Traffic jams on the motorway not only cost time, but also mean an economic loss. Logistical processes come to a standstill and people cannot do their work. The problem is the same all over the world. A unique solution has now been launched in Switzerland.
"ASTRA Bridge" is the name given to the project that was launched there, thanks also to state funding. A clever and unique concept for a mobile bridge, the advantages of which ASTRA director Jürg Röthlisberger underlines. "It is important for the traffic to remain on the motorway, because that is the safest and most efficient traffic area." The consortium of Marti Technik and Senn AG in collaboration with Cometto put wheels on this idea in the truest sense of the words. The requirement of the Swiss motorway operator ASTRA was for traffic to continue to flow in two lanes in such a way that the road surface could be renewed without congestion. For this purpose a pan-European tender was launched, which was won by the three companies mentioned.
Assembly in just two nights
The result is a 236 metre-long mobile bridge with a total weight of 1,250 metric tons. So that it can follow an S-curve with a radius of 1,000 metres, the bridge was produced in sections. It can be actively steered by about three degrees at each joint.
"The whole concept had to be designed in such a way that the assembly of the entire bridge on the motorway building site could be carried out in two consecutive nights", reports Toni Hauert, Head of Special Vehicles at Marti Technik AG. "That's why the bridge was designed modularly." 18 gantries and four ramp units were delivered, each of which is self-propelled by radio remote control and can be loaded and unloaded without the help of a crane. It is only necessary to use a crane for the four ramps, and of course also for the 19 intermediate segments between the gantries in a three-piece design.
Carousel drive for docking manoeuvre
On the first night, the bridge assembly took place in parallel with two assembly teams from both ends. First, the ramp tips had to be positioned on the road. Then the four ramp halves were moved into position and coupled with the ramp tips via huge short-stroke presses. After that, the mobile crane drove onto the ramp and lifted in the central intermediate segment with the coupling bolts. The first portal made a 90° carousel drive on the motorway and also docked to the massive coupling bolt. The crane could then position the associated intermediate decks on the left and right.
At the end of the first day of assembly, both halves of the bridge drove towards each other and were coupled together. Now traffic could drive over the approximately 136 metre-long bridge for the first time, which currently consists only of a 68 metre-long entrance ramp and a 68 metre-long exit ramp.
All 22 power packs connected together
In the second night of the assembly, the remaining gantries and intermediate decks were delivered for the missing 100 metres of length. In order to be able to mount them, the already assembled bridge had to be opened in order to proceed with the assembly. Finally, the bridge was coupled together again as a unit and manually moved to the section where the road surface was to be renewed. All 22 power packs were connected together in a master-and-slave program. According to Joachim Kolb, Sales Manager at Cometto, "this makes it possible to move, steer and stop this huge unit with just one radio remote control."
Before that was possible, however, Senn AG had to produce the complete steel construction in advance. The shell of the bridge was completed in 38,000 working hours and on time. Jörg Senn, Managing Director of Senn AG, makes the following comparison: "What we have done here is the equivalent of about 15 man-years of work."
Much lower hazard potential
The units were assembled at Marti Technik in Moosseedorf, where Cometto – the centre of excellence for self-propelled transport technology within the Faymonville Group – delivered the complete self-propelled vehicle equipment. In total, there were 92 electronically steered axles with an axle stroke of 700 millimetres each, as well as 22 power packs with radio remote controls and 22 hydraulic distribution boxes.
Back to the motorway project: the traffic was now flowing over the building site on two narrow carriageways on the bridge. "The hazard potential for the construction workers involved has been lowered enormously", says Jürg Merian, Project Manager of the ASTRA Bridge, "because the traffic no longer has to drive by them." And below, a 100 metre-long corridor opens up with a width of 5.2 metres and a height of 3.1 metres.
Satellite navigation system for precise positioning
In this area the construction machines were busy removing the old asphalt and laying the new. During the night the bridge moved 100 metres further to ensure the continuous progress of the work. Joachim Kolb tells the inside story here: "The complete bridge was equipped by Cometto with a satellite navigation system. This enables it to move "as if by an invisible hand" to the exact centimetre along the motorway – propelled to the MAX."
A success concept that ought to be welcomed with open arms elsewhere, too. Initial enquiries from the Netherlands and Japan have already been received. This innovative approach hits the nail on the head, because the problem is ultimately the same everywhere. So it can be concluded that the journey of the ASTRA Bridge and its proliferation is by no means finished.
Date of publication : 03/2023