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Invisible Connections - intelligent hidden connections of prefabricated elements

01 of November '20

The dynamic development of prefabrication and constant technological advances force manufacturers of accessories and connectors to look for ever more perfect systems that meet the expectations of investors, architects and builders alike.

Norwegian company Invisible Connections has specialized for years in providing smart solutions for precast connections. Its product range includes connectors for prefabricated beams (BSF), runners and stair landings (TSS) and TT slabs (DTS). The common feature of these solutions is the implementation of connections in a concealed manner and guaranteeing the maintenance of aesthetic qualities in accordance with the boldest visions of the architect.

frame structures

The classic support of beams on column supports can interfere with the visual effect of a clean structure. With the BSF Invisible Connections system, it is possible to shape nodes that look like those in monolithic structures, while maintaining the high surface quality of the elements characteristic of precast.

An extendable knife from the beam pocket to the concreted column pocket allows the implementation of connections at different angles, in vertical and horizontal planes, as well as the support of beams on columns of different shapes (such as circular).

With more than 30 years of experience, Invisible Connections facilitates the realization of interiors and facades with the exposure of concrete, associated with durability, strength and modernity. In addition to aesthetic qualities, the use of connectors also brings practical benefits - in place of classic reinforced concrete supports, a free space is created, for example, to carry out installations. It is also possible to lower the height of the storey (building), replacing with the BSF system the traditional solution of supporting secondary beams on the stringer.

Striking architectural detail, Usher Hall in Edinburgh

Photo: © Jordahl&Pfeifer

Designers have ready-made solutions, often complex beam-to-column or beam-to-beam junctions, with classified load capacities. Reducing the eccentricity of the application of vertical force by basing the knife close to the axis of the support has a positive effect on the distribution of internal forces and makes it possible to optimize the structure

Precast manufacturers appreciate the simple formwork and reinforcement of columns, as well as greater efficiency in storage and transportation, and resistance to damage to the elements.
Concealed joints are used in both reinforced concrete precast beams and composite beams (PFEIFER Hybridbeam®). Multi-story parking lots, office buildings, stadiums, sports and industrial halls, residential and public buildings - everywhere the BSF system finds its application.

An excellent example of the realization of an entirely prefabricated building using Invisible Connections systems is the parking lot at the Millenium Towers complex in Wroclaw. Architect Wojciech Jarząbek placed emphasis on the perfect integration of the building's mass into the existing surroundings of the office buildings. Fulfilling the designer's vision and achieving the visual effect of a clean structure would not have been possible without the use of modern technology in prefabrication and connections.

Prefabricated parking lot in Wroclaw

Photo: © Jordahl&Pfeifer


Wise design of staircases in residential buildings or office buildings can bring many benefits both at the construction stage and during operation. A very good solution is to use solid precast concrete elements as elements of stair runs and landings. The load-bearing structural connections in precast staircases are elements of the TSS Invisible Connections system. Thanks to the innovative method of extending the steel load-bearing component just before the realization of the support, the walls of the staircase can be made not only to the level of the landings, but immediately to a greater height - a great improvement in the process of their erection, which is obviously combined with a reduction in costs.

The construction and principle of Invisible Connections makes the connection of prefabricated structural elements remain invisible, the aesthetic value of the interior of the cage increases, and the standard of the building reaches the highest level.

The concealment of the connections in the concrete cross-section of the resting slab and the elimination of additional wet work at the construction site makes it possible to produce a precast architectural concrete building to the full extent. Among other reasons, it was decided to use the TSS Invisible Connections system in the staircases of the office buildings of the Browary Warszawskie investment. According to the investor's (Echo Investment) high requirements for the standard of the building, the material of prefabricated elements there was to be architectural concrete.

Often it is the architect's vision that determines the choice of products. It was no different in the case of designing the tallest building in the European Union - Varso Tower in Warsaw's Wola district. The typical space between concrete elements when connected using Invisible Connections elements is 20-40 mm. However, it is possible to increase this value and use special connectors. In the Varso Tower project, the gap width was set at 100 mm for architectural reasons. With the approval of the investor, HB Reavis, and in cooperation with the builders, custom connectors were designed and then used in this case. As a result, the stair treads and landings are offset from the wall, and a streak of light was routed in the resulting gap, giving the impression of moving through a staircase suspended in the air.

But the use of TSS connectors is not only an aesthetic value, it is also a real improvement in user comfort. They provide adequate acoustic insulation of the structural elements of staircases. The acoustic comfort of future residents was an important consideration in the planning of the "My Ursus" residential complex, where ROBYG S.A. decided to use the TSS 102 connector. This system element allows to reduce the transmission of impact sounds from the staircase to adjacent rooms by up to 25 dB (with a target sound transmission level of L'n,w = 42 dB).

"My Ursus" residential complex in Warsaw

Photo: © Jordahl&Pfeifer

Aesthetic qualities, the architect's vision, meeting acoustic comfort conditions - all these things are extremely important for both the investor and the later user. But TSS is first and foremost a responsible load-bearing element. Transferring large point forces of support is the most important aspect that convinces builders to use TSS. The maximum load carrying capacity reaches 100 kN, and the addition of elements with lower strengths to the product range also allows for optimal design. The ability to use fasteners in low-thickness joists is also not insignificant. The flat arrangement of steel tubes allows for free shaping of the slab in this regard.

The development of prefabricated construction, combined with the unlimited creative freedom of architects, requires engineering solutions that can keep up. In this regard, Invisible Connections' intelligent systems are second to none, becoming a benchmark for the future.

For more information, visit Jordahl&Pfeifer 's A&B website

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