New road to girder installation

What is claimed to be one of the longest ocean-crossing bridges in the world is under construction near Shanghai, China. The 36 km Hangzhou Bay Bridge will span the Hangzhou Bay on the East China Sea and the Qiantang River at the Yangtze River Delta. The bridge, which will be part of China's East Coast Superhighway, will have a six-lane, two-direction high-speed roadway. Construction, at the cost of CNY 11.8 billion (US$ 1.42 billion), started in 2003 and completion is scheduled for 2008.

The bridge comprises nine sections, including one central navigable cable-stayed bridge. Both north and south approaches are built by installing up to 70 m long post-tensioned concrete box-girder spans on top of low and high piers. Both the north and south high piers each cover a length of about 1,400 m, while the middle low piers cover a length of 9,380 m. Another part, of almost 20 km, includes a stretch of some 10,000 m built from 50 m girders.

The system

Italian specialist, DEAL, has supplied a system capable of self-loading, transporting, launching and installing the 50 m pre-cast girders weighing in excess of 1,500 tonnes. The heavy transport trailer system of this girder installation method was supplied by Scheuerle Fahrzeugfabrik in Germany, part of the Transporter Industry International (TII) group owned by entrepreneur Otto Rettenmaier.

The trailer system comprises four self-propelled trailers, each of 20 axle lines. Each line consists of two pendulum axles, each with four wheels, giving a total of 160 wheels per trailer. Each trailer has a Power Pack Unit (PPU) that feeds the hydrostatic drive and the other hydraulic functions of the trailer, including the hydraulic lift of the pendulum axles and the hydro-mechanical counter steering. A central computer, via an optional automatic guidance system fitted to the individual trailer modules, aligns the correct movements of the four trailers.

The combined carrying capacity of the trailers is some 1,500 tonnes, while the tare weight of the trailers, with the launching system, is almost 500 tonnes. With the DEAL launching system on top, the trailer system set up covers an area 76.3 m long and 25.8m wide. The launching system consists of the laying machine, conveyor carriages and gantry cranes.

The method

At the assembly tract on the bridge, the two front vehicles lower themselves on their hydraulic supports so that any forces can be safely transferred into the area of the bridge pier. Subsequently, the rear vehicles push forward the bridge section, which is positioned on lockable trolleys to the DEAL laying machine located on the front trailers. When the final position is reached, the rear trailers are also lowered by means of their hydraulic supports. The laying equipment now supports itself on the rear modules and removes the bridge segment from the vehicles. After this, the segment is placed in its final position while the Scheuerle transport system units make their way back to collect the next pre-cast girder.

This bridge installation method was developed by DEAL and Scheuerle to cope with the request to move on site and install ever larger and heavier bridge elements in an efficient and cost effective way. •