Wednesday, September 30, 2009

Vancouver's Bridges: Granville Street Bridge

Crossing False Creek a quarter mile east of the Burrard Street Bridge is the Granville Street Bridge.  It was opened in 1954 and was the third bridge at this location. To make up for the deficiencies in capacity of the Burrard Street Bridge, this bridge was built (by the City of Vancouver) with eight traffic lanes at a cost of $16.5 million.

Granville Street Bridge is a cantilever deck truss with long approaches at both ends that carry Highway 99 over city streets and Granville Island. The bridge provides 27.4 m (90 ft) of vertical clearance over False Creek. It carries vehicles, cyclists, and pedestrians. The cantilever truss is supported on large concrete caissons while the approaches are supported on two column concrete piers.
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Tuesday, September 29, 2009

Vancouver's Bridges: Burrard Street Bridge

A couple of miles south of the First Narrows, the Burrard Inlet flows for two miles into False Creek. This is a popular recreation area with water taxis, museums, restaurants, etc.

False Creek is crossed by three bridges. The bridge near the mouth of the Creek is the Burrard Street Bridge. As can be seen in the photo, vehicles approach False Creek on short, haunched concrete girders. Next they cross over two  longer, Warren truss spans before crossing over the Creek on the deck of a through Pratt truss that allows smaller vessels passage under the bridge.

What is most notable about this bridge is the elaborate piers on each side of the Creek that include pylons supporting galleries which vehicles drive under when crossing the bridge. The galleries are carefully designed in an Art Deco/Colonial style with pastel colored tiles and a great deal of ornamentation. The  bridge's architect was George Lister Sharp and the engineer was John R. Grant. It was built in 1932 and is considered to be a historic structure.

The deck includes five vehicle lanes as well as narrow sidewalks/bicycle lanes that are partially blocked by the legs of the tower. This has led to a dangerous situation with many accidents. There have been efforts by the City Council to replace a vehicle lane with a bike lane, which has been met with resistance by drivers, store owners, realtors, politicians, etc. It has also been suggested to widen the sidewalks by cantilevering them out over the sides of the bridge, which has also been met with opposition. The land under the bridge is owned by the Squamish First Nation, which has their own concerns about any changes to the bridge.

I think the City of Vancouver has the most politically active populace (especially with regard to bridges) in the world!
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Monday, September 28, 2009

Vancouver's Bridges: Second Narrows Bridges

Burrard Inlet is well protected and makes an excellent shipping channel and port for the City of Vancouver. It runs east for 25 miles and it's connected to the north by the Indian Arm Fjord, where it makes a rapid transition from city to wilderness.

The First Narrows is formed by a peninsula jutting into the mouth of Burrard Inlet and it's crossed by the Lion's Gate Bridge. The Second Narrows is about five miles to the east and is crossed by two bridges. Plans to build a bridge across the Second Narrows began with the Klondike Gold Rush at the end of the 19th century. However, it wasn't until after WWI that money became available to carry goods from the north into the Port of Vancouver.

The first bridge to cross the Second Narrows was built in 1925 as a vehicle bridge but also began carrying trains a year later. It suffered so many ship collisions that the center span was replaced with a lift span in 1933. A second bridge was added to the west in 1960. It was much taller and carried six lanes of highway traffic and so the original bridge was converted exclusively to train traffic. This railroad bridge was replaced in 1969 with a wider and taller steel truss lift bridge owned and maintained by the Canadian National Railway.

The highway bridge was renamed the Ironworkers Memorial Second Narrows Crossing in 1994 to honor the many workers who died while building the bridge. A span collapsed during construction throwing 79 workers into Burrard Inlet. Eighteen ironworkers died as well as a diver who was searching for the bodies. A Royal Commission found the accident was caused by a miscalculation of the strength of a temporary support by the bridge designers. There were three other accidents resulting in a total of 25 deaths during the construction of this bridge,

The highway bridge is a steel, cantilever truss with a 335 m (1100 ft) main span and 142 m (466 ft) long side spans. The total length is 1292 m (4242 ft), which includes several approach spans. The center span was cantilevered out from the two piers and cranes placed a dropped-in span in the middle. The bridge was designed by Swan Wooster and Partners who had also built the Lion's Gate Bridge. It is owned and maintained by the British Columbia Ministry of Transportation. It carries pedestrians, cyclists, and six lanes of Highway 1 traffic. Because there are weight restrictions on the Lion's Gate Bridge, this bridge gets most of the truck traffic across the Inlet. Like the Lion's Gate Bridge, it was recently seismically retrofitted and re-decked.
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Sunday, September 27, 2009

Vancouver's Bridges: Lion's Gate Bridge (2)

One more look at the Lion's Gate Bridge. Because of the heavy traffic on a three lane bridge, the middle lane switches directions to carry commuters into the City in the morning and back to the suburbs in the evening.

In the photo we can see that the deck of the three span suspension structure is stiffened by a truss and the deck of the approach spans is supported on plate girders. The approaches climb steeply in order to lift the deck 61 m (200 ft) above Burrard Inlet in 760 m (2500 ft). A large concrete block under the approach spans is used to anchor the suspension cable on each side of the bridge. The main span is 472.75 m (1552 ft) long and the side spans are 187.28 m (615 ft) in length.

The towers and approach span piers look very flexible, especially in the longitudinal direction. Undoubtably, the suspension cable is used to provide longitudinal stability to the bridge. I would imagine that time lapse photography would show quite a bit of movement of the deck. The bridge received a lot of work from 1990 to 2001 to replace the rusted north approach deck, to widen the suspension deck, and to prevent serious damage from an earthquake likely to occur in the next 475 years. It would have been easier and cheaper to have replaced the bridge with a tunnel or another crossing, but apparently the public is politically astute and very motivated and so they opposed all the proposals to add a bridge, add a tunnel, replace the bridge, etc.

The bridge was retrofitted to rock during the design earthquake. This is a strategy that has often been used as an inexpensive way to protect existing long-span bridges. Some engineers (most notably Prof. Nigel Priestley at UC San Diego) think that rocking is a perfectly reasonable behavior for bridges during earthquakes. However, a few engineers (most notable Prof. Nicos Makris at UC Berkeley) think that rocking is less likely to occur and that there are errors in the simple analysis procedure that Priestley proposed. We are currently having research done (by Prof. Bruce Kutter on the giant centrifuge at UC Davis) to see if our rocking assumptions are reasonable. An interesting article about the retrofit of the Lion's Gate Bridge was written by the Engineering News-Record and is available on-line.
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Saturday, September 26, 2009

Vancouver's Bridges: Lion's Gate Bridge

We are leaving Oregon for a while to look at bridges around Vancouver, British Columbia. The city is across the Strait of Georgia from Vancouver Island and about 20 miles north of the U.S. It's a pretty, very cosmopolitan city with a lot of interesting bridges.

At the north end of the city, crossing the first narrows of Burrard Inlet (the second narrows is a little to the east) is the Lion's Gate Bridge. The bridge was named after two mountain peaks north of the city that are represented by two stone lions that sit at the southern entrance to the bridge. My photo is an often seen view taken from a bridge crossing Highway 99/1A.

The Lion's Gate Bridge is a suspension bridge with a 472 m (1550 ft) long main span (the Golden Gate Bridge's main span is 1281 m (4200 ft) long). The total length of the Lion's Gate Bridge is 1823 m (5890 ft), the towers are 111 m (364 ft) above mean sea level, and the soffit is 61 m (200 ft) above mean sea level.

From time to time, different groups proposed building a bridge across the narrows but the voters always rejected it until lost jobs during the Great Depression proved to be sufficient inducement for a big public works project. The project developer and bridge owner was the Guinness family. The bridge was designed by Monsarrat and Pratley of Montreal and built by the Swan Wooster Engineering Company as well as several other firms. Construction began in March 1937 and the bridge was opened in November 1938 at a cost of about $6 million Canadian dollars. The bridge was sold to the province in 1955 (at about the same cost) and tolls ceased in 1963.

The bridge was too narrow for the amount of traffic it carried but the City was reluctant to do anything that would increase traffic into downtown. Eventually (from 2000 to 2001) they replaced the deck, segment by segment, using nighttime and weekend closures. The existing deck was lowered onto a barge and a new deck segment put in it's place. The two walkways were moved to the outside of the suspension cables and the three vehicle lanes were widened from 3 to 3.6 m (10 to 12 ft).

The deck on the Golden Gate Bridge was replaced in a similar fashion in the 1980s. This is a good solution for a regular suspension bridge but it is difficult to replace the deck of tied arch bridges, cable stayed bridges, and self-anchored suspension bridges because the deck is loaded axially.
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Friday, September 25, 2009

Oregon's Bridges: Coos Bay Bridge

As we continue our study of bridges along Oregon's coast, we come to the Coos Bay Bridge twenty miles south of the Umpqua River Bridge. It's amazing that the state of Oregon was able to build five long span bridges along it's coast in a single year and build a highway between California and Washington State in about a decade. In one fell swoop, people were able to drive along the coast from San Francisco to Seattle. I wonder how the money, material, and labor became available to get so many handsome bridges built in such a short time?

The Coos Bay Bridge (also called the McCullough Memorial Bridge) is a steel, cantilever truss bridge with a 793 ft main span, 458 ft long side spans, and thirteen reinforced concrete arch approach spans for a total length of 5305 ft. The steel truss segment was designed with curved top and bottom chords to match the arches of the concrete approach spans. It was the largest of the five bridges built as part of the Oregon Coast Bridges Project and cost slightly over $2 million in 1936.
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Thursday, September 24, 2009

Oregon's Bridges: Umpqua River Bridge

The Umpqua River Bridge has two 154 ft long reinforced concrete bow string arch spans on each side of a central, 430 ft long steel through truss swing span. It's the longest swing bridge in Oregon, one of only five still on the State highway system, and of historical significance for the technology it uses.

This bridge was built in 1936 by Teufel and Carlson of Seattle and designed by Oregon's chief bridge engineer, Conde McCullough. As you may have noticed, the Umpqua River Bridge is just one of several monumental bridges built along Oregon's coast (on US 101) and completed in 1936 as part of the Oregon's Coast Bridge Project. The swing span was built to allow the passage of tall sailing ships that were once common along Oregon's coast and the Umpqua River. This bridge was added to the National Register of Historic Places in 2005. Note the unusual barrier rail with concrete pylons at the ends of the bridge.

Like yesterday's Siuslaw River Bridge, the Umpqua River bridge is located several miles from the mouth of the river because a huge sandbar (the Oregon Dunes National Recreation Area) is along the coast. I may as well mention that the Cascadia Subduction zone also runs parallel to Oregon's Coast. It produced a huge earthquake and tsunami in 1700 and is expected to produce another large earthquake every 300 to 600 years. The worst-case scenario would be that the earthquake would damage bridges, preventing people fleeing the coast from reaching higher ground when the tsunami waves strike the coast. However, the state of Oregon should be credited for developing tsunami evacuation routes all along the coast.
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Wednesday, September 23, 2009

Oregon's Bridges: Siuslaw River Bridge

Continuing south along the Oregon coast is the city of Florence and the Siuslaw River Bridge. This is one of Conde McCullough's most ornate creations. A 140 ft long steel, bascule bridge was built between two 154 ft reinforced concrete bow string arches, which are connected to 20 concrete girder approach spans. Among the decorative features on this bridge are obelisks that support the movable span, pylons at the far ends of the arch spans, an ornamental railing, arch shaped two-column piers, X-bracing connecting the arch ribs, and haunched girders on the approach spans.

The Siuslaw Bridge has a total length of 1568 ft and it was built in 1936 by the Mercer-Fraser Company of Eureka, California. The bridge would be at the mouth of the Siuslaw River except there is a giant sandbar that makes it flow another four miles before it finds the Pacific. The city of Florence is on the north side of the river and has a population of about 8000 people. The economy used to be based on logging and fishing but now its mostly supported by tourism and by retired people moving into the area. Perhaps the movable bridge span was to allow the passage of boats loaded with timber from Oregon's interior.

We can see timber piles sticking out the river where a dock once stood. The river was crossed by a ferry before the bridge was built.
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Tuesday, September 22, 2009

Oregon's Bridges: Ten Mile Creek Bridge

I had trouble identifying this bridge photo because there are several similar bridges only a few miles apart. However, I believe this photo is of Ten Mile Creek Bridge because it is the only bow string arch in a low-lying area of Oregon's Coast. It is another bridge designed by state bridge engineer Conde McCullough.

McCullough began his career as a bridge engineer in Iowa working for the Marsh Engineering Company that had a patent on this type of bridge that they built all over Iowa and Kansas. Conde introduced it to the Pacific Northwest. It was a good choice for a region with loose, sandy soil that couldn't support a deck arch and with corrosive salt air that made steel bridges impractical.

The Ten Mile Creek Bridge is a 180 ft long bridge with a 120 ft long reinforced concrete tied arch. You can see the hangers supporting the concrete floor beams that hold up the deck. It was built in 1931 on US 101 for the State of Oregon. It has ornate, precast concrete barrier rails and four X-shaped cross beams that connect the two arch ribs.
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Monday, September 21, 2009

Oregon's Bridges: Alsea Bay Bridge (2)

A bridge is considered to have a lifespan of 75 years. Some bridge become so popular or are so expensive to replace that extraordinary efforts are performed to keep the bridge in service. Of course, 75 years is somewhat arbitrary. A bridge that is not worn down by heavy traffic or inclement weather and is well-maintained can stay in service well over 100 years. In fact, there are design recommendations to give important bridges a 100 year lifespan (with more concrete cover, more deck reinforcement, etc.).

The original Alsea Bay Bridge was designed by the great Conde McCullough and built in 1936 (see posting for February 5th). It was considered to be one of the finest examples of concrete bridge construction in the United States. It became eligible to be put on the National Register of Historic Places in 1981. However, the harsh salt water environment began to cause corrosion to the reinforcement, and despite efforts to preserve the bridge, it was finally replaced in 1991.

The new Alsea Bay Bridge (designed by HNTB) pays homage to the original structure in several ways. The central arch span resembles the arches on the original structure. The pedestrian observation platforms (with dramatic pylons) were preserved from the original structure. However, the bridge also updates the style from Gothic to Modern with Y-shaped piers and a parabolic line to the arch. The bridge was also modernized with a latex concrete deck and a thicker concrete cover to prevent corrosion of the reinforcement.
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Sunday, September 20, 2009

Oregon's Bridges: Yaquina Bay Bridge (2)

Traveling south from Portland on US101, we cross some beautiful bridges over bays and rivers along the coast. It reminds me of the many beautiful arch bridges around Big Sur on California's coast. There must be something about being near the ocean that brings out the best in bridge engineers.

The Yaquina Bay Bridge is about 100 miles southwest of Portland along Oregon's coast. It consists of a steel through arch main span, two steel deck arch side spans, five reinforced concrete arch spans on the south side of the Bay, and fifteen simply-supported girder approach spans.

The bridge was designed by Oregon State bridge engineer Conde McCullough and built by Gilpin and General Construction contractors in 1936 for $1.3 million. This bridge, like many of Conde's structures includes beautiful stairways leading to pedestrian viewing areas, highly ornamented railings, enormous, raked columns supporting fluted pylons, etc. These bridges provide a sublime visual experience for pedestrians and drivers.

Its incredible that this enormous, elegant structure was constructed in something close to a wilderness of northern Oregon in the 1930s.
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Saturday, September 19, 2009

Portland's Bridges: Ross Island Bridge

Upstream from the much maligned Marquam Bridge is the more appreciated Ross Island Bridge. Perhaps the public found the Ross Island Bridge more likable because the main truss span is in the shape of an arch. It was designed by Gustav Lindenthal (along with the Burnside and Sellwood Bridges) after a bribery scandal involving the original designers. The 1819 ft long truss bridge was built by Booth and Pomeroy for Multnomah County. They constructed the side spans on falsework and then used cantilever construction to build the main span, which is 535 ft long and rises 123 ft above the Willamette River. The bridge includes 29 reinforced concrete approach spans, for a total length of 3700 ft.

The Ross Island Bridge, along with the Burnside and Sellway Bridges, was completed in the mid-1920s, marking the end of a prolific period of bridge building for Multnomah County. Although it's called the Ross Island Bridge, it crosses the Willamette River about 800 ft north of Ross Island. It carries US 26 across the river and connects to a variety of streets and highways in south Portland. This bridge, along with the St Johns Bridge, was given to the Oregon Department of Transportation in the mid-1970s, when the county could no longer afford to maintain it.
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Friday, September 18, 2009

Portland's Bridges: Marquam Bridge

The Marquam Bridge is a double deck cantilever truss bridge that carries I-5 over the Willamette River. The main span is 440 ft long, the side spans are 301 ft long, and the deck is 57 ft wide. It carries four northbound lanes on the top deck and four southbound lanes on the bottom deck and provides 130 ft of vertical clearance over the river. The bridge was designed by the Oregon Dept. of Transportation (ODOT), the piers were built by Kiewit, and the superstructure was built by US Steel. It was opened in 1966 at a cost of $11 million.

This truss structure is connected to steel girder ramps including the beginning of one on the east side to connect to the Mount Hood Freeway, which was never built. The bridge was designed economically with little public input and it's considered to be an eyesore. I think it's a perfectly normal looking three span truss bridge, but for some reason it upsets Portland sensibilities. Perhaps it's because it carries 136,000 vehicles a day into and out of the city. In any event, there are committees that come up with various schemes for removing this bridge that are never acted upon.
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Thursday, September 17, 2009

Portland's Bridges: Hawthorne Bridge

There are four movable bridges crossing the Willamette River in midtown Portland. The Hawthorne Bridge is the southernmost of these bridges. It is the oldest lift bridge (built in 1910) operating in the United States and it's the oldest highway bridge and the busiest bicycle bridge in Portland.

The Hawthorne Bridge is a six span, 1382 ft long, truss bridge with a 244 ft long lift span. It has 49 ft of vertical clearance when it's closed and 159 ft when it's open. It replaced the second Madison Bridge, which was built in 1900 and destroyed by fire in 1902 (the bridge connects Madison Street to Hawthorne Blvd. in Portland). The 440 US ton counterweights are suspended from 165 ft tall towers. It was designed by John Waddell who invented the lift bridge (see comments) and designed the nearby Steel Bridge (see the September 12th posting). However, unlike the Steel Bridge, it has only a single deck with two lanes inside the truss and two lanes and wide bicycle lanes/sidewalks outside the truss (widened and restored in 1999). The bridge cost $511,000 and it's estimated to have a replacement cost of about $190 million.
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Wednesday, September 16, 2009

Portland's Bridges: Morrison Bridge (2)

One more look downstream at the Morrison Bridge from the deck of the Hawthorne Bridge. The side spans are deck trusses and the approach spans are steel girders. As I mentioned, there are several ramps and connectors that carry vehicles from streets and expressways on and off this bridge. Like the other movable (non-railroad) Willamette River crossings, this bridge is owned by Multnomah County.

The bascule span is usually opened once a day, which is fortunate since the roadway is so heavily traveled. There's about 69 ft of vertical clearance with the bridge closed. The machinery that performs this operation was manufactured by Northwest Marine and Iron Works of Portland and installed in 1957 by US Steel.

It seems like movable bridges aren't built as often anymore, although some unusual movable footbridges have been built lately. Most bridge owners aren't willing to invest in the much higher operating and maintenance costs. The alternative would be long retaining walls or approach spans to lift the crossing high above the water. I'm not sure whether retaining walls or approach spans would be more expensive. It probably varies from place to place. Still, an approach span would be required whenever there are streets that must be crossed over.

As I've previously mentioned, bridge building is a dangerous occupation. Construction of the Morrison Bridge took the life of a Mr. Davies when he was buried by a slide while checking footing reinforcement.
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Tuesday, September 15, 2009

Portland's Bridges: Morrison Bridge

There have been three Morrison Bridges at this location. The first bridge was designed and built by Charles Swigert of the Pacific Bridge Company in 1887. It was a timber truss bridge with a steel swing span and it was the first bridge in Portland across the Willamette River. It survived the flood of 1894 which rose to the bridge's deck and damaged the motor and railing. It was replaced with a wrought iron and steel swing bridge in 1905. It had a timber deck and carried street cars but no automobiles.

The current Morrison Bridge was built in 1958 at a cost of $13 million. It included an elaborate interchange with ramps for the I-5 and the I-84 expressways. It's a double leaf bascule bridge, similar in appearance to the Burnside Bridge, but with an airport motif instead of medieval battlements. It was designed by Sverdrup of St. Louis and by Moffat and Nichol of Portland and built by the American Bridge Division of US Steel.

Large cofferdams were build for the two main piers. While the east cofferdam was being de-watered, several struts buckled from the increased stress but adjacent struts prevented collapse of the cofferdam. While the new bridge was being built, the east side of the existing bridge was moved to the south and continued carrying traffic. Because the second bridge was kept in service, the west side of the third bridge doesn't connect to Morrison Street.

