6 Lexington Ave Posted January 7, 2014 #1 Posted January 7, 2014 Can someone please explain why welded rail isn't/cannot be used on elevated structures? Thanks!
Turbo19 Posted January 7, 2014 #2 Posted January 7, 2014 Can someone please explain why welded rail isn't/cannot be used on elevated structures? Thanks! Due to the construction of the rails and the otherwise limited protection from outdoor elements any sections of welded rails run the risk of either expanding in the heat or shrinking in the cold. It goes beyond this as well, though for clarity I won't go into further detail. It's not without saying that complications can be avoided with the proper care and maintenance, however with that arises the matter of additional expenses. As such it's up for the TA to either justify the added expenses or not, and as one can see they've chosen to not deal with the hassle.
Eric B Posted January 7, 2014 #3 Posted January 7, 2014 This is what I've always heard, but never got the whole sense of it. Wouldn't the rails still expand and contract even when on the ground?
bobtehpanda Posted January 7, 2014 #4 Posted January 7, 2014 This is what I've always heard, but never got the whole sense of it. Wouldn't the rails still expand and contract even when on the ground? While this is true, it's also probably easier to secure them on the ground with heavy concrete blocks as sleepers. Not to say that it doesn't happen when it's on the ground: http://www.washingtonpost.com/blogs/dr-gridlock/post/metro-heat-kink-in-rail-likely-caused-derailment/2012/07/07/gJQAKJTEUW_blog.html
Kamen Rider Posted January 7, 2014 #5 Posted January 7, 2014 They might just find it easier to stick to track panels. It's like playing with model train tracks. Problem with one, just take it out and pop in a new one.
Eric B Posted January 8, 2014 #6 Posted January 8, 2014 While this is true, it's also probably easier to secure them on the ground with heavy concrete blocks as sleepers. Not to say that it doesn't happen when it's on the ground: http://www.washingtonpost.com/blogs/dr-gridlock/post/metro-heat-kink-in-rail-likely-caused-derailment/2012/07/07/gJQAKJTEUW_blog.html OK, that would explain it. I didn't think in terms of sideways warping, so didn't know what would happen. I guess it would be harder to prevent that on the el where the tracks are exposed. I don't even know how they are fastened to the structure. Looks like the panels are just sitting on it.
m7zanr160s Posted January 8, 2014 #7 Posted January 8, 2014 OK, that would explain it. I didn't think in terms of sideways warping, so didn't know what would happen. I guess it would be harder to prevent that on the el where the tracks are exposed. I don't even know how they are fastened to the structure. Looks like the panels are just sitting on it. Exactly! How are those ties fastened to the els?
dp142 Posted January 8, 2014 #8 Posted January 8, 2014 From what I know in my years with TA in Track construction and maintenance, CWR (Continuously Welded Rail) isn't used on structure, as mentioned above, due to expanding and contracting in extreme temperatures. The Panels do just sit on the structure however the joints on east and west rails are staggered for safety and the ties are "clipped" underneath. large spring clamps are lagged into the tie with a lip that extends onto the girder to keep them in place. Once a panel is in it stays unless there is a capital construction job and the entire panel along with others is being replaced. Should a tie go bad a lift truck is brought along side the structure, the rails are unclipped from the ties, the tie unclipped from the structure underneath, the rails jacked up, the tie slid out and a new one slid in.
Vistausss Posted January 8, 2014 #9 Posted January 8, 2014 From what I know in my years with TA in Track construction and maintenance, CWR (Continuously Welded Rail) isn't used on structure, as mentioned above, due to expanding and contracting in extreme temperatures. The Panels do just sit on the structure however the joints on east and west rails are staggered for safety and the ties are "clipped" underneath. large spring clamps are lagged into the tie with a lip that extends onto the girder to keep them in place. Once a panel is in it stays unless there is a capital construction job and the entire panel along with others is being replaced. Should a tie go bad a lift truck is brought along side the structure, the rails are unclipped from the ties, the tie unclipped from the structure underneath, the rails jacked up, the tie slid out and a new one slid in.Onwindsor Plattsburgh One way to prevent expanding and contracting is by putting a steel bridge frame (along with the tracks welded on it) in a layer of concrete, but that does require the rest of the bridge to also be made out of concrete and therefore this is only used for concrete bridges, not for steel ELs.
