To minimise any risk of thermal bridging at the balcony connections, the Schöck Isokorb structural thermal breaks have been designed in throughout the project. Block A is a conventional recessed balcony installation; but Block B had a number of different requirements. The Schöck Regional Sales Manager responsible for the project, Ashley Houlton, explains the situation. “One of the UK’s largest manufacturers of prestressed hollowcore, Acheson & Glover, supplied the flooring and the diameter of the core allowed many of the Isokorbs to be cast easily inside. This involved casting in-lap reinforcement bars at AG's manufacturing facility and once on site, breaking out the cores to suit the balcony steelwork and introducing lap splice reinforcement within the hollow cores. The Isokorb products were then installed using a template to keep the spacing correct and to prevent any of the units twisting. The last step was to fill the broken out cores with insitu concrete. However, in a number of cases, the balcony span was perpendicular to the Precast Planks and here AG Precast offered an unpropped composite PlateSpan system. This allowed a fast, flexible solution to accommodate the Schöck Isokorb units within an insitu topping”.
Another factor though was the relatively large cantilever depth. This can easily influence the natural frequency and therefore the vibration behaviour of the free cantilever steel balconies. To assess how prone to vibration the chosen solution might be, Schöck has a software package available which uses geometric and material variables.
This calculates the Natural Frequency of the steel balconies. Experience has shown that adopting a limit frequency of 7.5Hz for steel balconies not only eliminates the possibility of undesirable vibration, it also enables the design of cost efficient structures. This was the case at Islington Wharf, where the balcony geometry, especially the cantilever length and spacing between the connections was critical. By using the ‘Natural Frequency’ calculation software it was possible to optimise the overall number of connectors required.
In addition to concrete-to-steel capability, the Schöck Isokorb range also provides solutions for concrete-to-concrete and steel-to-steel. The range meets full compliance with the relevant UK building regulations, has NHBC approval and offers LABC Registration. There is also the security of independent BBA Certification.