The latest BBA Certification awarded to the Schöck Isokorb is the culmination of an unprecedented standard of assessment by the BBA. It has resulted in a much more demanding new generation of Agrément Certificates for thermal break products and the emergence of a new ‘Leader Certificate’. This new ‘Leader Certificate’ incorporates significantly more detailed content on structural stability and performance of the balcony connector.
The rigorous assessment by the BBA involved tests for structural stability, fatigue stresses and fire. As a result, the enhanced Certificate includes a full description and specification of each component. Specification of threaded steel bars to connect the system to steel balcony; limitation for deflection of the concrete slab and steel; the requirement for fatigue stresses due to different temperatures and for natural frequency of the external concrete slab and steel balconies; thermal bridging at the junction between the balcony and the wall. In addition, it covers behaviour in relation to fire.
The BBA’s Project Manager, Seyed Tajallifar, emphasises that: “All future Agrément Certificates of this sort will follow this format. The items covered in the Schöck Certificate will be included in any other balcony connector Certificate when they are due for Reissue.”
Chris Willett, MD at Schöck comments: “We have always welcomed our collaboration with the BBA, which dates back over several years. This new generation BBA Agrément Certificate takes a huge step in providing the highest level of assurance to the construction industry and we are certain that it will lead to further specifications of our product in the future”.
For a free copy of the Schöck Thermal Bridging Guide and / or the Thermal Bridging Solutions brochure – contact the company on 01865 290 890 or visit www.schoeck.co.uk
On the north side of the Thames in central London, the three riverside embankments, Chelsea, Victoria and Albert, are the result of extensive civil engineering works that reclaimed marshy land, narrowed the width of the river and provided a large-scale new area of development during the late 19th century. Today almost 150 years later, much of the area is once again being transformed as the result of a scheme designed to replace many of the outdated buildings which have characterised these areas for so long. There will be high specification property construction, promenades and parks; and at Millbank, one of the major residential riverfront developments is Riverwalk.
Riverwalk features two organically shaped buildings of seven and seventeen storeys, connected by a central podium and incorporating 116 high specification one, two, three and four bedroom apartments, plus penthouses. The design focus is on light, space, service and exceptional views across the Thames. Aesthetically the buildings are enhanced by horizontal bands of limestone on the curving facades between the glazing and ceramic panels, with the stonework wrapping around the lower parts of the balconies to create a continuous organic shape.
With such a high specification development, early consideration was given to the avoidance of the thermal bridging at the critical balcony connections. Thermal bridges would result in higher heat transfer through the assembly and colder surface temperatures on the warm side of the assembly.
Some of the consequences of this being higher energy use for heating and cooling, non-compliance with UK Building Regulations, potential building structure corrosion and the risk of mould growth and associated health concerns from respiratory problems. To help minimise any risk of thermal bridging, the structural thermal break module specified throughout the Riverwalk development is the latest generation Schöck Isokorb for concrete-to-concrete applications, the type KXT.
This latest example of Schöck engineering means even better performance, which is critical in meeting the inceasingly stringent EU guidelines and the imminent need for nearly zero-energy building standards. The Schöck Isokorb type KXT pushes the technical boundaries in meeting these demands.
In addition, through close collaboration with its clients, Schöck has also now optimised the load capacity of the Isokorb range. As a result, the load capacities most frequently in demand have been identified and appropriate refinements applied to the product portfolio. The range now provides planners with not only a structurally optimised product solution for the construction of cantilevered components, but cost advantages as well.
Verifiable performance values
The product offers such a high level of insulation, that in Germany the Passivhaus Institute in Darmstadt has awarded the product with the low ‘thermal bridge construction‘ certificate and confirmed its suitability even for Passivhaus construction. The product has also just been awarded the very latest BBA certification. All units meet full compliance with the relevant UK building regulations, which require that the temperature factor used to indicate condensation risk (fRSI) must be greater than or equal to 0.75 for residential buildings. The range also provides Local Authority Building Control Registration and there is compliance too with the UK government Standard Assessment Procedure (SAP 2012) concerning CO2 emissions from buildings and respectively heat losses through non-repeating thermal bridges.
Here, the lambda values of the Schöck Isokorb enable energy loss in various connective situations to be reduced by as much as 84% to 91%.
For a free copy of the Schöck Thermal Bridging Guide and / or the Thermal Bridging Solutions brochure – contact the company on 01865 290 890 or visit www.schoeck.co.uk
Neaco’s aluminium decking has been specified for another landmark bridge project at Bécon-les-Bruyères train station which forms part of the extensive redevelopment of the Zac des Bruyeres Courbevoie in Paris.
The striking new footbridge is the key feature of first phase of modernisation carried out by contractors, Groupe GCC. It now facilitates access to routes for travelers and allows residents the passage of Asnieres-sur-Seine at Courbevoie. Bécon-les-Bruyères is one of the busiest stations in the suburbs, with more than 20,000 passengers per day, and is set to become a major interchange with upgraded platforms and passenger buildings. The overall development is being led by joint project managers, RFF and SNCF.
Neaco’s National Sales Manager, Peter Melia, comments: “Neaco can now boast an outstanding list of high profile bridge projects which have specified our Techdek system for pedestrian and cycle paths. The product is featured on some of the most acclaimed designs in the UK and Ireland, including the Gateshead Millennium Bridge, the Media City Footbridge in Salford Quays, the Twin Sails Bridge in Poole, the Peace Bridge in Londonderry and the Living Bridge in Limerick. We are delighted to add Paserelle Becon-les-Bruyeres to that list.”
“Techdek’s T-Bar profile provides a 74 per cent contact area on the surface yet drains water efficiently and its swage-locked construction between the bars enables high load bearing capability. The system is durable, maintenance-free and comes with the option of a serrated anti-slip surface for safer footing. This combination of attributes makes Techdek an ideal specification for the high traffic demands of an urban bridge and its versatile modular system can adapt to unusual angles and curvatures, allowing it to meet the creative aspects of designs like Paserelle Becon-les-Bruyeres.”
As well as offering bridge-friendly qualities, Techdek has many environmentally friendly attributes: the system is non-toxic, non-combustible, corrosive-free and 100 per cent recyclable with no downgrading of its properties and very little energy required for re-melting. Precision-manufactured off site and easy to assemble with no welding required, Techdek is suitable for many other applications, including staging, modesty screens, solar shading, maintenance galleries and roof access walkways.
Cembrit, the leading roofing and cladding specialist, is pleased to announce the UK launch of Windstopper Extreme – a new sheathing board that is ideal for a range of uses on UK construction projects. To coincide with the launch, Cembrit tested the board to BS EN 1634-1:2015 / BS 476:22 at the Building Research Establishment (BRE). Cembrit is delighted to report Windstopper Extreme passed the test achieving a one hour fire rating.
A sheathing board such as Windstopper Extreme is typically installed behind decorative rainscreen cladding to effectively ‘seal’ the internal environment of a building. It is an excellent alternative to cement particle board and has, following the successful fire test, proven fire resistance. Simon Mayes, National Sales Manager, Cladding and Building Boards, for Cembrit is sure that the architects, specifiers and contractors will appreciate the wide range of benefits that Windstopper Extreme offers: ‘The performance and versatility of Windstopper Extreme make it a noteworthy entrant onto the UK cladding and building board scene. We were already aware of its excellent qualities as a first class sheathing board and to add the one hour fire test on top of that extends the board’s appeal and application potential.’
Building Regulations and other documentation require building structural elements to provide minimum periods of fire resistance, usually expressed in minutes, which are generally based on the occupancy and size of the building. BS EN 1634-1:2015 / BS 476:22 determines the fire resistance of non-loadbearing elements, such as sheathing boards, of a building construction when subjected to certain heating and pressure conditions. When subjected to a 60 minute fire test, Windstopper Extreme passed with flying colours.
Cembrit Windstopper Extreme acts as a windproof membrane for exterior walls that can absorb and release moisture without affecting the durability, strength or performance of the board. This very low vapour transmission resistance, enables moisture generated inside a building to pass through to the outside. Insulation can be placed directly against the inner side of the board which is also resistant toward both rot and fungal growth. The Scandinavian heritage of Windstopper Extreme also ensures it can withstand considerable fluctuations in weather and climatic conditions.
The only cavity tray company in the UK awarded European Technical Approval and the longest-established in its specialised filed is displaying its latest products at the Scotland Build Show 2016.
Cavity Trays of Yeovil has a history dating back to the 1920’s and its approved products are accompanied with a performance warranty.
Its know-how and expertise derived over almost a century is available for the benefit of Architect, Builder and Client and its latest handbook is being distributed from the stand.
The Type X cavitray for gable abutments provides a swift and effective way of arresting and controlling rain penetrating masonry above a sloping abutment.
Trays are available to suit all styles and sizes of masonry from brick to block to stone.
Each approved Type X cavitray has a ready-shaped flashing already attached, and an adjustable back upstand that now extends to cover an even wider range of cavity widths, ensuring compatibility at all times.
The full name of this new product is the Bay Window Vertical Cavitray and it overcomes a problem experienced by many during the 2013/2014 wet winter: lateral transference.
Lateral transference or ‘sideways soak’ as it is often termed, refers to exterior skin masonry becoming saturated and then permitting saturation to permeate ‘sideways’ into the structure.
It can occur to the sides of a bay window between bay roof intersection level and the lower level where the lintel runs across the bay to support the wall above.
The Type BWVC cleverly links the two whilst maintaining masonry bonding and coursing.
Its presence halts horizontal wet permeation.
This product is compatible for use with other approved cavitrays for horizontal and sloping roofs.
Preformed damp courses and trays
A range of preformed damp courses and trays for use with timber frame construction demonstrate the benefits of building using pre-shaped damp-protection solutions rather than relying on site forming and fabrication.
Pre-shaped extends the protective qualities beyond just one face of the element requiring protection, guarding against misplacement and ensuring every touch-point is both uniformly and consistently addressed.
As recently appointed full members of the Construction Fixings Association, EJOT UK is helping to promote the work of the CFA by alerting those involved in the specification and installation of safety critical fixings, to the serious consequences of “getting it wrong”.
We are all familiar with this engineering teaser:
Question: What is the most important component on a car?
Answer: The nut that holds the steering wheel in place!
Take away the humour element, and the reality is exactly the same when you apply this to countless structural scenarios. The somber truth is that life and limb are the ultimate casualties when either the correct specification or installation process fails.
Brian Mack is technical business development manager for EJOT in the UK:
“The selection, installation and certification of construction fixings on any construction project is comparatively small in terms of time and resource when taking the overall project into consideration. Yet, at EJOT we have seen on countless occasions, the results of wrongly specified fixings and the many mistakes that have presented a serious threat to life.
“Incidents such as tunnel collapses, scaffold collapses and ducting/ME failures due to incorrectly specified, installed or set critical fixings can easily be avoided. It is vital that the correct anchoring system is chosen and that it is installed to the manufacturers recommendations; that includes drilling and preparation of the installation hole through to insertion and setting of the anchor. The Code of practice for the selection and installation of post-installed anchors in concrete and masonry, BS 8539:2012, underpins the whole process from design and testing, right through to final installation. It is a valuable document and THE source of reference for safety critical fasteners”.
Established in 1979, the CFA is non-profit making industry-wide body comprising the major manufacturers of construction fixings that have a significant UK presence.
The Association’s work in actively promoting best practice guidance through a range of resources, makes it the leading authority on construction fixings in the UK. The CFA has been instrumental in the development and publishing of BS8539 – a British Standard Code of Practice designed to assist the specification to installation chain, with a thoroughly comprehensive guide to the roles and responsibilities in providing a high quality and safe fixing installation.
