In continuity connections between precast concrete elements, the behaviour of the joint does not depend solely on the final load-bearing capacity of the connection. Before the joint is completed, the elements must be coupled, positioned at the required level and adjusted until the correct geometric configuration is achieved.

The erection stage is therefore not separate from the behaviour of the connection. Tolerances, supports, vertical alignment and temporary stability affect the correct execution of the joint and must be considered together with the transfer of forces between the reinforcement bars.

The B.S. Italia RS25 continuity connection system integrates these two requirements. It creates continuity between the reinforcement bars of the connected elements while also using an adjustable device to control the position of the element during erection, before the connection is definitively completed with a cementitious matrix.

Table of contents

Browse the sections of the article dedicated to the RS25 system.

• Continuity connections must also be controlled during erection
• Direct force transfer between reinforcement bars
• The role of adjustment in the correct execution of the joint
• The temporary stage and release from the mobile crane
• From the dry connection to the final configuration
• Tolerances must be managed before work begins on site
• A system integrating structural behaviour and the erection process

Continuity connections must also be controlled during erection

A structural connection is normally assessed in its final configuration. With precast elements, however, it is also necessary to consider what happens before the joint reaches that condition.

During erection, the bars and inserts installed in the two elements must be coupled despite the inevitable tolerances arising from production, foundation construction and installation operations. At the same time, the element must remain at the established level and achieve the correct vertical alignment.

The RS25 system therefore operates progressively. During the first stage, the connection relies on dry-coupled metal components that allow the element to be positioned and adjusted. Once the element has been brought to plumb and the devices have been locked, the connection is completed with the cementitious matrix provided by the system.

These are therefore not two independent functions. Adjustment during erection establishes the joint geometry within which the final connection will subsequently operate.

Direct force transfer between reinforcement bars

The principle behind continuity connection systems is to transfer forces between the reinforcement bars of the connected elements without overlapping them.

This configuration maintains the load path through the main reinforcement, preventing the connection from introducing unintended eccentricities into the joint components or the internal bars of the concrete elements.

Forces are transferred through the interaction between the reinforcement bar, metal components, mortar and surrounding concrete. In the continuity sleeves used with the system, the geometry of the metal component is designed to develop bond both on the internal surface, in contact with the cementitious matrix, and on the external surface, in contact with the confining concrete.

This double bond allows the sleeve to participate in the connection not merely as a housing for the bar, but as a component integrated into the concrete volume of the element.

The actual joint configuration may include different numbers and positions of RS25 devices and continuity sleeves. Their arrangement is not standardised independently of the project, but is defined according to the reinforcement bars to be connected and the structural requirements.

The role of adjustment in the correct execution of the joint

In connections between precast elements, adjustment should not be understood as a means of freely correcting any production or installation error. Its purpose is to accommodate the specified tolerances and allow the position of the element to be controlled within the configuration established by the design.

In the RS25 system, the adjustment device consists of the adjustment foot, fixing ring nut, socket installed in the upper element and anchoring base positioned in the lower element.

The foot is dry-installed between the two metal components. Its threaded section allows the position of the element to be adjusted while it is brought to plumb, while the fixing ring nut locks the connection once the required configuration has been reached.

Two aspects must, however, be distinguished.

The bearing level is established by the supports and metal shimming plates positioned before erection. The weight of the element must continue to be transferred to these supports throughout the adjustment operations.

Vertical alignment is instead corrected by adjusting the RS25 feet in a coordinated manner. Changing the position of the individual devices alters the alignment of the element until it is brought to plumb, without changing the level established by the supports.

Adjustment therefore forms part of a controlled sequence: the bearing condition is established first, vertical alignment is then corrected and the devices are finally locked.

The temporary stage and release from the mobile crane

During adjustment, the element must remain connected to the mobile crane and supported on the shimming plates. The RS25 device is not used to lift the column or replace the specified supports, but to create the mechanical connection required for adjustment and subsequent stabilisation.

The feet must be brought fully into contact with the bottoms of the anchoring bases, while the fixing ring nuts must initially be screwed on without being tightened. In this condition, the alignment of the element can still be adjusted.

