Rail Offset On Crane Runway Girders

[Eng_Struct]

Hi Group,

For one of my project, the contractor did not install the crane runway girders within the tolerence. The rails for crane are now at roughly 5/8" (15.9mm) offset from the centre of the web of the runway girder. Runway girder is wide flange beam with cap channel and has the web thickness of 5/8". AISE and CSA guide allow for 3/4 x Web thickness (11.91mm) which the on-site condition does not meet. The runway girders are design for wheel load of 45 kips (two wheel per trolly and 8ft apar).

The crane installer contractor has noted that he typically allow for 1/4 x Web thickness for rail offset. I am wondering if there is a way to justify living with 5/8" eccentricity? How would I analyze the impact of the eccentricity (note that the girders are already at 100% capacity considering impact load and side thrust).

I understand this offset will cause torsion on the beam that it will need to be checked for however i am thinking should the width of the rail, and thickness of the cap channel web allow the load distribute and get to centriod of the beam? I am also see online that the limit is there to avoid any fatigue related issues but wouldn't that be more of a problem for welded plate girders instead of hot rolled shape?

I am out of options now. Will adding intermediate stiffeners help? How will I come up stifferners spacing? The last option will be have the contractor fix the beam which will delay the project significantly.

Any advise will be super helpfull.

Thanks!

 

[canwesteng]

The only real option will be to fix the beam. None of the proposed solutions address the additional torsion, so you either need more capacity in the beam (you said you have none, so you need to reinforce it), or straighten the rail. How did the rail even get installed that far off, did you not use clips?

Another thing to consider - while a runway loaded to say 110% of its capacity probably doesn't actually have any issues in the real world, the offset will cause some rotation of the girder as the crane goes over it, possibly causing the flange of the wheel and rail to rub, so extra wear and poor travel.

 

[Eng_Struct]

The only real option will be to fix the beam. None of the proposed solutions address the additional torsion, so you either need more capacity in the beam (you said you have none, so you need to reinforce it), or straighten the rail. How did the rail even get installed that far off, did you not use clips?

Another thing to consider - while a runway loaded to say 110% of its capacity probably doesn't actually have any issues in the real world, the offset will cause some rotation of the girder as the crane goes over it, possibly causing the flange of the wheel and rail to rub, so extra wear and poor travel.

Note that the rails are installed in a straight line - the the runway girders that are off.

Sounds like being outside the allowable limits even by 4mm will be determental.

 

[canwesteng]

That would make more sense. There is a chance you are within tolerance near the middle of the beam, and the biggest offset is at the support then. In which case you may be able to show it works.

I like to get the holes for the rail clips shop drilled for this reason

 

[Ron247]

Is the Crane Installer and the Crane Rail Installer the same entity? Is the alignment of the cap channel to the W-section ok, or is that where the BooBoo is? Sweep of the combined section might can be corrected, but Cap to Beam alignment can't be easily corrected.

Stiffeners will not remove the eccentricity. One thought is to loosen the rail, force the sweep out to some degree, set in place with a cap channel/plate under the section for some distance to also reduce actual stress. One problem is how is the crane beam over the supports. The quantity and length of the BooBoos is a factor with any correction.

There is an AISC document on torsion that I think would estimate the added normal stress due to eccentricity. I guess people still use 103% at times. Your eccentricity does not sound that severe. Also, over what distance are you maxed out?

Also, the number of cycles of use would also indicate how severe the BooBoo is from a valid wear and tear perspective

 

[Eng_Struct]

I like to get the holes for the rail clips shop drilled for this reason

That would have been help. In my case, the are using hook bolts to install the rail.

 

[Eng_Struct]

Is the Crane Installer and the Crane Rail Installer the same entity? Is the alignment of the cap channel to the W-section ok, or is that where the BooBoo is? Sweep of the combined section might can be corrected, but Cap to Beam alignment can't be easily corrected.

The crane insaller and crane rail installer at the same entitiy. I have a 304mm wide flange with the depth between base of channel flanges 308. So there is not much room for cap channel to beam missalignment. Now I am thinking that the mistake could be due to the sweep in the member.

Stiffeners will not remove the eccentricity. One thought is to loosen the rail, force the sweep out to some degree, set in place with a cap channel/plate under the section for some distance to also reduce actual stress. One problem is how is the crane beam over the supports. The quantity and length of the BooBoos is a factor with any correction.

I don't think I follow entirely. We have 40ft clear span and 9 bays. The girders are simply supported on the columns with bottom flange connection to column cap plate and also attached to the building column via diaphragm. Not sure if removing the beams to take the sweep out at each bay will be practical.

 

[Ron247]

I was not talking about removing them, just loosen the rail, adjust, reinforce, release. The beam at the column did have to do with the fact you cannot change sweep at a column, since you are Simple Span, not an issue, rarely have I seen continuous beams but I have occasionally.

What I was suggesting to consider was to loosen the rail. Push out the sweep enough to get in tolerance if possible. Weld a length of plate or channel under the crane beam to hold the corrected sweep in place. This also adds section modulus, thus reducing stress. I don't see how you can be 100% stressed at all points along the beam. The reduced stress also can allow for the added normal stress due to torsion. The torsion adds normal stress which is the common Moment/Sx stress.