China Highway Planning and Design Institute (HPDI) chose TDV to install bridge design software RM and to assist and support the Chinese design team in close cooperation throughout the whole design process of longest stayed-cable bridge in the world.Introduction
Sutong Bridge, Cable stayed Bridge
Sutong Bridge lies between Nantong City and Changshu in the east of Jiangsu province and forms a link across Changjiang River. The total length covered by the project is 32.4 km. It consists of three parts: approach and link roads on both the north and south banks, and the main central crossing, which has a total length of 8.2 km. The main cable-stayed bridge has a double cable plane, and a double-pylon arrangement, with a steel box girder deck. Its spans range from 100 m to the main span of 1088 m, which is a world record, overtaking the Stonecutters Bridge in Hong Kong. The bridge over the other channel is 548 m long, and consists of a T-type steel girder bridge. The contract on the north bank includes approach roads of 15.1 km total length with two interchanges, a toll gate and a service zone; on the south bank the total length is 9.1 km, with one interchange.Girder
Cross-section of the Sutong Bridge girder
The bridge girder is a streamlined closed flat steel box girder. The total width including wind fairing is 41.0 m accommodating dual 8 traffic lanes. The cross-section height is 4.0 m. The steel box is generally stiffened in the longitudinal direction with closed steel troughs. Transverse plate diaphragms are provided with a typical distance of 4.0 m and with smaller distances down to 2.27m locally around the two pylons. The characteristic yield strengths of the structural steel are 345 MPa and 370 MPa.Pylons
The inverted Y-shaped pylons are about 300 m in height and are made of concrete grade C50 according to the Chinese standard JTJ0 - 89. The stay-cables are anchored inside steel boxes fixed to the concrete by shear studs at the pylon top. The maximum segment of a cable anchorage steel box weighs about 36 tons. The tie-beam between the pylon legs is fully post-tensioned for outward thrust from the pylon legs under service loads and seismic load. According to the project specifications and the review comments from COWI the cracking width of the concrete pylon wall is controlled within 0.2 mm.Stay Cables
The stay cables are arranged in double inclined cable planes with standard spacing of 16 m in the central span and 12 m near the ends of the back spans along the girder. To reduce the effect of wind loads, the cable stay systems are made of the parallel wire strand consisting of 7 mm wires, each with a cross sectional area of 38.48 mm2. The nominal tensile strength of the cables is 1770 MPa. Cable sizes range from a minimum of PES7-139 for the main span stays near the pylons to a maximum of PES7-313 for the longest backstay. The longest cable is about 577 m with a weight of 59 tons. The problem of cable vibration due to wind and possibly in combination with rain or parametric excitation has been studied during the design process. Different measures to minimize stay cable vibrations have been investigated including two kinds of cable surface treatments to prevent formation of rainwater flows on the cables and internal or additional external damping devices. The final measures will be chosen after detailed testing.Global Analysis
Numerical model of the Sutong Bridge
The RM2000 program developed by TDV, Austria, has been used for the global analysis of the Sutong cable-stayed bridge in the detailed design. The finite element model of the bridge is illustrated in the previous figure. The structural modelling keeps accordance with the planned construction schemes. Each of the stay-cables was divided into 8 sub-elements to consider cable-sag effects rather than approximating this effect by using effective module of elasticity. Other interacting non-linear effects such as P-delta effect, large displacements and shear displacements were also considered in the calculation. Creep and shrinkage effects were calculated according to the CEB/FIP 90 code. The flexibility of the pylon foundations was modelled with spring elements. The connection between the girder and both pylons were treated as nonlinear static spring elements with a gap value of 750 mm and a linear stiffness of 100 MN/m.
TDV was not only the provider of the software but also a part of the Consultant team and mainly responsible for the modelling, construction, stage analysis, optimization of the stressing procedure for cable stay, structural analysis and erection control.
Modelling this cable-stayed-bridge was a very delicate procedure because of the very complicated sequence of construction stages which had to be simulated for the erection of every single segment.