Polymeric Facades

: Advanced composites for retrofit

Abstract

Replacing a building’s façade offers the prospect of improving the whole lifeperformance of the building, in some instances as a favourable alternative to replacingthe entire structure. This presents the opportunity to exploit the properties of advancedcomposite materials for maximum benefit. ‘Upwards and outwards’ retrofit, whereextending floor slabs yields extra floor area, is permitted by a lightweight replacementfaçade, without the need to underpin foundations. For typical medium or high-riseoffice buildings, the extra let-able space obtained, and reduced heating andmaintenance costs, can work to offset the expense of implementation.The specific materials, manufacturing processes, and façade type, most appropriate forsuch a scheme have been investigated. A unitised façade of sandwich panels with foamcores and pultruded GFRP skins has formed the ‘design platform’ for researchconducted.It is paramount to resolve how the connections in such a façade system can meet themany requirements of an integrated building envelope. Structural integrity, enhancedenvironmental control, sustainability attributes, fire provisions, acoustic control, ease ofmanufacture, tolerance control, durability, lightness in weight, cost effectiveness andaesthetics must all be addressed simultaneously by any proposed design methodology.Investigating suitable connections through prototype development and review revealskey issues requiring targeted research. The permanent action acting on light, selfsupportingGFRP panels is small, however wind and occupancy loading impartsignificant imposed actions. Therefore, whilst creep deflection is often a significantconsideration for structural GFRP design, quantifying fatigue performance is a higherpriority for validating the ideology of polymeric facades.The unidirectional nature of pultrusion reinforcement yields a scenario of principlestresses at the panel interfaces, occurring in the weaker, secondary fibre, direction. As aconsequence a fatigue-testing programme is aimed at understanding the performanceand characteristics of pultruded angles compatible with ‘long-edge’ panel connections.The long-term performance of fibre-reinforced polymer (FRP) structures must beassessed if FRP is to win acceptance as a mainstream material for use in theconstruction industry. The environmental durability of wholly polymeric structures isoften called in to question. In response, accelerated testing is usually undertaken onartificially aged FRP specimens; lack of genuine naturally aged material has previouslyhindered research and validation of material related design life. Case studyinvestigation has permitted a full durability appraisal of naturally aged GFRP throughlaboratory testing campaign.Retrofit of existing buildings as an activity makes up 50% of all building constructionin the UK. This project aims to address the shortfall in industry-required designknowledge.The tensile strength of pultruded naturally aged GFRP has been shown to reduce byonly 0.65% over 17 years where natural exposure does not include UV irradiation, andby 13.1% where UV irradiation does occur as one element of exposure. The findingsexpose the degree of inaccuracy and fundamental flaws in existing predictive ageingmodels. The physical mechanisms of degradation do not match. A procedure toquantify the extent of polymer brittle hardening has been developed and applied as ananalytical tool.Mechanical testing campaign has pioneered the use of the RMS (Route Mean Square)procedure to present the performance of connection specimens as a continuous functionthroughout programmes of fatigue testing. Testing has shown that though a thresholdstrain for damage accumulation does exist in complex fatigue loading of connections,and for direct tension fatigue loading.

Date of Award	17 Mar 2014
Original language	English
Awarding Institution	University of Bath
Sponsors	Engineering and Physical Sciences Research Council & ARUP Group Limited
Supervisor	Tim Ibell (Supervisor)