Movable Bridges - Meridian Bridge (2)

I'm standing on the deck of the Meridian Bridge. In the distance you can see the Sutter Buttes, which are the remains of some old volcanos.

The steel tower supporting the swing span is a model of simplicity. The tubular legs on each side of the deck come together at the top and are braced with a strut. The cables come up from two floor beams, through the top of the tower, and then are attached to two floor beams on the other side.

I often wondered why the swing span of this type of bridge doesn't bang into the corners of the side spans when it moves. I looked closely at the gap between them and saw that it was curved, probably to the circumference of the circle the swing span makes as it rotates about the pivot span.

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

Movable Bridges - Meridian Bridge

This is the last movable bridge I have photos of on the Sacramento River. However, there are a few more movable bridges up north that I hope to photograph (maybe during the summer).

Bridge engineers are faced with a challenge providing a big enough channel opening with a swing bridge. Because the support is in the center, it's difficult to make the cantilever spans on each side large enough for ships to pass. We saw that the Spokane Street Bridge (April 28th and 29th) has a swing span on each side of the channel so that a very large opening can be created. The other swing bridges we looked at had truss superstructures to provide long stiff cantilever spans. The Meridian Bridge solves the problem in a different way, with a central tower and a cable stays to support the cantilever spans.

This bridge carries State Route 20 across the Sacramento River a little south of Colusa and a little west of Marysville. It was built in the 1970s (and along with the Spokane Street Bridge) provides a good example of how engineers can develop new solutions to address some of the disadvantages inherent with swing bridges. The tower is 50 ft tall and the leaves are about 180 ft long, providing a suitable opening for ships to pass.

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

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

Movable Bridges - Knights Landing Bridge (3)

A last look at the Knights Landing Bridge. Its a double leaf simple trunnion bascule bridge that carries State Route 113 over the Sacramento River. The counterweights are enclosed in the large bin-type abutments.

Balancing the bridge leafs with the counterweight requires careful planning. Because traffic travels on approach spans rather than directly on the counterweights, this bridge is more stable in the closed position. When the locks are opened at midspan, the bridge can be raised with a smaller motor than would be needed if the deck had been made heavier to resist the counterweight and live load behind the trunnion.

I believe this bridge can still be operated. At least, it looks in good shape. Perhaps it is only opened when a request is made to the U.S. Coast Guard several days in advance.

Movable Bridges - Knights Landing Bridge (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Movable Bridges - Knights Landing Bridge (2)

A view from the deck of the Knights Landing Bridge. In this view, we can see the top chord of the bascule span going through a slotted hole in the approach slab.  The trunnion must be a little bit in front of the approach slab, the counterweight sits below the slab, and it descends into the bin-like abutment when the operator raises the bridge.

This area has changed a lot over the years. When Dr. Knight first came here, this was a meeting place of Native Americans living along the Sacramento River and Cache Creek. A town and ferry were built to handle all the traffic moving along the river, but now its like a ghost town.

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

Movable Bridges - Knights Landing Bridge (1)

North of Sacramento are several interesting movable bridges across the Sacramento River.

The Knights Landing Bridge is the first double leaf bascule bridge across the river that isn't a through truss. I'm actually not sure what kind of structure it is. Are those pony girders with rectangular openings or is it some kind of Vierendeel truss?

I'm also not sure what kind of bascule bridge it is. Is it a double leaf simple trunnion bridge or is it a Scherzer rolling lift double leaf bascule bridge? I vote for the latter since the bridge is high up with counterweights that can pivot into the concrete boxes at the far ends.

The bridge carries State Route 113 over the Sacramento River in the town named after Dr. William Knight, a physician who founded the town of Knights Landing on an ancient Native American mound in 1842.

We'll take another look at this unusual bridge tomorrow.

Movable Bridges - Knights Landing Bridge (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Movable Bridges - I Street Bridge (2)

A closer look at the I Street Bridge. A swing railroad bridge has stood at this site since 1858. The current double-deck bridge was built in 1911. Note the round pivot pier supporting the swing span.

This bridge is 840 ft long with a 340 ft long swing span.A 34 ft tall boat can pass under it at low tide. Otherwise, the captain must signal to the bridge operator to get through. Boaters need to check with the US Coast Guard when planning a trip to find out the bridge's hours of operation,

Swing bridges, and especially swing railroad bridges are more complicated than bascule or lift bridges. Not only do they need locking devices that open and close, but the railroad tracks need to be retracted to open the bridge and extended for trains to pass. There are also devices to help the bridge resist wind (and seismic) loads.

This is one of the largest center bearing swing bridges ever built. It weighs about 6800 kips. At the turn of the 19th century, such big swing bridges had rim bearings with rollers along the perimeter. When this large bridge was successfully built and operated with a center bearing, no one wanted to go through the trouble of fabricating the conical rollers that supported a rim bearing swing bridge and they were no longer built.

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

Movable Bridges - I Street Bridge

I'm standing in downtown Sacramento looking across the river at the I Street Bridge, the CalSTRS Building, and the Sacramento Pyramid (or Ziggurat).

