What's Going on at the Bay Bridge | Hacker News Reader

What's Going on at the Bay Bridge

sci-experiments.com

114 pointssoundsop18 comments

The engineering issues are very interesting, but I find the social issues even more intriguing. What would happen if the bay bridge only re-opened to commercial traffic, and BART service was radically increased?

The bridge carries 280,000 thousand cars daily -- that's a lot of traffic driving around our city, people eating at restaurants, etc. Could we maintain that level of commerce while relying almost solely on public transportation?

Yes, and no. Certain areas of the city and Oakland would become further gentrified. There's a large demographic of folk who are happy riding BART but won't get on a bus or Muni.

How has car traffic been in SF this week without the bridge?

It's been absolutely dead. Probably less than 50% of what the norm is, from just my observances. It's actually quite nice (since I bike around). But, at the same time, it's really wreaking havoc on a lot of people's daily lives.

Traffic in SOMA is a lot less around evening rush hour, because there isn't a mess of cars backed up on the streets leading up to the I-80 enterance.

Traffic is worse, however, around the other bridges in the area, since the interchanges to the major freeways (101, 880) at those bridges do not have the capacity to handle the offload from the bay bridge traffic. Some of those interchanges only have one lane vs. multiple for the bay bridge entry and exit points, and not enough merge distance to make things smooth.

Parking at most BART stations is also pretty much at capacity, whereas usually there is plenty of empty spaces.

It seems to me that the eyebar was not designed correctly - it has a stress concentration point exactly where it cracked. (If you can visualize the forces acting on it, and then take the derivative you'll see the inflection point. It's important that the derivative of the forces be smooth.)

If I were making one, I'd make it in a tear shape. i.e. the shape you would get if you wrapped a rope halfway around a bar and pulled on it.

Interestingly the outside of the eyebar is (almost) the right shape. Someone filled in the inside to make it a circle. This is a mistake - the skin of metal is much stronger than the inside (that's one of the reasons cables are made of many many strands). By filling it in you are not making it stronger - you make it weaker, because now you have less skin on the inside, and additionally you have a stress concentration point.

The bay bridge was started in 1933, and construction ended in 1936. Metal fatigue and many other aspects of material science were unknown at that time. If the eyebar was original, or built to original specs, it's entirely possible that the failure mode it exhibited wasn't even predictable given 1930s knowledge of materials under stress.

So I'm not in too much of a rush to find someone to blame :)

Unless its case hardened, which I highly doubt this steel is, the "skin" of the metal isn't stronger.

You can plainly see rust, so chemical corrosion probably started a crack, which grew through cyclical loading and more corrosion over many years.

I should probably enforce a limit on the number of times I'm allowed to plug this book on HN every year: J.E. Gordon's Structures, Or Why Things Don't Fall Down

http://www.amazon.com/Structures-Things-Dont-Fall-Down/dp/03...

It's not exactly a young book, but it's newer than the Bay Bridge...

This is less technical and more readable, http://www.amazon.com/Engineer-Human-Failure-Successful-Desi... , and Petroski describes a bridge that failed as the result of a single eyebeam failure. In that case though, there were only 4 very short eyebeams supporting the roadbed, one at each corner. He didn't actually call them eyebeams, but hangers, but from the photos, they are the same thing.

By the same author I can recommend The New Science of Strong Materials: Or Why You Don't Fall Through the Floor. (The section on wooden planes is particularly interesting.)

http://www.amazon.co.uk/New-Science-Strong-Materials-Through...

That was a hell of a lot more informative than anything else I've read/watched in the last week.

Yeah, the author put a lot of work into this.

So why hasn't the news contacted this guy and borrowed him for their reporting, or is journalism dead? Or was I just being sarcastic (about journalism being dead that is)?

Furthermore, I hate our lawsuit happy society, but someone needs to be held accountable.

From what I understand the guy who wrote this has some connections with the contractors who are doing the work... point is, he's probably not supposed to have written this (despite it being a public bridge, public property, state tax-funded project).

I'm routinely startled by how little "sunshine" we have even on such high-profile projects.

Even information about the peripheral closures arouses my suspicion, rather than satisfying my curiosity.[1]

[1] I asked why I-80 was closed between 7th and 4th St exits (the latter being the last pre-bridge exit, which I use in my commute) and why the western span is closed at all, expecting a response referencing additional serendipitous work or inspection. Instead, Caltrans's public information officer Bart Nay replied in email "The closures you are referring to at 7th and 4th Streets are necessary to prevent vehicles from approaching the closed Bay Bridge." That just made me wonder "and what might we find out if we were allowed to 'approach'?"

Why would they hire this guy? He's obviously not a trained journalist. Only professional journalists are allowed to report on news.

Note: heavy sarcasm intended. Also, I've been in the industry. For topics like this, that really is the attitude.

And Murdoch wants to start charging for their basically non-existant "coverage" of stuff like this...

Here's a nice pdf of the enhancements to the eyebar repairs:

http://baybridgeinfo.org/sites/default/files/pdfs/eyebar_rep...

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