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.

Cable-Stayed Bridges - Stonecutters Bridge (10) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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).

Cable-Stayed Bridges - Stonecutters Bridge (9) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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. 

Cable-Stayed Bridges - Stonecutters Bridge (8) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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.

Cable-Stayed Bridges - Stonecutters Bridge (7) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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.

Cable-Stayed Bridges - Stonecutters Bridge (6) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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.

Cable-Stayed Bridges - Stonecutter's Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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.

Cable-Stayed Bridges - Ting Kau Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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.

Cable-Stayed Bridges - Ting Kau Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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).

Cable-Stayed Bridges: Stonecutters Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution 3.0 United States License.