Department of Architecture and Civil Engineering

Polymeric facades: advanced composites for retrofit

At a glance

Funding body: ESPRC and Arup (CASE award)
Principal investigators: Tim Ibell, Antony Darby Mark Evernden, Steve Lo
Researcher: Peter Gates
Industry partners: Dr Mikkel Krag (Arup Ltd)
Dates: 2009-2012

Abstract

Replacing a building’s façade offers the prospect of improving the whole life performance of the building, in some instances as a favourable alternative to replacing the entire structure. This presents the opportunity to exploit the properties of advanced composite materials for maximum benefit. ‘Upwards and outwards’ retrofit, where extending floor slabs yields extra floor area, is permitted by a lightweight replacement façade, without the need to underpin foundations. For typical medium or high-rise office buildings, the extra let-able space obtained, and reduced heating and maintenance costs, can work to offset the expense of implementation.

The specific materials, manufacturing processes, and façade type, most appropriate for such a scheme have been determined. A unitised façade of sandwich panels with foam cores and pultruded GFRP skins forms the ‘design platform’ for current research.

It is paramount to resolve how the connections in such a façade system can meet the many requirements of an integrated building envelope. Structural integrity, enhanced environmental control, sustainability attributes, fire provisions, acoustic control, ease of manufacture, tolerance control, durability, lightness in weight, cost effectiveness and aesthetics must all be addressed simultaneously by any proposed design methodology.

Investigating suitable connections through prototype development and review, targets objectives under the headings of Structural Integrity, Thermal Performance, and Constructability.

The permanent action acting on light, self-supporting GFRP panels is small, however wind and occupancy loading impart significant imposed actions. Therefore, whilst creep deflection is often a significant consideration for structural GFRP design, quantifying fatigue performance is a higher priority for validating the ideology of polymeric facades.

The unidirectional nature of pultrusion reinforcement yields a scenario of principle stresses at the panel interfaces, occurring in the weaker, secondary fibre, direction. As a consequence a fatigue-testing programme is aimed at pultruded angles compatible with ‘long-edge’ panel connections.

Retrofit of existing buildings as an activity makes up 50% of all building construction in the UK. This project aims to address the shortfall in industry-required design knowledge.