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Chapter 1. Introductionthe fiber addition. This represents the main reason that the first crack tensile strengthof FRCC is mainly related to the matrix strength and very low influenced by the fibercontents.Contrarily, the post-cracking tensile residual strengths are the most influenced mechanicalproperties due to the fiber bridging mechanisms. These quantities can beexperimental obtained by means of direct or indirect tensile tests. Due to the wellknowndifficulties in realizing experimental studies throughout direct uniaxial tests intension, the adoption of bending systems in pre-notched beams is the most commonmethod (as largely used in the most widespread international standards and codes)for the FRCC characterization. However, although the bending response involves onlymode I of failure, is quite different from the uniaxial tension: for example a FRCC, witha strain-softening response in tension, could behave in strain-hardening manner inbending. The possible classification of FRCC, based on the critical volume fractions offibers to achieve strain-hardening or deflection-hardening responses under tensionand/or flexion, V f cr i (tensi on) and V f cr i (bendi ng ) respectively (being V f the fiber volumefraction), is proposed in Figure 1.2.In compression, the effect of fibers on the peak strength can be practically considerednegligible. Actually, for the compressive stress ranges, the constitutive behavior up topeak strength for the plain concrete is commonly similar for the FRCC. Then, fibersmainly improve the ductility of the composite in post-peak region (this fact is validnot only under compression states but in general under all modes of loading: such astension, shear, torsion and flexion).Several recently published experimental researches, related to the mechanical characterizationof FRCC, allow to clarify relevant aspects of such a material. Among others,the evaluation of the workability dependence on the fiber distributions by Ferrara andMeda [2006] and the analysis of the fiber orientations on the compaction proceduresby Gettu et al. [2005] can be taken as a reference of experimental campaigns aimed atstudying the proprieties of FRCC at fresh state. Experimental tests aimed at investigatingthe FRCC failure behavior in compression and tension have been performed, amongothers, by Ezeldin and Balaguru [1992] and Barros and Figueiras [1999], respectively.Also, the work by Shannag et al. [1997] that defines the mechanisms governing the fiberpull-out response, and those by Buratti et al. [2011] and Tlemat et al. [2006] that analyzethe post-cracking behavior of three- and four-point bending tests, respectively. Finally,it should be noted the failure behavior evaluations of Steel Fiber Reinforced Concrete(SFRC) subjected to multiaxial compressive states by Fantilli et al. [2011] and to theBrazilian test conditions by Liu et al. [1997]. Moreover, fibers spread up within the4
1.2. Theoretical proposals for concrete-like materialsσ pcSTRESSσ ccHPFRCC typical(Strain-hardening andmultiple cracking)HPFRCCTensile Strain Hardening:V f ≥ ( V fcri) tensionεccMatrixFRC typical;strain-softeningSTRAIN(or elongation)DFRCCε pcFRCCOMPOSITESDeflection Hardening:( V fcri ) bending ≤ V f ≤ ( V fcri ) tensionTensile Strain Softening:V f < ( V fcri ) tensionDeflection Softening:V f < ( V fcri) bendingLOADf ccMatrix(Deflection-hardeningand multiple cracking)Deflection-softeningMORf rδcDEFLECTIONδuFigure 1.2: FRC composites based on the classification proposed by Naaman and Reinhardt[2006].concrete matrix also influence its durability [Mechtcherine, 2012], as they control thecrack opening and reduce the diffusion phenomena which lead to corrosion [El-Dieb,2009]. While the benefits of fibers on strength and ductility have been demonstratedin Valle and Buyukozturk [1993] and Khaloo and Kim [1997] based on direct shear testresults on FRCC specimens characterized by different strength levels. Also, the positiveeffect of fibers on the dynamic response under impact actions has been investigated byXu et al. [2012].1.2 Theoretical proposals for concrete-like materialsIn the recent past, several theoretical models have been proposed for investigatingthe mechanical behavior of cement-based material like concrete and FRCC. Plentyof these researches deal with the investigation of the fracture behavior of both plainconcrete and FRCC and are aimed at obtaining a realistic prediction of the physical5
Page 1 and 2: Dottorato di Ricercain Ingegneria d
Page 7: AcknowledgementsI would like to exp
Page 10 and 11: Abstractinclusion of fibers and the
Page 13: ContentsAcknowledgementsAbstractTab
Page 16 and 17: Contents8.6.1 Tensile tests . . . .
Page 18 and 19: List of Figures2.1 Fine and coarse
Page 20 and 21: List of Figures4.16 Pull-out simula
Page 22 and 23: List of Figures6.14 Crack paths of
Page 25: List of Tables2.1 Mix design per cu
Page 28 and 29: Chapter 1. Introduction1.1.1 Fiber
Page 32 and 33: Chapter 1. Introductionand mechanic
Page 34 and 35: Chapter 1. Introduction[Vrech and E
Page 36 and 37: Chapter 1. IntroductionDespite the
Page 38 and 39: Chapter 1. Introduction(Figure 1.4)
Page 40 and 41: Chapter 1. IntroductionFigure 1.8:
Page 42 and 43: Chapter 1. Introductionfor structur
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Page 46 and 47: Chapter 1. Introduction• "c" if 0
Page 48 and 49: Chapter 1. Introductionsumed due to
Page 50 and 51: Chapter 1. Introductionaleatoric na
Page 52 and 53: Chapter 1. IntroductionFigure 1.13:
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Chapter 3. Zero-thickness interface
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4 Bond behavior of fibers in cement
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4.2. Bond behavior of fibers in con
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4.3. Elasto-plastic joint/interface
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4.4. Fracture energy-based interfac
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4.4. Fracture energy-based interfac
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4.5. Numerical results and experime
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4.6. Closing remarksMPa3.02.5Pi N2.
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5 Model performance and numericalpr
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5.1. Numerical analysesones mention
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5.1. Numerical analysesshown in Fig
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5.1. Numerical analysesconsidered,
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5.1. Numerical analysestic behavior
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5.1. Numerical analysesσ MPa121086
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5.2. Cracking analysis of the propo
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4 03 02 01 001 0 09 08 07 06 05 04
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5.3. Closing remarksconnecting node
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Chapter 6. Structural scale failure
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7 Cracked hinge numerical modelfor
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7.1. Basic assumptionsSection at no
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7.1. Basic assumptions1997, Stankow
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7.2. Bond-slip bridging of fibers o
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7.4. Numerical predictionsvertical
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7.5. Closing remarksthe experimenta
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Chapter 8. Elasto-plastic microplan
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Chapter 9. Conclusionsof first-crac
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Chapter 9. Conclusionsfibers in con
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Chapter 9. Conclusions9.6 Future re
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BibliographyN. Banthia and N. Nanda
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BibliographyM. Butler, V. Mechtcher
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BibliographyCUR. Bepaling van de Bu
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BibliographyEN-12390-3. Testing of
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BibliographyT. Guttema. Ein Beitrag
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BibliographyE. Kuhl, P. Steinmann,
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BibliographyO. Manzoli, J. Oliver,
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BibliographyK. Park, G. Paulino, an
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BibliographyI. Singh, B. Mishra, an
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BibliographyG. Wells and L. Sluys.
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