Emergency support quickly in place

Traffic Bridge Dordrecht

Like a patient being wheeled into the emergency room of a hospital. In February of this year, the Combinatie STERK (a collaboration of KnookStaal and Swarco) received the request to address the problems with the Verkeersbrug over the Oude Maas between Dordrecht and Zwijndrecht with great priority. Two supports turned out to be inadequate after reckoning for the V&R, with a high risk of collapse due to a construction that was too weak. Quick action was called for. By September the job was done: the operation was a success and the bridge was safe to use again..

Commissioned by Rijkswaterstaat, Combinatie STERK has been performing maintenance on twelve bridges and four locks in the South Holland South region since 2021. This framework contract includes the Van Brienenoord Bridge, the Merwede Bridges in Papendrecht and Gorinchem, the Spijkenisse Bridge and thus also the Verkeersbrug Dordrecht (Bridge over the Oude Maas). Requests for Modifications (VTWs) are regularly received by the combination and occasionally there is an emergency case among them. 

Cams

"The Verkeersbrug Dordrecht is a monumental bridge from 1939 that is scheduled for a major renovation starting around 2027," begins Arnold den Hoedt, project manager of Combinatie STERK. "As part of the V&R programming, engineering firm Witteveen+Bos made structural calculations for the bridge, which showed that several superstructures could not handle the required force. Therefore, vehicles weighing 20 tons or more were no longer allowed to pass the bridge. Piers 15 and 20 of the approach bridge from Dordrecht were suspect. The reinforcement in the concrete ridge structure used to hold the decks together was found to be inadequate, creating a high risk of collapse of the deck bearings. An emergency operation was required."

Together with Witteveen+Bos, Combinatie STERK accelerated its work. "And then the importance of very good cooperation starts to count," Den Hoedt says. "Very quickly several solutions were devised for each support point and put into a Trade-Off Matrix with criteria such as project duration, security of supply, nuisance impact, constructive risks, effectiveness and costs. Two optimal solutions were chosen in consultation with the client, Rijkswaterstaat. Witteveen+Bos drew up a Final Design, which was then optimized and developed with us into an Implementation Design. In this way you can save hours of welding work with just half an hour of extra calculation." 

Good agreements

Rather, Pillar 15 is located on the long approach bridge from Dordrecht and on a business park. Den Hoedt: "Here there was no room to transfer the forces to the subsoil. The ridge bearing here is right next to a pillar. So we made a balancing structure to span the ridge bearing. That structure consists of a spindle girder on either side of the pillar and below it fourteen cross beams supporting the pillar. Pillar 20 is located near the bridge next to Dokweg, which runs underneath, and on the railroad premises of ProRail and NS, where the subsoil also turned out to be heavily polluted. This meant extra communication with these parties, ground investigation and loss of time, which we could not afford. In the end, we were able to make good working arrangements with the stakeholders involved and created our own cordoned-off construction site on the railroad site. There was an understanding of the situation among the stakeholders which allowed us to maintain speed and control safety."

Building in top gear

For pillar 20, the solution consists of a steel frame on a pile foundation under the ridge bearing. This 8-meter-high frame (weighing 30 tons) was built in Moerdijk by KnookStaal in three transportable sections, preserved in Werkendam in a gray color and assembled on site in mid-September and driven into place under the bridge. It includes two rectangular truss sections and a double spindle girder at the top to accommodate the sloping position of the bridge. Den Hoedt: "Work even continued in the evenings and weekends to meet the schedule. Every weld was also 100% visually, magnetically and ultrasonically inspected. Consider that we received the first steel deliveries in mid-May and by mid-September the frame was already in place. Meanwhile, by mid-August, the support at pillar 15 was already in place. This was construction in top gear."

For the foundation, Kandt BV made in segments two tubular piles with a diameter of 660 mm to about 27 meters and a support was made on the pile of the existing foundation of the pillar. The frame was suspended from the side of a trailer, driven under the bridge and mounted on the foundation. Den Hoedt: "Between ridge and frame is a support package of steel plate, hard plastic plate and injection medium. The whole thing is a semi-passive construction that is pre-tensioned using an auger installation. Thus, the force is not transferred directly to the frames, but to the original structure. If the ridge fails, the new structure will seamlessly take over without significant displacement. You wouldn't be able to feel or see that while standing on the bridge. By the way, a monitoring system is built in to find out when the ridge bearing collapses and the force is taken over by the support structure."

In conclusion, Den Hoedt would like to emphasize again the incredibly fast process: "The research period, design phase, translation into execution design, procurement, fabrication and installation: everything was handled efficiently and proceeded with overlaps. This was only possible in good consultation with Rijkswaterstaat and the partner companies, Witteveen+Bos in particular, and through the good collaboration with the stakeholders."