Slim Duct DYNA Grip® Stay Cables: The Mersch Stay Cable Bridge
In the community of Mersch in Luxembourg, a new, 260m long, 4 span stay cable bridge with span lengths of 2 x 43.3m and 2 x 86.7m and two 30m high pylons was recently built. The Pont Haubané Mersch is the world’s first stay cable bridge to feature stainless steel slim ducts. Beginning with the preliminary planning stage, DSI provided advice for the project and took on architectural and technical responsibilities once the project had been awarded.
For the special stainless steel stay cable ducts (stainless steel grades 1.4307 and 1.4404), DSI searched for a suitable partner for the welding work, special components and surface processing. Furthermore, an assembly concept had to be developed for the stainless steel ducts that are considerably more susceptible to damage and less elastic than common ducts. Finally, a new strand lifting concept was used that was a European first. The existing welding machine also had to be remodeled completely in order to meet the changed requirements.
The Hintzen Edelstahlverarbeitung Company produced the technically and architecturally vital special components – vandalism protection pipes, transition ducts, sleeves and flange ducts – and carried out the welding work on the continuous ducts. The Börsting Company, a specialist for stainless steel surface processing, presented several different polished sections to the customer in advance and achieved the chosen surface appearance professionally on all stainless steel parts.
20-80m long Types DG-P37 and DG-P31 DYNA Grip® Stay Cables were used for this project; the Type DG-P31 stay cables were filled with 27 strands. In total, DSI supplied 42t of grade 1860N/mm², 150mm² strand for the stay cables. For the slim duct that had been chosen by the engineer (Slim-Duct, 156.0 x 3.0mm), DSI had to provide procedural concept studies for the supporting strands due to the limited space available.
Finally, the decision was made to push the strands in from the bridge deck towards the pylon using different compaction clamps. Thanks to the equipment that had been especially adapted by DSI, the up to 80m long stay cable strands could be pushed in completely. Afterwards, the stay cables were stressed in two steps using the Con-Ten Method developed by DSI.
After a construction time of approximately 3 months from site setup to technical approval, the complete work was handed over to the customer without any complaints. In particular the fact that there were no visible welding seams on the stainless steel components including the continuous ducts illustrates the high quality of the products and processes that were used. The quality was decisively influenced by the ATIS post-treatment robot supplied by the Alpin Technik Company. The robot was developed during construction work and used once stay cable assembly had been completed. The robot applied the final polishing to the continuous stainless steel ducts using special rotation brushes shortly before the bridge was opened to traffic.
This new development by DSI and Alpin Technik will be used for the regular main assessments of stay cable bridges with stainless steel ducts to permanently maintain the stainless steel appearance and surface structure.