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How do gapless rails deal with thermal expansion?
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Gapless railroads have their joints welded together to reduce noise. The lack of a gap between rail sections also reduces wear on both the track and the wheels. However, because the weld essentially produces one very long track, the individual sections have no room to expand as they get warm on hot days. What prevents the track from warping beyond usability? (Yes, I have heard of tracks warping beyond safety margins on extremely hot days, but I'm wondering about just normal expansion between normal weather extremes.)
rail
edited Sep 6 at 10:49
Ghanima
1034
asked Sep 5 at 19:04
BillDOe
28316
add a comment |Â
up vote
4
down vote
favorite
Gapless railroads have their joints welded together to reduce noise. The lack of a gap between rail sections also reduces wear on both the track and the wheels. However, because the weld essentially produces one very long track, the individual sections have no room to expand as they get warm on hot days. What prevents the track from warping beyond usability? (Yes, I have heard of tracks warping beyond safety margins on extremely hot days, but I'm wondering about just normal expansion between normal weather extremes.)
rail
edited Sep 6 at 10:49
Ghanima
1034
asked Sep 5 at 19:04
BillDOe
28316
Related: engineering.stackexchange.com/questions/7526/…
– hazzey♦
Sep 5 at 19:26
Certainly related but not quite the same. It was my understanding that the gap in rail track sections was to accommodate expansion and contraction. This question specifically asks about gapless rails.
– BillDOe
Sep 5 at 23:11
Thanks, all for the answers. When I Googled this, I searched "gapless rail" (and variations) but didn't think to add "thermal expansion" in the search term (DUH!).
– BillDOe
Sep 7 at 20:57
add a comment |Â
up vote
4
down vote
favorite
up vote
4
down vote
favorite
Gapless railroads have their joints welded together to reduce noise. The lack of a gap between rail sections also reduces wear on both the track and the wheels. However, because the weld essentially produces one very long track, the individual sections have no room to expand as they get warm on hot days. What prevents the track from warping beyond usability? (Yes, I have heard of tracks warping beyond safety margins on extremely hot days, but I'm wondering about just normal expansion between normal weather extremes.)
rail
edited Sep 6 at 10:49
Ghanima
1034
asked Sep 5 at 19:04
BillDOe
28316
Gapless railroads have their joints welded together to reduce noise. The lack of a gap between rail sections also reduces wear on both the track and the wheels. However, because the weld essentially produces one very long track, the individual sections have no room to expand as they get warm on hot days. What prevents the track from warping beyond usability? (Yes, I have heard of tracks warping beyond safety margins on extremely hot days, but I'm wondering about just normal expansion between normal weather extremes.)
rail
edited Sep 6 at 10:49
Ghanima
1034
asked Sep 5 at 19:04
BillDOe
28316
edited Sep 6 at 10:49
Ghanima
1034
edited Sep 6 at 10:49
Ghanima
1034
edited Sep 6 at 10:49
Ghanima
1034
1034
asked Sep 5 at 19:04
BillDOe
28316
asked Sep 5 at 19:04
BillDOe
28316
asked Sep 5 at 19:04
BillDOe
28316
28316
Related: engineering.stackexchange.com/questions/7526/…
– hazzey♦
Sep 5 at 19:26
Certainly related but not quite the same. It was my understanding that the gap in rail track sections was to accommodate expansion and contraction. This question specifically asks about gapless rails.
– BillDOe
Sep 5 at 23:11
Thanks, all for the answers. When I Googled this, I searched "gapless rail" (and variations) but didn't think to add "thermal expansion" in the search term (DUH!).
– BillDOe
Sep 7 at 20:57
add a comment |Â
Related: engineering.stackexchange.com/questions/7526/…
– hazzey♦
Sep 5 at 19:26
Certainly related but not quite the same. It was my understanding that the gap in rail track sections was to accommodate expansion and contraction. This question specifically asks about gapless rails.
– BillDOe
Sep 5 at 23:11
Thanks, all for the answers. When I Googled this, I searched "gapless rail" (and variations) but didn't think to add "thermal expansion" in the search term (DUH!).
