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Dutch Safety Board completes report on AZ stadium roof collapse

The Dutch Safety Board (OVV) has completed an investigation into the partial roof collapse at AZ Alkmaar’s AFAS Stadion, with the Eredivisie football club confirming that it is working on replacing the structure.

The OVV report, which detailed “a number of different shortcomings”, found that the collapse was caused by the failure of welded joints in four roof trusses.

The report also noted that the design of the roof construction had not been correctly tested according to building standards and that the “complex transition in profile shape” in the first joint that failed had not been correctly accounted for. The wind load was also deemed inappropriate for the roof design and the finished welds were thinner than specified in the design, according to the report.

“None of the parties involved in the construction recognised these shortcomings,” OVV said. “The inspection of the safety of the design and construction of the roof structure was inadequate.”

The roof collapse occurred in August 2019 amid strong winds in the Netherlands. The incident saw the centre of the Molenaar Stand cave in on itself and did not cause any injuries.

The OVV report has been released after engineering and consultancy firm Royal HaskoningDHV earlier this year completed its own investigation into the incident. The firm, which was hired by AZ, found that a failed top rail girder connection was to blame, with its report stating that welds were too thin and the joints had design errors.

OVV’s investigation revealed that a crack occurred in one of the failed welded joints shortly after construction was completed before growing over the course of time, making the joints “ever weaker”. The stadium, which has a capacity of 17,000, opened back in 2006.

The investigation also found evidence of “severe rust formation” and noted that the owner of the stadium had “no clear picture” of the structural safety of the building as no further examinations of the technical condition of the joints were carried out during the period of use of the stadium.

“The municipal authorities also carried out no active monitoring of structural safety during use,” the report added. “The roof eventually collapsed under a load which was far lower than the load which the structure was designed to withstand.”

The investigation also found that the situation at AFAS Stadion is not an isolated incident, with an outline inventory revealing that over the past 20 years, at least 60 serious structural problems have been identified during the use of a building.

OVV has recommended the introduction of a statutory requirement for certain public-access buildings whereby owners must carry out periodic investigations into the structural safety of the building.

To members of the TOPoverleg Veiligheid construction committee, OVV recommended that a system be introduced to learn lessons from the AFAS Stadion incident. OVV also proposed that the Dutch Football Association (KNVB) encourage all license holders to comply with stadium structural safety protocols within the shortest possible timeframe.

Following the release of the OVV report, AZ general manager Robert Eenhoorn said: “We are pleased that the Dutch Safety Board has presented their report, after Royal HaskoningDHV had previously reported their extensive conclusions. We are going to carefully study what lessons can be drawn – for all concerned – and are pleased to present this chapter. AZ is now fully focused on the future, in which, apart from the new roof, health is of course paramount.”

Image: Dutch Safety Board