dp142 Posted January 9, 2014 #10 Posted January 9, 2014 Oddly enough, yesterday me and my guys went on a trouble call. The 3rd. rail (contact rail) is continously welded in a length of 1000'. In the middle (500') there is a anchor attached to a tie and the contact rail. The gaps in between contact rails are 5' with cables bridging the gaps. One half the contact rail contracted and the electrical taps on the contact rail were being pulled off the rail and some into the insulators holding up the contact rail. I guess being the contact rail contracted the way it did is reason enough for the powers that be to decide not to weld the runing rails continously on the outside.
realizm Posted January 10, 2014 #11 Posted January 10, 2014 From what I know in my years with TA in Track construction and maintenance, CWR (Continuously Welded Rail) isn't used on structure, as mentioned above, due to expanding and contracting in extreme temperatures. The Panels do just sit on the structure however the joints on east and west rails are staggered for safety and the ties are "clipped" underneath. large spring clamps are lagged into the tie with a lip that extends onto the girder to keep them in place. Once a panel is in it stays unless there is a capital construction job and the entire panel along with others is being replaced. Should a tie go bad a lift truck is brought along side the structure, the rails are unclipped from the ties, the tie unclipped from the structure underneath, the rails jacked up, the tie slid out and a new one slid in. Oddly enough, yesterday me and my guys went on a trouble call. The 3rd. rail (contact rail) is continously welded in a length of 1000'. In the middle (500') there is a anchor attached to a tie and the contact rail. The gaps in between contact rails are 5' with cables bridging the gaps. One half the contact rail contracted and the electrical taps on the contact rail were being pulled off the rail and some into the insulators holding up the contact rail. I guess being the contact rail contracted the way it did is reason enough for the powers that be to decide not to weld the runing rails continously on the outside. This is good information, many thanks for sharing this with us as an experienced MTA track worker.
Dandre Posted January 10, 2014 #12 Posted January 10, 2014 How can you have continuous welded rail in a signal block system that relies on gaps with insulated joints?
dp142 Posted January 10, 2014 #13 Posted January 10, 2014 How can you have continuous welded rail in a signal block system that relies on gaps with insulated joints? Just as you posted - with insulated Joints (IJ's) It's how it's done in the hole. Doesn't matter if it's a welded joint or made up with joint bars. It still conducts. CWR rail is maintenance free. That's less "Track Walkers" ( title for a none supervisory inspector) needed walking tracks every night inspecting joints. They only have to physically inspect switch areas.
Dandre Posted January 10, 2014 #14 Posted January 10, 2014 I think you misunderstood. Continuous rail is one long rail and any sections are welded together, unlike the current nyc subway that has the track sections joined together by a joint bar like you said. The insulated joints don't conduct electricity until the train wheels goes over them and completes the circuit, so the signal rail has to be cut into sections in every signal block and cannot be welded at all. It needs to be physically separated into pieces and there has to be fiberglass between the rails that are joined together so the metal doesnt touch each other. The signal rails never touch metal to metal where the insulated joints are, so there cant be continuous welded rail on the signal rail, there are too many insulated joints.
dp142 Posted January 11, 2014 #15 Posted January 11, 2014 I understand completely. In the tunnels where we have CWR every 10 rails are welded. Then there is a mechanical joint (Joint Bar) in between. It maybe a IJ if the track calls for it or just regular joint bars. Where an IJ is needed the rail is cut, the holes are drilled and the Rail shaped piece of Fiberglass is placed in-between the rails with large fiberglass joint bars attached on the gauge side and free shoe side of the rail. The 3 holes on the north end of the IJ along with the 3 holes on the south end of the IJ then have a short steel joint bar over those 3 holes only and not across the actual joint itself. At each step of making up the IJ Signal dept. Paints the rails the joints bars the bolts, Pretty much the whole assemble with a heavy red insulating paint. We do Signal rail one night putting in 2 "stringers" as they are called then the 3rd rail side the next night. Both Signal & 3rd rail love CWR. Less bonding for them to do
Dandre Posted January 11, 2014 #16 Posted January 11, 2014 I knew the 3rd rail was continuous, but didn't know they would do that with signal rails.
dp142 Posted January 11, 2014 #17 Posted January 11, 2014 Yes. Both the signal and negative rail are welded in rail lengths of 10. Then there is a mechanical connection Joint bars or IJ (if needed) in between every 10 rail run. At one time they were welded after being put in as stick rails. Now, they are welded in the yard and loaded on the CWR train where they are dropped, as a 10 rail length, on location. The rails sit on rollers inside modified cars. Then a sling is hooked to one end of the rail on the CWR train and the other end of the sling tied down to a running rail in service and the train moves slowly forward with the CWR rail being pulled off and landing on the track. 2 on the signal side. 2 on the 3rd rail side. The next night one side goes in and the following night the other side goes in. YUP! It's done that simple.
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