Cisc Crane Guide
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. RE: Steel construction problem, overhead crane rail.
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. RE: Steel construction problem, overhead crane rail (Mechanical). 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. RE: Steel construction problem, overhead crane rail (Structural) 21 Dec 11 20:25. 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.
Crane Guide Wire
RE: Steel construction problem, overhead crane rail (Mechanical). 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.
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This is based on the assumption that the crane runway longitudinal braking forces are resisted by bracing rather than by frame action. RE: Steel construction problem, overhead crane rail (Mechanical). 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.
Cisc Crane Guild
RE: Steel construction problem, overhead crane rail (Structural) 22 Dec 11 17:28. 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. RE: Steel construction problem, overhead crane rail (Structural) 22 Dec 11 17:48. We call all recite the words of Fisher from Design Guide 7.
It is not the be all & end all document on design of crane buildings particularly when dealing with very large OTC's IMO; and particularly when dealing with thermal issues. Bottom line in these buildings is something has to give. So you must design to allow for movement. Making flexible cap plates may be one way to achieve this but that comes with problems as well. These buildings need to be designed with intimate knowledge of the cranes themselves. They are an extension of that machine.
Reading design guides is not enough. RE: Steel construction problem, overhead crane rail (Structural) 24 Dec 11 09:55. Are the bolts failing by yielding (suggests a strength issue) or in a brittle manner (suggests a material/fatigue problem).
Have you checked any other connections for problems? We've done a lot of inspections of buildings with cranes hung from the roof trusses, and it's rare that we DON'T find loose bolts all over the place. In the most recent building we looked at, we arranged for all the bolts at key locations to be checked and tightened until some permanent remedial works are carried out.
Since that has been done, crane breakdowns have reduced significantly. Might just be a coincidence.