– BillDOe
Sep 7 at 20:57
Related: engineering.stackexchange.com/questions/7526/…
– hazzey♦
Sep 5 at 19:26
Related: engineering.stackexchange.com/questions/7526/…
– hazzey♦
Sep 5 at 19:26
Certainly related but not quite the same. It was my understanding that the gap in rail track sections was to accommodate expansion and contraction. This question specifically asks about gapless rails.
– BillDOe
Sep 5 at 23:11
Certainly related but not quite the same. It was my understanding that the gap in rail track sections was to accommodate expansion and contraction. This question specifically asks about gapless rails.
– BillDOe
Sep 5 at 23:11
Thanks, all for the answers. When I Googled this, I searched "gapless rail" (and variations) but didn't think to add "thermal expansion" in the search term (DUH!).
– BillDOe
Sep 7 at 20:57
Thanks, all for the answers. When I Googled this, I searched "gapless rail" (and variations) but didn't think to add "thermal expansion" in the search term (DUH!).
– BillDOe
Sep 7 at 20:57
add a comment |Â
3 Answers
3
active
oldest
votes
up vote
2
down vote
accepted
What I found looking a many web sites : The continuous rails are usually in 1/4 mile ( USA) lengths made by welding together standard rails .They are hydraulically pretensioned for a particular average temperature/length depending on location ( in cold weather construction the rail may be heated to increase length). They require very good roadbed and they are firmly anchored to it so that the thermal expansion/contraction strain is held at each cross tie ( avoiding a cumulative effect of a few feet of movement at the 1/4 mile joint ). So they have a tensile strain that is greater in cold weather and may go negative in very hot weather. And, some railroads will make welds at the 1/4 mile joints.
answered Sep 5 at 21:35
blacksmith37
90327
add a comment |Â
up vote
8
down vote
The tracks are preheated and welded at a calculated temperature (that depends on the local weather) at the time of installation.
When the track cools to the ambient temperature, this leaves a tensile stress in them. This tensile stress increases on colder days, and decreases on hotter days. As long as the stress remains tensile there is no warping.
On extremely hot days the stress may become compressive. This can lead to buckling of the rails.
edited Sep 6 at 8:41
AndyT
2,968726
answered Sep 5 at 19:24
user190081
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
1
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
add a comment |Â
up vote
0
down vote
To take it back to the basic engineering principle: a change in temperature of something changes its stress-free length. That is, the length it would be if there was no stress on it.
For gapless rails (I'd call them Continually Welded Rails or CWR in the UK), the position of the rail is restrained by the connection of the rail to the sleeper or the slab below it. So the length is unable to change.
If you change the stress-free length without changing the actual length, you create stress. If your rail has got colder, it wants to get shorter, and this causes tensile stress; if your rail gets hotter it wants to get longer, and this causes compressive stress.
Failure occurs when the rail supports can't provide enough restraint against this tensile or compressive stress. On curved track this will manifest itself as the curve radius decreasing under tensile stress / cold weather, or radius increasing under compressive stress / hot weather. For a straight section of track this usually only happens under compressive stress / hot weather, where the track will buckle, snaking left and right, which makes the path of the rail longer, hence relieving the compressive stress.
So, what prevents the track warping is friction between the track and its connection to the sleeper, and friction between the sleeper and the ballast. When too excessive a temperature change occurs, the failure point is normally the friction between the sleeper and the ballast.
Note that as per user190081 and blacksmith37's answers, the stress-free length at installation may not be the distance between sleepers, as the rail may either be mechanically stretched or heated. This is as failure in hot weather is far more of a problem than failure in cold weather, so a distance between the sleepers equal to the stress-free length at a relatively high temperature makes failure less likely. There is obviously a limit to this though, as failure at cold temperature extremes is still physically possible.
answered Sep 6 at 10:34
AndyT
2,968726
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
What I found looking a many web sites : The continuous rails are usually in 1/4 mile ( USA) lengths made by welding together standard rails .They are hydraulically pretensioned for a particular average temperature/length depending on location ( in cold weather construction the rail may be heated to increase length). They require very good roadbed and they are firmly anchored to it so that the thermal expansion/contraction strain is held at each cross tie ( avoiding a cumulative effect of a few feet of movement at the 1/4 mile joint ). So they have a tensile strain that is greater in cold weather and may go negative in very hot weather. And, some railroads will make welds at the 1/4 mile joints.
