Königswinter · The next full closure of the B42 between Bonn and Königswinter is imminent: Königswinter's Drachenbrücke will be closed for four days from Thursday due to concrete replacement work. We explain what exactly has to be done on and under the 650-metre-long bridge.
„He“ needs rest, lots of rest. Doing nothing during the long weekend, that is the main task from Thursday onwards for the new concrete that is to stabilise the Königswinter Drachenbrücke. However, the B42, which runs over the 650-metre-long old town crossing, will have to be closed for four days for this. The closure begins at 7 a.m. on Thursday, 8 June, and is scheduled to last until 5 a.m. on Monday, 12 June.
During this time, the main road will be closed in both directions between the Bad Honnef-Rhöndorf and Königswinter junctions. The concreting work is almost the final stage of the extensive renovation of the Drachenbrücke, which began in autumn 2020 and was originally scheduled to last only one year. However, the weather and the lack of building materials repeatedly caused delays on the large construction site. During the work, which will last almost two and a half years, the B42 is fully closed for the third time.
Most of the time, this caused long traffic jams - especially in the centre of Königswinter, but also on the diversion and alternative routes in the Siebengebirge. Bumper to bumper, two and a half years ago and a year ago, cars struggled along the signposted diversion route through the narrow streets of Königswinter. It was not only in the old town and on Rheinallee that traffic could only move at walking speed. On the B42, too, drivers needed a lot of patience at the exits. And: In addition, the slip road in Königswinter-Oberdollendorf in the direction of Bad Honnef is still closed due to the simultaneous tunnel renovation.
Rainer Herzog, spokesman of the responsible regional branch Rhein-Berg of the State Enterprise Roads NRW, explains what the specialists will be doing from Thursday onwards while traffic is at a standstill: "During this period, stabilising steel girders will be installed underneath the bridge and the concreting work required for this will be carried out," says Herzog. The bridge must remain completely vibration-free during the so-called initial hardening of the concrete, he said. "The required hardening time is at least 24 hours," the press spokesman knows.
The fact that the closure lasting several days until 5 a.m. on Monday, 12 June, is almost without alternative is not so much due to the construction work itself, but to the fact that the freshly filled concrete has to harden for such a long time with peace and quiet - and this "vibration-free", as Klaus Otto, who has taken over the construction supervision for the large-scale project of the Drachenbrücke renovation for the Landesbetrieb Straßenbau NRW, says. "When trucks roll over it, it goes up and down up to ten centimetres in the middle," Otto reports.
The steel girders that are being concreted in are part of the elaborate corset construction that is being put on the Drachenbrücke. Part of this corset of steel and concrete are the so-called anchor blocks. These are attached to the four outer sides of the motorway crossing and concreted in place. In the next step, the steel cables pass through these anchor blocks and are finally pulled together in a kind of guide tube, giving the bridge a long-lasting hold. "It works like pressing a row of books against each other to lift them up," Klaus Otto explains the principle used. The good thing is: with the closure on Corpus Christi weekend, the work is finally turning onto the home straight and heading towards completion.
Regional diversion routes via the L144 (Schmelztalstraße) and L331 (Ferdinand-Mülhens-Straße) are signposted for car traffic. Heavy goods traffic is recommended to use the A3, A560 and A59 (see diagram). Appropriate diversion signs already on the motorway and in Linz on the L253 indicate the closure of the B42 and the diversion route.
The city of Königswinter asks all road users to follow the signposted diversion and "only approach the old town of Königswinter in justified cases", as Florian Striewe, spokesman for the city of Königswinter, explained. In order to ensure the necessary emergency routes and passageways in the old town and in the district of Niederdollendorf, the city is therefore setting up individual closures and no-parking zones on the streets Hauptstraße, An der Helte, Drachenfelsstraße, Wilhelmstraße and Küferweg. In addition, the city will close the railway crossing at Bahnhofstraße to traffic in order to prevent additional motor vehicle traffic, Striewe said.
Two lanes of traffic on Drachenbrücke again after renovation
When the renovation of the Drachenbrücke is completed, the engineers of the NRW State Road Authority plan to reopen the B42 to two lanes of traffic in each direction. The prerequisite for this, however, is that the concrete is given sufficient rest during the Corpus Christi weekend.
The Drachenbrücke: Only one lane of traffic since autumn 2018
Since autumn 2018, the Königswinter Drachenbrücke, the connecting structure between Bonn and Bad Honnef to the south and to the north, has only been passable with one lane in each direction. A new structural engineering guideline from 2017 ensured that the bridge high above Königswinter's old town suddenly found itself with severe structural deficits. As a result, in June 2020, the state agency Straßen NRW began to reinforce the Drachenbrücke.
For this purpose, the experts fixed 3300 steel brackets to the concrete bridge, which are part of the massive steel corset to give the Drachenbrücke, which was completed in 1962, permanently more stability. At 85 points on each of the bridge's outer sides, two steel tie rods are inserted through holes drilled from top to bottom. Steel girders are then bolted to these in turn underneath the bridge and tensioned upwards. Finally, four longitudinal steel cables, each 320 metres long, are used. Their enormous length can be explained by the fact that the 650-metre-long Drachenbrücke consists of four elements: two bridge segments on the city side and two on the mountain side, which are connected to each other.
Original text: Mario Quadt
Translation: Mareike Graepel