We have an electric overhead crane that was manufactured in 1892 using riveted girder construction. The maufacturer has recommended that it be taken out of service. I assume their reasoning is that the bridge has reached its fatigue cycle limits. In addition, we are aware that the steel will work harden over time becoming brittle. Does anyone have a method(s) to determine the integrity of the materials (rivets & steel) for this bridge?
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Integrity of Riveted Crane Bridge. 1
- Thread starter RLJ
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Hi!
After more than 100 years it is still functioning? With revets, however, the fatigue problem does not seem to be as critical as for welding, but I suggest radiographic examination of the base metal around the critical areas as midspan, trolley wheel path,supports and around some of the holes in a random manner looking for possible fatigue induced cracks. Be aware of brittle fracture of this kind of cracking when reaching a critical size.
Good luck.
After more than 100 years it is still functioning? With revets, however, the fatigue problem does not seem to be as critical as for welding, but I suggest radiographic examination of the base metal around the critical areas as midspan, trolley wheel path,supports and around some of the holes in a random manner looking for possible fatigue induced cracks. Be aware of brittle fracture of this kind of cracking when reaching a critical size.
Good luck.
Gourile is right that rivets do not pose a fatigue problem as much as bolts would. The railroad industry was the last to let go of rivets for just that reason.
Gourile is also correct that the concern would be fatigue not only around the rivet holes, but also due to the details of the crane support beams. Many "traditional" ways of framing cranes were done for many years before the effects of bad details were understood re: fatigue.
There are two primary culprits that usually occur. One is the use of knee braces that are installed to brace the rail beam longitudinally. The braces develop vertical forces in the beams which produce a lifting force at the column. This is resisted by the web connections to the adjoining beam, resulting in a stress reversal, and therefore, cyclic tensile forces around the web fasteners.
The other issue is the habit of connecting the webs of the beams, at the columns, to the side columns to brace against the lateral forces from the crane. This produces cracking in the webs of the runway beams at the columns. The preferred method of bracing is to attache the beam laterally at the top flange only, taking the lateral force more directly.
Both of these create the potential for cracking in the steel which can be discovered by a number of means...check with local testing labs for the most appropriate method.
Also...the older steel was much more brittle than steels now used, so cracking is not just possible, but probable.
Gourile is also correct that the concern would be fatigue not only around the rivet holes, but also due to the details of the crane support beams. Many "traditional" ways of framing cranes were done for many years before the effects of bad details were understood re: fatigue.
There are two primary culprits that usually occur. One is the use of knee braces that are installed to brace the rail beam longitudinally. The braces develop vertical forces in the beams which produce a lifting force at the column. This is resisted by the web connections to the adjoining beam, resulting in a stress reversal, and therefore, cyclic tensile forces around the web fasteners.
The other issue is the habit of connecting the webs of the beams, at the columns, to the side columns to brace against the lateral forces from the crane. This produces cracking in the webs of the runway beams at the columns. The preferred method of bracing is to attache the beam laterally at the top flange only, taking the lateral force more directly.
Both of these create the potential for cracking in the steel which can be discovered by a number of means...check with local testing labs for the most appropriate method.
Also...the older steel was much more brittle than steels now used, so cracking is not just possible, but probable.
- Thread starter
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DaveVikingPE
Structural
Please take a lot of photographs! Also, do you have as-built drawings, design calcs, etc.? This sounds pretty amazing!
CONTACT THE LOCAL ASME CHAPTER, IT CAN BE NOMINATED AS AN HISTORICAL ENGINEERING LANDMARK.
- Thread starter
- #9
Since this thread was orginally posted we have purchased a new crane for this area. We do have orignal drawings but unfortunately no design calculations. Another regret is that the crane had to be cut into pieces for removal. The original manufacturer was not interested in any preservation. Thanks again for the helpful information!
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