17 September 2012

Sixth Street bridge designs published

In April, I mentioned a design competition for a US$400m replacement of Sixth Street Bridge in Los Angeles.

Three firms (out of nine) have been selected as finalists to develop design options, and their efforts so far were made public last week. Public consultations are happening today and tomorrow. A decision on the winner is due in early October.

Here are the designs (lots more pictures here). Click on any image for a larger version



Parsons Brinckerhoff

Quick reaction: The PB design is frankly bizarre, a bridge that looks like a twin arch (echoing the existing bridge) but is actually a very odd cable-stayed bridge. It's hard to see how it can possibly be economic for a bridge on this scale. The Aecom design, a Calatravesque extradosed bridge with a shot of gold bling (surely a Las Vegas feature, not a Los Angeles one) is likely to be the most economic to build. Visually, I like the style of the HNTB design, although the repeating arches away from the main river span seem to give it a grossness of scale that is not normally desirable in a city-centre structure.

What do you think? Post in the comments if you have an opinion!


Ed Hollis said...

I prefer the HNTB proposal, although that may be biased by the quality of their renderings! The form seems to be the most natural, albeit a little over the top, away from the main spans, as you say.

Not a fan of the token gold on Aecom's, personally. Can imagine it dulling down and losing its appeal pretty quickly. I did enjoy the absolutely massive sweeping pedestrian ramps in the third image, however.

The geometry of the Parsons Brinckerhoff design, I find a bit awkward. Also, the structure seems unrealistically slender for a road bridge?

Imre said...

My first thoughts about the bridge designs, based on the pictures at http://la.curbed.com (linked):

-HNTB: the series of arches looks very impressive in the aerial "photo", but it is not a common viewpoint. Of course, it lends itself to show the bridge and its settings. The "green belt" below the bridge is much more appealing than the legs of today's bridge. The myriads of stairs and ramps zigzagging up and down the arches' legs look somewhat chaotic. Also, if the "green belt" along the bridge is supposed to be a recreational area, then sound barriers along the highway could add to it's value - of course the bridge deck would loose its visual slenderness. Another odd feature is that the "central" arch above the river/canal crossing is less prominent than the next ones. Looking at the aerial picture, it's not apparent why these next spans need to be larger - their piers could probably be located closer to each other. Finally, judging by eye, the unsupported deck spans between the arches are approx. 60-70% of those below the arches. If so, the question is how effective the stay cables are.

-AECOM's design seems to focus only on crossing the river below, without the "green belt" seen in the HNTB design. In some pictures the pedestrian ramp seems to be connected to the bridge deck, and in others it looks detached. If it happened to be be detached, providing no access to the river banks from "above", that would be a serious drawback in my opinion. If the main purpose of the bridge is to cross the industrial area below, then the scenic lighting of the walkway and the plants seem out of place. I can also imagine that the "concrete environment" under the LA sun is quite hostile for the plants. The lack of a safety barrier for cars is also strange. Probably less important, but the pylons - usually strinking verical features - seem rather small in contrast to the nearby electricity masts.
To sum up my opinion about this design: to me it suggests the philosophy to make it economical as possible to applease the decision makers looking at the budget, but add some "eye-catchers" to make it appealing to the public.

To place the pier into the river (without the heavy cutwater seen at AECOM) was a striking idea of Parsons Brickerhoff, and the resulting 2 large spans look very elegant with the pylon/arch resembling wings - at least to me. Judging from the other pictures, the stay cables "replace" the springings of the arch at the other piers. Placing the walkway in the middle of the bridge, elevated above street level can be an elegant solution to let the pedestrians have a look at the surroundings - question is if the industrial area is worth it or not. On the other hand, one of the main purposes of the walkway seems to be providing access to the outlook platform on the pylon leg, and to one river bank - but why not both of them?

Patrick S. O'Donnell said...

The issues I have with the HNTB design are the long climb from ground level to the bridge deck. They offer many chances with stair cases on practically each arch leg, but I doubt they'll get used all that often. It appears this is the equivalent of an eight story climb. Only the fittest would take part. Also the hollowed out areas of the adjoining arch legs meet where the stair cases pass through would only serve as a place where druggies and homeless gather to defecate / urinate / do drugs.
I’m not all that enthused about these options. As much as I like suspension and cable-stayed bridges, the AECOM proposal should be my first choice, but I agree with you about the “bling”. The HNTB would most likely be the most expensive with all those arches the entire length whereas the other two options have economical typical long runway approaches up to the signature river spans.

Bridge Ink said...

In a way, the HTNB proposal reminds me of Ponte do Milenio in Orense, Spain, with its wild stairways.

Anonymous said...

All entries are quite disappointing. Aecom's is particularly ugly, leaving HNTB's and Parsons Brickerhoff as probable winners.

I must say that I prefer the oddness of PB's bridge to the massive redundancy of HNTB's solution.