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Allan

what is the hybrid? are those pictures of the hybrid or cable stay? maybe i'm just to dumb to get it

Brian Libby

Sorry Allan, you're not too dumb (although you did write "to" instead of "too"). It's my mistake for not specifying. All these images are of the hybrid bridge.

Brian Libby

And I'm just teasing about the "to/too" thing. This blog is full of typos, so no one is immune.

Allan

What is the 'hybrid' a hybrid of? A cable-stay and some other bridge? What is the other bridge?


I'm more too lazy to proof my comments than too uneducated to realize that my grammar was incorrect :)

Bob R.

I'm not a civil engineer, but I think I can sum up the "hybrid" terminology:

The bridge is a hybrid between a pure cable-stayed design, and a pure suspension bridge design.

In a suspension bridge, the main cables form an upside-down arch, and then a series of small cables runs straight down from the arch to the bridge deck.

In a cable-stayed design, the cables radiate out from a tower or towers, basically in straight lines from the towers to the bridge deck connection.

Also, generally speaking, cable stayed bridges generally anchor the cables to the center of the towers, sometimes going to the middle of the bridge deck with only one row of cables, instead of the two usually found in a suspension bridge.

In the hybrid design, shown above, you can find elements of both types. There is the upside-down arch, and two rows of cables, like a common suspension bridge, but also cables that anchor directly from the towers to the deck at angles, from the cable-stayed design.

Here's a question: All of the discussion I've seen so far has stated the advantages of the hybrid design over a pure cable-stayed design (less height, less bulk), but I haven't seen anything about what makes the hybrid better, from a practical perspective, than a pure suspension bridge. Is it cost? Is it the uniqueness of the design?

Count me in as a fan of the "wave" design. I wouldn't mind this hybrid, however, but I thought the wave, for a variety of reasons, was more "Portland". I'd still like to see a pure cable-stayed design somewhere, too -- we don't have an example of that form in Portland, and we are a "city of bridges" after all -- it would be nice to have one of everything. :-)

Brian

I am a civil engineer, or more importantly, a structural engineer. Bob R. is spot-on in his description of the different bridge types.

To answer the question of what advantages a hybrid bridge has over a pure suspension bridge, the hybrid shares the loads between the cable stayed type cables and the suspension bridge type cables. This means that if the bridge was a pure suspension bridge, the cables that form an upside-down arch would have to be much larger. Perhaps more importantly the anchorage of these cables on either end of the bridge would have to be much larger creating a larger footprint on either end of the brige.

Another advantage of the hybrid bridge (hybridge?) is that, because it's a combination of two types of bridges, there is some sharing of the bridge loads between the two cable types. With a pure suspension type bridge, the entire bridge is being carried by the suspended cables. If there is a problem with that cable, then there is a problem with your bridge.

Bob R.

Thanks, Brian.

Allan

Thanks guys.

I am a fan of the 'wave' bridge as well, but The shorter towers of the hybrid bridge do seem desirable, so i'm more in favor of this than the straight cable-stayed bridge.

Gwen

As someone who sat through the bridge selection process, I've been experiencing a mixture of dismay, concern, and a pinch of hopeful encouragement as this process unfolds. I was a wave frame supporter. I am not a cost estimator or an engineer. So I took Trimet's cost estimator's word on the very high cost difference between the two types of bridges. However, I was deeply disappointed with the way the proposed cable stay schemes would work on that stretch of the river. It really felt like we had two bad choices - and a false dichotomy - design vs budget, all over again.

So I for one am excited about Rosales hybrid because it does at least one thing better than the wave - it's structure provides more open views to people on the bridge, for instance. Further, Rosales went beyond his charge to offer Trimet an opportunity to do the city a solid with a really nice looking bridge for this crossing that also happens to offer a bit of innovation.

As someone who sat through plenty of long meetings about the bridge, I would find it deeply disturbing if the fix were in for a cable-stayed bridge. I have zero time or interest in being a rubber stamp for anyone. That being said, I've decided to instead focus on what I believe was an extremely positive and masterful, if late breaking, contribution to the Portland-Milwaukie Light Rail project: the hybrid bridge design. I feel like we've found a way to address Trimet's potentially legitimate concerns regarding material availability and cost and take care of those of us who did not want to regret the bridge every time we laid eyes on it in decades to come.

dennis

the hybrid bridge is definitely growing on me and every time I cross the Marquam Bridge, I think that this hybrid bridge would hold its own better next to the two big bridges and wont be drowned out as much.

