The integral technique makes a complete comeback

Koen Van Regenmortel is particularly proud of the maintenance-friendly application of the integral bridge technology in different places on the track. “Joints are subject to wear, no matter which road surface you use, and require intensive maintenance. Not to mention the noise nuisance that they cause with every passing vehicle. Therefore, we made the connections with piers and abutments integral to the maximum extent possible. Obviously, this requires a great deal of ingenuity: from engineering phase to execution, because all these connections are subject to all kinds of stress. Every part needs to be adjusted." 

" a bridge deck of 670 metre long without a single joint!" 

"You shouldn’t underestimate what this means: absorbing every motion, from the shrinkage during the curing of the concrete bridge deck up to the weather-dependent temperature effects and daily stress effects during the use of the bridge deck. We really had to pull out all the stops. Our concrete specialists explored the limits of the material and we spent more than half a year on laboratory analyses to create a specific type of concrete that was sufficiently strong to absorb all forces without cracking.”

“But, above all, it was the insights of head engineer Ivan Van Wassenhove that turned the A11 viaduct at the Baudouin Canal into a new reference in terms of integral bridge designing. “The most expensive part of a bridge’s maintenance are the joints: bearing supports, expansion joints... If you can eliminate these, you can easily reduce the maintenance cost by 30%. We already knew from an earlier project that the integral technique can offer a great solution if you’re able to overcome its disadvantages. This is exactly what Jan De Nul has been able to do here. A viaduct with 22 spans, each 35 metre long, without joints, an integral length of 670 metre. This part of the project is truly unique in Europe.”

Slim piers

Apart from the high-strength concrete that was especially developed by Jan De Nul, the design of slim bridge piers appeared to be crucial. Not the typical round piers but piers with flattened laths that are flexible in the longitudinal direction of the viaduct, making the viaduct extremely resistant to all external forces."

But, the simpler the result, the more complicated the building methodology. “We’ve built the viaduct in two parts: from the abutments towards the centre. We kept both parts under a 150-tonne pre-stressing force using stay ropes to pull the whole construction a couple of millimetres aside. Once the middle section was concreted, we could loosen the pre-stressing force. In this way, the bridge deck was made a little bit too long to compensate for the unavoidable shrinkage of curing concrete.”

 

 

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