Giant Spherical Bearing 🇨🇳 (2017-06)

Impressions from a large size spherical bearing

The temporary bearing is being used to rotate a bridge during its construction. It is at a railway bridge construction site. A large bearing is being lifted by a mobile crane. Precisely, the calotte is being hoisted by a mobile crane. It is part of a temporary spherical bearing. The bearing is used for the swivel construction method of a cast-in-place railway bridge, which is part of a new high-speed railway line in China. The new line has to pass over existing railway lines and highways in the area of Shangqiu City.
Bridge swivel construction refers to a construction method in which the bridge structure is built at a temporary axis alignment and then positioned in the final location by swivel action. The swivel construction method can reduce dangers to an operational railway line/highway through building a bridge superstructure at the side of the existing line (railway, highway). Dangers of falling objects and interference with train operation during the construction process can be vastly reduced. The actual rotation process takes only a short period of time.
On top of the foundation of the bridge pier a spherical bearing is placed and the pier construction continues afterwards on top of the bearing. The (upper) spherical part (calotte) of the bearing is placed on the lower concave counterpart at site. The void in the calotte has to meet the center pin of the lower part. Then it can be completely lowered down. To reduce friction PTFE elements and grease are used in combination with a very smooth surface of the calotte. The bridge superstructure will be built using the balanced cantilever method (in this case). The bridge construction does not interfere with the train operation of the existing electrified railway. Once the bridge pier and superstructure have been build the bridge will be rotated to its final alignment around a vertical axis. Then the moving function of the bearing is no longer needed. A permanent rigid connection between bridge pier and foundation is being established then. The two parts of the bridge superstructure will be stitched together once the final position is reached.

Details of the parts of the (temporary) spherical bearing and adjacent structural members are shown in this video. The footage covers various locations (i. e. different bridges). The spherical bearing is arriving at site by truck. Then the lower part of the bearing is placed on the pile cap of the bridge pier. It is going to be surrounded by reinforced concrete. The calotte of the bearing gets temporarily stored at site. The same happens to temporary sand pot bearings. They are needed for additional support of the bridge during construction. The concave part of the bearing is lubricated with grease. PTFE elements that work as sliding elements in contact with the calotte are placed into machined recesses. A thick grease layer on the lower bearing part covers the PTFE elements as well. On top of the spherical bearing bridge pier construction continues. Post-tensioned concrete member (pier base) follows on top of the spherical bearing. It is cast on a scaffolding. Starter bars from pier foundation and pier base will be connected after rotation process. Concrete anchor points for the hydraulic jacks that pull strands horizontally to achieve the rotation of the pier will be prepared. Pre-rotation situation: The bridge superstructure is aligned roughly parallel to the existing railway line. Due to balanced cantilever construction method there is a temporarily rigid connection between bridge superstructure and pier. Monitoring of the achieved rotation angle between foundation and pier is done via a large scale placed on the structure. After rotation a rigid connection is being created to permanently block the spherical bearing and to allow for transfer of the forces from the pier to the foundation. A monolithic connection is achieved. The newly aligned bridge superstructures need to be connected by a closure segment in the center of the bridge.

Credits:

High-speed railway bridge swivels into position in Henan, China by New China TV
https://youtu.be/EQMWI7IDxxo

OpenStreetMap

Hungarian Rhapsody No. 2 (by Liszt)
YouTube Audio Library