Structural anchor strengthens JuBi building

That the collapse of the parking garage at Eindhoven Airport in 2017 would have far-reaching consequences was clear pretty quickly. There was also work to be done at the National Property Administration, which, with more than 13,000 properties, is responsible for the largest and most diverse property portfolio in the Netherlands. Since then, the entire stock has been screened for possible wide slab floor problems. At 21 properties it has been determined that measures are indeed necessary, including the enormous JuBi building on the Turfmarkt in The Hague. The wide slab floors are currently being reinforced by Interboor Midsland with the unique RAB anchor, while the building remains in use as usual. 

With a gross floor area of 122,000 square meters, the JuBi Building is one of the larger buildings in the portfolio of the National Property Administration. The Government Office houses both the Ministry of Justice and Security and the Ministry of Interior and Kingdom Relations and was commissioned in 2013. "Shortly after the collapse of the parking garage in Eindhoven, we launched an investigation. Initially we focused on the most significant risks and scrutinized buildings built after 2000," says Rob van Rossum, program manager at Rijksvastgoedbedrijf. "Out of that came a shortlist of several buildings with potential risks in the critical seams of the wide slab floors. The JuBi building and the courthouse in Zwolle were the first to be addressed. The building in Zwolle has now been completely repaired, the repair work in the JuBi building is now in full swing."

Interboor Midsland is definitely an expert by experience when it comes to repairing wide slab floors. "During the collapse of the parking garage, we were working on the Voorzetgebouw Hoog Catharijne building in Utrecht," says Onno Dikkerboom of Interboor Midsland. "This office building was under construction at the time with the same wide slab floors. To avoid having to strip the entire building, a structural anchor was devised by Van Rossum Raadgevende Ingenieurs to reinforce the pour seam, without having to apply additional reinforcement." Interboor Midsland was asked to help think about the technical feasibility. "And so we had the first in the Netherlands by reinforcing the first building with the structural anchor. Not much later, in cooperation with the anchor's supplier B+BTec, the renovation anchor broad plate floors (RAB) was developed according to the same principle, a method that is now being applied here in The Hague." Together with Van Rossum Raadgevende Ingenieurs, B+BTec, Verwol Interieur Realisatie and Warmtebouw Utrecht, TerraCarta completes the 'RAB team' and uses its high-end scanning techniques to determine the correct position of the anchors between spheres, reinforcement and other obstacles. 

The Rijksvastgoedbedrijf did not take any chances and tested three reinforcement methods in a test site in Lelystad even before the tender phase for the JuBi building and the District Court in Zwolle. "The purpose of this trial set-up was mainly to determine the inconvenience of the different methods, so that we can take this into account when choosing an appropriate repair method for the different buildings and users," says project leader Niels Andressen of the Rijksvastgoedbedrijf. "It is true that there was a construction fault, but not of such a nature that the safety of the building users was compromised. In this regard, the RAB method gave the least amount of inconvenience. During the European tender, another noise test was then carried out on site, also involving the participation council. They too judged that this was the most appropriate method for the building." Dikkerboom adds: "Besides being low-noise and dust-free - we work with a closed system - our technology is extremely flexible, even in limited, tight spaces between the pipes and ducts under the ceiling. We can move quite easily from one part to another part of a building without causing too much inconvenience, thus perfectly anticipating the wishes of the building user."

Despite the limited inconvenience, the State Property Agency did choose to reinforce the building one floor at a time and also to clear it mostly empty. "That simply works more pleasantly for all parties," says Van Rossum. "On top of that, in some cases the seams of the floors are located exactly under a partition or ceiling island, elements that are then temporarily dismantled. Moreover, we immediately take the opportunity to replace other equipment. In turn, Interboor Midsland can go about its business undisturbed." The work is progressing very well. "This is already the ninth building we have repaired for us," says Dikkerboom. "We have taken care of almost all types and thicknesses of floors with a lot or little reinforcement, with or without concrete core activation. Based on calculations by Van Rossum Raadgevende Ingenieurs, we determine the number of RAB anchors to be applied. On site, we scan the floor at the bottom and locate the drilling points, then use a diamond drill rig to drill right into the pressure zone of the floor. Then we place the anchor, fill it with a pure epoxy and apply it at the right time according to calculation. This is how we bring the floor to its original design strength."

The methodology "inspects" itself. Dikkerboom: "The RAB anchor has an inspection hole. While filling and torqueing the anchor, a drop of epoxy ('overflow') comes out of the inspection hole. If the epoxy does not come out, something has gone wrong and we reposition the anchor. So the technique is 'fool proof.'" At the JuBi building, a RAB anchor is placed about every 20 centimeters at the seams to be reinforced. A total of about 50,000 anchors are involved! Interboor Midsland started work in September 2021 and expects to be active on the Turfmarkt until spring 2023. "Over the past two years, we have developed the technology to the point where we can repair buildings of this size with limited manpower and a team of about six to eight employees. In parallel with the JuBi building, which by the way is a wonderful reference for us, we are reinforcing several more buildings for other clients." 

With the RAB anchor, not too much disruption occurs from the original ceiling finish, Van Rossum concludes. "The existing coves are used as much as possible. If that doesn't work, a new cove is made in the same style. So the tranquility that the interior exudes will be maintained even after the modifications."