Brian Mack continues:
“As a trade association, the CFA is providing education, advice, training and technical support to all functions involved in the provision of safety critical fixings in the industry. Here at EJOT UK, we are delighted to be now involved with this process”.
In brief, the CFA are currently providing these resources:
For Specifiers: CPD seminars reviewing the design and selection of fixings in line with BS 8539 and current European Technical Approvals.
For Contractors: CPD seminars designed to explain their responsibilities and how to implement these duties under BS 8539. This also looks at creating ‘competent installers and testers’ for projects.
For Installers: Certified training in the correct installation of all construction fixings to concrete and masonry.
For Testers: Certified training in the correct procedures for testing to the requirements of BS 8539 – both for proof testing and allowable load determination.
For further information about the Construction Fixings Association, its full members and its comprehensive toolkit for BS 8539, visit the Construction Fixings Association website at www.the-cfa.co.uk
Lightweight support structures, such as free-cantilevered steel balconies, can be prone to vibration when people move about on them more heavily than usual. As designs become ever more lightweight and competitive in cost terms, particularly with very large cantilevers, the vibration behaviour of a structure takes on even more importance.
So when considering the development and structural design of steel balconies, there are a whole host of influencing variables that should be taken into account. In selecting the method of connection to the building slab, the challenge lies not only in choosing a component that ensures effectiveness as a thermal break; but one that offers a safe structural design solution as well. An additional factor is that it also needs to be compliant with the necessary serviceability requirements.
Acceptability of vibrations
The Building Regulations Part L defines the limit values for thermal bridges; and Eurocode 3 specifies the required verifications, such as for vibration, in serviceability limit state. Such verification is the responsibility of the structural engineer, whose function it is to calculate the natural frequency of the construction depending on its utilisation. That being said, when considering the design of the balcony construction and thermal insulating element, it is prudent to ensure that the natural frequency is greater than the limit frequency specified by the structural engineer. Generally, vibration of floors is considered to be a serviceability issue, primarily related to discomfort. As the perception of discomfort varies from one individual to another, no precise limit can be imposed that will guarantee satisfaction for everyone during the lifetime of the balcony. Assessment of acceptable vibration is therefore not straightforward. However, a logical approach is to design structures so that their natural frequency is sufficiently beyond potential excitation frequencies.
Depending on the type and utilisation of the structure, published 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.
If planned properly, the Isokorb type KS for concrete-to-steel thermal connectivity allows almost any balcony geometry to be designed without constraints. To assess how prone to vibration separated balconies using the Isokorb type KS might be, Schöck has employed the latest Natural Frequency Calculator software package. This is a free service which uses geometric and material variables and enables project teams to identify the optimum solution for steel cantilever balcony connections early in the design process. In most cases it will be found that the natural frequencies of normal balcony constructions are still above the recommended limit frequencies when utilising the Isokorb type KS.
The Schöck Isokorb type KS incorporates 80mm of insulation and is 180 mm wide and between 180 and 280mm high, to allow flexible adjustment for differing slab thicknesses. It can be prefabricated, reducing assembly time on site and can bear extremely heavy loads. This combination of features makes the unit ideal in meeting the various thermal and structural demands involved in the design of modern balconies. Which in the case of cantilever steel balconies, with a thermally broken connection to a concrete slab, normally sees the elements exposed to both vertical and horizontal bending moments and shear forces. The KS has a shear-bending interaction which, based on project specific loadings, allows for a much more flexible design and results in greater tolerance when designing steel balconies.
Recommendations for planning and designing steel balconies
The following factors influence the natural frequency and therefore the vibration behaviour of free cantilever steel balconies. Particular attention should be paid to these factors when planning and designing thermally broken steel balconies:
·Balcony geometry, especially 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
Demandingly large balconies at Rathbone Market
A good example of unusually large cantilever steel balconies being incorporated is on the Rathbone Market scheme, part of the Canning Town and Custom House regeneration programme. A three-phase development delivering a new library, around 652 new homes and a new market square at the heart of the scheme. Here the balconies are an unusually demanding 2.3 metres in depth.