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State of The Art Technologies

The connection of precast components on construction sites has always been a difficult challenge due to manufacturing tolerances and the need to transfer loads through the structure; even more so when you factor in a required resilience to a seismic events. Precast components are inherently stiff, so it is essential that the connection components are robust enough to allow the structure to absorb the energy of the earthquake, whilst providing enough robustness to avoid collapse.

There are a number of ways of doing this such as via:
• Grouted Coupler to connect walls and columns to foundations
• Wire Loop Box to connect walls together
• Precast Coupler to connect precast elements
• Dowel Systems for connecting slabs to walls

Moment® Grout Coupler

Grout coupler are traditionally used in the bottom of a column or wall as a means to connect on to starter bars protruding from the foundation. Although they might often be designed as a pin connection, the reality is that this will transfer moment from the foundation in to the wall or column and should therefore always be made of a ductile material that does not compromise the ductility of the steel reinforcement that it is coupling together. To that end, the coupler should always be of a “bar break” type where there is a considerable factor of safety between the bar failure and the coupler failure capacities.

Grout Coupler on Site

Moment® Wire Loop Box

Wire loop boxes are prefabricated components with a constant rebate geometry and 1 or 2 high strength (c. 1600-1800MPa) wire loops. Loops from adjacent elements then overlap during installation of the panels and are secured using a reinforcing bar and a high early strength grout to complete the connection.

They are usually used to connect 2 adjacent precast panels together, where the interlocking rebar and wire loops provides robustness in the event of an Earthquake to ensure that grout degradation would not result in complete collapse.

81Loop Box Used on Site

Moment® Connection Loop

Connection Loop is a single-wire loop used to connect 2 precast boxes for the prefabricated prefinished volumetric construction (PPVC).

In order to connect 2 precast elements, both precast elements has to be cast with the Moment® Connection Loop at the wall. A rebar will then be inserted through the intersection of 2 loops. After placing the rebar, the gap between the precast elements will need to be grouted using a 40Mpa or 70MPa non shrink grout depending on the application. Material strength of the Moment® Connection Loop is 1770N/mm  and complies to EN12385-4:2002+A1.

Moment Connection Loop PPVC

HEK Precast Coupler

The HEK Precast coupler is an innovative and versatile solution for fast and easy connection of precast concrete elements.

Cast-in DEMU Fixing anchors i.e. T-FIXX®, bolt or bar anchors transfer the tension and shear force into the precast element.

The main advantage of the system is the fast and efficient positioning of precast elements. The connection can be subjected to load immediately after installation. This results in a substantial improvement in construction time.

 HALFEN HEK Precast couplerHEK Precast Coupler Application with DEMU Fixing Anchor

Invisible Connections

Shear dowel systems are always a challenge as they generally require very tight tolerances to ensure effective load transfer, so systems without grout and oversized holes are almost impossible. Traditionally, precast slabs such as stair landings used to be supported by a steel angle bolted to the wall. Installation was slow, required high degrees of accuracy, tied up the crane with costly hook- time and could only be used on straight walls.

But by keeping the grouting to a minimum, one such technology – Invisible Connections – has revolutionized the use of precast all throughout Northern Europe; it is a patented system, with its origins in Norway, to connect precast concrete without use of corbels or steel angles, and is used extensively throughout Europe due to the independently tested and certified European Technical Approval (ETA [4]) that provides engineers with peace of mind about the capacities.

The product range of Invisible Connections consists mainly of TSS Telescopic Stair Connectors & BSF Telescopic Beam Connectors.

85         BSF Telescopic Beam Connectors

Another topic relating to Invisible Connections will be covered as a future topic in our Academy site.

 

There are many good technologies available, but a dependence on local testing and local reference projects will hinder and slow down their introduction. An increased readiness to accept the certification schemes for prequalification that exist overseas such as ETA[4] and ICC certification where appropriate, will mean that the technologies can help keep pace with the requirements of the precast industry.

 

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September 1, 2017