Green Line / Central Corridor construction thread (archive)

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MNdible
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Re: Green Line (Central)

Postby MNdible » December 19th, 2012, 9:53 pm

This raises a question for me -- once these long lengths of rail are welded together, how is thermal expansion handled? I mean during seasonal temperature shifts, not during the actual welding. By my crude math, a 200' length of rail should be expected to expand 2.5" between MN temperature extremes.

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Re: Green Line (Central)

Postby mulad » December 19th, 2012, 10:25 pm

That's an interesting question. Unfortunately, I don't have an answer.

I just wanted to briefly mention that Cedar Street in downtown Saint Paul fully reopened today. Watch your step if you're walking along there, though -- I took a peek at it on Monday night and there are some significant gaps between the guideway (the concrete encasing the tracks) and the adjacent road surface. I presume that's part of the floating slab system to reduce vibration by MPR. The gaps between the different masses of concrete seem just wide enough for a foot to get stuck in and twist/break an ankle. Presumably the spaces will get filled in with some rubberized material soon enough...

So that just leaves the Washington Avenue transit mall as the last segment to reopen. The last weekly update message for the area indicated that the sidewalks aren't finished along Northrop Mall and won't be done for a while yet.

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Re: Green Line (Central)

Postby UptownSport » December 20th, 2012, 12:13 am

Steel doesn't expand anything compared to the a-fore-mantioned.
Otherwise, pipes would break, engines would seize, skyscrapers would visibly grow and usw

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Le Sueur
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Re: Green Line (Central)

Postby Le Sueur » December 20th, 2012, 3:37 am

I think the key here is assuming the growth is "unrestrained" but MNdible does have the thermal expansion rate of steel correct if was calling MN's "temperature extremes" about 170 degrees Fahrenheit.

Everything I could find pointed to a .000011mm/degree C (average alloys would differ)
So 60,960mm x 94.4 degree C x .000011mm = 63.3mm or 2.49 inches.

Average Temperature swings in MN are something like half that. So maybe 1.25 inches over 200ft of unrestrained rail.

To answer the question "how is thermal expansion handled?" most of the expansion and contraction force can be "restrained." The Rail Anchors, and the Reinforced Cement in this case force the rail to compress or stretch instead of buckling or breaking. One answer I read, a rail worker mentioned repairing a breaks (gaps) of 3-16 inches to give you an idea of the rails ability to normally stretch (more than I thought it could).

In extreme cases a Breather Switch is used to allow the rail to somewhat freely expand.
On that note here's what wiki has to say about Continuous Welded Rail

Hope that's all close to acurate/useful. I was interested in this as I love rail and have see a Sun Kink in person. Thanks for the good question!

And only to joke:
UptownSport wrote:Otherwise, pipes would break, engines would seize, skyscrapers would visibly grow
These things all happen no? Just not all the time.

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Re: Green Line (Central)

Postby LRV Op Dude » December 21st, 2012, 12:51 pm

Blog: Old-Twin Cities Transit New-Twin Cities Transit

You Tube: Old, New

AKA: Bus Driver Dude

MNdible
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Re: Green Line (Central)

Postby MNdible » December 21st, 2012, 1:34 pm

Le Sueur wrote:I think the key here is assuming the growth is "unrestrained" but MNdible does have the thermal expansion rate of steel correct if was calling MN's "temperature extremes" about 170 degrees Fahrenheit.

Everything I could find pointed to a .000011mm/degree C (average alloys would differ)
So 60,960mm x 94.4 degree C x .000011mm = 63.3mm or 2.49 inches.

Average Temperature swings in MN are something like half that. So maybe 1.25 inches over 200ft of unrestrained rail.
Thanks for the helpful information. It had not occurred to me that the ties could actually constrain the expansion, but it does make sense that setting the rail in tension would help accommodate the expansion. For my math, I was assuming that the temperature swing was from -30F to 120F (assuming that a rail sitting in the sun could get quite a bit hotter than ambient air temperature). But what I hadn't accommodated was that the rail is probably set at a temperature that's about half way between the extremes, so half of the delta would be expansion, and the other half contraction.
UptownSport wrote:Otherwise, pipes would break, engines would seize, skyscrapers would visibly grow
Most of the things you reference are in temperate conditions -- pipes are buried underground and stay at a fairly constant temperature, skyscrapers are conditioned (although the exterior cladding of a building is typically only spanning a couple of floors at most and must have expansion joints to accommodate differential expansion). Engines do expand and contract significantly relative to their size, but the sizes that the expansion is being applied to is much much smaller (2" piston instead of 200' length of rail), and all of the parts are expanding or contracting together and at roughly the same rate.

The most comparable example would be bridge structures, which obviously do contain pretty substantial expansion joints to accommodate this.

And obviously, most rail (excluding this new-fangled CWR stuff) does have a gap between segments to handle expansion. The pictures of the sun kinks demonstrate the surprising forces that steel expansion can generate.

