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The use of steel fiber reinforced concrete (SFRC) in structures with high physical-mechanical characteristics allows engineers to reduce the weight and costs of the structures, to simplify the technology of their production, to reduce or completely eliminate the manual labor needed for reinforcement, at the same time increasing reliability and durability. Commonly accepted technology is exploiting randomly distributed in the concrete volume fibers with random each fiber orientation. In structural members subjected to bending, major loads are bearing fibers located close to outer member surfaces. The majority of fibers are slightly loaded. The aim of the present research is to create an SFRC construction with non-homogeneously distributed fibers. We prepared layered SFRC prismatic specimens. Each layer had different amount of short fibers. Specimens were tested by four point bending till the rupture. Material fracture process was modelled based on the single fiber pull-out test results. Modelling results were compared with the experimental curves for beams. Predictions generated by the model were validated by 4PBT of 100 × 100 × 400 mm prisms. Investigation had shown higher load-bearing capacity of layered concrete plates comparing with plate having homogeneously distributed the same amount of fibers. This mechanism is strongly dependent on fiber concentration. A high amount of fibers is leading to new failure mechanisms—pull-out of FRC blocks and decrease of load-bearing capacity. Fracture surface analysis was realized for broken prisms with the goal to analyze fracture process and to improve accuracy of the elaborated model. The general conclusion with regard to modelling results is that the agreement with experimental data is good, numeric modelling results successfully align with the experimental data. Modelling has indicated the existence of additional failure processes besides simple fiber pull-out, which could be expected when fiber concentration exceeds the critical value.

Results of damage and failure investigation in a concrete reinforced by short polymeric fibers are reported in the present work. Two types of fibers were used in experiments 30 mm and 6 mm long. Pull-out experiments were realized, for fibers oriented under different angles to pulling out force direction. Detailed experimental data analysis was performed. Prisms with different concentrations of fibers were fabricated and tested for four point bending. Two numerical models were used for fiber concrete prisms mechanical behavior modeling under four point bending. Modeling results were compared with experimental data.

Short composite fibres are a relatively new product for concrete disperse reinforcement. In this experimental research, 14 different composite fibres were developed and single fibre pull-out micromechanics was investigated. Three main groups of composite fibre were—composite glass fibres (GF), composite carbon fibres (CF) and hybrid fibres (HF). Composite fibre manufacturing consisted of glass, carbon or combined fibre filament preparation, impregnation with epoxy resin, epoxy curing, quality control and cutting in short discrete macro- fibres. All three composite fibre groups were manufactured with straight, uneven and undulated geometries. Fibre surface finish was smooth and rough. Uneven fibre geometry was achieved by not aligning all fibre filaments in fibre tow. Undulated geometry was a result of interlaced fibres. The rough fibre outer surface finish was achieved by adding an extra layer of epoxy resin containing fine quartz grains. All macro-fibres were cut in 50 mm length. Single fibre pull-out samples with a pre-defined crack between two concrete parts were prepared to investigate fibre pull-out behaviour. Fibre pull-out laws were obtained and analysed. Composite fibre improvement geometry and surface with roughening outer surface made a huge impact on fibre pull-out resistance.

Traditional fiberconcrete structures have fibres in the mix oriented in all spatial directions, distributed in the struc­tural element volume homogenously, what not easy to obtain in practice. In many situations, structurally more effective is the insertion of fibres into the concrete structural element body by forming layers, with a predetermined fibre concentration and orientation in every layer. In the present investigation, layered fibre concrete is under investigation. Short steel fibres were at­tached to flexible warps with the necessary fibres concentration and orientation. Warps were placed into the prismatic mould separating them by concrete layers without fibres. Prisms were matured and tested under four-point bending. The bending-affected mechanical behaviour of cracked fibre concrete was simulated numerically by using a developed struc­tural model. Comparing the simulation results with experimental data, material micromechanical fracture mechanisms were analysed and evaluated.