answered Sep 5 at 21:35
blacksmith37
90327
add a comment |Â
up vote
2
down vote
accepted
What I found looking a many web sites : The continuous rails are usually in 1/4 mile ( USA) lengths made by welding together standard rails .They are hydraulically pretensioned for a particular average temperature/length depending on location ( in cold weather construction the rail may be heated to increase length). They require very good roadbed and they are firmly anchored to it so that the thermal expansion/contraction strain is held at each cross tie ( avoiding a cumulative effect of a few feet of movement at the 1/4 mile joint ). So they have a tensile strain that is greater in cold weather and may go negative in very hot weather. And, some railroads will make welds at the 1/4 mile joints.
answered Sep 5 at 21:35
blacksmith37
90327
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
What I found looking a many web sites : The continuous rails are usually in 1/4 mile ( USA) lengths made by welding together standard rails .They are hydraulically pretensioned for a particular average temperature/length depending on location ( in cold weather construction the rail may be heated to increase length). They require very good roadbed and they are firmly anchored to it so that the thermal expansion/contraction strain is held at each cross tie ( avoiding a cumulative effect of a few feet of movement at the 1/4 mile joint ). So they have a tensile strain that is greater in cold weather and may go negative in very hot weather. And, some railroads will make welds at the 1/4 mile joints.
answered Sep 5 at 21:35
blacksmith37
90327
What I found looking a many web sites : The continuous rails are usually in 1/4 mile ( USA) lengths made by welding together standard rails .They are hydraulically pretensioned for a particular average temperature/length depending on location ( in cold weather construction the rail may be heated to increase length). They require very good roadbed and they are firmly anchored to it so that the thermal expansion/contraction strain is held at each cross tie ( avoiding a cumulative effect of a few feet of movement at the 1/4 mile joint ). So they have a tensile strain that is greater in cold weather and may go negative in very hot weather. And, some railroads will make welds at the 1/4 mile joints.
answered Sep 5 at 21:35
blacksmith37
90327
answered Sep 5 at 21:35
blacksmith37
90327
answered Sep 5 at 21:35
blacksmith37
90327
answered Sep 5 at 21:35
blacksmith37
90327
90327
add a comment |Â
add a comment |Â
up vote
8
down vote
The tracks are preheated and welded at a calculated temperature (that depends on the local weather) at the time of installation.
When the track cools to the ambient temperature, this leaves a tensile stress in them. This tensile stress increases on colder days, and decreases on hotter days. As long as the stress remains tensile there is no warping.
On extremely hot days the stress may become compressive. This can lead to buckling of the rails.
edited Sep 6 at 8:41
AndyT
2,968726
answered Sep 5 at 19:24
user190081
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
1
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
add a comment |Â
up vote
8
down vote
The tracks are preheated and welded at a calculated temperature (that depends on the local weather) at the time of installation.
When the track cools to the ambient temperature, this leaves a tensile stress in them. This tensile stress increases on colder days, and decreases on hotter days. As long as the stress remains tensile there is no warping.
On extremely hot days the stress may become compressive. This can lead to buckling of the rails.
edited Sep 6 at 8:41
AndyT
2,968726
answered Sep 5 at 19:24
user190081
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
1
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
add a comment |Â
up vote
8
down vote
up vote
8
down vote
The tracks are preheated and welded at a calculated temperature (that depends on the local weather) at the time of installation.
When the track cools to the ambient temperature, this leaves a tensile stress in them. This tensile stress increases on colder days, and decreases on hotter days. As long as the stress remains tensile there is no warping.
On extremely hot days the stress may become compressive. This can lead to buckling of the rails.
edited Sep 6 at 8:41
AndyT
2,968726
answered Sep 5 at 19:24
user190081
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
The tracks are preheated and welded at a calculated temperature (that depends on the local weather) at the time of installation.
