lots of cranes are modified for a second go but need thourough review.

Extention will be on the end with the lowest stresses (not in the middle), and in order to minimise deflection (1/700 sounds familiar, also in europe) the construction can be strengthened.

In Europe you'll need to provide calculations and a first commisioning by a 'notified body'.
The commisioning will include load testing. Next to that we have to comply to European standards (98/37/EG), which means that the builder has to issue a declaration of conformity to european standards which includes risk analysis, calcuatlions, drawings, welding procedures, etc. etc.

All this paperwork and dynamic calculations makes it an unsuitable job for an average welder and structural engineer anyway over here. It's all about responsability, especially if you're employing people working with the crane or loading other peoples stuf on other peoples trucks things could get nasty for you it something goes wrong.

T.T
10-17-2008, 07:24 PM
the crane is in very good condition.it came out of haroland n wolf shipyard in belfast were the titanic was built. just wanted ta no the formula for calculatin the weight it could lift.

MoonRise
10-17-2008, 08:32 PM
There is no -one- formula.

There are several and it depends on the specifics of the design and construction and loading and support(s).

Which is why the engineer goes to school (university) and also gets a professional exam and license in order to -be- an engineer.

And as mentioned, there are also paperwork trails and liability concerns.

ElGuapo
10-18-2008, 05:05 AM
It's looks easy.

Just figure out the bending moment due to the weight of the crane and divide that by the moment of inertia of the cross section divided half the height of the beam.
That's the bending stress, add the shear stress and add them using the Huber & Hencky theory. That will give you a value for the nett load. Increase it with the applicable safety factors and consider the material strength with with material factors and then you'll know if the static strength will be sufficient. The bending stress alone will amount to approx 55N/mm2 with a 16 T load without safety margins which is pretty daft for the (probably) fillet welds between the bottom and side plates. So that means you need a calculation considering the number of load variations in the lifespan of the crane.

Then there's also the deflection criteria which will probably limit the applicable load. The deflection will cause downward forces to split into downward and horizontal forces. Imagine holding a beam with two persons and one standing in the middle of the beam compared to a rope.

Then there's the carriages on the end of the crane with wheels, drives and rails what about them.

And there's more than just the beams. I assume the crane runs on a rail in a building. You'll have to calculate the strength of the supports and beams in the building. You wouldn't want the building to collapse when the crane is loaded and there's a gust of wind.

Even a crane manufacturer will have trouble calculating the whole project because some data will just not get available. As I said already in Europe we have the machine directive, which makes you proof you are constructing a safe machine. Even crane manufacturers are still in denial of this directive, but that will change.

Over here I'd tackle it like this...
Get a mechanical engineer who knows his/her buisiness regarding cranes. I don't know which british standards apply, but over here we have NEN 2018 and further especially for cranes. For the building you need a structural engineer. Next to that you'll need someone who can make a decent report and do the things the machine directive obliges you to like preparing the declaration of conformity. And like it or not, you are officially the manufacturer of the crane because you ordered and shaped the modification, so you/your firm can sign the declaration of confirmity and are responsible for it, you can't shift that unless you sell the old crane to a crane constructing company. Then they take responsability for the old stuff (which will cost you i guess).

That's all there is to it. Don't expect to get the paperwork done for less then 10.000 euro's.

So that's about my daily job. Now back to my freshly bought lathe and my welder.

Burning2nd
11-22-2008, 03:25 PM
Osha would Pwn u for not knowing at my shop....

every crane ive seen has the ton rateing right on the side... clear as can be..

what kinda moter?

ElGuapo
12-09-2008, 12:23 PM
Wat pre-flow and upslope are you using?

T.T
12-27-2008, 05:59 PM
heres the pics of the crane before it wuz lengthend.it is now up and running and all the paperwork done and dusted,i also strengthened it with extra steel plate top and bottom,can anyone guess what the s.w.l is?will post pics of the finished article shortly,merry christmas

ElGuapo
12-28-2008, 05:06 AM
2x20T i guess.

T.T
12-28-2008, 08:08 PM
25 tonne my friend the total lifting weight.the motors have a limit switch which cuts out the two motors if the s.w.l is exceeded.good guess though.it will be put to work soon to lift a piling rig of the undercarrage to change the slew ring.hope to hav pics

ElGuapo
12-29-2008, 01:04 AM
That's a total 25T i assume. Are you going to use 1 hoist or the two in the picture.
I guess the fatigue load of the fillet weld between the side plates and the horizontal flanges is the limiting factor.

I quickly assumed the fatigue stress of that fillet weld to be 50N/mm2 but it seems to be 30N/mm2, at least if you calculate an overall safety of 1,5 and a load safety of 1,2.

You'll probably have to do a load test at 1,25x SWL Start collecting scrap metal. Or have some crane company or weigh bridge certifier lend you some ballast weights. Waterweights isn't an option. (too big).

T.T
12-29-2008, 05:44 AM
il use just one for now but i hav the two motors running individual.on the original crane the two motors run as a train,dont no if its a good idea or not.your spot on about the fillet joints plus we used balus weights of the piling rigs to determine the s.w.l:cool2:

T.T
12-29-2008, 06:03 AM
piling rigs at work in my own county donegal,mulroy bay bridge