North Washington St Bridge

BeeLine

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JeffDowntown

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I am having an interesting mind trip concerning the Y shaped bridge piers. When I see the sets of four lined up in photos, my mind immediately thinks the roadway should be running perpendicular to the actual bridge direction. It is just something about the pier shape.
 

intellirock617

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First set of 8 tub girders for the span from the North Abutment (Charlestown side) to Pier 5 have been set and spliced.
 

Stlin

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That looks a lot less special now that it's been topped with those standard girders
 

AmericanFolkLegend

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To Charlie's point, those are not standard plate girders. The tub girders were chosen at least partly for their aesthetic. I do wonder how the white paint will age though.
 

intellirock617

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As of this past week, tub girders have been set up to the area over the former swing-span. Infill steel continues to be erected from the Charlestown side towards the Boston side.
 

AmericanFolkLegend

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I've been told by someone on the project that the welds at the bridge diaphragms are cracking. That would explain why they stopped making any progress with the stay-in-place forms.
The good news is MADOT QA/QC caught the problem. The bad news is this sounds to me like a design issue. And if it's a design issue, I would not be surprised if it took 6 months or more for the engineer to design and MADOT to approve a solution.
 

Patrick Winn

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I've been told by someone on the project that the welds at the bridge diaphragms are cracking. That would explain why they stopped making any progress with the stay-in-place forms.
The good news is MADOT QA/QC caught the problem. The bad news is this sounds to me like a design issue. And if it's a design issue, I would not be surprised if it took 6 months or more for the engineer to design and MADOT to approve a solution.
No mention of this problem in MassDOT's most recent email update on 10/29. Here's their report on upcoming work:
DESCRIPTION OF SCHEDULED WORK
  • Building the piers:
    • Pier 1 (closest to the North End): Grout work, final jacking, and concrete pour
    • Pier 2: Grout work, install rebar, final jacking, and concrete pour
    • Pier 3: complete
    • Pier 4: Complete
    • Pier 5 (closest to Charlestown): Complete
  • Installing, moving, and maintaining silt curtains and barges in the water
  • Installing utilities
  • Installing and moving temporary bents for steel erection
  • Warehouse pier and column repairs
 

Jahvon09

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Seems that it's always the same with the MBTA; Just when you might think that they are making some progress, along comes another monkey wrench that's thrown in the mix to slow things down!! Hah!! :unsure:
 
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AmericanFolkLegend

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Alright, I did some more digging and found out what's going on with the welds. Kind of interesting actually:
  • The bridge piers for this project are actually four individual piers at each location. This was a design choice made by the engineer.
  • Most large bridges have monolithic bridge piers (the first two at this link) or at least individual piers that are tied together with a concrete cap (the last example at that previous link).
  • A monolithic bridge pier provides better resilience against seismic loads.
  • The design of the N. Washington St bridge piers can't meet the seismic loads required. So they need to make it up by overengineering the diaphragms that connect the tub girders to meet those loads above the piers.
  • So they've got these super thick diaphragms that they are supposed to connect to the tub girders with a full pan weld. Fine, that can be done, just takes a long time to heat up the steel and get it super hot for the entire thickness of the diaphragm.
  • Problem comes when the super thick/hot weld cools down. If it cools down too quickly it cracks. That seems to be what's happening here.
So MADOT (who is administering the job on behalf of the COB) flipped out. They completely shut down the project. Curiously, they're kind of treating it as a safety issue - like it would be too dangerous to have anyone working on the bridge. Which is just silly because they let guys crawl all over the project to install the diaphragms in the first place. Anyway, the contractor (JF White) will need to come up with a procedure to keep the welds from cooling down too quickly and cracking. My guess is MADOT will make them prove the procedure works with a sample weld off the bridge. This problem will only be exacerbated in the winter. So we could be in for several months of no progress on the bridge.

TL/DR - There are QA/QC problems with some of the bridge welds. Don't expect any work on this bridge for weeks or months. 😥
 

bigpicture7

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Alright, I did some more digging and found out what's going on with the welds. Kind of interesting actually:
  • The bridge piers for this project are actually four individual piers at each location. This was a design choice made by the engineer.
  • Most large bridges have monolithic bridge piers (the first two at this link) or at least individual piers that are tied together with a concrete cap (the last example at that previous link).
  • A monolithic bridge pier provides better resilience against seismic loads.
  • The design of the N. Washington St bridge piers can't meet the seismic loads required. So they need to make it up by overengineering the diaphragms that connect the tub girders to meet those loads above the piers.
  • So they've got these super thick diaphragms that they are supposed to connect to the tub girders with a full pan weld. Fine, that can be done, just takes a long time to heat up the steel and get it super hot for the entire thickness of the diaphragm.
  • Problem comes when the super thick/hot weld cools down. If it cools down too quickly it cracks. That seems to be what's happening here.
So MADOT (who is administering the job on behalf of the COB) flipped out. They completely shut down the project. Curiously, they're kind of treating it as a safety issue - like it would be too dangerous to have anyone working on the bridge. Which is just silly because they let guys crawl all over the project to install the diaphragms in the first place. Anyway, the contractor (JF White) will need to come up with a procedure to keep the welds from cooling down too quickly and cracking. My guess is MADOT will make them prove the procedure works with a sample weld off the bridge. This problem will only be exacerbated in the winter. So we could be in for several months of no progress on the bridge.

TL/DR - There are QA/QC problems with some of the bridge welds. Don't expect any work on this bridge for weeks or months. 😥
Thanks so much for all of this background (& sad to learn this). I had almost typed out a long reply to your Oct 29th post, but held off since I was sensing it was way too speculative. The gist of what I was going to share, though, is that structural weld inspection is always a big deal, and it's not hugely uncommon to catch and correct workmanship issues. Now we know that the design itself is making the welding more challenging.

A tiny nitpick: by "the engineer" you mean the bridge design firm ("bridges as structural art," per their own branding). It was very unlikely a single structural engineer made this design choice to put form over function, though I'm sure one or more was tasked with figuring out how to make the design work after it was aesthetically conceptualized (and ultimately someone signed off on it). Whomever it was, in their defense, something like this can seem like it's going to work fine on paper but welding can be quite finicky. Not making excuses: someone should have thought to analyze and/or test this beforehand. Huge pieces of metal act as giant heatsinks during welding, sucking away heat from the requisite heat affected zone of the weld. Yours truly has made this mistake on a comparatively much smaller aerospace component many years ago; issue caught in prototyping and switched to a new manufacturing approach, thankfully.

The good news: there are robust non-destructive methods for weld inspection, so, while it may be tough to figure out how to get this welding done, what is comparatively more straightforward (assuming attention is paid to it) is inspecting whether proper welds are achieved in the end.
 
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Charlie_mta

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A tiny nitpick: by "the engineer" you mean the bridge design firm ("bridges as structural art," per their own branding). It was very unlikely a single structural engineer made this design choice to put form over function....
In construction contracts, it's not uncommon to use the term "engineer" or "designer" to designate the design firm.
 

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