When the track cools to the ambient temperature, this leaves a tensile stress in them. This tensile stress increases on colder days, and decreases on hotter days. As long as the stress remains tensile there is no warping.
On extremely hot days the stress may become compressive. This can lead to buckling of the rails.
edited Sep 6 at 8:41
AndyT
2,968726
answered Sep 5 at 19:24
user190081
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited Sep 6 at 8:41
AndyT
2,968726
edited Sep 6 at 8:41
AndyT
2,968726
edited Sep 6 at 8:41
AndyT
2,968726
2,968726
answered Sep 5 at 19:24
user190081
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered Sep 5 at 19:24
user190081
913
answered Sep 5 at 19:24
user190081
913
913
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
user190081 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
1
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
add a comment |Â
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
1
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Does it mean, tension stresses are present at the cold days?
– Sam Farjamirad
Sep 5 at 19:37
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
Yes. Well, the track is always experiencing a tensile stress, in cold days that tensile stress will increase, and on hot days it will decrease.
– user190081
Sep 5 at 19:40
1
1
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
Not quite "always" tensile, perhaps "intended to be tensile within generally expected operating conditions". I've made an edit to reflect this.
– AndyT
Sep 6 at 8:42
add a comment |Â
up vote
0
down vote
To take it back to the basic engineering principle: a change in temperature of something changes its stress-free length. That is, the length it would be if there was no stress on it.
For gapless rails (I'd call them Continually Welded Rails or CWR in the UK), the position of the rail is restrained by the connection of the rail to the sleeper or the slab below it. So the length is unable to change.
If you change the stress-free length without changing the actual length, you create stress. If your rail has got colder, it wants to get shorter, and this causes tensile stress; if your rail gets hotter it wants to get longer, and this causes compressive stress.
Failure occurs when the rail supports can't provide enough restraint against this tensile or compressive stress. On curved track this will manifest itself as the curve radius decreasing under tensile stress / cold weather, or radius increasing under compressive stress / hot weather. For a straight section of track this usually only happens under compressive stress / hot weather, where the track will buckle, snaking left and right, which makes the path of the rail longer, hence relieving the compressive stress.
So, what prevents the track warping is friction between the track and its connection to the sleeper, and friction between the sleeper and the ballast. When too excessive a temperature change occurs, the failure point is normally the friction between the sleeper and the ballast.
Note that as per user190081 and blacksmith37's answers, the stress-free length at installation may not be the distance between sleepers, as the rail may either be mechanically stretched or heated. This is as failure in hot weather is far more of a problem than failure in cold weather, so a distance between the sleepers equal to the stress-free length at a relatively high temperature makes failure less likely. There is obviously a limit to this though, as failure at cold temperature extremes is still physically possible.
answered Sep 6 at 10:34
AndyT
2,968726
add a comment |Â
up vote
0
down vote
To take it back to the basic engineering principle: a change in temperature of something changes its stress-free length. That is, the length it would be if there was no stress on it.
For gapless rails (I'd call them Continually Welded Rails or CWR in the UK), the position of the rail is restrained by the connection of the rail to the sleeper or the slab below it. So the length is unable to change.
If you change the stress-free length without changing the actual length, you create stress. If your rail has got colder, it wants to get shorter, and this causes tensile stress; if your rail gets hotter it wants to get longer, and this causes compressive stress.
Failure occurs when the rail supports can't provide enough restraint against this tensile or compressive stress. On curved track this will manifest itself as the curve radius decreasing under tensile stress / cold weather, or radius increasing under compressive stress / hot weather. For a straight section of track this usually only happens under compressive stress / hot weather, where the track will buckle, snaking left and right, which makes the path of the rail longer, hence relieving the compressive stress.
So, what prevents the track warping is friction between the track and its connection to the sleeper, and friction between the sleeper and the ballast. When too excessive a temperature change occurs, the failure point is normally the friction between the sleeper and the ballast.
