Bending And Shear Behavior Of Ultra-high Performance Fiber .
High Performance Structures and Materials V79Bending and shear behavior of ultra-highperformance fiber reinforced concreteC. Magureanu, I. Sosa, C. Negrutiu & B. HeghesReinforced Concrete and Steel Structures Department,Technical University of Cluj-Napoca, RomaniaAbstractThis paper presents the experimental research regarding the physical-mechanicalproperties and the bending and shear behavior of the ultra high performanceconcrete. The cementitious composite with 2% volume of steel fibers was testedfor the following characteristics: the compressive and tensile strength, the stressstrain characteristic curve for compression strength and flexural strength.Furthermore, a series of reinforced elements were tested and analyzed in terms ofmaximum crack width, deformations and maximum compressive strain. Thespecimens subject to 90 C thermal treatment for 5 days displayed an increase ofcompressive strength up to 180 MPa at the age of 6 days. The experimental dataobtained on specimens with a thermal curing regime are evaluated bycomparison with specimens with a water-curing regime.Keywords: ultra high performance concrete, compression, tension, splitting,flexure, shear, bending, fiber.1 IntroductionUltra high performance fiber reinforced concrete (UHPFRC) stands for concreteswith compressive strengths exceeding 150 MPa [1]. The concrete compositionincludes high cement content, mineral admixture (usually silica fume), steelfibers and a very low water/binder ratio, ensured by the use of last generationsuperplasticizers [1–4]. UHPFRC incorporates very fine sands or quartz sandswith granule size up to 1 mm. Besides the superior physical-mechanicalproperties compared with ordinary concrete and even high strength concrete,UHPFRC presents very good ductility and durability properties [1–6].WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)doi:10.2495/HPSM100081
80 High Performance Structures and Materials V2 Mechanical properties2.1 Experimental programThe experimental program comprised the study of the mechanical properties ofultra-high performance with fibers (UHPFRC) and without fibers (UHPC). Bothmixtures used Portland cement type CEM I 52.5R, gray silica fume and very finesand with granulometry of 0-0.3 mm and 0.4-1.2 mm. The coarse aggregateswere eliminated. The flowability of the concrete was insured by the polymerether-carboxylate superplasticizers. The composition of the two concretes ispresented in Table 1.Two curing regimes were applied for specimens used for mechanicalproperties determinations:- thermal treatment for 5 days with a constant temperature of 90 C.- water curing for 5 days with a constant temperature of 20 2 C.Subsequently, the specimens were kept in the laboratory environment(temperature 20 2 C and relative humidity 60 5%) until testing.The strength and deformability characteristics were determined with a digitalhydraulic testing machine with deformation control, type ADVANTEST 9. Thedisplacements were measured using LVDTs. A general view of the testingmachine is displayed in Figure 1.Table 1:Concrete composition.MaterialsCement CEM 52.5RWater/cement ratio (w/c)Water/binder ratio (w/b)Sand (0-0.3) (0.4-1.2 mm)Silica fumeSuperplasticizersSteel fibersFigure 0.1381.180.260.03050.174Mechanical properties testing machine.WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
High Performance Structures and Materials V812.2 Fresh concrete propertiesThe flowability of the concrete was investigated with the slump flow testconducted immediately after the mixing process ended. It was observed that thesteel fibers incorporation does not have a major influence on the concreteflowability, the slump flow measurement being about 120 mm.The water/cement ratio was 0.174. All specimens were produced from thesame batch in order to eliminate the influence of the mixing condition.The specimens had the following geometry: 70x70x70mm and 100x100x100mm cubes, 40x40x160mm and 100x100x300mm prisms.The specimens were demolded 24h after casting.2.3 Compressive and splitting tensile strengthThe compressive strength (fc) was measured on 70x70x70 mm cubes. Thesplitting tensile strength (fct,sp) was measured on 100x100x100mm cubes. Thetesting ages were 6, 14 and 28 days for both (T), thermal treatment (5days, 90 C)and (W), water curing regime (5 days, water, temperature 20 2 C). The resultsare listed in Table 2 for the compressive strength and in Table 3 for the splittingtensile strength.The compressive strength of thermal treated specimens is about 15% higherfor UHPFRC compared to UHPC.It can be observed an increase of about 220% of the splitting tensile strengthof UHPFRC compared with UHPC for the thermal treated specimens.2.4 Flexural strengthThe flexural strength was investigated by performing a 3 point bending test using40x40x160 mm and 100x100x300 mm prismatic specimens. The specimenswere thermal treated 128.8138.2UHPFRCSpecimengeometry[mm]Compressive strength.UHPCTable 2:Concrete Age1428daysWIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
