'CRAFTING PRE CAST CONCRETE’
Prefabrication and offsite manufacturing of entire facades of buildings can be considered to be a well-established construction method in the UK; however the technology for pre-casting such panels were limited by project budgets, the design of the components and the skills of the mould makers.
Pre-cast concrete cladding technology is still utilised today, benefitting from up-front input from architects which is brought about by the symbiosis of an understanding of the technology and the ability to digitally model the forms of the moulds required to manufacture pre-cast concrete elements. Consequently, the resultant buildings delivered are be far more varied in form and geometry than their pre-cast clad predecessors.
Building D, Royal Exchange Kingston is one such example. Conceived by renowned architectural designer Simon Bowden, this fourteen storey building is elliptical in plan, and is clad in an insulated pre-cast panelised system. The design features fluted panels which include compound curves arranged around the plan form. Whilst the technology to fabricate such panels has been in existence since the 1960s, the cost of doing so could be quite owing to the skills involved in making the moulding for each panel.
“The use of 3D modelling on this project has enabled us to resolve complex junctions of the desired profile where the vertical meets the curving horizontals, and to marshal the decorative features within the profiles both visually, and pragmatically to ensure panel jointing and sealing is fully controlled. It also assists with 3D hygrothermal analysis of the façade to prove the proposals, as well as assisting in much more detailed sequencing analysis, to clearly show the interaction of the pre-cast panel system with the prefabricated glazing system, step by step to assist with a successful site installation.” Technical Director, Barry Clarke
In order to deliver this elegant and complicated design for this project the designers (first the architects and then the subcontractors) were required to make the panels digitally. Digitally crafting the panels enables mould makers to understand and create the formwork to facilitate the construction of the panels and the sequencing of their installation. The panels are to be fabricated offsite and brought to site for installation. Combining this with an offsite prefabricated glazing system allows for an efficient encapsulation of the basic building frame.
The up-front digital design process is similar to that deployed in the virtual fabrication of the stone cladding at Bath Riverside, however the construction of the system differs because the cladding panels are fixed back to a secondary streel structure attached to the buildings re-in forced concrete frame.
The architect’s role in designing a cladding system of this nature extends further – to include full up front co-ordination exercise between all of the other trades involved in the construction of the façade to ensure statutory approvals are acquired. This process also requires considerable input from the design team; including structural engineers, façade consultants and the project fire engineer in order to ensure that the crafted components can be successfully integrated into the façade of the building.
One of the challenges faced when designing an insulated precast panelised system is the coordination of the firestopping, waterproofing and vapour control at the system supports, its positioning with respect to the building frame and the interdependence with other components.
Offsite manufacture will provide a confidence in the precision of the reinforced concrete elements and their interfaces with the other key façade elements. Confidence in the installation can be accrued by the fact that the designers have co-ordinated the components by constructing the building virtually.
THE VIRTUAL CRAFTING AND ASSEMBLY OF CLADDING SYSTEMS
Chelsea Creek Building H1, is a 30 storey tower which is clad in glistening, white Portland Stone coloured cladding. The concept architect, Squire and Partners vision for Building H1 is for a building with clean lines and a sharp aesthetic. This design features geometrically formed façade components which undulate in plan, and also in elevation.
If such a façade were to be traditionally crafted and constructed, then stonework could have provided a way to construct it; however this would not be financially viable in today’s world.
The cladding systems used in Building D, Royal Exchange might give a satisfactory aesthetic however, a pre-cast concrete cladding system could be too heavy to be applied to such a tall building without major structural enhancements.
The manufacture of building components can extend to include entire façade systems; which combine multiple building components and a lighter weight approach to construction.