Leviat’s Nicolas De Vrieze and Nobert Omony answer readers’ questions on balcony connectors.
Ancon steel-to- concrete (STC) balcony connector first-fix brackets awaiting connection of balconies, alongside already completed balconies.
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’s steel-to-concrete (STC) balcony connectors are designed to anchor steel balcony structures with reinforced concrete slabs. A proven solution for high-rise construction, the connectors provide excellent loadbearing capabilities, ensuring the balcony can withstand various forces and movements without compromising structural integrity.
When both the balcony and the main building structure are constructed using concrete, Halfen HIT connectors ensure rigidity and structural stability, as well as superior thermal efficiency and fire resistance. Concrete-to-concrete connections can also provide enhanced impact sound insulation – a critical factor in ensuring occupant comfort and minimising noise transmission between the balcony and interior spaces.
What are the main design challenges 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, and secondary structure protrusions. Large cavities, pier arrangements, and slab zone components also need to be factored into the design of balcony connectors. We encourage specifiers to engage with us early in the design process in order to arrive at the most appropriate solutions.
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, in order to prevent thermal bridging, which can result in higher energy consumption and structural damage through condensation and mould. By reducing heat transfer through the connector, these systems help maintain comfortable indoor temperatures and improve the energy efficiency of the building envelope.
The slab edge is often a heavily congested zone. What are the main challenges here?
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. Our standard balcony products were not suitable, so we’ve redesigned the anchor vertical centres, reducing them from 120mm to 70mm to avoid the congested zones. This hybrid solution, combining Ancon STC20A and Ancon STC24A, still supports the same applied loads.
How does slab congestion and thermal bridging impact concrete-to-concrete balcony connectors and in particular post-tensioned concrete slabs?
Balconies on post-tensioned concrete frames are typically made from 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. Our solution is the Halfen HIT Insulated Balcony Connector System for post tensioned applications. This allows balconies to be cast together with the main slab and then simultaneously stressed. Transition pieces placed between the 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 provides two main benefits for the contractor. First, formwork can be installed and subsequently removed at the same time and then be reused on the next level or phase. Second, concrete is poured simultaneously and tensioned all at once, driving significant efficiencies on construction sites.
How important are robustness and versatility when it comes to specifying steel-to-concrete thermal break connectors?
They are both important considerations for this type of connector. Leviat’s durable Ancon STC system employs adjustable components, such as a variable bracket projection and serrated slots, to ensure greater design flexibility. A good example, is a recent wall application at Peterborough College in Cambridgeshire. Here, 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. The solution was to incorporate other anchoring products into our Ancon steel-to-concrete system thereby creating a hybrid of standard Ancon STC and Ancon BTP Headed Anchors to solve the problem. This kind of versatility enables us to provide vast arrays of balcony solutions.
What 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, including ISO 14001 and ISO 9001.
For further information, please visit the Leviat website.
Source: Architecture Today