Monterey County, California Bridge: Mazda Raceway Pedestrian Overcrossing

July 2016 (36.5859, -121.7495) Mazda Raceway POC

A modern timber bowstring truss carries pedestrians over the Mazda Raceway in the Laguna Seca Recreation Area. This interesting structure is almost hidden behind all the advertisements on display.

The top and bottom chords of the bridge are glulam members secured to the diagonal truss members with metal plates and bolts (shown below). The walkway is housed within a plywood structure built on the inside of the truss. 

Pedestrian overcrossings built over freeways usually have a fencing on the inside to prevent people from throwing things onto the cars below. Maybe the plywood serves a similar purpose?

A few bracing members on the inside completes the job of securing the structure's shape.

Google Earth provides an excellent view of the racecourse in 3D with our bowstring truss bridge in the foreground (the raceway looks more painterly than photographic!). We had to pay $8 to gain admission to the park so we could photograph the bridge.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Sonoma County, California Bridges: Balshaw Bridge across the Petaluma River

August 2014 (38.2344 Degrees, -122.6398 Degrees) 

A couple of blocks upstream from yesterday's 'D' Street Bridge is the Balshaw Pedestrian Bridge, a 120 ft long timber bowstring truss that was built in 1989. The bridge was constructed in a yard in Santa Rosa, carried by barge, and assembled across the Petaluma River in downtown Petaluma. Like many urban bridges, this one was named after a city councilman.

Timber truss bridges (like the previously studied Rancho Murieta Bridge) can be nice, but the top chord is splitting on this bridge and no thought was put into creating an attractive handrail. This rail dominates and makes the bridge look like it's being supported by the steel railing.

Sonoma County, California Bridges: Balshaw Bridge across the Petaluma River by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (4)

March 2013 (38.49477 Degrees, -121.08421 Degrees) Cosumnes River Bridge

A few more photos of the Cosumnes River Footbridge. When I first saw this bridge from a distance, I just assumed I was looking at an old steel truss.

The bridge portals are unadorned vertical steel I girders with a Glulam top chord. The deck is 12 ft wide and composed of 2-1/2 inch thick Glulam panels. I'm not sure about the vertical clearance. The bridge had to be designed for a 10 kip maintenance vehicle. I wonder if it controlled the design?

A look at the underside of the bridge deck, which is supported by Glulam floor beams and stringers. Steel rods provide lateral stability at the top and bottom chords. The superstructure was designed by Western Wood Structures, the substructure was designed by Quincy Engineering, and the bridge was built by Viking Contractors. Western Wood Structures has a nice website with a description of this bridge.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (4) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (3)

March 2013 (38.49477 Degrees, -121.08421 Degrees) Cosumnes River Bridge

Another view of the Cosumnes River Footbridge, which was completed in 2008. The bowstring truss (and the parallel chord approach spans) are composed entirely of diagonal load bearing members. The only vertical elements are at the supports.

The trick to building timber structures is to provide well-designed connections. The steel plate connectors look like they were manufactured especially for this bridge. Also, the trusses use diagonal steel rods at the top and bottom chords instead of the usual sway bracing.

There are several websites that discuss this unusual structural including StructureMag which has some nice construction photos and the section properties of most of the bridge members.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (2)

March 2013 (38.49477 Degrees, -121.08421 Degrees) Cosumnes River Bridge

Another view of the Cosumnes River Footbridge. The exterior concrete is faced with rounded river stones. I wonder if they glued facing stones to the formwork or placed them after the concrete hardened?

The bridge is a nice combination of structural steel for the vertical members over the supports and the connecting hardware, glulam wood for the other truss elements, and stone faced reinforced concrete for the retaining walls, abutments, and piers.

What makes this bridge so impressive is that the glulam effortlessly bends upward to form the top chord of the bowstring truss. Talking to the residents at Rancho Murieta, they all expressed impatience at how long the bridge took to get built and satisfaction with how nice the finished product was.

Rancho Murieta is pleasant but slightly cultish because the relaxed lifestyle the residents enjoy is separated from the rest of the world. We'll take a closer look at their bridge tomorrow.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (1)

March 2013 (38.49477 Degrees, -121.08421 Degrees) Cosumnes River Bridge

The most interesting of the three bridges that cross the Cosumnes River in Rancho Murieta is this new timber bowstring truss pedestrian bridge.  I first saw it looking upstream from the State Route 16 Bridge, but I couldn't figure out how to get to it, since it's inside a gated community. I was thinking about kayaking down the Cosumnes River to photograph it when my wife suggested that we should just drive up to the entrance to Rancho Murieta and ask if we could photograph the bridge.

As I've often mentioned, truss bridges are seldom built nowadays, but this is a nice contemporary truss bridge and it looks especially nice in wood. The bridge was designed by Western Wood Structures and engineered by Quincy Engineering. Western Wood specializes in big, Glulam structures and Quincy Engineering is made up almost entirely of former Caltrans bridge engineers.

We'll take a closer look at this interesting bridge tomorrow.

Sacramento County, California Bridges: Rancho Murieta Footbridge across the Cosumnes River (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.