Carultch
Senior Member
- Location
- Massachusetts
It is common for installation manuals of rail systems to call for expansion joints every perhaps 40 ft, or similar. There's a lot of effort that goes in to properly planning compliance with these requirements, especially on long span systems.
My question is, are the expansion joints actually effective?
Every expansion group is usually rigidly fastened, possibly a dozen times throughout that length. That leaves only a couple feet at the end near the expansion joint, that actually will move within the joint. So the remaining majority of the length is constrained to absorb the expansion as thermal stress within each span length.
If there is flexibility in the supports, like a standing seam roof, I can see the purpose of expansion joint, to prevent any given seam from overbending. I also see the need when a rail system expansion joint coincides with an expansion joint in the structure below. But when there isn't flexibility in the supports, such as L-feet that are bolted to a dunnage array of steel beams, are thermal expansion joints actually effective?
Another mystery is that Ironridge and Unirac's expansion limits are very different. Unirac calls for 40 ft, and Ironridge now calls for 100 ft (more than twice as much). At one point, Ironridge called for 50 ft, which seems much more consistent with a 1/2" change in length of aluminum for typical US temperatures.
My question is, are the expansion joints actually effective?
Every expansion group is usually rigidly fastened, possibly a dozen times throughout that length. That leaves only a couple feet at the end near the expansion joint, that actually will move within the joint. So the remaining majority of the length is constrained to absorb the expansion as thermal stress within each span length.
If there is flexibility in the supports, like a standing seam roof, I can see the purpose of expansion joint, to prevent any given seam from overbending. I also see the need when a rail system expansion joint coincides with an expansion joint in the structure below. But when there isn't flexibility in the supports, such as L-feet that are bolted to a dunnage array of steel beams, are thermal expansion joints actually effective?
Another mystery is that Ironridge and Unirac's expansion limits are very different. Unirac calls for 40 ft, and Ironridge now calls for 100 ft (more than twice as much). At one point, Ironridge called for 50 ft, which seems much more consistent with a 1/2" change in length of aluminum for typical US temperatures.