X-Ray Imaging for the Observation of Mode I Fracture in Fibre Reinforced Concrete

In this study X-ray imaging is used to investigate the mechanisms of fracture in fibre reinforced concrete. The investigation looks at the performance of discrete end-hooked fibres crossing a cracking plane at various angles and loaded normal to the plane. The angle of a fibre crossing a crack is found to be an important parameter in determining the mode of failure and bending of the fibres were observed up to approximately 5 mm into the matrix from the fibre exit point. The tests show a probability that some fibres pullout from longer embedded side under Mode I fracture. In the non-destructive observation procedure presented here, the internal actions of the fibres at the various stages of loading can be determined. X-Ray imaging is shown to be a valuable tool in understanding steel fibre-concrete behaviour

Fibres as shear reinforcement in RC beams: an overview on assessment of material properties and design approaches

It is recognized that understanding at a material level is needed in the development of rational, physical-mechanical, models for predicting the behaviour of fibre reinforced concrete at service and strength limit conditions. To this end, understanding the post-cracking mechanisms of the fibres, and their symbiotic relationship with the cementitious matrix that surrounds them, is required for the development of realistic modelling approaches that accurately represent empirical observations. Several experimental test setups and inverse analysis procedures have been proposed to derive the fundamental stress-crack width (–w) law, but a consensus still does not exists on the best strategy for its determination. In structures governed by shear, fibre reinforcement increases the stiffness and shear stress transfer across a crack, but a methodology to capture the contribution of fibres in this regards is challenging. To overcome this, a clear strategy is needed in deriving relationships that simulate fibre reinforcement mechanisms in the mobilized fracture modes and, also, develop design approaches capable of capturing the relevant contributions of the fibres. This study firstly reviews current inverse analysis models used to describe the tensile (Model I fracture) relationship for FRC and, secondly, discusses a newly proposed model, referred to as the integrated shear model (ISM). The ISM is developed from mesoscale observations from gamma- and X-ray imaging on FRC elements under Modes I and II fracture conditions. The resulting model is compared to test data reported in the literature and a good correlation is observed.The authors wish to acknowledge the grant SFRH/BSAB/114302/2016 provided by FCT and the Australian Research Council grant DP150104107, as well as the support provided by the UNSW for the research activities carried out under the status of Visiting Professorial Fellow for the first author. The support of the FCT through the project PTDC/ECM EST/2635/2014 is also acknowledged

Variable Engagement Model for the Design of Fibre Reinforced Concrete Structures

In this paper a model is developed to describe the behaviour of randomly orientated discontinuous fibres in reinforced composites subject to uniaxial tension. The model is built by integrating the behaviour of single, randomly oriented, fibres over 3D space and is capable of describing the peak and post-peak response of fibre-cement-based composites in tension. The model is used to form a constitutive law for use in finite element analysis of reactive powder concrete members with a prestressed reactive powder beam failing in shear analysed. A good correlation between the theoretical and experimental results attained

An integrated approach for predicting the shear capacity of fibre reinforced concrete beams

This paper describes the development of an integrated design approach for determining shear capacity of flexurally reinforced steel fibre reinforced concrete members. The approach considers fibre distribution profile, fibre pull-out resistance and the modified compression field theory integrated using a comprehensive strategy. To assess the performance of the developed model, a database consisting of 122 steel fibre reinforced and prestressed concrete beams failing in shear was assembled from available literature. The model predictions were shown to correlate well with the test data. The performance of the analytical model was also compared to predictions attained by the two approaches recommended by the fib Model Code 2010, one based on an empirical equation and the other on the modified compression field theory approach. The predictive performance of the proposed approach was also assessed by using the Demerit Points Classification (DPC), being the prediction as better as lower is the total penalty points provided by the classification. The model developed in this paper demonstrated a superior performance to those of the Model Code, with a higher predictive performance in terms of safety and reliability.The authors wish to acknowledge the grant SFRH/BSAB/114302/2016 provided by FCT and the Australian Research Council grant DP150104107, as well as the support provided by the UNSW Sydney for the research activities carried out under the status of Visiting Professorial Fellow for the first author. The support of the FCT through the project PTDC/ECM-EST/2635/2014 is also acknowledged.info:eu-repo/semantics/publishedVersio

Thermoregulation of Male Elaphe Spiloides in an Agriculturally-Fragmented Forest in Illinois

Anthropogenic forest fragmentation increases the amount of edge habitat. Although edges are harsh environments for many native species, ratsnakes often prefer this habitat. We examined thermoregulatory effectiveness of Central Ratsnakes (Elaphe spiloides) using forest edges preferentially to determine if edge preference is driven by increased thermoregulatory efficiencies. Six male subjects were located every 1-2 days using radio-telemetry and temperature sensitive transmitters. Subjects did not thermoregulate more efficiently in edges than in forest. Snakes were thermoconformers in both habitat types suggesting edge preference might be driven by other factors

Thermoregulation of male Elaphe spiloides in an agriculturally-fragmented forest in Illinois

Anthropogenic forest fragmentation increases the amount of edge habitat. Although edges are harsh environments for many native species, ratsnakes often prefer this habitat. We examined thermoregulatory effectiveness of Central Ratsnakes (Elaphe spiloides) using forest edges preferentially to determine if edge preference is driven by increased thermoregulatory efficiencies. Six male subjects were located every 1-2 days using radio-telemetry and temperature sensitive transmitters. Subjects did not thermoregulate more efficiently in edges than in forest. Snakes were thermoconformers in both habitat types suggesting edge preference might be driven by other factors

Thermoregulation of male Elaphe spiloides in an agriculturally-fragmented forest in Illinois

Anthropogenic forest fragmentation increases the amount of edge habitat. Although edges are harsh environments for many native species, ratsnakes often prefer this habitat. We examined thermoregulatory effectiveness of Central Ratsnakes (Elaphe spiloides) using forest edges preferentially to determine if edge preference is driven by increased thermoregulatory efficiencies. Six male subjects were located every 1-2 days using radio-telemetry and temperature sensitive transmitters. Subjects did not thermoregulate more efficiently in edges than in forest. Snakes were thermoconformers in both habitat types suggesting edge preference might be driven by other factors