California Bridges - Route 105/110 Separation (2)

We've spent the last week looking at unusual supports for freeway interchanges in California. We've studied the use of outriggers (on the 880/980/24 Interchange in Oakland), bridges on bridges (on the 5/110 Interchange in Los Angeles), and holes in bridge decks (on the 405/90 Interchange in Los Angeles). However, if we get really desperate, we can always use a C-bent like the one I designed for the 105/110 Interchange (shown in the photo).

There's no room for a column under the deck and no room for a second column on the right side of the bridge. So at this location the column is offset several feet from the center of the superstructure. These C-bents have to be designed for the large moments and shears due to the eccentric loads they carry. This is difficult for dead and live load, but it can be extremely problematic for earthquake loads.

Architects typically design a special look for freeways and interchanges. On this interchange the columns have a special shape and the outside of the barrier rails have a texture that we called fish scales (although the architect probably wasn't thinking about fishes).

California Bridges - Route 105/110 Separation (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

California Bridges - The Distribution Structure

Another bridge on bridge, this one part of the Distribution Structure that connects traffic to I-80, I-580, and I-880 just east of San Francisco Bay (see Google Earth Map below). The bridges were built in the 1950s, but one structure was replaced after the Cypress Viaduct collapse and the rest have been retrofitted. Because of the large traffic volume, no one is eager to replace the entire interchange. Its at the other end of the Cypress Viaduct Replacement from the Stack. The interchange is also called the MacArthur Maze and a section of it was replaced after a tanker truck crashed and burned on it a couple of years ago.

The photo shows another situation where a support was required over a river channel. Therefore, a small bridge was built over the channel to support the column. We can see the railroad tracks in the foreground that prevented the designer from placing the column beyond the channel. Bridges are built to carry people and goods over obstacles. Sometimes the bridge's supports also need bridges when there are a variety of obstacles to be avoided.

California Bridges - The Distribution Structure by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

California Bridges - Northwest Connector

I've mentioned bridges on bridges but I also wanted to show bridges through bridges. The Northwest Connector is a continuous 13 span RC box girder (except for two precast box girder spans over I-405) on single column bents (and end diaphragm abutments). This bridge is just a little east of Venice, California.

This long connector spans over I-405, State Route 90, Slauson Avenue, and Jefferson Boulevard (see figure above). Because of all the bridges underneath, one of the columns  on the Northwest Connector pierces the deck of a lower structure. Although this idea may seem clever, it looks dangerous to drivers, especially during earthquakes. Unless the opening is large, the two bridges (with different periods) will move in different directions during earthquakes, possibly damaging the column and possibly both bridges.

California Bridges - Northwest Connector OC by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

California Bridges - Elysian Viaduct

The Elysian Park Viaduct is a long steel girder and RC box girder (4 cell) bridge on multicolumn and single column bents and pile foundations. Its part of a network of connectors between I-5 and I-110 in Los Angeles. I've written about how hard it is to find a place to put your columns in urban interchanges. At the Elysian Park Viaduct the engineers had to design a bridge to support one of the single column bents over the Arroyo Seco Flood Control Channel.

I like the somewhat paradoxical concept of a bridge supporting a bridge. When the science writer Douglas Hofsteader has a group of people at his disposal, he likes to have them sit on each other's laps in a ring. There's something odd about the fact that the entire group is self-supporting. Can a bridge superstructure support some of its columns? A special prize for the best self-supporting bridge drawing sent to this blog!

I have a few more bridge on bridge photos to share. I also have several photos of a bridge column going through a hole in one bridge deck to support a higher level bridge. I always wondered what would happen when the two bridges start moving out-of-phase during an earthquake? Can you think of any other odd alignments between bridges in an interchange?

You can spot the Elysian Viaduct on the southwest side of the interchange shown in the Google Earth Map below (Bridge #53-1424). Like many of the bridges in Los Angeles at the time of the Northridge earthquake, the columns on Elysian Viaduct had been encased in steel shells and the bridge had almost no damage.

In Greek mythology, the Elysian Fields are the final resting place for the souls of heroes. Of course, there are Elysian Parks all over the world including one just west of this interchange (and north of Dodger Stadium).

California Bridges - Elysian Viaduct by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

California Bridges - Oakland Stack (3)

One last look at the Stack in Oakland California. I was wrong when I wrote that this interchange was part of the 'modern' aesthetic of the 1950s. The I-980 was a segment built in the 1980s to connect I-24 to I-880. When a mile of the I-880 collapsed during the Loma Prieta earthquake, the I-980 was used to divert traffic.

Although the interchange is only 20 years old, there is something 'modern' about its lines and contours. I've always been fond of the textured concrete forms used on the columns and bent caps. I also like the incongruent white column casings that give the interchange the look of a collage by Braque or of a tubular painting by Leger.
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California Bridges - Oakland Stack (3) by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

California Bridges - Oakland Stack (2)

Another photo of the Stack. These interchanges may not be art, but I enjoy the sense of freedom and spaciousness of these long curved connectors. I like the white steel casings like band-aids on some of the gray concrete columns. I even like the horizontal sign structure in the middle of this photo.

Note the nice job of designing the green landscapes around the structures by Caltrans' landscape architects. These 1960s era interchanges express a modern aesthetic with their trim lines, parabolic curves, and effective use of light and shadow.

California Bridges - Oakland Stack (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

California Bridges - The Oakland Stack

We are currently looking at complicated urban interchanges in California. There are a number of themes I want to explore. Can a connector or ramp on a busy urban freeway ever be a work of art? Is there something pleasing about the connectors as they step around each other? Does the subsequent seismic retrofit to these structures add or detract from their appearance?

Three routes (I-980, I-880, and I-24) come together in Oakland, California as 'The Stack.' During the Loma Prieta Earthquake this interchange, which looks like a big 'X' from the air, had similar damage to the four ends: crumbled interior diaphragms from too many cable restrainers holding the superstructures together at the hinges.

The concrete barrier rail had to be isolated from the columns to prevent a smaller effective column length and subsequently larger shear forces. I wonder if those knee joints have to carry the column plastic moment? Probably the columns are pinned to the bent caps, which became standard policy after Loma Prieta.

We'll continue looking at urban interchanges over the next week to see if we can learn anything important through the process.

California Bridges - The Oakland Stack by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.