The majestic appearance of Hangzhou Bay Trans-sea Bridge. Till now, 65% of the Hangzhou Bay Trans-sea Bridge that was contracted to China Railway Engineering Corporation (CREC) has been completed.

From a bird's-eye view, the Hangzhou Bay Bridge will look just like a dragon lying curled on the waves of the Hangzhou Bay area, east China's Zhejiang Province.

The 10 billion yuan, S-shaped bridge will shorten the ground distance between Ningbo and Shanghai. Its completion will add two records to bridge construction history. Around 36 kilometers in length, it will be the longest trans-ocean bridge in the world. It will also have been the most difficult to construct.

A bridge over Hangzhou Bay was once little more than a fantasy for most experts in the field. At an early meeting to discuss the feasibility of the project, one expert said, "I think it is the infeasibility report, not the feasibility report that we should study."

The expert's opinion was justified. At the time, China had no bridge-building program and lacked the technology, equipment and experienced personnel to undertake such a project.

Hangzhou Bay is one of the world's three major gulfs and has strongest winds and biggest waves of them all. The waves frequently change direction making it difficult for construction vessels to maintain a position. Maritime operations are only possible for half the year. Seawater and strong currents have a corrosive effect on the steel infrastructure and just 10 kilometers beneath the seabed there are large pockets of natural gas, making construction extremely hazardous.

When China announced plans to build this bridge, many foreign companies submitted a tender for the project, among them three leading construction companies from the United States. At the advisory meeting in Manhattan in 2002, senior representatives from all three companies campaigned for the project. However, when the Chinese elaborated on several difficult problems associated with the bridge's construction, the US companies expressed concern.

"I'm sorry but we've never encountered such conditions," admitted one American expert after a silence. "However, if we were to build the Hangzhou Bay Bridge, I'm sure we would find a way to overcome these difficulties."

It might have been a shortcut if China had employed foreign experts for the design, construction and management of the bridge. However, after thorough consideration, the authorities in Ningbo City decided to keep the project local and gave it to the All China Federation of Trade Unions, their third key project following the Three Gorges Project and the Qinghai-Tibet Railway. When inviting tenders project management, for the first time, allowed individual construction companies and design companies to form partnerships and bid jointly.

"We want to take advantage of this major project to create a new path for China's bridge construction industry," they announced.

Project Leader Wang Yong told reporters that "only by relying on our own efforts and developing our own intellectual property can China be competitive at an international level in the bridge construction industry."

However, ambition alone will not be enough to build the world's longest trans-ocean bridge. A scientific and innovative approach is essential. Feasibility studies in over 140 fields on the Hangzhou Bay Area took 10 years of persistent exploration and scientific investigation.

Construction is now underway but it has not often been straightforward. Considering the difficulty of offshore construction, some components of the bridge have to be completed on land, including bridge foundations, piers and box girders, a kind of bridge panel. Upon completion they will be transported to the area and maneuvered into position.

To combat the corrosive effect of the seawater, a large quantity of coal ash and slag powder has to be mixed with standard concrete to produce a special high-density variety. This concrete will not only survive the mandatory 100 years, but will provide a model for research into corrosion-resistant concrete at an international level.

Steel piles that are 1.5-1.6 meters in diameter and 71-88 meters in length are used in the construction of the bridge. In earlier domestic projects the largest piles were no longer than 80 meters and were first produced in sections, then transported to the site for assembly and positioning. However, because of the unique Hangzhou Bay environment, it is impossible to work on the piles at sea; hence workers must complete the process on land.

The diameter of the piles is longer than that of a large table, and the length is higher than that of a 30-storey building when erected. For their construction, numerous studies and tests were conducted before scientists finally settled on a spiral welding method.

The first logistical problem to be tackled was how to raise the snatching capacity of the machines for concrete box girders weighing between 900 tons and 1,430 tons. Each piece is 50 meters in length and 1,430 tons in weight. Neither hoisting machines nor boats are capable of lifting them. There is also no way to conduct on-site casting. The only feasible option was to use an erecting machine moving along the completed sections of the bridge to extend the bridge deck from the shore to the shoal area.

Until now, the record weight for box girders placed in this way was set at 900 tons. Technologists had to raise that record by a further 530 tons overnight. Dozens of experts from Zhejiang University, Tongji University and Southwest Transportation University worked on the problem while Italian and German companies provided technical support. China Shaanxi Construction Machinery Company and Guizhou Tire Factory also joined the campaign. On July 28, 2005, with the aid of an erecting machine and five other pieces of equipment, a 640-tire girder transport vehicle, known as the "Centipede of 1,000 Feet", steadily placed a box girder on two bridge piers. The Italian experts praised Chinese engineers saying "the Hangzhou Bay Project has performed a miracle!"

In the process of pre-casting the concrete, China Tiesiju Civil Engineering Group Co. Ltd. found that blowholes and cracks were easily produced on the surface of the concrete structure. This would not only affect the appearance of the structure, but its resistance to seawater erosion. After further experimentation, technologists discovered that cloth-covered templates improved the color and the density of the concrete and reduced the occurrence of blowholes and bubbles.

The cracking of large pre-cast concrete structures has always been a problem in bridge construction. China Zhongtie Major Bridge Engineering Group Co. Ltd. (MBEC) used low strength early stretching technology in the production of the 70 meter box girders to avoid cracks. This involved squeezing the prefabricated structures two or three days after the initial casting when the density of the structures had not yet reached the maximum level.

Moving machines weighing 800 tons are used to transport box girders during construction. Tiers are 1.6 meters in diameter and have no tire tubing. Technologists fill them with water when they are being used in construction. The technical staff of an Italian company involved required 15 days to fit all the tires. Technologists at MBEC questioned this turnaround, believing it could be done in far less time. They redeveloped the existing technology and were able to improving the trajectory to just four days. Foreign experts were stunned by the success of the developments.

The bridge's project leaders have set up a race-oriented competition as an incentive for innovative technicians. "There is a 500 thousand yuan award for first place winner of the yearly award and a100 thousand yuan award for the quarterly winner. Rewards are also given for smaller inventions."

More than 6,000 workers from 24 units have participated in the competition, resulting in more than 250 scientific and technological innovations over the last two years and reducing the cost of the bridge by nearly 100 million yuan.

So far, the incomplete bridge has withstood more than 10 typhoons and astronomical tides including "Matsa" and "Kanu". Jin Jianming, Deputy Leader of the project, said that so far, the bridge had used 55% of its total investment without any security or personnel accidents being reported.

The Hangzhou Bay Bridge is expected to be completed ahead of schedule by 2008.

By People's Daily Online