Resumen de Structural design and characterisation of FRC precast segments
Lin Liao
Concrete technology has changed greatly in the past decades. Steel fibre reinforced concrete (SFRC) is an example of the development in this field. It is obtained by adding fibres that act as a reinforcement of the cement matrix, improving the tenacity, cracking control and durability of the concrete members. In certain applications, SFRC has become an alternative material to concrete reinforced with conventional steel rebar. Despite of numerous advantages of SFRC, problems and uncertainties still exist regarding the design, the characterization and the performance of this material. Furthermore, the structural design and the properties of SFRC in real-scale elements as well as the fibre distribution are not properly clarified. All these issues need to be addressed in order to promote the safe and efficient use of the material. The objective of this doctoral thesis is to develop a systematic and innovative approach for the design optimization and characterisation of FRC precast segment. In total, 4 subjects are covered: a critical study related to the design of FRC precast segment considering the ductility requirements of the Model Code 2010; the experimental and analytical study of concrete blocks subjected to concentrated loads; the design procedure and experimental research on FRC precast segment for shafts and the anisotropy of the FRC precast segment. The first subject presents an analysis of the technical requirements demanded by the Model Code 2010 when steel fibres are the only reinforcement for concrete elements. According to this revision, an alternative approach according to the Model Code 2010 which is more compatible with the requirements of the application in tunnels is proposed. This approach may lead to the reduction of the fibre content required to guarantee a minimum ductility of the element. In order to evaluate the repercussion of the ductility criteria in terms of fibre consumption, a case study of Metro L9 of Barcelona is presented. The second subject contributes to the understanding about the behaviour of concrete blocks subjected to concentrated load. An experimental programme is performed to evaluate the influence of the height-to-length ratios in the mechanical response of the blocks. Based on the observations derived, a strut-and-tie model is adopted to assess the value of the loads Fcr and Fmax for short blocks and long blocks. A case study of Metro Line 9 in Barcelona is conducted, and the results of the study indicates that with an appropriate safety factors for the SLS and the ULS, no traditional reinforcement is required to resist the tensile stresses due to the concentrated loads applied by the jacks of the tunnel boring machine. The third subject is to verify that it is viable to replace the traditional reinforcement with steel fibres in the segmental lining ring of shaft constructed with vertical shaft machine. An analytical formulation based on MC 2010 is proposed to evaluate the minimum requirements the FRC must fulfil to carry out this replacement. Likewise, an experimental campaign was performed to characterize the mechanical behaviour of both conventional and self-compacting concrete reinforced with fibre content (Cf) between 30 and 60 kg/m3. Posteriorly, another full-scale experimental campaign of bending test on segments is performed to verify the ductile behaviour of two types of segments under failure scenario. These results are used to validate the proposed formula. The last subject focuses on the study of the anisotropy in terms of fibre distribution and local mechanical response of segments with conventional and self-compacting SFRC. For that, a large number of cores extracted from real-scale segments are tested for the fibre distribution with the inductive method and, then, for the mechanical response with the Barcelona test. A conceptual model for the fibre orientation is proposed based on the average values obtained from the tests.
