Feasibility of Concrete Shells using Flexible Mould Prefabricated Concrete Elements

Abstract

Shell structures appear quite often in our daily life. From aircraft fuselages to storage silos and boat hulls, these structures are employed for their structural efficiency and the aesthetics they provide. They are characterised by a small thickness in comparison to their other dimensions and by curvature in their unstressed state. Despite their structural efficiency transferring loads in their plane, thin concrete shells are not employed quite often. The traditional construction method is a labour intensive process which includes the fabrication of a formwork system, usually made out of plywood, on which concrete is cast. The necessary reinforcement in the form of bars although it is quickly placed, it has the drawback of requiring frequent joints and overlapping. Its bending and assembling is also considered difficult for curved shapes like shells. As it can be seen, great costs emerge from this process and this was a trigger factor for the formation of the research question. A different approach for the construction of shells employs prefabricated elements which are connected on site and create the complete thickness of the concrete shell. Although high construction speed and high quality are achieved with this method, significant reduction of costs is still not feasible, as the formwork is very expensive and re-use of it, is only occasionally possible. However, an adjustable mould can produce elements of different dimensions, shape and curvature, decreasing substantially the formwork costs which comprise large part of the total shell construction costs. The flexible mould method and the principle of deformation after casting that were introduced by Prof. R.H. Schipper find application in this project. This project aims to answer whether it is possible to construct a concrete shell using the flexible mould prefabricated elements, without putting aat risk the stability of the structure. A comparison between the structural feasibility of a monolithic shell and the one of a segmented prefabricated shell is the method that will be utilised to answer the research question.