Saturday, January 31, 2009

Cable-Stayed Bridges: Stonecutters Bridge

The Stonecutters Bridge will be the world's second longest cable-stayed bridge when it is completed later this year. Brian West, the project manager, was kind enough to give me a tour when I visited Hong Kong in October.
Cable-stayed bridges require a great deal of construction engineering. In fact, the construction engineering is often more challenging than the design engineering.

The bridge will have a main span of 1018 meters from Tsing Yi Island to Stonecutters Island across Rambler Channel, the busiest shipping channel in the busiest port in the world. The bridge segments were manufactured in a factory in Shanghai, checked to make sure the segments fit together, and then disassembled and shipped to Hong Kong. Each bridge segment was brought into place on a barge, jacked up to the end of the superstructure, and attached to prestrung cables. The cables on the main span are 28 meters apart and on the back spans they are 18 meters apart. The back span is shorter to balance the bridge because the main spans are steel while the back spans are reinforced concrete.

The soil conditions were different from what they originally assumed, resulting in a year's delay while they redesigned and built a pile cap with very deep piles for the towers. The towers were constructed using piggyback formwork and with a stainless steel shell above a certain level attached with shear studs. The main span superstructure was built with a gap to go around the towers. The towers are wider at the bottom, and so they have to carefully jack-up the superstructure to avoid it banging it against the bottom of the towers. The cables are made of parallel strands, assembled in the factory, and shipped to the site on big drums. The cables are impregnated with black high density polyethylene (HDPE). The outside is covered in a skin of white HDPE. They laid the cable out on the deck before attaching it to tower and deck. They attached little rollers to the cable so it wouldn't rub against the deck as it was lifted up onto the towers. The longest cable is 560 m. The superstructure has lock-up devices that allow temperature movement but will ‘lock-up’ for sudden movement such as a typhoon (or earthquake).
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Cable-Stayed Bridges: Stonecutters Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

Friday, January 30, 2009

Arch Bridges: The Rio Grande Gorge Bridge

The Rio Grande Gorge Bridge is a cantilever truss carrying New Mexico State Route 64 over the Rio Grande River. The bridge is 650' tall with 300' approach spans and a 600' main span. It was built in 1965 and voted the most beautiful long-span steel bridge by the American Institute of Steel Construction.

This bridge is a popular location for filming movies. On the day this photo was taken (in June of 2008), workers were getting ready to close the bridge to shoot a scene in Terminator 4. The bridge is 10 miles west of Taos and less than a mile east of Spaceship Earth, a desert community with many unique, energy efficient homes.

The bridge has sidewalks that allow visitors to study the Rio Grande Gorge, an earthquake rift zone where stresses between the Pacific and the North American Plates cause occasional earthquakes. If a large earthquake were to occur, this bridge would be extremely vulnerable since it wasn't designed to resist much shaking or a possible offset if the rift were to open.
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Arch Bridges: The Rio Grande Gorge Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

Tuesday, January 27, 2009

Arch Bridges: The Caesarea Aqueduct

The Caesarea Aqueduct was built by King Herod to bring water to the city of Caesarea, which he had built to honor Emperor Augustus Caesar. The aqueduct was 10 km long and brought water south from Mount Carmel.
Caesarea became the capital of Palestine after the Romans razed Jerusalem, and maintenance of the aqueduct was taken over by the Roman army. A second aqueduct was added as the population grew. Stone tablets were places at intervals along the aqueduct announcing that the construction had been completed by the 10th Roman Legion.
The aqueduct was constructed by building stone pedestals to support a wooden form for the placement of voussoirs (the wedge shaped stones that form the arch). Once the keystone was in place, the form could be removed.  The area around the arches was then filled with rectangular stones and a channel was built on top, which can still be seen in this photo.
The aqueducts remained in service for around 1200 years until they fell into disrepair and were replaced by a canal. Today, portions of the aqueducts can be found along the Mediterranean, including at this popular beach east of the modern city of Caesarea. When I was there, Roman pottery shards and other ancient debris was still lying in the sand.
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Arch Bridges: The Caesarea Aqueduct by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.

Monday, January 26, 2009

Arch Bridges: Lupu Bridge

This viaduct includes the world's longest arch (at 550 meters), crossing over the Huangpu River in Shanghai. Its name, like the other Huangpu River crossings, comes from the two districts that are connected: Luwan District to the north and Pudong District to the south. The main span is a steel, basket-handle arch with truncated deck arches at the approaches. The arch ribs are 9 meter by 5 meter steel boxes.

Shanghai's other Huangpu crossings are cable-stayed bridges, and it is said that an arch was chosen at additional expense, to provide something unique to the city. This is similar to the East Bay Bridge in San Francisco Bay which is being build at additional expense, with a self-anchored suspension span to provide something special to the Bay Area.
Another nice feature of the Lupu Bridge is that there are elevators and a guide to take visitors across the top, which is 100 meters above the Huangpu River. From the viewing platform, you can see the 2010 Shanghai Expo being constructed under the bridge.

Creative Commons License
Arch Bridges: Lupu Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.