Application of FRC constitutive models to modelling of slabs

Fibre reinforcement technology has advanced significantly in recent years and, as a result, expanded into different applications. In particular, steel fibre-reinforced concrete has been successfully employed in flat slabs of several buildings in Europe with fibres as the only reinforcement. However, design methods for fibre-reinforced concrete (FRC) structures do not consider differences that may result from material characterisation tests that are not representative of the structural behaviour and fibre orientation of real-scale elements. In this regard, this paper presents a numerical study in which two constitutive models for FRC based on the bending test are applied to estimate the flexural behaviour of full-scale slabs of different dimensions. Likewise, a parametric study is conducted to analyse how the parameters of these constitutive models affect the flexural response of the slabs, and a numerical fit of the experimental data is performed. Finite element simulations using the constitutive models overestimate the experimental results. The parametric study also reveals that the parameter r2 (stress after cracking) has a particularly importance influence on the response. Furthermore, enhanced sectional behaviour of the slabs was observed as their width was increased.Peer Reviewe

Plastic fibres as the only reinforcement for flat suspended slabs: Parametric study and design considerations

The use of constitutive equations from the standards to model flat suspended slabs reinforced only with plastic fibres leads to an overestimation of the experimental response of these elements. To address such problem, a parametric study is conducted. In this study, the influence of the parameters from the constitutive equations on the structural behaviour of the slabs is analysed and the ones that provide the best fit with the experimental results are found through a non-linear regression. Based on this analysis, the existence of a network effect was identified and a design philosophy for suspended slabs reinforced only with plastic fibres is proposed. Thereby, this paper represents a meaningful contribution to provide a step towards the development of a rational and design-oriented constitutive model for real-scale hyperstatic slabs-type elementsPeer Reviewe

Adaptation of rice to flooded soils

This paper and its companion (Colmer et al., 2014) review research on the adaptation of rice (Oryza sativa L.) to the wide range of semi-aquatic environments in which it grows. The paper considers well-regulated flooding to 5-20 cm depth; the companion considers deeper flooding in rainfed conditions. Flooded environments are dominated by the very slow diffusion of gases in water and the resulting changes in soil chemical and biological conditions. Adaptations to these potentially toxic conditions hinge on an optimum ventilation network in the plant, providing O₂ to the roots and rhizosphere, both being critical for favourable nutrition and tolerance of reduced-soil toxins. Rice has become a model for studying adaptation to flooded soils and flood-prone environments because of its relatively simple genome and large genetic diversity, and its extreme tolerance of flooded soils compared with other crop species.39 page(s