Ask the Expert: Balcony Connectors
Next in our 'Ask the Expert' series, we sit down with Nicolas De Vrieze, Product Manager, Structural Thermal Breaks & Acoustics and Nobert Omony, Lead Engineer, Structural Connections & Fixings at Leviat as they discuss the importance of balcony connectors.
What are the main types of balcony connectors available?
Balcony connectors form a critical link between the balcony and the building structure, transferring loads and accommodating potential movements. Ancon Steel-to-Concrete (STC) balcony connectors are designed to anchor steel balcony structures with reinforced concrete slabs. A proven solution for high rise construction, these STC connectors provide excellent load-bearing capabilities, ensuring the balcony can withstand various forces and movements without compromising structural integrity. This structural rigidity is crucial for maintaining the safety and longevity of the balcony structure.
When both the balcony and the main building structure are constructed using concrete, our concrete-to-concrete balcony connectors, Halfen HIT, can ensure rigidity and structural stability, whilst offering superior thermal efficiency and fire resistance.
Additionally, concrete-to-concrete connections can provide enhanced impact sound insulation, a critical factor in ensuring occupant comfort and minimising noise transmission between the balcony and interior spaces.
If you could highlight one particular aspect of Ancon Steel-to-Concrete thermal break connectors what would it be?
It would be the robustness and versatility of Leviat’s Ancon STC system. By featuring adjustable components such as a variable bracket projection and serrated slots, this allows for greater design flexibility.
A good example would be a recent wall application in Peterborough College. In this instance, we had a thin structural reinforced concrete wall that would not allow a B20 rebar to be bent according to BS EN 1992 design code requirements in order to take the high applied load. We therefore had to incorporate other anchoring products into our STC system thereby creating a hybrid of standard STC and BTP Headed Anchor to solve the problem.
This kind of versatility enables us to provide vast arrays of solutions and it has made Leviat the number one choice for complex steel-to-concrete balcony connection problems with a number of structural consultants, balcony fabricators and designers.
The slab edge is often a heavily congested zone. Can you illustrate this challenge in terms of Ancon STC balcony connectors on a recent project?
We are currently working on an international project in Lithuania where some areas of the slab edge have two layers of reinforcement top and bottom. This meant that our standard balcony products could not be fitted, so we have redesigned the anchor vertical centres, reducing them from 120mm to 70mm to avoid the congested zones, while still supporting the same applied loads. We switched to a hybrid solution combining Ancon STC20A and Ancon STC24A.
How do steel-to-concrete balcony connectors address the issue of thermal bridging?
Due to the high thermal conductivity of steel, an efficient thermal separation in the connection is essential to prevent thermal bridges as these result in higher energy consumption, and can cause structural damage through condensation and mould. By reducing heat transfer through the connector, these systems help maintain comfortable indoor temperatures, and improve the overall energy efficiency of the building envelope.
How does slab congestion and thermal bridging impact concrete-to-concrete balcony connectors and in particular post-tensioned concrete slabs?
Typically, balconies on post-tensioned concrete frames are constructed of conventionally reinforced concrete. This is a viable method but designers and installers can encounter rebar congestion and clashes at the joint between the balcony and main slab. It’s why we developed the Halfen HIT Insulated Balcony Connector System, for post tensioned applications which allows that can allow balconies to be cast together with the main slab and then simultaneously stressed – something which has never been possible before with conventionally reinforced concrete balconies.
Transition pieces placed between standard load bearing Halfen HIT balcony connector elements enable post tensioning cables to run directly through the structural thermal break at the interface between the balcony and supporting slab, enabling stressing to take place at the edge of the balcony rather than at the thermal break location. This considerably relieves reinforcement congestion and speeds up the installation process. Transition pieces are designed for use with all types and configurations of post tensioning cables currently available on the market, using either bonded or unbonded strands.
This solution offers a number of benefits for the contractor. Firstly, formwork can be installed and subsequently removed at the same time and then be reused on the next level or phase. In addition, concrete is poured simultaneously and tensioned all at once, driving significant efficiencies on construction sites.
Which types of quality assurance should specifiers look for when choosing balcony connectors?
The need for standards to be maintained throughout building projects has never been more relevant. Leviat factories are EN 1090 accredited, the European Standard that governs the fabrication of structural steelwork. All fabrications leaving our factory will have a CE mark or a UKCA/CEUKNI appropriate to the market being supplied. Leviat also has various other approvals from BSI in terms of quality assurance systems and environmental management having achieved ISO 14001 / ISO 9001.
What are the main design complications when it comes to balcony connectors?
To avoid potential clashes or interference, balcony connectors need to be designed and carefully coordinated while taking into consideration masonry support systems, Damp Proof Coursing (DPC) and Secondary Structure Protrusions (SFS). Large cavities, pier arrangements and slab zone components also need to be factored into the design of balcony connectors.
Leviat encourages specifiers to engage with us early in the design process in order to arrive at the most appropriate solutions.
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