Interest to structural application of textile reinforced polymer matrix composite materials (CM) is growing during last years. In different branches of machine building, aerospace, automotive and others industries we can find structural elements preferably be produced using such reinforcement. At the same time, such materials are exhibiting elastic and strength properties scatter. In the framework of the present investigation, we observe yarn penetrated by a resin in a composite as a reinforcing “macro” fiber. Such “macro” fiber mechanical properties were measured experimentally, for this purpose was produced and was tested by tension until fracture fiber samples, having different length. Then was elaborated and was realized structural strength probabilistic model. In the textile geometry, was picked out repeating structural element – polymer matrix volume with two curved “macro” fiber’s chunks inside it. Complete composite material volume is possible to represent as a set of repeating structural elements. External loads application leads to disperse structural elements failure. Neighboring to ruptured elements are overloaded leading to higher probability to fail for them. Using FEM was modeled stress state in “macro” fibers inside CM. Then, was numerically obtained stress distribution in composite material, having different number of broken loops. Probabilities of different numbers of failed elements were calculated. Strength probability function, based on Weibull approach was obtained. CM samples were tested under tension and obtained results were compared with numerical modeling as well as were analyzed.

This work had three stages. In the first stage was examined pull-out process for steel fiber was embedded into a concrete by one end and was pulled out of concrete under the angle to pulling out force direction. Angle was varied. On the obtained forcedisplacement diagrams were observed jumps. For such mechanical behavior explanation, fiber channel in concrete surface microscopical experimental investigation, using microscope KEYENCE VHX2000, was performed. At the second stage were obtained diagrams for load- crack opening displacement for breaking homogeneously reinforced and layered fiberconcrete prisms (with dimensions 10x10x40cm) subjected to 4-point bending. After testing was analyzed main crack. At the third stage elaborated prediction model for the fiberconcrete beam, failure under bending, using the following data: a) diagrams for fibers pulling out at different angles; b) experimental data about steel-straight fibers locations in the main crack. Experimental and theoretical (modeling) data were compared., {"references":["Cabrera G.J. (1996) Deterioration of Concrete due to Reinforcement\nSteel Corrosion. Cement and Concrete Composites, Vol.18, pp.47-59.","Kooiman A. (2000) Modeling Steel Fiber Reinforced Concrete for\nStructural Design. Ph.D. thesis. Delft University of Technology, CN\nDelft, Netherland.","Krasnikovs A., Kononova O., Khabbaz A., Machanovsky E.,\nMachanovsky A.. \"Post – Cracking Behavior of High Strength (Nano\nLevel Designed) Fiber Concrete Prediction and Validation\".\nNanotechnology in Construction 4th International Symposium\",\nAgiosNikolaos, Crete, Greece, May 20-22, 2012, pp.1-6","Krasnikovs, A, Kononova O., Eiduks M., Kalinka J., Kharkova G.,\nGalushchak A., Machanovsky A. \"Fiber orientation in viscous fluid flow\nwith and without vibration\". Journal of Vibroengineering. Volume12,\nIssue 4, ISSN 1392-8716,Lithuania, p. 523-532, 2010.g.","Naaman, A.E., Shah, S.P. Pullout mechanism in steel fiber reinforced\nconcrete, ASCE J Struct Div. – 102 (1976), pp.1537-1548.","Papenfuss, C., V´an, P., and Muschik, W. Mesoscopic theory of\nmicrocracks. Arch. Mech., 2003, 55(5–6), pp. 481–499.","Pupurs, A., Pakrasti\tš, L., Kras\tikovs, A. Stress-State Analysis ofFibre\nReinforced Concrete (Frc). Construction Science.Vol.7, 2006, pp.160-\n171.","Pupurs A., Varna J. Energy release rate based fiber/matrix debond\ngrowth infatigue. Part I: Self-similar crack growth, Mechanics of\nAdvanced Materials and Structures, In Press (2010).","Stahli P., Custer R., van Mier J.G.M. (2008) On Flow Properties, Fibre\nDistribution, Fibre Orientation and Flexural Behaviour of FRC.\nMaterials and structures, Vol.41., pp. 189 – 196.\n[10] VictorC.Li&Stang H., \"Interface Property Characterization and\nStrengthening Mechanisms in Fiber Reinforced Cement Based\nComposites\", Advanced Cement Based Materials, 6, pp.1-20, 1997.\n[11] Stroeven, P., 'The analysis of fibre distributions in fibre reinforced\nmaterials', J. Microscopy 111 1977 pp. 283-295.\n[12] http://www.lrpv.gov.lv/sites/default/files/media/vestnesis/20101220.pdf\n[13] http://www.keyence.co.uk/products/microscope/microscope /vhx2000/\nvhx2000_ specifications_1.php"]}