Excessive camber in crane girder?

[Brancap]

Hi guys,

I have a problem and would like to know your opinion or experiences. We are constructing a single box girder bridge cranes of about 18m span.
According to CMAA, camber should be "equal" (they use that word) to a calculation that, for our case is 16mm.
After measuring, we found that our girder has 37mm respectively. I don´t believe is easy get exactly a 16mm camber, but this number look excessive.
Supposing trolley has enough power to climb it, Would that camber be a trouble?

Thanks in advance for your answers.

 

[LittleWheels]

There are crane tolerances for various classes and functional fabrication tolerances from ISO and others. What standards are required by the contract?

 

[Brancap]

Thanks for your replay LittleWheels. That point was not specified, just that the crane would be calculated under CMAA standard.

 

[FLCraneBuilder]

is this camber measured while crane is in the air? - or while on a floor with two supports at say 1/3 points along the girder length
did you measure to the floor or with a laser?
if measured to floor, the floor may be depressed in center (common occurrence)

from a serviceability perspective, excessive camber will not cause problem so long as trolley can go uphill a bit.
knowing quite a bit about hoist & trolley design, I highly doubt this is a problem. the extra HP required to climb this is minuscule.

be reminded that camber is set such that the girder will deflect to negative under full load
in this case, it sounds like the girder might deflect to flat when fully loaded -
all in all, I say this is a non-problem


FYI - we built cranes that had to climb 4" in 37' x 1150 ft long (was a bridge over the Mississippi river)

extra HP required was minimal

 

[dik]

I'm not into the design of 'serious' industrial cranes but with a 16mm deflection on an 18m span would normally not be cambered. If a symmetrical section I would put the 'natural' deflection upwards.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[FLCraneBuilder]

I did make the assumption the camber was "up".....

 

[dik]

That the normal manner in which I achieve cambers. The easy natural way without having to produce an actual camber. Up was understood, but just relying on the natural camber to provide the camber needed.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Brancap]

Thank you all for your replies. Camber is up. It was measured with a fishing line and a piece of measuring tape on the middle point. The girder was on the floor laying over supports on the ends, where carriages will be.
As LittleWheels asked about what fabrication tolerances standard we were using, I found the AISC has a Beam Cambering Tolerances standard. But following this criteria, we would be out for about 10mm.
Dik, is there any limit point after which the girder should be curved versus not needed?

 

[dik]

It depends on the span and the project, but for 18m, I'd be looking for a deflection in excess of 25mm before intentionally cambering.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik