Thursday, July 29, 2010

Cable-Stayed Bridges - Suez Canal Peace Bridge (3)



A slightly closer look at the Suez Canal Peace Bridge. We were staying in Cairo when some of my engineer friends took me to see this bridge. As we drove across the desert, we would sometimes see a lone man sitting on the side of the road beside a pyramid of melons.

We were riding in a new Mercedes, but it got a flat in the middle of the desert. The driver got out, jacked up the car, and changed the flat tire while we remained in air conditioned comfort. It must have been 120 degrees Fahrenheit outside.

I had just given a talk on earthquake design. I can't remember now if it was at Cairo University or at the bridge department, but I do remember being surprised to see more than half the engineers were women, all with their faces covered.

In order to get to the bridge, we had to take a ferry across the Suez Canal into the Sinai Peninsula. There was a long line of cars, but the driver just drove ahead and cut to the front of the line. We got onto the next ferry and arrived just in time for our tour.

The Israelis controlled the Sinai after fierce fighting in 1973 but they gave it back to the Egyptians for a kind of peace. For hundreds of years before that, it was controlled Turkey. We'll take a closer look this bridge tomorrow.
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Wednesday, July 28, 2010

Cable-Stayed Bridges - The Suez Canal Peace Bridge (2)


We've left North America for the boundary between Africa and Asia.

The Suez Canal connects the Red Sea to the Mediterranean. There used to be a swing bridge across the Suez, but it was destroyed during one of the wars between Egypt and Israel.

When I asked the project engineer what was the biggest problem building this bridge, he said it was removing all of the land mines. I guess that's why they called it (hopefully) the Peace Bridge. We'll take a closer look at this interesting structure tomorrow.
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Tuesday, July 27, 2010

Cable-Stayed Bridges - Great River Bridge


Back on the California Zephyr traveling east from Denver. I took this photo while crossing the Mississippi River between Burlington, Iowa and Gulf Port, Illinois.

Although my photo (through a train window) isn't great, it does show an impressive looking bridge. I took it from the BNSF Railroad Bridge, a series of through trusses (with a swing span for the shipping channel) about a mile south of the Great River Bridge carrying I-34.

The I-34 bridge was built in the 1990s to replace a two lane steel structure that had been built in 1917 and was in terrible shape. Construction on the new bridge continued despite a series of floods (that destroyed the construction offices) and the bridge opened in 1993. Its a single tower cable-stayed bridge with a main span of 660 ft and a total length of 1245 ft. The cables are arranged in a fan and the two-legged, H-shaped tower stands about 300 ft above the Mississippi River. The bridge carries five traffic lanes and provides 60 ft of vertical clearance for ships traveling on the river.

The bridge is owned and maintained by the Iowa DOT. I wonder if it was designed by the Iowa DOT as well? I was hoping to find an entry in Structurae that would give some references to books and articles about the bridge but I wasn't successful. I did find some good information at John Weeks website. I believe he's gathered information on all the bridges across the Mississippi River.

The tower foundations go through 90 feet of weak material before reaching bedrock. Although I couldn't find a reference to the construction material, it looks like a reinforced concrete tower (and a steel girder superstructure). The bridge has unequal spans, the tower is placed in the middle of the river, there are more cables on the west side and there are additional lifter cables to adjust for seasonal temperature changes; which must have made for a very challenging design project.
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Monday, July 26, 2010

Cable-Stayed Bridges - Sundial Bridge (8)


One last look at the Sundial Bridge. What I called a crackled glaze on the pedestal supporting the tower actually looks like broken pieces of white ceramic pottery grouted onto the surface. This was a technique used to great effect by Calatrava's countryman Antonio Gaudi in Park Guell (and in many other works).

This is a nice view of the bridge from under the deck, reinforcing yesterday's statement that you can't take a bad photo of this bridge.

The watercolor below must have been an early conceptual sketch Caltrava made to visualize the forces in his bridge. Writing this blog reminded me of some of the recent posts from the Tall Bridge Guy on painting, painted bridges, and on 3D computer graphics.


It's apparent that Calatrava is expert in all three forms of expression. His video of the Calgary Bridge was a thoughtful exploration of how the bridge would look at different times of day and at different times of the year. His roughest sketches are full of thought and feeling, And even though this bridge is painted white, it has elements of mosaic and sculpture.
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Sunday, July 25, 2010

Cable-Stayed Bridges - Sundial Bridge (7)


The completed Sundial Bridge is very pretty, due to the perseverance of the investors, engineers, fabricators, builders, as well as due to Calatrava's design. It's hard to take an ugly photo of the bridge. This is largely because all the details and transitions have been carefully thought out.

Are all Calatrava's bridges white? It's a nice color for them since it accentuates the clean lines of the structure. Note how the end of the barrier rail has a crackle glaze, which is most often seen on Asian pottery. The tower supports have the same crackle texture.

The thin trapezoidal slots in the tower are repeated in the lights at the ends of the rails as well as in the metal railings. I like how the metal rails project outward from the deck before coming back in.

I wonder what it's like riding a bike on the glass surface? I don't like riding my bike on the metal grating of movable bridges, especially when it's wet. I imagine wet glass is even worse!
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Saturday, July 24, 2010

Cable-Stayed Bridges - Sundial Bridge (6)


Looking down at the tower base of the Sundial Bridge. The tower arches back over the two legs of the base, helping to balance it. From this view, the bridge looks like a sculpture, like one of the structures designed from steel plates by the sculptor Richard Serra. Our aesthetic response to a Calatrava bridge is both for it's interesting shape as well as for how it carries a superstructure over an obstacle.

I assumed the bridge ran east and west across the southward flowing Sacramento River, but looking at Google Earth I can see that the bridge actually goes north and south across a bend in the river. We can see the shadow of the tower pointing to the west in the photo below, suggesting it was taken in the morning.

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Friday, July 23, 2010

Cable-Stayed Bridges - Sundial Bridge (5)


A composite view of the tower model, the tower during construction, and the tower on the completed bridge. I imagine the back bearings are in tension and the front bearing is in compression to resist the overturning force of the cables pulling on the tower. However, it's possible that since the tower leans backward and has such a heavy base that all three bearings stay in compression (and shear). Also the large tower base can resist the bending and shear from the cables pulling on the tower.

The cables are in a harp-arrangement. They are attached to steel arms on the side of the tower and to the vertical elements in the superstructure segments. They call this kind of bridge a 'cantilever spar' to differentiate it from cable-stayed bridges that support the superstructure by balancing the load on each side of the tower.

Note the vertical slots along the edge of the tower. Its possible they have a structural function, but I doubt it. They look more like ornamentation, like the openings they used to put in the sides of a Buick. Also, the glass deck looks nice on the bridge. However, at first, the tiles were prone to shattering whenever a hard object was accidentally dropped on them.

The tower points north and is used as a sundial in the park surrounding the bridge. The shadow moves fast enough so that you can perceive the Earth spinning on it's axis.
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Thursday, July 22, 2010

Cable-Stayed Bridge - Sundial Bridge (4)


The superstructure that carries foot (and bicycle) traffic on the Sundial Bridge is built from triangular segments with a central spoke, similar to the vertebrae that supports human beings. Calatrava's work is often inspired by the human figure or by human structural elements.

In this photo we can see the unpainted tower behind the assembled superstructure with additional superstructure elements in the foreground. Cable stays are in rolled-up coils beside them. All that remains to do is put the remaining superstructure elements together and hang them from the tower.
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Wednesday, July 21, 2010

Cable-Stayed Bridge - Sundial Bridge (3)


A view under the tower of the Sundial Bridge. Note the concrete pedestals, which were used to jack the tower into place. Afterwards, the tower was painted and the columns were removed.

I was a little surprised that the tower sat on bearings. I imagined a strong earthquake could easily knock it over. Apparently its self-weight provides a sufficient restoring moment to keep it stable for seismic and wind loads.

Also note how the superstructure is attached to the tower at this location. To the west are cables that descend from the tower and support the superstructure. Unlike a conventional cable-stayed bridge, there is no back span to balance the tower and support the main span. Instead the tower slopes backward to support the main span.
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Tuesday, July 20, 2010

Cable-Stayed Bridges - Sundial Bridge (2)

Since we looked at a Calatrava-like bridge yesterday, I thought we might as well look at the real thing today.

I visited Calatrava's Sundial Bridge while it was being constructed (it's located on the Sacramento River just south of Redding in Turtle Bay). The engineer in charge felt that this project was different from a regular bridge construction project. For one thing, no one had any idea how much the bridge would cost. The owners just kept providing money until it got built. Also, the engineer complained that Calatrava provided very little engineering support for the project. Most of the details and much of the analysis was done by the project engineer. Finally, there were a lot of delays with the fabrication of the steel segments used to assemble the tower. The geometry of the sections and how they fit together must have been a matter of some concern since there were several models of the tower constructed of cardboard on the engineer's desk. I don't think Caltrava ever visited the site while the bridge was being constructed. Despite all of the problems, the owners were fortunate that they persevered and got an original Caltrava-designed bridge in the end.

In this photo, the tower is sitting on three bearings on the east side of the river while the skeletal superstructure is being assembled. Once the east side of the bridge was assembled, they had to take apart the crane and rebuild it on the west side of the river. We'll take another look at this interesting bridge tomorrow.

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Monday, July 19, 2010

Cable-Stayed Bridges - Denver Millenium Bridge

On a cross country train trip, I was surprised to see this odd bridge at the Denver Railway Station. The tilted pylon dwarfs the pedestrian overpass that it supports. It has five cable-stays anchored into the ground and a dozen more supporting the 130 ft long concrete deck on tubular steel members.

They could have built this bridge without a tower by raising it up a step and deepening the superstructure. However, in that case they wouldn't have gotten this rather whimsical, Calatrava-like structure.
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Sunday, July 18, 2010

Cable-Stayed Bridges - Stonecutters Bridge (10)


We're looking back at the heavy concrete back spans that balance the main span of the Stonecutters Bridge. You can just see the portal of the tunnel that carries Highway 8 under the mountain on the west side of the bridge.

Hong Kong is a pretty city and the port north of Stonecutters Bridge must be the busiest in the world. As far as you can see looking south there are enormous container ships waiting to unload their cargo.
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Saturday, July 17, 2010

Cable-Stayed Bridges - Higashi Kobe Bridge (3)


The Hanshin Expressway Corporation underestimated the seismicity of the Kansai Region. Consequently, many of the bridges on the newly-built Wangan Expressway were damaged during the 1995 Kobe Earthquake.

The side spans on the Higashi Kobe Bridge had hold-down devices that broke, allowing the deck to rise about a meter. Most of the other devices that restrained or attached the superstructure to the substructure were also broken. Fortunately, most of the cables and their anchorages were undamaged.

In this three-span cable-stayed bridge, the towers are isolated from the superstructure, which prevented tower damage and allowed the bridge to quickly reopen.
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Friday, July 16, 2010

Cable-Stayed Bridges - Chi Lu Bridge



Cable-stayed bridges require careful design to prevent significant damage during earthquakes. The best design isolates the tower from the superstructure.

The Chi-Lu Bridge was almost completed (just awaiting a closure pour) when the 1999 Chi Chi Taiwan Earthquake occurred. It is a single tower cable-stayed bridge with two, 120 m (400 ft) spans. The bridge was in an especially vulnerable condition and it suffered a great deal of damage during the earthquake. Several cables were damaged and one pulled out of the tower anchorage. The tower was heavily damaged. The ends of the main spans moved back and forth several feet during the earthquake, severely damaging the supports.

I'm surprised the superstructure could resist the the cable-stay forces with an incomplete superstructure even without an earthquake. However, the superstructure gaps resulted in an unbalanced load, large torsional forces in the tower, and less resistance from the superstructure. There were large cracks and spalls not only to the cover but to the structural concrete in the tower, from the deck all the way to the bottom cables.

I don't think designing the towers of cable-stayed bridges to resist large earthquakes through hinging is a good idea. Even if the tower is able to support the cable stresses after forming a plastic hinge, the bridge wouldn't be functional after the earthquake. Designing the tower to remain elastic and providing dampers to absorb energy from the earthquake would allow the bridge to remain in service.
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Thursday, July 15, 2010

Cable-Stayed Bridges - Stonecutters Bridge (9)


A photo showing the winches lifting a 28 m (92 ft) superstructure segment from the barge into place on the bridge. Cantilever construction requires the main and side span segments to be assembled simultaneously to prevent large moments from overstressing the towers. Construction of cable-stayed bridges often requires more engineering than the design of the finished bridge.

In this photo, the far ends of the box girders are supported transversely with cables while the whole assembly is raised by the winches. Once the segment is in place and supported by cable-stays, the additional supports can be removed.

I recall that this bridge cost about $300 million US, which was reported as high, but seems pretty reasonable for a kilometer long main span bridge structure to me (the second longest cable-stayed bridge in the world). Construction prices fluctuate depending on how much work is out there. A few years ago when this bridge was being built prices were high, but now there is less work and prices have dropped (at least in California).
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Tuesday, July 13, 2010

Cable-Stayed Bridges - Stonecutters Bridge (8)

Another photo of the construction of Stonecutters Bridge. The tower on the east side of Rambler Channel sits on what was once Stonecutters Island (but is now part of the mainland). I wonder if there were thousands of stone cutters practicing their craft here 100 years ago?

In this photo they are removing one of the 224 cables from drums shipped from Nippon Steel at a fabrication plant in Shanghai. The longest cable is 670m (2,198ft) long and they have from 187 to 421 - 7mm high-strength galvanized wires. The cables (made up of parallel strands) were shipped to Hong Kong. The drums were lifted onto the deck and set into a device that slowly unrolls the heavy cable as workers spread it onto the deck.  A crane then lifts the cable where it is attached to the towers and then stressed from a gantry under the girders.

The lower three sets of cables are anchored into the reinforced concrete towers while the upper 25 sets of cables are installed into anchorage boxes in the steel portion of the towers. At the top of each tower, space was left for a tuned mass damper, should they be required to reduce vibrations. 
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Monday, July 12, 2010

Cable-Stayed Bridges - Stonecutters Bridge (7)


A view of the transition from steel to concrete   on the back span of Stonecutter Bridge. I think this transition looks pretty good. The approach to this bridge on Tsing Yi Island goes through a maze of ramps and connectors before plunging into a tunnel.

You can see rails (along the inside edges of the steel box girders) that will carry a painter's traveller. There will be one on each back span and a third under the main span. A large crew will spend their careers keeping this bridge painted (and inspected for possible damage).

You can also see the much bigger cable anchorages on the concrete spans. These short back spans are balancing the long, main span and have to be carefully designed with stronger cables and a bigger anchorage assembly.
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Sunday, July 11, 2010

Cable-Stayed Bridges - Stonecutters Bridge (6)


A good view of Stonecutters Bridge across Rambler Channel at the entrance to Kwai Chung Container Port.

The cables are in a semi-fan arrangement but look almost vertical in the photo. The 174 ft wide superstructure was designed to reduce air-resistance with two orthotropic steel boxes that are 240 ft above the channel. My feeling is the bridge was most vulnerable to wind loads while it was being constructed (the superstructure of the Cooper River Bridge was anchored during construction). Wind loads control the design and so testing was a major component for this project. Fortunately, there are no sources of large earthquakes in the region.

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Saturday, July 10, 2010

Cable-Stayed Bridges - Stonecutters Bridge (5)


I have often complained about towers on cable-stayed bridges that abruptly change shape above the deck. In this photo we can see that the towers have a narrow cone-like shape going through the superstructure, which is very pleasing.

I wonder why the towers of suspension bridges don't usually have the same problem with the transition above and below the deck? Perhaps its just because they are often older bridges and have stolid two-legged shapes. On a cable-stayed bridge the engineer has to place the tower and the cables so they don't interfere with traffic while supporting the deck. You would think the shape would be the result of structural analysis, but my experience has been that its determined by an architect's vision and the engineers just have to make it work.
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Friday, July 9, 2010

Cable-Stayed Bridges - Stonecutters Bridge (4)

A photo of a cable on rollers so it won't get frayed while being dragged across the deck. There must be a blue protective covering around the cable that's removed after it's in place. I  imagine the cable is attached to the superstructure first and then anchored to the tower (because the superstructure is more flexible). The tower was assembled very quickly using a piggyback form system. Cable anchor boxes were attached to the inside of the tower and then the cables were inserted into it and secured. The soil conditions turned out to be different than they had originally assumed, which delayed the project while they built deeper tower foundations. The top of the tower has a stainless steel surface with shear studs. They must have used this surface as a form for pouring the top of the tower. The superstructure segments on the main span are 28 meters long and on the back span they are 18 meters long and made of reinforced concrete instead of steel to balance the bridge during construction (and after).
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Thursday, July 8, 2010

Cable-Stayed Bridges - Stonecutters Bridge (3)

I'm standing on Tsing Yi Island looking east across Rambler Channel toward Kowloon, just north of Hong Kong Island. Yesterday, I said that the steel structure attached to the tower was a rack and pinion elevator, but in this photo it's pretty clear that it supports the tower crane.

Note the winches at the ends of the cantilevered spans. Barges bring the superstructure segments into position where they're lifted up by the winches and hung from the towers with cables.

The two steel box girder sections are held apart by long steel floor beams. The openings between the steel boxes give the bridge a nice appearance but I'd worry about someone falling through the deck!
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Wednesday, July 7, 2010

Cable-Stayed Bridges - Stonecutter's Bridge (2)

I thought we could take another look at Stonecutters Bridge as long as we're in Hong Kong. It was being built when I visited and it opened for traffic on December 20, 2009.



This structure originated from a design competition won by bridge architect Dissing+Wetling and developed by Ove Arup.

The towers are made of reinforced concrete that was topped in stainless steel. Each cable had its own drum which was rolled onto the deck, attached to roller skates, and then lifted into the tower anchorages with a crane. After each main deck section was lifted up and attached to the precut cables a heavier back span segment was lifted into place to balance it.

Note the rack and pinion elevator to carry workers up and down the 960 ft tall towers. In the Google Earth photo (below) we can see the many different bridges carrying vehicles to and from Tsing Yi Island. Stonecutters Bridge is at the lower right end of the island. The Google Earth photo is from 2009 and so you can see a gap in the center of the bridge before the last piece was put in place.

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Tuesday, July 6, 2010

Cable-Stayed Bridges - Ting Kau Bridge (2)

A view of the Ting Kau Bridge (part of Route 3) from the deck of the Tsing Ma Suspension Bridge (part of the link from the mainland to Lantau Island).
The Happy Pontist commented that the very long (longitudinal) cables aren't for providing stability from wind loads (as I suggested) but to stiffen the central tower. He directs us to Michel Virlogeux's paper,
Bridges with Multiple Cable-Stayed Spans, published by the International Association for Bridge and Structural Engineering (IABSE) in 2001. I haven't read this paper (it costs $28 to download) but I believe the long cables make the central tower more resistant to longitudinal movement. A three span cable-stayed bridge uses the pier at each end as a tower anchor. The central tower of a four-span cable-stayed bridge is between long flexible spans that don't provide sufficient longitudinal restraint and require long cables to anchor it to the adjacent towers.
Although the Happy Pontist doesn't mention it, I believe the transverse cables (arranged like the cables around a ship's mast) make the three towers more resistant to transverse movement.
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Monday, July 5, 2010

Cable-Stayed Bridges - Ting Kau Bridge

The Ting Kau Bridge is a unusual cable-stayed structure across Rambler Channel in Hong Kong, China. It has three single-legged towers (560 ft, 640 ft, 520 ft) that are stabilized with transverse cables above and below the deck. Moreover, the central tower is supported by extremely long (1530 ft) cables extending to the far towers. The extra cables are to help resist the strong winds and typhoon loads that blow through the channel.

This bridge also carries the highest daily traffic in Hong Kong and the largest number of container trucks between Mainland China and the container port in Hong Kong. It is a six lane bridge built in 1988 with a total length of 3864 ft and with main spans of 1470 ft and 1560 ft.

Driving across the bridge, one is struck by the hundreds of container ships waiting to enter the port. Also, by the distinctive yellow on the steel anchorages at the top of the towers and on the steel girder superstructure.
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