This double-deck swing bridge carries two sets of railroad tracks on the bottom deck and motor vehicles (and pedestrians) on the top deck. The swing mechanism is still very active. The bridge was built by the American Bridge Company in 1912 and its currently owned by Union Pacific.

Movable Bridges - I Street Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States 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 - Freeport Bridge (2)

A view from the east side of the Freeport Bridge. Movable bridges often have open grid decks to reduce their weight. However they can be scary if you are riding across them on a motorcycle or a bicycle.

The east side of the bridge has a pony truss approach span, a through truss span, and then the bascule spans. The west side has a steel stringer approach, so it must be slightly shorter.

North of Freeport, State Route 160 ends, the road becomes Freeport Boulevard, and highway traffic switches to nearby I-5 into the City of Sacramento.

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

Movable Bridges - Freeport Bridge

Just south of Sacramento in the tiny town of Freeport is another bascule bridge across the Sacramento River. It's nearly identical to the Paintersville Bridge, only painted green instead of yellow.

The Freeport Bridge was built in 1930 and carries traffic between SR160 on the east side of the river and SR E9 on the west side. It has more elaborate fenders protecting the piers on each side of the 200 ft channel opening, perhaps because it sits next to a dock lined with weekend pleasure craft.

The spaces around the huge counterweights are so tight, that its remarkable that the truss members never get hit as the weights swing past. There must a large industry of mechanics and engineers whose job is to constantly maintain these massive machines. Movable bridges are much more dangerous than fixed structures. Every year people in a hurry or who aren't paying sufficient attention die while trying to cross a bridge that is moving or open.  There's hundreds of these bridges in California and thousands of them in the U.S. However, my feeling is that it's cheaper to build a long tall bridge over a river, rather than to put up with all the problems of owning a movable bridge.

We'll take one more look at the Freeport Bridge tomorrow and then continue up river into the City of Sacramento and beyond to study a few more movable bridges.

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

Movable Bridges - Sutter Slough Bridge

Like the previously studied Steamboat Slough and Three Mile Slough Bridges, the Sutter Slough Bridge crosses a tributary flowing into the Sacramento River. Movable Bridge Engineering lists Sutter Slough as a fixed swing bridge (by which I assume it means it no longer can move). There's a lot of old bridges that can't move, probably because no ships or barges travel past anymore.

I believe swing bridges were more popular before WWII when they were thought to be economical and there was less objection to having a pier in the middle of the waterway. After the war, the US government would help pay the cost of replacing or removing obstructions in waterways. Most of these obstructions were old swing bridges.

Sutter Slough Bridge was built in 1939 in Courtland California. The swing mechanism sits on a three column bent. The bridge carries two-way traffic (on two lanes), it has a total length of 397 ft, and it carries an average of 6020 vehicles a day.

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

Movable Bridges - Paintersville Bridge

In the late 1910s, Sacramento County improved the road between Isleton and Paintersville and provided free ferry service across the river at these two towns. The ferries were replaced with bascule bridges in the early 1920s. The two bridges are almost identical, except the Isleton Bridge has tied arch approaches and the Paintersville Bridge has through truss approaches. They both have the Joseph Strauss patented heel trunnion double leaf spans for a 200 ft channel opening. They are both on concrete piers with timber piles protecting the piers at the channel opening. The two bridges are about 20 miles apart. Thirty years later the bridge at Walnut Grove was built between the older bridges.

Movable Bridges - Paintersville Bridge 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 - Steamboat Slough Bridge

All the bridges at the southern end of the Sacramento River (north of the Rio Vista lift bridge) are heel trunnion double leaf bascule structures. They must have put a half dozen of these movable bridges between Sacramento and Rio Vista during the 1920s. Perhaps there was more ship traffic in those days. Riding my bike along the river today, all I see are a few speedboats. I wonder if a bridge operator is always on duty just in case?

Steamboat Slough Bridge doesn't actually cross the Sacramento River. It carries State Route 160 traffic over Steamboat Slough on the west side of the river. It's a 68.9 m long bridge that was built in 1924.

All of these bridges have height restrictions due to the huge, concrete counterweights (and low cross-beams). The bridges are almost identical with short spans to support the counterweights and long through truss movable spans. They just have different approach spans when a longer bridge is needed.

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

Movable Bridges - Walnut Grove Bridge

Continuing upstream along the Sacramento River we come to another double leaf bascule bridge. It is much like the previously viewed Isleton bridge, but without the tied arch eastern approach. The river has narrowed slightly where two branches come together in Walnut Grove. The bridge was built in 1952.

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

Movable Bridges - Isleton Bridge (2)

Another view of the Isleton Bridge. It was built in 1923 and possibly widened (it currently has one lane in each direction) or maybe some other work was done in 1953.

I'm looking at the bridge log, which says it has nine spans (I count eight), its 190.2 meters long (why metric units?), and its rated GGGGG (not for permit vehicles).

The river doesn't look very deep. I often see dredging equipment working on the shipping channel, which must quickly fill with silt. The only collision protection appears to be a single timber pile on each side of the piers supporting the heel trunnions.

