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: