Beam deflected
Beam deflected
(OP)
The horizontal beam for the overhead crane showed in the here attached photo is noticed deflected by naked eyes, more probably due to overloading.
Since the deflection is permanent (plastic deformation), shall it be considered rejected or there is some maximun allowable deflection value.
The spam is arounf 10 meters.
Thanks in advance for any input on this point.
Since the deflection is permanent (plastic deformation), shall it be considered rejected or there is some maximun allowable deflection value.
The spam is arounf 10 meters.
Thanks in advance for any input on this point.






RE: Beam deflected
it could be "acceptable" but the amount of analysis would be "daunting", IMHO.
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RE: Beam deflected
I can't think why the beam would be considered rejected if serviceable otherwise. Structural members can be cold-rolled to a radius and still be used for the design loads.
Just FYI, I can't see any deflection in the photo onscreen.
It may be possible to straighten a member also.
RE: Beam deflected
I also have the general rule of if something looks like junk, not always, but it probably is junk. Meaning if you spent the time to determine if the beam is sound, replace it anyway. In my experience things that look in bad shape tend to get noticed and not in a good way.
RE: Beam deflected
RE: Beam deflected
RE: Beam deflected
The bridge beam is typically designed according to a combination of ASCE 7, CMAA 70 or CMAA 74, and AISE Technical Report 13 (if applicable). AISC Design Guide #7 also has a lot of useful information.
It's my understanding that the bridge beam is typically designed for the full rated load + vertical impact factors + longitudinal tractive forces + lateral thrust forces. These bridge beam design is often times governed by fatigue considerations or deflection requirements (Light-duty crane L/600, Heavy duty crane L/1000). Unloaded the beam should have relatively no deflection as the self-weight of the beam and hoist is typically very small compared to the rated load capacity. Therefore, the fact that this beam has deflected so much is either a sign that the bridge beam was designed improperly or that the beam was significantly overloaded.
I'd run some calculations to check the bridge beam to see how it stands from a code perspective. If you find that the bridge beam is significantly underdesigned it's likely other elements of the crane may be as well...
RE: Beam deflected
RE: Beam deflected
RE: Beam deflected
I’d check with the crane manufacturer. They should give you good guidance on these matters as regards their crane. The crane actually looks to be in pretty good condition. I would stretch a wire along/above the top of the crane beam and record the deflection without a load, say at the 1/8th or 1/5th points. Then load the beam with 2 and/or 5 tonne loads with the trolley at the center of the beam, and measure deflection again. Then go to the manuf’er. with this info., they will know the grades of the beam materials, etc., and should be able to make some judgements on the condition of their crane. This should not be a difficult problem for you to put some preliminary numbers on too. Remember, when you load a beam like this until yielding starts in the flanges, you will get some permanent deflection, which is what you might see when your beam is unloaded. But, at the same time the plastic mechanism has started and the deflection will grow quickly without much increase in load.
RE: Beam deflected
RE: Beam deflected
RE: Beam deflected
1) Beware of optical illusions - get up there & run a string line, laser or other measuring method. Know the magnitude of the problem
2) This topic is often visited in the CMAA spec writing meetings I participate in. One school of thought is this reverse CAMBER (and we are talking camber) is irrelevant except for serviceability as noted by others above.
3) For this crane, the trolley is a free rolling unit - what we call a push trolley. It will tend to free roll to the center of crane if its excessively cambered. This can be a significant problem if not dangerous - depending on circumstances
4) Thanks to other posters for noting the 5:1 factor is NOT applied to structural members. I get tired to explaining this to our clients engineering staff or the spec writers at various engineering firms
5) While up there measuring camber, closely inspect for other anomalies that might not be otherwise visible... all components from the hoist chain to the beam to the end truck frame to the end truck wheels to the rail to the building. If there is excessive camber, and its thought to be a "new" condition, then all aspects to the crane system should be carefully evaluated.
6) We once found that a main girder had 4" of reverse camber on a 4 month old 5 ton crane.... The owner initially thought our girder design was inadequate. Then we found that a 20,000# coil up-ender (under this crane) had been pulled off its foundations - along with the epoxy anchors that held it in place
7) There are numerous charts out there that tell you what the "minimum" girder size should be on a crane of this type
I suggest a quick check to insure its properly sized.
RE: Beam deflected
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RE: Beam deflected
RE: Beam deflected
ZCP
www.phoenix-engineer.com
RE: Beam deflected
Quando Omni Flunkus Moritati