Quick installation of 19 very large prestressed beams on the CREPS site in Pays de la Loire

Exceptional convoys and "commando" pose

In the summer of 2021, the CREPS (Center for Resources, Expertise and Sporting Performance) for the Pays De La Loire region will leave its premises in the Broussais park in Nantes to settle, on 5 hectares, on the site from la Babinière to Chapelle-sur-Erdre (44).

On an area of ​​11.700 m², the new CREPS will have four strategic centers: Administrative, Sports, Training and Innovation.

Under construction by GCC Nantes, the sports center building will consist of an archery pitch, a table tennis room, another for weight training and two multi-sports halls. Covering a floor area of ​​over 5.700 m² (each room represents 1.500 m²), it required 4.700 m³ of concrete for the realization of foundations, vertical walls, floors and pavements.

One of the peculiarities of the site consists in the realization of the archery pitch overlooking the table tennis hall. To design the slab that will host this sporting discipline, GCC Nantes has installed 19 prestressed beams of 14 tonnes and a span of 21 meters.

Difficulty: the installation of the beams requires the temporary use of a self-propelled 230 T crane placed within the radius of action of one of the site's two fixed cranes, hampering its use and de facto impacting the productivity of the site.

To resolve this difficulty, GCC Nantes has teamed up with KP1, the French leader in prefabricated prestressed concrete construction systems, to both ensure the production of 19 large beams and together optimize the logistics of their delivery and installation.

Thanks to exceptional convoys, the prestressed beams were thus delivered to the site and laid without shoring on the building in a record time of 3 days, between July 15 and July 17, 2020. To allow the convoys to access the site without difficulty and reduce nuisance as much as possible, a secure entrance has been specially created for the occasion.

Optimal planning

KP1 took up the challenge of delivering all XXL beams within three days in response to the company's specifications. A tense flow that required the mobilization of two of its factories, one in Limay (78) and the second in Camarsac (33). A total of ten exceptional 2nd category convoys *, each carrying two beams with a total weight of 28 tonnes, departed from these sites.

An essential link between the GCC works supervisor and the KP1 logistics department, the KP1 planning and scheduling manager ensured that deadlines were met with the arrival of trucks two hours apart every day. Timing necessary to unload and install the beams directly on the site.

* The last truck carried a single beam.

Tailor-made design and manufacture

“Choosing KP1 meant calling on a single manufacturer both for these XXL beams but also for the slabs, some of which needed to be reinforced. A real advantage in the organization of the site because we had a single point of contact for the entire floor. », Underlines Chloé GUILLOU, works supervisor at GCC Nantes.

The KP1 design office and the GCC company worked together upstream in order to validate all the execution plans for the prefabricated concrete structure. Beyond the dimensioning of the "I" beams (L. 21 mx W 45 cm x H 95 cm), particular care has been taken in the design of the pre-slabs positioned in R + 3 at nearly 10 m high . Installed without shoring, they had to withstand greater loads. They have been reinforced with reinforcement and greater thicknesses, varying between 6 and 12 cm depending on the spans (2,15 to 5,90 m). Technical know-how, mastered by few manufacturers, which eliminates the need for additional supports and scaffolding. A real time saver and savings for the GCC Nantes agency. A guarantee of safety also for the workers. They no longer need to climb more than 10 m in height.

The beams were manufactured in KP1 factories with adequate production tools for this type of non-standard structure. Once the beam frames were shaped, assembled and mounted using a specific machine, they were sent to the manufacturing workshop. A team carried out the installation of the prestressed steels in the reinforcement cages and the reservations if necessary before starting the pouring of the self-consolidating concrete in a mold 90 m long. This bed length thus made it possible to produce four beams simultaneously after the steaming operation. Ready on average in 2 1/2 days, the beams were manufactured just a few days before delivery.