In column-foundation vertical connections for precast concrete elements, one of the most relevant critical aspects concerns the simultaneous management of assembly tolerances, the immediate stability of the column and the behaviour of the joint during installation phases.

In traditional systems, the absorption of geometric deviations is often entrusted to configurations that introduce discontinuities in the concrete core at the base of the column, resulting in increased stress concentrations, greater local reinforcement congestion and less effective control of the connection behaviour.

The BELT system developed by B.S. Italia was created to directly manage these issues through a configuration specifically designed for column-foundation and column-column vertical connections in systems for precast elements. The system maintains the operational advantages required during installation – fast assembly, high coupling tolerances and the capacity to immediately support the expected loads – while introducing more controlled management of the structural joint.

Table of contents

• Assembly tolerances and vertical alignment control
• Continuity of the concrete core and connection behaviour
• Confinement of the base area and joint reinforcement
• Grout filling and force transfer
• BELT in column-column connections
• BELT in continuity connection systems for precast elements

Assembly tolerances and vertical alignment control

During the installation of precast columns, control of dimensional tolerances is a fundamental aspect for ensuring correct structural alignment and continuity of the subsequent work phases.

The BELT system uses CS and CSL shoes integrated into the precast column and ABR or ABD anchor bolts arranged in the foundation. This configuration allows wide coupling tolerances and enables vertical adjustment of the bearing level through millimetric adjustment of the column position during the plumbing phase.

The system configuration is designed to control some of the main operational criticalities during installation:

• compensation of geometric deviations;
• precise verticality adjustment;
• control of the bearing level;
• reduction of interference during assembly.

This approach improves the geometric control of the structure from the earliest operational phases, reducing the need for subsequent corrective work.

Continuity of the concrete core and connection behaviour

One of the distinctive technical aspects of the BELT system is the elimination of the vertical metal plates commonly used in other types of connection.

In the BELT system, the connection is configured by avoiding the vertical separation of the main concrete body at the base of the column. This allows greater continuity of the resisting core and provides a more uniform joint behaviour during load transfer.

The interface of the overlapping reinforcement is designed in accordance with NTC 2018 and allows the connection to be integrated into the overall structural behaviour of the precast column.

The joint configuration also helps to:

• reduce local discontinuities in stress transfer;
• limit stress concentrations in the base area;
• improve the interaction between reinforcement and concrete;
• maintain greater continuity in the structural behaviour of the column.

Confinement of the base area and joint reinforcement

In column-foundation connections, the lower area of the precast element is subject to high stress concentrations, especially during the initial assembly phases and under the most demanding service conditions.

For this reason, the BELT system is designed to allow confinement and reinforcement of the column base through integrated stirrups both in the lower area of the element and in the areas where the section is locally reduced by the presence of the connection.

The integration of stirrups makes it possible to:

• improve local confinement of the joint;
• control concentrated stresses more effectively;
• increase shear transfer capacity;
• maintain a more uniform connection behaviour.

This approach provides a more controlled joint, both from a structural point of view and during the operational assembly phases.

Grout filling and force transfer

After positioning and adjusting the column, the system requires grout filling of the hole crossed by the anchor bolt.

The grout contributes to the behaviour of the connection by improving the interaction between metal components and confined concrete. In particular, the filling makes it possible to:

• increase shear resistance at the base of the column;
• improve the transfer of actions between anchor bolt, shoe and concrete;
• reduce localised effects in the hole area;
• increase protection of the connection against weathering.

The behaviour of the joint therefore evolves from the temporary assembly phase to the final configuration of the connection, maintaining control of force transfer and stability of the precast column.

BELT in column-column connections

The same operating logic is also applied in column-column vertical connections, used when height, weight or structural configuration require the precast column to be divided into several segments.

In these applications too, the system allows:

• high coupling tolerances;
• millimetric position adjustment;
• control of verticality during installation;
• confinement of the connection area;
• increased shear resistance through grout.

The system configuration therefore makes it possible to maintain operational continuity and geometric control also in connections between precast segments developed over several levels.

BELT in continuity connection systems for precast elements

Within the continuity connection systems developed by B.S. Italia, BELT is a specific solution for managing column-column vertical connections and column-foundation vertical connections.

The combination of installation tolerances, millimetric adjustment, continuity of the concrete core, stirrup confinement and controlled shear transfer makes it possible to directly address the structural and operational criticalities typical of vertical connections in systems for precast concrete elements.

The same category also includes systems based on different principles of force transfer, such as injection sleeve systems, used to create continuity connections between reinforcements through a confined cementitious matrix. The choice of the connection system depends on the joint configuration, installation methods and the structural behaviour required of the precast connection.