Yadgar Tayfur, PhD
Optimisation for serviceability of fabric-formed concrete structures
Concrete is one of the most widely used materials in the world. According to new research, as much as 40% of concrete used in conventional buildings does not serve a function (in carrying the applied loads) but does add extra selfweight to the structure. Such an inefficient use of concrete not only plays a role in increasing structural costs but also increases embodied energy. This is because cement production is shown to contribute around 5% of total global CO2 emissions. A way to challenge this inefficiency (underutilisation of concrete material) is to structurally optimise concrete members so that their geometry reflects their performance requirements. The optimised concrete member shapes can then be realised using flexible formwork. Considering concrete beams, optimisation for strength is straightforward as it simply involves removing concrete from where it is unnecessary. However, strength-optimised concrete members show a significant loss in stiffness compared to an equivalent prismatic beam and this may make them fail to satisfy the equally important serviceability limit states (including deflections and cracking). The optimisation of a beam to satisfy both strength and serviceability requirements simultaneously is much more complex than strength alone as it is not obvious where material should be added or removed along the member in order to satisfy the chosen serviceability criteria. In this thesis, research has been undertaken to develop numerical methods to optimise fabric-formed concrete structures for both ultimate and serviceability limit states. The theoretical part of this work has been implemented in two phases. In phase one, new numerical methods have been developed to predict the behaviour of both statically determinate and indeterminate beams. In the second phase, shape and topology optimisation methods have been developed to iteratively optimise those members for both strength and serviceability. Laboratory experiments were carried out to verify the proposed methods, and the test results are shown to be in good agreement with the model prediction and optimisation criteria. A parametric study was conducted to investigate optimisation of statically determinate and indeterminate concrete beams and showed that up to about 30% reduction in concrete material can be successfully achieved without compromising strength and serviceability conditions. This work transforms flexible-formwork research into the realms of fully optimised form-found structures which satisfy both strength and serviceability. This is the first time that this research has been conducted, and it opens up the possibility for fabric-formed concrete structures to be used with confidence.
Supervisors: Professor Tim Ibell, Dr Antony Darby, Dr Mark Evernden, Dr John Orr
Download thesis for full details and all test information