82 High Performance Structures and Materials VCube 100x100x100CuringCube 100x100x100TypeCube 100x100x100Mechanical [mm]Cube 100x100x100Splitting tensile strength.UHPCTable 3:CuringPrism100x100x300TypePrism100x100x300Prism 11.512.716.6UHPFRCSpecimengeometry[mm]Prism 40x40x160Flexural strength.UHPCTable 4:[MPa](a)Figure 2:Concrete Age61428daysConcrete Age1428days(b)(a) Flexure failure of UHPFRC; (b) flexure failure of UHPC.The testing procedures using ADVANTEST9 testing machine and the failureof the specimens are illustrated in Figure 2.Fiber reinforced concrete (UHPFRC) showed a flexural strength 150-165%higher than un-reinforced concrete (UHPC). The geometry of the specimensinfluenced the flexural strength, smaller specimens exhibiting a higher strength,as seen in Table 4.WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
High Performance Structures and Materials V83P(kN)Macro-crack ofteningLinear-elasticbehavior (P 0.9Pmax)(microcracks)Figure 3:(ductile failure)Δ (µm)Load P(kN) vs. mid span deflection Δ (µm) curve (UHPFRC).P (kN)Macro-crack localization(brittle failure)Linear-elasticbehavior (P Pmax)(microcracks)Figure 4:Δ (µm)Load P(kN) vs. mid span deflection Δ (µm) curve (UHPC).The flexural behavior of the two types of concrete can be observed byanalyzing the load-deflection curves in Figures 3 and 4. UHPFRC displayed aductile behavior.The middle span deflection at maximum load, as well as the ultimate middlespan deflection, is about three times higher for UHPFRC compared to UHPC(900μm compared to 300μm). The peak load of UHPFRC was 1.5 times higherthan the peak load of UHPC.3 Bending and shear behavior of UHPC beams3.1 Experimental programThe bending and shear behavior was tested on four I-shaped beams withidentical cross sections.WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
84 High Performance Structures and Materials VThe bending beams had a total length of 3.2 m with a span of 3 mm. Theshear beams had a total length of 1.67m and a span of 1.5m. The beams aredescribed in Table 5.Beams’ reinforcement and geometry are described in Figures 5, 6, 7, and 8.The beams were demolded after 24h and afterwards were subject to thermaltreatment for 5 days with a constant temperature of 90 C and a relative humidityof 40%.Table 5:Beam typesWithout fibersWith fibersBeam description.LoadBending ShearTS1TS2TSF1TSF2Figure 5:TSF1 reinforcement and geometry.Figure 6:TS1 reinforcement and geometry.WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
High Performance Structures and Materials VFigure 7:TS2 reinforcement and geometry.Figure 8:TSF2 reinforcement and geometry.853.2 Testing procedureThe beams’ age was 28 days when tested. Tested beams’ measurement included:-displacements measured in 5 sections for bending and 3 sections for shear with0.1mm precision;-middle span displacement with transducers with 0.03mm precision-cracks width by 0.1mm precision apparatus-cracks distanceAspects regarding test setups are displayed in Figure 9.3.3 Tests results3.3.1 BendingThe results are plotted in Table 6 and the following observations can be made:a) Bending beam with re-bars only:-maximum crack width Wmaxcr 0.1mm-maximum displacement for the serviceability limit state (l/250) wasrecorded for M/Mu 0.57b) Bending beam with re-bars and steel fibers:-maximum crack width Wmaxcr 0.1mmWIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
86 High Performance Structures and Materials V-maximum displacement for the serviceability limit state (l/250) wasrecorded for M/Mu 0.46The bending moments ratio of the two beams for a crack widthWcrmax 0.1mmis MTS10.1/ MTSF10.1 0.62. The fiber addition almost doubles the maximumbending moment, as expressed by the moment ratio of the two beams MTS10.1/MTSF10.1 1.87.The ultimate strain in compression for the beam with fiber addition is 3.14times higher than that of the beam without fibers.Load-mid span displacement curves can be analyzed in Figure 10.The failure of the beams is presented in Figure 11.3.3.2 ShearTests results are plotted in Table 7. A maximum inclined crack of 0.1mm isproduced for a load ratio P/ Pu 0.2 in the stirrups reinforced beam (1 leg(a)(b)Figure 9:(a) Bending setup test; (b) shear setup test.Table 871.00Bending tests results.Δ[mm][mm]0.1 7.9 (l/250)0.2 8.2 (l/190)0.5 12.5 (l/160)14.5 (l/70)0.05 9 (l/333)0.115.2 (l/200)0.222.1 (l/135)0.326.8 (l/111)71.0 2.055.50WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)NotesM bendingmomentMu maximumbending momentWcrmax maximumcrack widthