Here’s what happened at the January 12th ST Capital Committee meeting, the video for which is archived online. Nothing earth-shaking, but if I sit through a 90-minute video a post is going to come out of it:
- Sound Transit is negotiating with Microsoft to build a pedestrian bridge across SR520 near the station on the company’s dime.
- Civil Engineering nerds will enjoy the discussion beginning at approximately the 25-minute mark. Building light rail on a floating bridge introduces types of motion that have all dealt with separately before, but never in quite this combination. A gathering of the best and brightest have come up with two feasible solutions for the transition from the bridge piers to the floating sections, with the favored one known as CESURA — involving lots of little actuators to keep it steady.
- The discussion of S. 200th Street design mostly covered what we already know. However, the owner of the airport parking immediately adjacent to the station has some TOD plans for the property, and ST is working with him to design the interface with the station in a sensible way.
Civil engineers will geek out? Hmm, I’ll have to watch it when I get off work!
I remember working on a prelim floating bridge design back in 2008 when doing consulting work at Sound Transit. Quite the crazy scenario. Rail has never been permenantly built on a floating bridge before so we came up with some pretty gnarly perlim solutions. Also hard adding something that needs to be flat to a bridge with a curved deck designed for cars and drainage. Basically got to spent a week in a conference room with a huge white board, a bunch of engineers, and an unlimited supply of coffee.
Man, it would be a fun project to work on again. There’s something really exciting about trying to invent the wheel! /geeking out
The discussion of the bridge transition structure actually starts at around 21:45 in the video.
Bridge “piers” maybe?
I thought Martin was talking about the Evergreen Point bridge and the Hood Canal bridge as peers.
Yeah, things are moving really slowly on the engineering verification front. Here is that report from the Independent Review Team engineers in 2008 (drafts of it were circulating four full years ago now!):
http://www.wsdot.wa.gov/partners/irt/MaterialsSources/IRT-LightRailTrainImpacts-Final_Report.pdf .
It says this on page 10:
“Prototype testing and vetting of the track bridge concept design needs to be performed as soon as possible. This type of track bridge has never been utilized before, and there are no historical data available for the IRT to judge the feasibility of this concept.””
Now we’ve got people saying producing and testing BOTH the joints at the transition from floating components to where the pillars support the roadbed AND the unprecedented new joints for between the pontoons AND the track bridge should have been well underway before ST2 went on the ballot. That’s a heavy charge.
We’re no closer now to knowing whether that or any of the other engineering hurdles can be overcome safely. Getting this highway facility to function safely and durably as a railbed seems, well, almost preposterous. The resulting structure would be topheavy, and too rigid. That would result in an increased failure risk, and an accelerated structure deterioration rate.
Will it be three more years of people who know better looking the other way before it becomes too painfully obvious that no reputable Civil Engineering firm provides written assurances that the extensive reengineering of that highway infrastructure – especially the bridges and ramps – will not damage or degrade what would be left of it?
The audacity of the “plan” is immense. Somebody would grind off roadway surface, and build up on the concrete pontoon floating bridge some sort of as-yet-undesigned heavy train trackbed and rails, a maintenance road, and twin-pylon-supported 1500 volt dc power lines. The electrical catenary structures would be secured to the tops of the pontoons by unknown means, and setting the footings would require drilling down into a rebar mesh located by ground-penetrating radar.
The thin concrete structures out there floating on that big lake already are 23 years old. They are subjected to extreme stresses during storms. Given concrete’s poor shear strength characteristics and the fact that these structures were not designed to be converted this way, a very real risk exists that safety margins, and the useful life of these valuable highway components, will be degraded significantly by that proposed reengineering work.
Sound Transit has not even hired an engineering firm yet to quantify these risks, let alone assure it, other governments, and the public that this proposal is feasible.
This gave me a good laugh. You’re referencing and basing all your analysis off a 3+ year-old document that you didn’t read. And you quote the 5th introductory page in a 286 page document? The whole purpose of the remaining 281 pages are to shed some light on the very quote you use.
1) There is a known method of attaching OCS poles to concrete. They’re called bolts. In the document, there is a design proposal for attaching the OCS system to the bridge deck.
2) There are models in the document that reference live and dead loading of the LRT system and its effects on the structure of the bridge.
3) There are thousands of electrified rail bridges that go over water and it’s fairly easy to resolve. The running tunnels for ULink use stray current mitigation. This problem is addressed in the document.
4) Concrete has poor shear and tension properties when there is no reinforcement in it. The bridge, like 99% of all concrete structures, has reinforcement embedded in the concrete. Again, in the document.
5) We don’t need ground radar to find the rebar. The bridge is only 23 years old. We still HAVE the plans. Additionally, you don’t just drill into it. Typically, the concrete is removed, rebar exposed & cleaned, the proper connections are tied into the structure, and the concrete is repoured in the gap. It’s done all the time on roadway bridges when infrastructure, like light poles or big signs, is added.
6) I hear people say it all the time, but where are all these “other” people who question the feasibility of the project? Are they civil engineers and experts?
7) Of course Sound Transit has hired an engineering firm to work on it. I was working on it around the time this document was released three years ago. With the system opening in 2022ish, they’ll have had at least 8-10 years in design to figure it out.
8) Engineers sign off on risky stuff all the time. That’s part of the profession and the risks accepted. Imagine the poor bastard who has to sign & seal the DBT design. Biggest bored tunnel ever conceved, under a major city, and in a seismic area. Never been done before. But that stops nobody.
9) Imagine back in the day when we FIRST built a floating bridge. There were probably people who sounded exactly like you. “We can’t build a floating bridge out of concrete. Cars and concrete are too heavy. It’ll sink.”
10) Nothing is impossible. I think you’re just angry that part of the bridge is being converted to LRT.
Well, that all said, time to get back to making the impossible possible.
Nom De Blog, you’re cooking up a robust batch of FUD. Mmmmmm….FUD!
Mike B, thanks for your assertive support.