Honoring Los Angeles' Sixth Street Bridge

Among Los Angeles' least-celebrated treasures are her bridges. Not that they don't have their admirers, but the glorious concrete and steel spans that cross the Los Angeles River, as well as her tributary the Arroyo Seco, just don't tend to get a lot of attention. They seem to do a lot of filming down at the bridges and along the river, but nobody talks about the bridges much. There has been an exception lately, which is the Sixth Street Bridge, only the attention it has been receiving isn't exactly the good kind.

Apparently, the concrete of the Sixth Street Bridge has been diagnosed as having Alkali-Silica Reaction, or
ASR. This is a chemical reaction among the concrete's ingredients that eventually causes the concrete to expand. This expansion creates internal pressures inside the concrete, which increase until the concrete starts breaking apart. (Mind you, not breaking apart as in exploding, but more like crumbling.)

About a year ago, the L.A. City Council voted to replace the bridge, and earlier this week they announced the winning entry from among 3 teams that participated in the competition. There is a YouTube channel at this link, where you can see short videos of all 3 competition entries.  The 3 teams were Parsons Brinckerhoff, AECOM, and HNTB with Michael Maltzan. HNTB/Maltzan won, and you can read more about the new bridge over at CurbedLA.

Back when I worked at Studio Works, we were just a stones throw from the 6th St. Bridge. I made many a trip across it at lunch time, for the excellent tacos at Carnitas Michoacan. It's just across the river, about a block or two beyond the end of the bridge on the left side, corner of Whittier and Soto. Those have to be some of the best tacos in L.A.  If you look closely at the taco stand, you can see that the place used to be a filling station. Look up above the counters where you order, and you can see the garage doors still up there in the ceiling. But I digress (and I'm making myself hungry!)

Since we've been having some pretty outrageously bright and clear mornings of late, and you never know when the next 7.0 is going to come rumbling through and reduce our beloved viaduct to a pile of steel and rubble, I went out and spent some time around, under, and on the bridge. I was reminiscing, and studying, as well as just enjoying. I'm not quite ready to mourn, but I will when the time comes for that.

I started off by checking out the bridge from the east side, and eventually made my way across the 7th Street Bridge, which is the next one to the south. I got out and walked back out on the 7th St. Bridge and took some pictures looking north. Click to embiggen.

The distinguishing feature of the Sixth Street Bridge is its mirrored pair of eccentric steel arches that carry the roadway across the L.A. River. The vast majority of the bridge is concrete, and just that center portion employs steel as the primary structural element. It is this hybrid combination of materials that makes the bridge so unique. There are a lot of concrete bridges out there, and a lot of steel ones. It's not uncommon to see a steel bridge with concrete abutments or piers, but you rarely see the two materials integrated so artfully into one structure.

In plan, the bridge isn't a straight line. It bends in the middle, so that the western flank is nearly straight east-west, but the eastern flank aims slightly south-easterly. This heightens the visibility of the steel arches as you approach from the west, since they are not in a straight line with your direction of travel.

You can see this in the image below, taken from alongside the western approach:

Another interesting thing I noticed above is that if you look at the row of light posts, and follow the line of any particular one downward, as it passes by the guardrail and down below the road bed, most of them continue all the way down to the ground as solid piers. Some, however, terminate in a corbel that doesn't go straight down. In the image below, you can see how the supporting concrete pier actually curves elegantly back inward.

The unfortunate addition of a chain-link enclosure somewhat obscures this detail but here it is close up. I love it when I find examples of Theme and Variation in design and this is a good one.

Also visible, upon closer examination, is ample cracking. When they say it has a 70% chance of failing in a 7.0 earthquake, I believe it.

I'd never been under the bridge before, in the actual river bed, and didn't know exactly how to get down there, given that the river is flanked by active railroad yards along both sides through this whole area of downtown. Unexpectedly, as I walked along the length of the western approach, I noticed this tunnel. No gates or signs or anything, just a tunnel. There was a vehicle with flashing hazard lights at the other end.

The tunnel led to the river bed directly, passing under the rail yards. There was a little filming action of some kind going on down there, with a spotless white RX-8 and two guys in suits and sunglasses trying repeatedly to make it to the car in time, or something like that.

It was pretty fantastic down there in the river bed. The sunlight and blue sky were glorious, and what little water there flowed happily past.  There were other photographers out and about admiring the bridge as well, and I made some new friends.

Then it was back up topside, to examine the tops of the arch-trusses up close.

I like how the sidewalk splits and the steel arch rises out of the center of the walkway.

I had a great time and intend to return. Based on the information I found online, I believe we have at least another year before they tear it down. And hopefully that 7.0 will hold off too. It makes me sad to lose such a great iconic work, but by all appearances it can't be helped.

And so, it seems the appropriate thing to do is to celebrate the monumental achievement that was the Sixth Street Bridge in the time we have left.