Steel construction problem, overhead crane rail 3

[johg]

We have some problems with the bolted connection in our steel construction. Due to the overhead cranes the construction is not static. Due to that fact there are some issues.
I would like to discuss these problems and even the correction on these issues.

It is a real challenge to find the right solution. We have some experts to look at it, but not very satisfying.

 

[Teguci]

I would love to have the details

 

[johg]

We have found some loose bolts in the connections and some broken bolts. The 4 overhead cranes can move each 200 tons. We are afraid there is a principal fault in the detail construction. As we checked the calculations we did not find any clues.

 

[msquared48]

You need to post some pictures and details, plus give more descriptive information here. Too sketchy to give you what you need right now.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[connectegr]

Broken bolts are probably a bigger design problem than just cyclical loading. Did the design consider the thrust and impact of the crane movement? Properly installed bolts can loosen from vibration, but this is uncommon. But if the bolts are elongating they are designed incorrectly. There are simple installation steps that can help if nuts are loosening from vibration, such as double nuts, damaged threads, etc. But, a bolt simply loaded in shear rarely loosens, even if loaded cyclically. Yielding of the bolts is the best explanation of both your conditions, loosened and broken bolts. Photos of the damaged bolts would be helpful. Also photos of the connection.

http://www.FerrellEngineering.com

 

[hokie66]

We do have some people on the forum with experience in industrial structures with travelling cranes, but there can be a myriad of problems. Maybe if you can give a better description of where the failures are, or some photos, we could give some advice. I am sure your "experts" have more information than you have given us.

For your education, you might have a read of the CISC Publication, "Crane Supporting Steel Structures: Design Guide" by MacCrimmon. Also some of the publications by James Fisher.

 

[johg]

I will upload some pictures and sketches tomorrow, Due to time difference 23:00hr local.
Thanks for the information so far.

 

[Forensic74]

I suggest contacting CSD, they know what they're doing... heck, Fisher works part time for them...

http://www.csd-eng.com/

 

[Teguci]

I am very familiar with loose and broken bolts installed between crane runway girders and crane columns. In fact, I recently repaired an old runway where the standard fix for years had been to retighten the loose bolts. Cracks had formed in the ends of the girders starting in the webs and ripping horizontally due to the plastic hinge formed in the ends of the girder between the outside column flange and the inside bolts (think of the bolts prying down the end of the deflected girder).

Would like to see more info.

 

[dik]

A good place for your posting...

If you can show us a photo of the general arrangement of the column/girder/crane rail intersection as well as close up photos of the girder ends, bolt failures, and the general bearing of the girder end on the support, it would be appreciated.

The cause of the broken bolts sounds interesting... to others as well.

Dik

 

[johg]

We have specified two problems
1. Broken bolt M30(fatique) connection of crane rail beam. We think the bolt takes forces due not calculated for. It is only calculated for shear. Due to crane movement it will have shear stress and tension stress.

2. Broken bolt M20(stress) connection support to crane rail beam. Due to bending an additional force other then shear will be applied.

For details see attachment

 

[Forensic74]

I think both are fatigue related. So many variables. Could even be the flatness tolerance of the crane beam bottom flange. If its not flat you start putting cycles on the bolts.

At 200T, I would not have detailed it this way. Look into AIST and CISC manuals, but definitely get an engineer out there who specializes in crane runways..

 

[Teguci]

For 200T+ cranes, continuous spans are going to cause significant problems due to reversal of stresses and the need for plastic hinging to accommodate the deflections from the moving load. Although the hinge zone is often small, because the loads are many cycles, this small area of overstress will eventually embrittle the steel.

Whether the failure is in the bolts, the girder webs, or the connection welds, this is a problem that will be chased from one maintenance issue to the next. For example, the problem is currently identified in 2 failed bolts. Repairs for broken bolts include: reaming the holes and installing larger diameters, using higher performing bolts, extending the connection plate and installing more bolts. Strengthening the bolts means the overstress will shift from the bolts to either the girder or the connection welds.

By the way, make sure all of your bolts are installed slip critical.

 

[johg]

Thank you all for your input. Does anyone have a collegea or associate in Europa whom I could invite to discuss the details.
Prefarable The Netherlands, Germany or Belgium.
Your answers tell me that we where on the wright track. We just need to
find the wright man(specialist) for the job.

Many thanks
John

 

[hokie66]

Agree with Teguci that the continuity of the runway is the main issue, and will continue to provide maintenance problems. This will need frequent periodic inspection. I won't presume to get in the way of your engineers, but the solution to your Problem 2 may be as simple as removing those bolts outside the cap plate which are subject to prying forces and provide little benefit. This is based on the assumption that the crane runway longitudinal braking forces are resisted by bracing rather than by frame action.

 

[johg]

Your are correct with problem 2, we suggested the same. The structural engineer is checking the calculations. We thougt that only the bolt in the support are sufficient. I have some doubts, why the bolts have been broken. We are substituting the bolts which have been broken including the once in the same connection. We need to investigate all these bolts.
The structural engineer is working for same firm who fabricated the construction. We need to have an independent specialist, who is not biased in any way. We are talking about serious injuries if something goes wrong.

 

[hokie66]

Good decision to retain an independent industrial structures engineer, and good luck.

 

[ToadJones]

Teguci-

"by the way, make sure all of your bolts are installed slip critical"

Why is this the first option of some many designers?

Is it for pretension reasons? Pretension and SC are not the same.

I have dealt with many crane runway issues over the years and sometimes thought that slip critical joints were part of the problem; not the solution.

In particular, if one is using slip critical connections in a girder to column cap connection in a setting where thermal expansion is a MAJOR issue....do you design these connections for these astronomical thermal forces (+/- 100 degree F in a day)?
If you are using SC bolts in a long span runway girder how do you account for the expansion of a runway girder especially if the bracing scheme for the building does not lend itself to proper thermal expansion (seen this many times)? If the girder has to move thermally and the columns are restrained, something has to give.

I have seen 3" thick column cap plates broken almost completely from the columns on 300 Ton crane runways.

 

[ToadJones]

also....its well documented that any kind of fixed end girder on a crane runway is a bad idea. The fatigue problems be come obvious after studying a few examples.

 

[Forensic74]

Toad,
Thicker cap plates are more likely to crack than thin ones, far more material is yielding for a given rotation. Thinner, more flexible, is better so it goes along for the ride without yielding.

You want the bolts pretensioned so that the two faying surfaces are drawn together so that the passage of the crane doesn't force them together and cause stress cycles on the bolt.