Once the element has been brought to plumb, the fixing ring nuts are locked. Before the mobile crane is released, it must be verified that each foot is correctly seated on the bottom of its anchoring base and that all fixing ring nuts have been tightened in the specified position.

This step allows the dry mechanical connection to perform its function during the temporary stage. In the configurations provided by the system, vertical alignment and stability can therefore be maintained without temporary shoring.

The absence of shoring does not, however, eliminate the need for checks. On the contrary, it makes it even more important to verify the correct position of every component before releasing the element from the mobile crane.

From the dry connection to the final configuration

Locking the RS25 devices completes the adjustment stage, but does not yet complete the continuity connection.

The final configuration is achieved by filling the sleeves and the specified volume at the base of the element with B.S. Grout, a high-strength, shrinkage-compensated mortar developed for the system.

The cementitious matrix performs an essential role in transferring forces. It fills the spaces between the bars and sleeves, establishes contact with the prepared surfaces and completes the connection between the two elements.

Filling must be carried out continuously, allowing air to escape and verifying that the mortar reaches all the specified volumes. Before application, the concrete surfaces and reinforcement must be free from dust, rust, cement laitance, oil or other substances that could interfere with bonding.

The connection thus changes from a temporary configuration, in which the dry-coupled metal components operate, to a final configuration in which the bars, sleeves, cementitious matrix and concrete work together.

The behaviour of the joint cannot therefore be attributed solely to the adjustment device or to the sleeve. It depends on the continuity of the entire sequence: preparation of the inserts, coupling, plumbing, locking and filling.

Tolerances must be managed before work begins on site

The ability to adjust the element during erection does not replace geometric control during design and production.

Sockets, sleeves, anchoring bases and bars must be positioned so that they are mutually compatible. Dedicated templates are therefore used to secure the components during reinforcement-cage assembly and foundation construction.

The templates transfer the geometry of the joint to the two elements to be connected. Their configuration varies according to the dimensions and reinforcement of the column, since the insert positions must also be coordinated with the arrangement of the bars and stirrups.

Before casting, it must be verified that the components are correctly secured. After casting, the sleeves and anchoring bases must be protected against water and debris that could obstruct insertion of the devices during erection.

RS25 therefore accommodates the residual tolerances arising during erection, but requires production and foundation construction to follow the same design geometry. Adjustability cannot compensate for the random or uncoordinated positioning of the inserts.

A system integrating structural behaviour and the erection process

The principal technical feature of the RS25 system is the integration of two stages that, in conventional connections, may require separate devices and operations.

During erection, the dry connection allows the vertical alignment of the element to be adjusted and the element to be stabilised in the specified position. After filling, the cementitious matrix completes the transfer of forces between the reinforcement bars and activates the continuity connection.

This approach can be applied to different configurations, including vertical column-to-foundation connections and vertical column-to-column connections. In every case, however, the arrangement of the components must be defined according to the specific joint and the expected forces.

RS25 is therefore neither solely an adjustment device nor a simple anchoring element. It forms part of a connection in which structural behaviour, tolerances and erection operations must be designed as aspects of the same problem.

RS25 is one of the continuity connection systems developed by B.S. Italia to connect precast concrete elements by coordinating reinforcement continuity, coupling tolerances and erection operations.

Frequently asked questions about the RS25 system

At what stage does RS25 transfer forces between the reinforcement bars?

During erection, the dry-coupled components provide adjustment and temporary stability. The continuity connection is completed with the cementitious matrix, which enables the final transfer of forces between the reinforcement bars.

Does RS25 adjustment alter the bearing level?

The bearing level is established by the metal shimming plates. The RS25 feet are used primarily to adjust vertical alignment, while the element remains supported on the plates during plumbing operations.

Does RS25 always eliminate the need for shoring?

In the configurations provided by the system, the adjustment feet can maintain vertical alignment and stability without temporary shoring. Before the mobile crane is released, the seating of the feet and locking of the fixing ring nuts must be checked.

Can adjustability compensate for any positioning error?

No. The system accommodates the tolerances provided by the configuration, but the sockets, sleeves, anchoring bases and reinforcement must be positioned in accordance with the design drawings and positioning templates.