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Calculated responsibility for Varne Buiten

‘Varne Buiten – living in a green and gentle landscape’ – the strap line used to advertise a new complex of 30 luxury apartments in Heiloo VIRO was involved with the adaptive structural calculations.

VIRO structural engineers are usually involved from the very early design stages of a construction project, but this case was different. Construction was already at an advanced stage when we were approached by construction and development firm Lokhorst. ‘The balconies were sagging more than had been intended, which meant drainage from the balcony panels could no longer be guaranteed. Lokhorst had heard about my experience with calculations for pre-fabricated concrete through a common connection, and that was how I came to be asked to take a look at the construction.’ We’re talking to Michèl Hermans, Civil Engineering Project Engineer at VIRO in Echt.

Certainty trumps all

The situation needed both an explanation and a solution to the unanticipated defect. It was only a short while before that the roof of the AZ football stadium in Alkmaar had collapsed, and against this backdrop, the local authority was understandably eager to rule out any possible risk of a construction defect. ‘Our initial calculations did not highlight anything explicit that would have caused the balcony panels to deform.’ Thankfully, a construction defect was ruled out. In addition to weight and stability calculations by the main structural engineer, suppliers of floors, pre-fabricated concrete, and balcony panels also perform their own calculations for their building components. It ultimately turned out that the principles on which these calculations were based were not always the same.

Redistributing forces

‘We were then asked to supply an unambiguous calculation of all floors as quickly as possible – so the ground floor, first and second floors, and the roof deck. The local authority wanted a single, integrated document. The complexity came primarily from the fact that the building was already finished, and we had to base our calculations on the reinforcement that had already started to collapse. Floors are plotted in a specific way. The local authority wanted us to calculate all floors in a 3D environment. When you do that, you always get slightly different results than in the original 2D calculation. Then, using our 3D calculations we produced what’s known as a mechanics diagram. We applied that to the existing situation and the actual material behaviour, and began working with that. Put very simply, suppose that the floor in one location has too little capacity and in another an overcapacity – according to the standard, you can redistribute the forces, and the structure can still absorb all loads. This way, we were able to demonstrate that the structure satisfied the safety requirements set out in the applicable legislation. That was the main concern of the local authority and our client.’