Transfer Plates / Beams

In buildings it is sometimes needed to transfer, at a certain level, some of the vertical loads to other alignments in order to obtain bigger spans at the lower levels. In this way, a more economic structure, with smaller column or wall spacing’s can be envisaged for the upper floors, while at the lower levels, in particular at the ground level, bigger inter-column distances can be adopted. This is often the case at office buildings or hotels where lobbies and other facilities require more open space.

The transition from the smallest grid structures to larger column spacing is done by means of a transfer structure (with beams or slabs).

In order to transmit the high concentrated forces from the columns or wall, that have no continuity to the foundations, the transfer structures require considerable rigidity and strength. The design of the transfer system is dependant not only on the flexural behavior (resistance and deformability), but, in general, is considerably influenced by shear or punching resistance.

Due to the considerably high forces involved, the transition structure usually requires large depths and great amounts of reinforcement. Post-tensioning is obviously, in these cases, a very effective way to reduce both depth and reinforcement content.

The arrangement is simplified, making it possible to have top, bottom and face reinforcements kept nearly as any standard case. Prestressing also provides a positive measure against early age shrinkage cracking in concrete.

The tendon layout may be based on draped tendons or on top and bottom layers of horizontal tendons. In the first case, apart from the favorable effects of load balancing, an important contribution for the shear or punching resistance is obtained by the inclined component of the cables near the supports.

Considering the usually small slenderness’s of these structures and the type of loads applied (concentrated loads) the shear resistance should normally be modeled by a combination of concrete arches and struts with the tension ties provided by the post-tensioning and general reinforcement.

When the transfer structures thickness is considerably high (2.5m to 5m) it is usual to adopt a multiple layer construction concept.

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