Australia's Bridges: Ryde Bridges across the Parramatta River west of Sydney (2)

March 2011 (-33.824 deg., 151.095 deg.) Ryde Bridges

A closer look at the Ryde bridges reveals that the counterweights, cables, and motors have been removed from the old vertical lift bridge. It's just as well since the new bridge prevents tall vessels from going under these bridges. 

The old bridge has three through truss spans in the middle of the river while the new bridge provides the same length spans with continuous steel girders. Placing the piers together helps prevent collisions and prevents the two dissimilar bridges from being more of an eyesore (despite having differently-shaped piers).

Australia's Bridges: Ryde Bridges across the Parramatta River west of Sydney (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Australia's Bridges: Ryde Bridges across the Parramatta River west of Sydney (1)

March 2011 (-33.824 deg., 151.095 deg.) Ryde Bridges

The Parramatta Ferry leaves the Circular Quay in Sydney every hour (when the tide is in) and travels up and down the Parramatta River. After going under the Sydney Harbour and Gladesville Bridges there are no river crossings until Ryde. 

In 1934 a vertical lift bridge was built at Ryde. They must have realized that a movable bridge wasn't needed because a stationary steel girder bridge at the same deck elevation was placed beside it in the early 1990s. The first bridge now carries three lanes of northbound Metroroad 3 and the new bridge carries the three southbound lanes.

Australia's Bridges: Ryde Bridges across the Parramatta River west of Sydney (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Movable Bridges - Tower Bridge (2)

The Tower Bridge spans the Sacramento River on a straight line from the state capitol on M Street into West Sacramento. My feeling is that Sacramento has changed a lot since the bridge was built.

For instance, at the turn of the 19th century, Sacramento was a railroad town and a swing bridge carrying the Sacramento Northern (SN) Railroad was built at this site in 1912.  The Tower Bridge replaced the swing bridge in the early 1930s but continued to carry the SNRR (along with cars and pedestrians) until 1962.

In this photo you can see the cables attached to the lift span (and counterweights). The total bridge length is 737 ft, the roadway is 52 ft wide, the lift span is 209 ft long, and the towers are 160 ft tall (and supported by 50 ft deep caissons).

Movable Bridges - Tower Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Movable Bridges - Three Mile Slough Bridge

I found that I skipped an attractive vertical lift bridge on my march up the Sacramento River. I thought we might as well go back and take a look at it as a break from all the bascule bridges. Actually, I've learned quite a bit about bascule bridges by reading Movable Bridge Engineering by Terry L. Koglin. I think they are more complicated and interesting than the generally simpler lift and swing bridges, but still its nice to enjoy a change.

The Three Mile Slough Bridge is actually a little south of the Rio Vista Bridge, across one of the sloughs that twist and turn in California's Inland Delta. I imagine it's easy to get lost, even with a GPS device, when traveling by boat through the hundreds of islands.

At one time Three Mile Slough must have been an important waterway to have merited such a big bridge. Perhaps the slough is still used to carry ships and barges into Stockton. I like the counterweights with their unusual shapes. I also like the chains hanging from the counterweights, although I'm not sure what they're for. This bridge is much simpler than the Rio Vista Bridge with its parabolic-shaped top chord. It looks like the operator's house sits on top of the lift span!

The Three Mile Slough Bridge was built in 1949. It's 750 ft long and provides 105 ft of vertical clearance and 150 ft of channel width. Apparently the bridge is in poor shape although (or because) it carries about 1000 vehicles a day. It's a steel, vertical lift, through truss bridge with long approaches and a 175 ft long lift span.

I realized that the reason I see so few big ships on the Sacramento River these days is because they built a shipping channel just west of the river. The channel is straight and wide compared to the meandering Sacramento River.

Movable Bridges - Three Mile Slough Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Movable Bridges - Rio Vista Bridge (2)

A view of the Rio Vista Bridge in the closed position. The bridge consists of two long truss approaches and a vertical lift span (for tall ships traveling on the Sacramento River). Despite the fenders surrounding the towers, the bridge is occasionally hit by ships, especially in the winter when the Tule Fog blankets the valley. An Italian freighter once knocked out an approach span on it's way to the Port of Sacramento.

I find it irritating that the San Francisco Chronicle uses Caltrans as a scapegoat whenever a ship collides with one of our bridges. They claim that the resulting oil spill is due to Caltrans not employing enough collision protection  on our bridges. I don't think there is any protection if a large vessel is traveling over 10 knots.

This bridge got a seismic retrofit in the 1990s. I think that most bridges were retrofitted in the closed position since they are only opened a few times a day (the opposite for railroad bridges). This retrofit employed lead rubber bearings for the approaches and viscous dampers at the towers (in case the anchor bolts broke). I believe there was also something done to keep the counterweights from swinging into the towers during an earthquake.

Movable Bridges - Rio Vista Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Movable Bridges - Rio Vista Bridge

The Rio Vista Bridge is actually called the Sacramento River Bridge, but so is every other bridge over the Sacramento River (it's also called the Helene Madere Memorial Bridge). It's a vertical lift bridge built in 1960 that provides 270 ft of channel width and 146 ft of vertical clearance between the towers.

Vertical lift bridges have pulleys at the top of the towers. Cables are connected to the lift span and go up and over the pulleys where they are connected to counterweights hanging from the towers. The machinery  for lifting and lowering the span are mounted at the top of each tower. There is also equipment to keep the span level while it is lifted. The operator's house can be seen at the bottom of the far tower.

Although this bridge looks to be in a rural location, traffic can get backed up for miles on State Route 12 whenever the bridge is opened. We'll take a closer look at this bridge tomorrow.

Movable Bridges - Rio Vista Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.