I guess it's remarkable that the bridge has survived for so long. No collisions, no flood damage, and no earthquakes. I don't see a seismic retrofit, but maybe short spans on pier walls aren't particularly vulnerable. In the Google Earth photo below we can see the Sacramento River emptying into the Delta at the bottom left and the Isleton Bridge at the upper right.

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

Movable Bridges - Isleton Bridge

Since the Rio Vista Bridge is near the mouth of the Sacramento River, I thought we could continue upstream. The only other river we've explored with so many movable bridges is the Harlem River in New York City.

So far we've looked at a swing bridge (The Spokane Street Bridge) and a vertical lift bridge (The Rio Vista Bridge). The next bridge across the Sacramento River is a double leaf bascule bridge. These are probably the most popular movable bridges because they can open quickly, they provide a wide channel, and they look like a bridge.

State Route 160 switches from side to side as it follows the Sacramento River upstream. The Isleton Bridge takes SR160 back to the west side as we move upstream. The bridge is 600 ft long and includes two tied arch spans as well as the movable bridge. In the open position it provides 200 ft of channel clearance.

I believe this is a heel trunnion bridge. That means the two leaves pivot on the supports (the heel trunnions) that are under the trapezoids. The counterweights are allowed to rotate downward and as the weights fall, the trapezoids become pinched, which pulls the two leafs into the vertical position. Note the little spans on each side of bascule bridge with triangular trusses to support the counterweight trunnions.

We'll take another look at this interesting bridge tomorrow.

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

American River Bridges: Harold M. Richey Memorial Bridge

There's a park with river access near my house. I like to wheel my kayak to the park and kayak up and down the American River. However, I must remember to turn around under this bridge or else I'll be pulled into the rapids downstream and I won't be able to paddle back upstream. Kayaking on the river is strange because there are enormous rocks in the water that suddenly come almost to the surface and give me a sharp attack of vertigo.

This bridge's columns have that nice texture that they glue onto the concrete forms before they pour the concrete. The column's style seems very 1960's to me, but I don't have any information about when it was built. I do know that it is a six span, reinforced concrete box girder bridge on single column bents and its about 1000 ft long. Like yesterday's Fair Oaks Bridge, the Harold Richey Bridge is owned by the Sacramento County Parks and Recreation Department.

This bridge is usually crowded with families and cyclists, especially on the weekends. There are elaborate rules on the bridge deck about the right-of-way for pedestrians, equestrians, cyclists, etc. that I've never quite figured out. The bridge is named after Harold M. Richey and it was dedicated to him in 1987. I think that Richey was a county commission who was a strong supporter of the bike trail, and the bridge was dedicated to him after he died.

American River Bridges: Harold M. Richey Memorial Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

American River Bridges: Fair Oaks and Sunrise Bridges

Continuing downstream along the American River we come to the Fair Oaks Pedestrian Bridge. In the distance we can see the Sunrise Boulevard Bridge.

Wikipedia says that the Fair Oaks Bridge is a Pratt Truss since the diagonals all move downward towards the center of the bridge. The Wikepedia article has the best description on the Internet of the different kind of truss bridges.

There is also a long article about the Fair Oaks Bridge. Apparently several bridges were built at this site that were washed away by floods. The dams across the river eventually reduced the occurrence of flooding. The current bridge was built in 1907. It has two 220 ft long truss spans supported on a tall masonry pier in the center of the river. It was closed to traffic in 1967 and ownership was transferred to the Sacramento County Parks and Recreation Department. It was listed as a National Historic Site in 2006. More information on this bridge is available on another Wikepedia Website.

The Fair Oaks Bridge was another favorite location for rope climbing practice, although one had to be patient with all the questions that were asked (and we had to keep our equipment out of the way of cyclists). As I mentioned the Sunrise Bridge, a five span steel stringer bridge that was built in 1955, can be seen in the distance. The Sunrise and Hazel Bridges carry most of the vehicle traffic across this part of the American River. The next vehicle crossing is about fourteen miles downstream.

American River Bridges: Fair Oaks and Sunrise Bridges by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

American River Bridges: Hazel Avenue Bridge

This is actually called the American River Bridge but to avoid confusion with the many other bridges with the same name, I'm renaming it after the road that it carries.

Continuing the themes of the tremendous demand that growing communities place on more highway capacity, we can see the Hazel Avenue Bridge is getting widened. The bridge is just downstream from the Nimbus Dam and about four miles downstream from the Lake Natoma Crossing (and three miles upstream from the Sunrise Blvd Crossing). Moreover, this is where the American River Bike Trail (a much used recreational and alternative commuter resource) crosses the river. The widening will increase the capacity of the road and provide better safety for cyclists.

The existing bridge is a four span reinforced concrete box girder structure on single column piers built in 1966 (see below).  The widening will increase the deck from four to six lanes and support it on two column piers. The widening will also provide little bastions for cyclists and pedestrians to move off the traveled way and enjoy the view.

American River Bridges: Hazel Avenue Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.