The third Morrison bridge is 760 ft long, 90 ft wide, and with a  284 ft long double leaf bascule span. The deck of the bascule span was made of grated steel to reduce its weight. The bridge is the largest machine in Oregon with 36 ft tall gears driving the 940 US ton counterweights inside each pier. It carries 50,000 vehicles a day as well as bicycle and pedestrian traffic. Its scheduled for a seismic upgrade in the near future.
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Monday, September 14, 2009

Portland's Bridges: Burnside, Morrison, and Hawthorne Bridges

This photo was taken from the Oregon Health and Science University (OHSU) on a hill west of the Willamette River. You take the Portland Tram up to the University Hospital.  I wondered how they handled emergencies, especially if the tram were to lose power, but apparently they have adequate back-up systems. In the foreground are three moveable bridges and above the horizon is Mount St. Helens, which was cone shaped before it erupted in 1980.

We studied the Burnside Bascule Bridge yesterday. The Morrison Bridge is also a bascule bridge, which means the center leaf spans meet at midspan and swing up and down with the help of motors and counterweights (behind the pivot point). The Hawthorne Bridge is the oldest vertical lift bridge still in operation in the United States. We will take a closer look at these two bridges in the next few days.
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Sunday, September 13, 2009

Portland's Bridges: Burnside Bridge

It is appropriate that a movable bridge was named after Dan Burnside since he was instrumental in  having the Willamette River dredged (in 1866) in order to make it a shipping channel. The original bridge at this site (built in 1894) was a swing bridge. When this bridge became outmoded because it was slow to open and close, it was replaced with a faster moving bascule bridge in 1926.

The double-leaf bascule span was designed by Joseph Strauss who later designed the Golden Gate Bridge. The design of the fixed spans was begun by Hedrick and Robert Kremers of Portland. It was completed by Gustav Linderthal after Robert was arrested for bribery and collusion. I don't know what it was like in Portland in the 1920s, but I know that in many places you can't get a bridge built without some bribery and collusion due to corrupt politics. The bridge was built by the Pacific Bridge Company.

The design of the Burnside Bridge included the services of Houghtaling and Dougan Architects of Portland who created a Disney fantasy similar to St. Johns Bridge. The main piers have octagonal towers attached to crenelated battlements that make the bridge resemble a medieval castle. This was part of the City Beautiful Movement that was initiated during the 1893 Chicago World's Fair, and which also influenced the design of several Los Angeles bridges.

One interesting peculiarity of the Burnside Bridge is that the bascule leafs were made of reinforced concrete which made them extremely heavy and required counterweights inside the two piers weighing 1700 US tons. Moreover, the lifting operation is controlled by the operator on the nearby Hawthorne Bridge.

The Burnside Bridge has a center span 251 ft in length that provides 64 ft of vertical clearance when it is closed. It has two 261 ft long steel truss approach spans and 34 steel girder spans for a total bridge length of 2308 ft. The bridge carried streetcars and electric trolleys until the 1950s. In 1995, one of the six vehicle lanes was converted to a bicycle path. In 2002 it became one of the first bridges in Portland to get a seismic retrofit. In 2007 the aging deck was replaced. Bridges are considered to have a 75 year life and the first thing to go is their decks which get a terrible beating, especially due to the heavier trucks currently using our roads.

This bridge provides shelter for an illegal skatepark under its east end. Politicians tend to allow these parks to exist even though the bridge owner now has liability for people using their right of way. In California, we tried to remove a skatepark in Oakland, because the construction of the park covers the bottom of the columns with concrete, which shortens the column's effective length and tends to make them fail in shear during earthquakes. However, the California politicians were more concerned with pleasing the local communities then worrying about an earthquake that might not occur for many years.
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Saturday, September 12, 2009

Portland's Bridges: Steel Bridge

The Steel Bridge (over the Willamette River in Portland, Oregon) is a very unusual 'telescoping lift bridge' that can raise its lower deck without disturbing traffic on its upper deck and it can raise both decks to allow for the passage of large vessels. In the closed position it provides about 26 ft of vertical clearance. With the lower deck raised it provides 72 ft of vertical clearance. With both decks raised it provides 162 ft of vertical clearance. It has independent counterweights to lift each span.

The Steel Bridge is also unusual for the variety of vehicles that it can accommodate on its two decks. In this photo we can see a light rail train traveling on the upper deck while three diesel locomotives are crossing on the lower deck. The average daily traffic includes 23000 trucks, buses, cars, and motorcycles, 200 light rail trains and trolleys, 40 freight and Amtrak trains, over 2000 bicycles, and uncounted pedestrians. It carries railroad, pedestrian, and bicycle traffic on the lower deck and highway, light rail, and streetcar traffic on its upper deck.

