Universities and universities of applied sciences cannot trust solely on construction drawings if they wish to know whether their buildings are safe. Professor Nijsse stresses that they must also check whether the floors that have actually been put in place are structurally sound.
Professor Nijsse expressed this view in Delta, Delft University of Technology’s magazine, in response to the news about the closure of the Polak Building and the buildings of other educational institutions in the Netherlands. The floor structures in question seemed to be like those of a multi-storey car park at Eindhoven Airport that collapsed last June.
Wide-span slabs, thin concrete slabs that had to be roughened at the construction site, were used to build the car park. These slabs support hollow concrete balls, or bubbles, that are held in place by reinforcing steel. Concrete is then poured to create voided biaxial slabs. The purpose of the technology is to reduce the amount of concrete required, and therefore also structural weight and environmental impact in terms of materials required, without losing structural performance.
In the Eindhoven case, the upper surfaces of the thin slabs had not been roughened, as a result of which the concrete layer that was poured failed to attach properly.
Professor Nijsse believes that the omission is symptomatic of the acute degeneration that is occurring in the construction sector. “It was a serious failure on the part of the contractor, the regulatory authorities and every other party involved in the process. Every expert recognises that kind of smooth slab in an instant and knows that concrete should never be poured on that surface.”
In his opinion, contractors have become like employment agencies of the worst kind. “They have all elements delivered – floors, columns, walls – and have all these different elements put together at the site by others. When a construction process that is being implemented by many parties is ‘managed’ remotely, maintaining oversight and safeguarding the integrity of that process is virtually impossible.”
In his view, the collapse of the car park was the result of an error in execution rather than a structural defect. It serves little purpose to go through building plans when the current situation is as it is. “Risks can only be accurately identified by taking core samples of all floors built using the BubbleDeck method.”