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Re: Green Line (Central)

Postby UptownSport » December 21st, 2012, 3:52 pm

MNdible wrote: But what I hadn't accommodated was that the rail is probably set at a temperature that's about half way between the extremes, so half of the delta would be expansion, and the other half contraction.
Good point-
Obviously not thinking about tiny fractions adding up over vast distances. Suppose that's why rail 'floats', has either a spike only holding it down, or the spring thingy they have on cement ties

Seen crew on 35W flyover doing something Wednesday, so as said, they're still working in Winter

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Re: Green Line (Central)

Postby Silophant » December 21st, 2012, 6:17 pm

Got this bulletin from the Met Council today. No news in it, I don't think, but it's a cool summary of how much is really going on along the line.

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Re: Green Line (Central)

Postby spectre000 » December 21st, 2012, 11:15 pm

Silophant wrote:Got this bulletin from the Met Council today. No news in it, I don't think, but it's a cool summary of how much is really going on along the line.
I'm intrigued about the mention of the Sears site as well as the former Bus Barn site (I94 and Snelling). Lots of potential on those large plots of land.

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Re: Green Line (Central)

Postby trkaiser » December 27th, 2012, 2:02 pm

I drove the entire line today and took some fun pics. I especially like how things are looking near the MPR headquarters and in Lowertown. It's looking so close to completion! I can't wait for spring to see the landscaping and little details shaping up.

http://tomabouttown.wordpress.com/2012/ ... ne-update/

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Re: Green Line (Central)

Postby twincitizen » December 28th, 2012, 5:18 pm

The TPT documentary "One Street, 1000 Dreams" is airing a few more times, specifically tonight at 8PM and 2AM. I'm gonna try to catch one of the airings tonight.

https://www.tpt.org/index2.php?a=programs&id=22516

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Le Sueur
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Re: Green Line (Central)

Postby Le Sueur » December 30th, 2012, 3:54 am

^^^Checked this out. Very interesting history about the Faust I never knew about. Also, can you imagine current LRVs being built in Minneapolis?

And, Strib update on central corridor business:
http://www.startribune.com/local/stpaul/185176732.html

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Re: Green Line (Central)

Postby Didier » December 30th, 2012, 11:00 am

I was glad to see a story finally portraying the other side -- that not all business owners are fleeing University. Raymond Avenue in 10 years, as one example, will be fascinating to see.

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Nick
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Re: Green Line (Central)

Postby Nick » January 1st, 2013, 5:30 pm

Amenity area!
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Re: Green Line (Central)

Postby Nick » January 1st, 2013, 5:34 pm

This is super nit-picky, but I'm disappointed by the signage along the Green Line. MetroTransit usually has such good attention to detail when it comes to things like graphic design and making things look nice. Why is "TO DOWNTOWN MINNEAPOLIS" in all caps and "to downtown St. Paul" not? Why isn't the Green Line label centered better? And why don't the new Washington Avenue roadsigns match the rest of the signs in the city? If this ends up being my biggest problem with a billion dollar project I'll be happy, but it just seems like a really silly thing to skimp on.
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Re: Green Line (Central)

Postby mulad » January 1st, 2013, 7:19 pm

I hadn't noticed the uppercase/lowercase problem, but the off-center "Green Line" definitely jumped out at me when I first saw the signage. I don't have much of an opinion on the Washington Ave signs other than that someone may have gone a little too far in trying to make things more pedestrian-scale (other than a somewhat squished font, that pole just seems short...)

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Re: Green Line (Central)

Postby Didier » January 1st, 2013, 8:50 pm

Without any evidence except for your photos, the "To downtown St. Paul" and "TO DOWNTOWN MINNEAPOLIS" signs shown are different styles. So my assumption is that the larger yellow background template is upper-lower case and the small blue signs are all upper-case. Is that the case?

If so, that doesn't bother me as much. As long as things are consistent among similar signs.

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Re: Green Line (Central)

Postby kellonathan » January 1st, 2013, 10:03 pm

This is also a super nit-picky issue but, am I the only person who are annoyed by inconstant usages between "to downtown St. Paul" and "to downtown Saint Paul"?
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Re: Green Line (Central)

Postby seanrichardryan » January 1st, 2013, 11:34 pm

Why are there cafe tables in the median?
Q. What, what? A. In da butt.

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Nick
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Re: Green Line (Central)

Postby Nick » January 1st, 2013, 11:56 pm

Didier wrote:Without any evidence except for your photos, the "To downtown St. Paul" and "TO DOWNTOWN MINNEAPOLIS" signs shown are different styles. So my assumption is that the larger yellow background template is upper-lower case and the small blue signs are all upper-case. Is that the case?

If so, that doesn't bother me as much. As long as things are consistent among similar signs.
The blue signs at the entrance have the lower and upper case. The picture with the "to downtown Saint Paul" is there for the off center Green Line label.


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