Reinforcement in Tailor-made Concrete Structures

Licentiatavhandling, 2011

In tailor-made concrete structures of complex geometries, the formability of concrete is an asset. To use this formability in load-bearing structures, the concrete needs to be reinforced. During the past century steel bars were used; however, in recent decades, alternative reinforcement methods have been introduced. To survey the applicability of several reinforcement methods, a literature review was made; the key findings are discussed. Despite the advantages of many of the alternative reinforcement materials, it was realised that conventional reinforcement is, in most application, the best alternative in terms of the structural integrity provided. Moreover, a major advantage of conventional reinforcement is that it is regulated in standards and design codes worldwide, which facilitates the application. The inclusion of steel fibres can provide additional structural integrity or, in some applications, replace the conventional reinforcement. As fibres do not require any concrete cover, this can be a solution for thinner sections. The geometry of tailor-made concrete structures can deviate considerably from the standard structural idealisations, e.g. beams and slabs. Hence, two methods for the design of conventional reinforcement, based on linear finite element analyses using shell elements, were investigated in order to enable a rational design procedure. Both methods, which rely on a sandwich analogy, make it possible to calculate in a rational way the amount of reinforcement needed in unique structures. To enable the use of steel fibre reinforcement in tailor-made concrete structures, the modelling techniques, including the non-linear behaviour of steel fibre concrete, need to be developed further. This topic was addressed in a study of fibre reinforced concrete beams, which compared experiments, FE analysis, and design according to fib Model Code 2010. Good agreement was shown when load-deection curves from experiments were compared with FE analysis; however, the design method presented in fib Model Code 2010 underestimated the capacity of these beams. The underestimation increased with increasing fibre contents. In addition to the investigation, future research is proposed; a rational design method is needed that should include several features not covered in the two methods discussed, e.g., the effect of inclined shear cracking, the choice of optimal reinforcement direction, optimization for production, and the inclusion of design with steel fibre reinforcement.