The Stadium Roof in Nantong, China, Opens and Closes by Means of Hydraulics

Irene Kremer, Enerpac BV
Collaboration spéciale

The new Nantong stadium in the Chinese Jiangsu province is China's first large stadium with a roof that can be opened and closed. It is exceptional that for the first time in history, the propulsion and stabilisation of the movable roof parts takes place hydraulically. Enerpac signed a contract for the development and installation of the advanced propulsion and operating system whereby trolleys play an important role.

Below the stadium roof a soccer field, 400 m of athletics track, and various accommodations are located. The stadium has a total surface of 48 000 m2. This stadium forms part of a much larger complex with among other things an exhibition centre. In total, said complex takes up a surface of 150 000 m2. With this the complex that is also compared to the Olympic Stadium in Peking is the largest and most functional one in the history of the Jiangsu province. With the construction an investment of 1,1 billion RMB (China Yuan Renminbi) or almost 107 million euro was involved.

Semi-spherical shells
The construction is very impressive to see. The movable roof part consists of two enormous semi-spherical steel and glass shells which literally ride across the semi-open, dome-shaped stadium roof which is also made of a complex steel construction.

One of the two shells weighs at least 1100 t and during the opening and closing, each shell spans a distance of approximately 60 m. To be able to move this heavy steel construction smoothly and without excessive torque forces, Enerpac developed a strong hydraulic propulsion system with an advanced electronic control and operation system added to that. It is the first time that hydraulics is applied during the opening and closing of a movable roof.

Hydraulic winches
Transporting the movable roof shells takes place with the aid of 16 steel cables in total, with a thickness of 64 mm using eight heavy winches (four per roof shell), each with 136 t of tensile force. To close the stadium roof, the cables lift up the roof shells synchronously and position them in the roof top using a cable pulley. Opening is simply done using gravity. As it is, the roof shells gradually lower themselves downwards across the roof into their starting position, whereby the cables hold up the weight of the shell.

The cable drum of each winch is driven by a combination of six hydro-motors and planet gear reduction gearboxes with a low number of revolutions and a high torque. The system reliability and thus the safety are guaranteed by this amount. Even if two of the motor combinations would fail simultaneously, normal operation is still possible.

Trolleys across rails
The semi-spherical shells are supported by 44 trolleys in total; 22 for each roof part. These trolleys move across rails which form part of the roof construction and thus function as the wheels of the roof shells. Due to the support with the trolleys, the whole roof forms a so-called super-static spatial mechanism.

As the solution for the complicated multipoint drive of the movable roof shells, each trolley has its own hydraulic unit. This unit consists of a pump and different correction cylinders which can be corrected in three directions with each fulcrum of the movable roof shells during opening and closing. Using pressure and relocation sensors, any (rail) blockage of the trolley is constantly checked, either as a result of an installation error of the chief arch, or even a deviating movement during the opening or closing. Using the data of the sensors the hydraulic pressure and the report of the correction cylinders are driven, and the pulling force of the steel cable can be adjusted.

Vertical and horizontal correction
A difference in height, if any, between the roof shells and the fixed roof can be compensated with the vertical correction cylinder on the trolley. Such a difference can occur due to distortions in the steel construction of the fixed roof and the movable roof shells. To this effect, the operating system measures the cylinder stroke and oil pressure in the correction cylinder. Using the measured values, the operating system calculates the load of the trolley during the opening and closing of the roof shells. Based on a certain strategy and algorithms, the system drives a proportional servo valve to adjust the pressure and the shifting of the lift cylinder as such. This way the load of each trolley can basically be kept the same and overloading is avoided.

Furthermore, the vertical cylinders on the trolleys also played a role during the installation and putting into operation. Thus the vertical hydraulic cylinder was used to check the installation height of the trolley and correct errors, if any, made during the production and installation of the steel construction. The vertical hydraulic cylinder was furthermore used to readjust the load of the trolley during the decreasing of the welding stress in the steel construction.

The two diagonally-placed hydraulic cylinders on the trolley compensate for the unavoidable horizontal oscillations of the trolley across the rail and prevent a 'derailing' in the cross direction. For this, the forces on the guide wheels are checked with sensors in real time during the whole opening- and closing process of the roof parts. If the force on the guide wheel becomes too great, the operating system shall immediately (sideways correction) drive the two diagonally-placed hydraulic cylinders to reduce the force on the guide wheel and thus avoid a sideways force on the arch construction which is too great.

Advanced and safe, controlled hydraulic movement
The hydraulic driving of the movable stadium roof as developed and installed by Enerpac, is clearly something new for China as well as regarding stadium construction. An important advantage of the hydraulic system is the high level of reliability and with this great safety. Besides that, the application of hydraulics offers the big advantage that the opening and closing of the roof shells can take place very gradually, smoothly, synchronously and especially without large torque forces.

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