Structural anchor eliminates bulb floor problem

The outcome of the investigation into the collapse of the parking garage at Eindhoven Airport has far-reaching consequences. The wide slab floors of a large number of buildings in the Netherlands will have to be reinforced due to possible delamination between the compression layer and bulbous wide slab floor. Van Rossum Raadgevende Ingenieurs, together with B+Btec and Interboor Midsland, developed a method to eliminate this problem once and for all. Various new and existing buildings have already been structurally reinforced in this way.

Spiritual father of the structural anchor is Van Rossum Raadgevende Ingenieurs. "The ball started rolling during the construction of an office building in Utrecht," says Arno Melssen of Van Rossum. "Shortly after the release of the first assessment guideline by bureau Hageman, which led the investigation into the collapse of the parking garage, this office building was to be put into service. To make sure the bulb plate floors in Utrecht would comply, we tested them against the assessment guideline for existing construction. The floors turned out to be only just compliant. If we tested them based on the new construction requirements, the floors would not comply. In short, we faced a challenge just before completion and with a huge time constraint on commissioning."

Through-and-through anchor

"To avoid having to strip the entire building, we devised a method to reinforce the floor without raising discussions about technical elaboration or technical foundations," Melssen continued. "With the structural anchor, we found a solution that fits within the framework of the regulations, a method that reinforces the pour seam without having to apply additional reinforcement. The result is a through-and-through anchor to connect and tension the wide slab floor and compression layer. In this way, possible delamination between the two parts is eliminated. The through-and-through anchor was tested at the time on test pieces from the parking garage, left over from the study, and found to be fully functional."

Cross section of the structural anchor.

Low-noise and dust-free

Interboor Midsland was asked by Van Rossum RI to help think about the technical feasibility. "To achieve a fully effective connection between the concrete and the anchor itself, pre-tensioning the anchor is incredibly important so that the deformation length of the anchor is as small as possible," explains Onno Dikkerboom of Interboor Midsland. "To achieve this, the anchor is applied through-and-through, the borehole injected with adhesive and the anchor fitted with a conical washer at the top and bottom. Even before the adhesive has cured, the anchor is pre-tensioned. In this way, we installed some 2,700 anchors in the office building in Utrecht. To limit inconvenience, we used a hollow diamond drill. It is a low-noise and dust-free technique."

It is important that when drilling the holes, no reinforcement or pipes present in the floor are punctured. Mapping the components is work for specialists and has been entrusted to Terra Carta. "She is a member of our 'RAB team' (Van Rossum, B+BTec, TerraCarta & Interboor Midsland) and an indispensable link with knowledge and high-quality scanning techniques. TerraCarta scans and marks between spheres, rebar and other obstacles the correct position to mount the anchors."

Renovation anchor

The office building in Utrecht was the first in the Netherlands of reinforcing with the through-and-through anchor. "Meanwhile, several buildings have already been reinforced in this way," says Dikkerboom. Melssen adds: "In order to also reinforce existing buildings, without too much inconvenience, the renovation anchor was developed together with B+BTec according to the same principle. The basis is identical to the push-through anchor with the difference that the anchor is not applied completely through-and-through, but is glued to the top of the compression layer and pre-tensioned in much the same way. This anchor has also already been successfully applied to several projects, such as the KBF hotel in Amsterdam and Entre Deux in Maastricht. The potential is enormous."