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In addition to major maintenance on bridges, locks, tunnels and viaducts, Rijswaterstaat faces another challenge. Thousands of steel gantries above the highways are nearing the end of their original lifespan. The reuse of existing portals is being emphatically considered. This offers opportunities for the market, but also places high demands on knowledge, execution and responsibility.
An important starting point is that many portals at the time were designed and realized according to the VDC 2005 standard. This means that the components used, including girder tubes, end plates and diagonals, as well as the structural construction, are well documented and traceable. This uniformity provides the basis for reuse. Thousands of portals are expected to be taken off the road, assessed and redeployed where possible over the next few years.
The process begins with a thorough inspection. This involves determining whether a portal is actually built to the applicable standard. Dimensions, material thicknesses and connections are checked. Portals that do not comply or are of older generations are in principle not eligible for reuse. For suitable portals, an intensive process of disassembly, conservation and repair follows.
After disassembly, portals are blasted and re-inspected. Any defects, such as distorted diagonals or imperfections in welds, are repaired according to current standards. This requires specialized knowledge: welds must be re-qualified and all adjustments must be shown to meet current requirements. Non-destructive investigations are then carried out and the portal is given a new preservation system. If carried out correctly, the service life can be extended by about 40 years.
Reuse of portals is not a simple cycle of ‘disassemble, paint and replace. During disassembly, stresses can be released that affect the structure, such as settlement of the substructure. Hidden defects may also come to light, such as cracking, fatigue or internal corrosion. This requires a deep understanding of the behavior and structure of the structure. Portals can also possibly be adapted to a new location, for example by changing their length. This is possible, provided they remain within the structural class.
Requirements from the Department of Public Works regarding the deployment of renovation portals are becoming increasingly stringent. Not every party has the necessary expertise to perform this work. Fully understanding the process - from design and dismantling to repair and reinstatement - is essential to manage risk. A renovated portal must return to full compliance with the original and current requirements.
Thus, the deployment of renoportals does offer opportunities within the Dutch infrastructure challenge. At the same time, it requires a standardized approach and a high level of craftsmanship. With clear guidelines from Rijkswaterstaat and expert execution by market parties, reuse can be a sustainable and responsible solution for the future.
Henk van den Ochtend - Director of Birkhoff Steelworks