Note that as per user190081 and blacksmith37's answers, the stress-free length at installation may not be the distance between sleepers, as the rail may either be mechanically stretched or heated. This is as failure in hot weather is far more of a problem than failure in cold weather, so a distance between the sleepers equal to the stress-free length at a relatively high temperature makes failure less likely. There is obviously a limit to this though, as failure at cold temperature extremes is still physically possible.
answered Sep 6 at 10:34
AndyT
2,968726
add a comment |Â
up vote
0
down vote
up vote
0
down vote
To take it back to the basic engineering principle: a change in temperature of something changes its stress-free length. That is, the length it would be if there was no stress on it.
For gapless rails (I'd call them Continually Welded Rails or CWR in the UK), the position of the rail is restrained by the connection of the rail to the sleeper or the slab below it. So the length is unable to change.
If you change the stress-free length without changing the actual length, you create stress. If your rail has got colder, it wants to get shorter, and this causes tensile stress; if your rail gets hotter it wants to get longer, and this causes compressive stress.
Failure occurs when the rail supports can't provide enough restraint against this tensile or compressive stress. On curved track this will manifest itself as the curve radius decreasing under tensile stress / cold weather, or radius increasing under compressive stress / hot weather. For a straight section of track this usually only happens under compressive stress / hot weather, where the track will buckle, snaking left and right, which makes the path of the rail longer, hence relieving the compressive stress.
So, what prevents the track warping is friction between the track and its connection to the sleeper, and friction between the sleeper and the ballast. When too excessive a temperature change occurs, the failure point is normally the friction between the sleeper and the ballast.
Note that as per user190081 and blacksmith37's answers, the stress-free length at installation may not be the distance between sleepers, as the rail may either be mechanically stretched or heated. This is as failure in hot weather is far more of a problem than failure in cold weather, so a distance between the sleepers equal to the stress-free length at a relatively high temperature makes failure less likely. There is obviously a limit to this though, as failure at cold temperature extremes is still physically possible.
answered Sep 6 at 10:34
AndyT
2,968726
To take it back to the basic engineering principle: a change in temperature of something changes its stress-free length. That is, the length it would be if there was no stress on it.
For gapless rails (I'd call them Continually Welded Rails or CWR in the UK), the position of the rail is restrained by the connection of the rail to the sleeper or the slab below it. So the length is unable to change.
If you change the stress-free length without changing the actual length, you create stress. If your rail has got colder, it wants to get shorter, and this causes tensile stress; if your rail gets hotter it wants to get longer, and this causes compressive stress.
Failure occurs when the rail supports can't provide enough restraint against this tensile or compressive stress. On curved track this will manifest itself as the curve radius decreasing under tensile stress / cold weather, or radius increasing under compressive stress / hot weather. For a straight section of track this usually only happens under compressive stress / hot weather, where the track will buckle, snaking left and right, which makes the path of the rail longer, hence relieving the compressive stress.
So, what prevents the track warping is friction between the track and its connection to the sleeper, and friction between the sleeper and the ballast. When too excessive a temperature change occurs, the failure point is normally the friction between the sleeper and the ballast.
Note that as per user190081 and blacksmith37's answers, the stress-free length at installation may not be the distance between sleepers, as the rail may either be mechanically stretched or heated. This is as failure in hot weather is far more of a problem than failure in cold weather, so a distance between the sleepers equal to the stress-free length at a relatively high temperature makes failure less likely. There is obviously a limit to this though, as failure at cold temperature extremes is still physically possible.
answered Sep 6 at 10:34
AndyT
2,968726
answered Sep 6 at 10:34
AndyT
2,968726
answered Sep 6 at 10:34
AndyT
2,968726
answered Sep 6 at 10:34
AndyT
2,968726
2,968726
add a comment |Â
add a comment |Â
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Related: engineering.stackexchange.com/questions/7526/…
– hazzey♦
Sep 5 at 19:26
Certainly related but not quite the same. It was my understanding that the gap in rail track sections was to accommodate expansion and contraction. This question specifically asks about gapless rails.
– BillDOe
Sep 5 at 23:11
Thanks, all for the answers. When I Googled this, I searched "gapless rail" (and variations) but didn't think to add "thermal expansion" in the search term (DUH!).
– BillDOe
Sep 7 at 20:57