The Steel Bridge was designed by Waddel and Harrington (consultants from Kansas City) with support from the Oregon Railway and Navigation Company and the Union Pacific Railroad. The two railroad companies also built the bridge, which was completed in 1912. It replaced the previous Steel Bridge from 1888 that was so named because it had replaced an even earlier wrought iron bridge.

The Steel Bridge is composed of a 290 ft long steel Pratt truss on each side of the 211 ft long lift span. The superstructure is supported on short concrete piers on caisson foundations. Wikipedia has a nice website for this bridge that includes several drawings of the structure and the lift mechanism.
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Friday, September 11, 2009

Portland's Bridges: Broadway Bridge

About half a mile upstream from the Fremont Bridge (across the Willamette River) is the Broadway Bridge. It is an unusual Rall-type bascule bridge, which was chosen as the low bidder in a competition. However, the complex mechanism (it rolls back on rails as it lifts) has required frequent repairs and has been more expensive in the long run.

The bridge was designed by Ralph Modjeski and built by the Pennsylvania Steel Company over two years at a cost of $1.6 million. It had the world's longest double leaf bascule span when it was completed in 1913.

The main piers are reinforced concrete faced and topped with granite. The approach piers are 12 ft diameter concrete-filled steel pipes tied together with cross-bracing. A 278 ft double-leaf bascule span is supported on the main piers and crosses over the shipping channel. It provides 70 ft vertical clearance when closed and is opened about once a day. An operator's house is above each of the main piers (on the other side of the bridge). The approach spans are steel, camelback trusses. A reinforced concrete ramp on the west side goes over Union Station and carries traffic on and off the bridge. A similar ramp on the east side goes over Highway 99 and light rail tracks.

The bridge is 1742 ft long and 70 ft wide. It has two lanes of traffic in each direction and two broad sidewalks. It carries about 2700 vehicles and 1200 bicycles a day. It has been frequently repaired and renovated over the years. The concrete deck was replaced with a steel grating in 1948 to make it easier to lift. The steel deck was replaced with a fiber-reiforced composite material in 2005.

I'll just mention that Portland, Oregon is a very nice, attractive city with a very efficient transportation system. The area around the Willamette River is particularly pleasant and attracts large crowds on the weekends.
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Thursday, September 10, 2009

Portland's Bridges: Fremont Bridge (2)

The Fremont Bridge crosses the Willamette River several miles upstream from St. Johns Suspension Bridge.

If you look closely at today's photo, you can see St. Johns Bridge under the Fremont Bridge. The Burlington Northern Railroad Bridge 5.1 sits between them, but I think it must be obscured by a bend in the river. It was originally a swing bridge that was converted to a vertical lift bridge in 1989.

We previously looked at the Fremont Bridge on February 17, 2009. Although these through arch bridges are often built as cantilever structures that are held back with towers and cables, the center span of this bridge was built in California, taken apart and reassembled at Swan Island. put on a barge for the 1.7 mile trip to the bridge site, and lifted onto the 'below-deck' part of the bridge.

The Fremont Bridge is a double-deck structure with four lanes of traffic in each direction. At 1255 ft it has the longest arch span in Oregon. We previously studied the Lupu Bridge in Shanghai which will shortly lose its title of having the longest arch span to the Chaotianmen Bridge (with a 5712 ft span), which is also in China.
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Portland's Bridges: Fremont Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Wednesday, September 9, 2009

Portland's Bridges: Bridge of the Gods (2)

