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external envelope
‘Adopting a limit frequency of 7.5 Hz for steel balconies not only eliminates the possibility of undesirable vibration, it also enables the design of cost-efficient structures’
and efficient. When selecting the method of connection to the building slab, the challenge lies in choosing a component that will ensure both an effective thermal break and a structural and design solution that is safe – and all still compliant with the necessary serviceability requirements. In the case of cantilever steel balconies, with a thermally
broken connection to a concrete slab, the elements are normally exposed to both vertical and horizontal bending moments and shear forces. To meet the various criteria demanded in these circumstances, the optimum solution is a heat-insulating load-bearing element that can bear extremely heavy loads for the thermal partitioning of free cantilever balconies.
Natural Frequency Calculator
To assess how prone to vibration the chosen solution might be, a software package which calculates the frequency of the steel balconies that can be employed. One example, the Natural Frequency Calculator, uses geometric and material variables. Depending on the type and utilisation of the structure, pub- lished data indicates limit frequencies of between 4 Hz and 7.5 Hz. Experience has shown that adopting a limit frequency of 7.5 Hz for steel balconies not only eliminates the possibility of undesirable vibration, it also enables the design of cost efficient structures. As has been established, a number of factors can influence the natural frequency and therefore the vibration behaviour of
free cantilever steel balconies. It is recommended that particular attention should be paid
to the following factors when planning and designing thermally broken steel balconies: •balcony geometry: the cantilever length and spacing between the connections
•rigidity and proper execution of the stub bracket, especially on stepped thresholds
•sufficient transverse rigidity of the balcony construction •incorporation of the stiffness of the chosen thermal insulating element into the planning process.
Case study: Rathbone Market, Canning Town
An example of large cantilever balconies incorporated into a project is the third and final phase of the Rathbone Market scheme in east London, part of the Canning Town and Custom House regeneration programme. The scheme is delivering a new library, around 652 new homes and a new market square bordered by around 35,000 ft2
of shops, cafes, offices and
community facilities. This final phase will see 216 new homes in a mix of one, two and three-bed designs within three blocks, ranging in height from six to 14 storeys. The apartments on the upper levels are designed with large 2.3 m depth balconies, which is a demanding specification, and use of natural frequency calculation was crucial in delivering the right balcony specification.
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GLASS BALUSTRADES Structural glass and posted balustrades
Demon Designs offer an unrivalled range of balustrade systems from bespoke, fabricated steel and stainless steel to modular systems.
We offer structural glass balustrades from a number of suppliers, and can tailor the installation to suit the customer.
We can also offer a vast range of posted balustrades from budget, modular and mild steel to superb quality, fabricated stainless steel systems, to suit most budgets and lead times. With our modular systems, we can usually offer a very fast turnaround time.
Please contact us for details
01903 733206 |
info@demon-designs.co.uk www.demon-designs.co.uk
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