Resumen de Optimization of design procedures and quality control for frc
Fibre reinforced concrete (FRC) presents objectively proven advantages in terms of post-cracking strength and manufacturing procedures. As a result, FRC with structural responsibility is increasingly being used in the construction industry. However, some concerns still remain regarding design and performance given the uncertainties concerning the effect of the distribution and orientation of the fibres. In this context, further research is required to improve current tools to characterize and design FRC structures.
The main topics addressed in this thesis are oriented to analyse the influence of fibres at the design stage, verify whether the constitutive models are representative and suitable to predict the response of real-scale elements and simplify FRC quality control. At the design stage, the influence of size-effect on the bending tests used to determine the constitutive model has been analysed. Additionally, a model to estimate the residual strength of FRC based on the orientation of the fibres is proposed. Flexural tests on real-scale slabs reinforced with rebars and fibres have been analysed and compared to numerical simulations using the constitutive model of the Model Code 2010 (MC2010). Finally, a correlation based on the Barcelona test (BCN) is proposed as an alternative to the three-point bending test in quality control.
The first part of the study focuses on the pre-design stage of FRC. Standard and non-standard specimens were tested under a three-point bending test (3PBT) configuration to calculate the parameters defining the MC2010 constitutive model for FRC. The results revealed that the size-effect in small non-standard specimens can be mitigated if, instead of the CMOD, the rotation of the sample is used as the reference parameter to determine the residual strengths associated to the constitutive law.
Subsequently, a model to estimate the post-cracking strength of FRC is presented. Given a degree of isotropy and a content of fibres, the model assigns a position and an orientation to each fibre. Assuming that only fibres contribute to the tensile strength after cracking, the pull-out load of all the fibres combined with the sectional equilibrium can be used to determine the post-cracking strength of FRC. The estimations of the post-cracking strength curves are able to reflect the influence of the specimen dimension as well as the content and the orientation of the fibres.
After the pre-design stage, real-scale slabs with different combinations of rebars and fibres were tested to analyse the influence of fibres on the flexural behaviour, cracking patterns and ductility. The experimental results were used to verify the predicted flexural response of the slabs simulated by means of sectional analyses and finite element methods based on the constitutive law of the MC2010. The simulations revealed a general overestimation of the flexural performance when compared to the experimental results.
The last part of the study aims to present an alternative method to optimize and streamline quality control of FRC based on a correlation between the 3PBT and the BCN. For this purpose, an experimental programme on mixes with different rheologies, compressive strengths and types and contents of fibres was conducted. The procedure to determine such a correlation is described while showing the importance of considering confidence intervals in the presence of results with high variability as in FRC.