Although the current Bridge of the Gods isn't as dramatic as the original land bridge, it still makes an attractive statement across the Columbia River Gorge. This bridge is an important link for hikers on the Pacific Crest Trail. It costs pedestrians 50 cents to cross this toll bridge with two traffic lanes, no sidewalks, and narrow shoulders. The toll booth remains open 24 hours a day for emergency vehicles needing access between Oregon and Washington State. Its the third oldest bridge across the river.
In 1920, the US War Department gave the Interstate Construction Corporation a permit to build the bridge but progress was so slow that in 1926 they sold the permit to the Wauna Toll Bridge Company for $600,000. When completed, the balanced cantilever truss bridge had a main span of 708 ft with anchor arms of 212 ft. The total bridge length including approach spans was 1858 ft with a width of 35 ft. This bridge was 91 ft above the river and had a wooden deck.
When the Bonneville Dam was completed in 1938, the bridge was raised 44 ft to prevent it from being inundated when the reservoir became full. This project was completed in 1940 for $760,000. In the photo it looks like the truss was put on falsework, the concrete pier walls were raised 40 ft, and the superstructure was lifted onto the raised piers.
The bridge changed ownership several times after the dam was built. Today, the bridge is owned and operated by the Port of Cascade Locks. In 1966, a second bond of $300,000 was used to rehabilitate the bridge. At some point the wooden deck was replaced perhaps by a steel deck covered with asphalt. Revenues from tolls pay for maintenance, painting, inspections, and bond repayment. The total cost of the bridge including construction, lifting, and rehabilitation was a few million dollars. It would probably cost $30 million to build this bridge today.
There is an excellent website by the current owners that provides more information and photos of the bridge.
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Portland's Bridges: Bridge of the Gods (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Tuesday, September 8, 2009

Portland's Bridges: Bridge of the Gods

Yesterday we looked at bridges that evoke spiritual thoughts and so by coincidence (or by divine providence) our next river crossing is called the Bridge of the Gods. Its about 40 miles east of St. Johns Bridge across the Columbia River and behind Bonneville Dam.

Flying over the area on a day with low clouds can be a spectacular experience because Mt. Hood, Mt. Adams, Mt. St. Helens, and Mt. Ranier all stick their heads out of the clouds like huge gods. At least that's what Native American legend teaches. A thousand years ago, a land bridge crossed the Columbia River and these gods were fighting so violently, that the bridge was eventually destroyed. Like most legends, this story has more than a grain of truth. The constant volcanic eruptions and earthquakes in the area may well have destroyed the original Bridge of the Gods.

Today, a human-made bridge is where the Bridge of the Gods once stood. It's a steel, cantilever truss with a 706 ft main span. It was built in 1926 by the Wauna Toll Bridge Company of Walla Walla. It was originally 1127 ft in length, but after the dam was built, the bridge was raised and lengthened to 1856 ft to avoid the encroaching waters.

We'll take another look at this interesting structure tomorrow.
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Portland's Bridges: Bridge of the Gods by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Monday, September 7, 2009

Portland's Bridges: St. Johns Bridge (3)

The back spans of St. Johns Bridge are supported on tall reinforced concrete piers in a Gothic arch shape similar to its towers. They also are reminiscent of the towers on the Brooklyn Bridge. Perhaps this shape, originally used for the churches of medieval Europe was consciously chosen by bridge engineers to add importance to their work.

This bridge was named after a saint and the piers are in Cathedral Park, so the church-like architecture could be appropriate. However, I think that bridge engineers like Roebling, Linderthal, Steinman, and McCullough were saying that big bridges were the churches of the industrial age because they best express our yearning for the spiritual. Perhaps there's also a touch of American Transcendentalism in using religious icons for structures that span rivers, canyons, valleys, and other landscapes that suggest a deeper meaning or revelation in nature.
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Portland's Bridges: St. Johns Bridge (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Sunday, September 6, 2009

Portland's Bridges: St. Johns Bridge (2)

St. Johns Bridge was designed by David Steinman who had been an assistant to Gustav Linderthal on the 1917 Hell Gate Bridge (see blogs of July 20th and 21st). Those bridges were also designed with a concern for their appearance that was separate from their function. As a result of this excessive decorativeness, the bridge resembles a ride at Disneyland.

The bridge was built in the St Johns neighborhood of northern Portland, hence its name. It's the only suspension bridge in Portland and its completion ended ferry service across the Willamette River. The main span is 1207 ft long and its total length is 2067 ft. The suspension cables are composed of 91 - 1.5 inch diameter steel rope strands that were manufactured and pulled across the river by John A. Roebling and Sons Inc.

Multnomah County was reluctant to build a bridge so far from downtown Portland and so the local residents had to lobby hard to get the $4.25 million bond approved in the 1928 election. The Great Depression began soon after construction began and so the bridge served as secure employment for the region. Perhaps that explains why the bridge was $1 million under the budget when it was completed. It was originally owned by Multnomah County but by the 1970s the county couldn't afford to maintain the bridge and ownership was eventually transfered to the State of Oregon. From 2003 through 2005 the bridge was extensively renovated (at a cost of over $38 million).
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Portland's Bridges: St. Johns Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.