But I am still confused to why the city hasn't named this bridge the Cesar Chavez Bridge and be done with this whole stupid naming issue....seriously, how hard does this have to be for the city?

ws

The Rosales hybrid in the pictures above looks great to me. It's graceful. That's what I want to see on the river. I hope that in the actual bridge built, the support tower tops will have some kind of finishing detail, rather than just being chopped off square as shown in the pics.

I never really liked the wave bridge. That thing was just too weird, even for the part of Portland that feels the need to keep trying to be weird. I like a design that looks like it knows what it's doing. That one just didn't. It looked like the weird squiggly line for a mouth that Charlie Brown got after he ate something bad.

Bob R and Brian, thanks for those excellent and helpful explanations of bridge engineering.

Kat Callon

"This was an encouraging point, because the bridge is being located in a counter-intuitive way when it comes to access for most Portlanders. Instead of being located close to downtown, it's being placed down by the South Waterfront district."

I am an art history student (used to major in mechanical engineering) at PSU, and a somewhat frequent topic of discussion on campus has been in regard to all of the rail work downtown as well as the canceling of bus lines throughout the metro area due to budget shortfalls. I was told by a professor that the new rail lines won't provide transportation for the areas which most needed it and seem to have been planned around cost rather than practicality (even though his opinion is that the system is a waste of millions of dollars). My oldest son takes the 33 to Grant High School M-F, but last we heard, the route will be cut. Driving to the PSU art building via 5th avenue and only being able to drive down one of the three lanes (the others are rail and bus) upsets me. Why do we need two systems on one road when we can't even provide busing for our public school children? I feel our public transportation planning is currently misguided.

Just the other day I when I was visiting the ReStore on SE Morrison and drove by paved over rail tracks I couldn't help but wonder how much money had gone into that rail project (now not running) at the expense of more viable options. I can't help but think it could be imprudent to build a bridge "Field of Dreams" style- if we build it they will come- if there is more need elsewhere. I love Boston, and maybe that area did develop, but their Big Dig is an emblem of fiscal irresponsibility even with great intentions. If the project goes through, I hope it is successful, but before it is funded, I believe we have more pressing and immediate needs (like funding our current bus lines rather than building another bridge across the river).

dennis

Kat, actually a little history point about those abandoned tracks you see, those were for cars that were much lighter than we have today. Even if the city wanted to reuse some of these old tracks, they would not fit the current trains that are being used.

While I agree with you on the bus cuts are a wrong way to go, I am confused to why you are complaining about the designated roads for public transportation? 5th and 6th have been designated public transportation roads for quite a while now, so the adding light rail to those two streets doesnt change the fact that those two roads have always been limited access for cars...unless you werent living here a couple years ago, then I can understand that confusion.

Also confused with the Big Dig reference, the Big Dig was a massive overhaul to a highway system that meant burying a highway, this is a bridge for light rail and pedestrians....I dont think a city should just do projects for cars....as for the "Field of Dreams" reference, I am also confused with that....I am pretty sure we have already built light rail and they have come....so expanding it seems to make sense...or am I missing something here?

John Russell

One thing I'm really enjoying in that second to last picture is how nicely the curves of the hybrid design mirror the structure of the nearby Ross Island bridge. Plus one for the hybrid.

A B

Yeah, I noticed how it mirrors the Ross too, thats a very nice detail.

Now that the schematic design is out of the way...are there going to be stairs and switchbacks onto the greenway/pedestrian path? (Like at the Eastbank Esplanade)

Is the light-rail going to merge with the existing tracks on Moody?

What is the status of the greenway/ped path? Will it be built at the same time?

When will the hybridge be built!?

kww

I fail to see how a cable stay bridge is 'cookie cutter' or somehow "being The Men's Wearhouse or J.C. Penny in this metaphor".

Just because a bridge design is different and expensive (Wave), doesn't make it better.

Cable stay designs are proven, aesthetically pleasing and will result with the best view from the bridge itself.

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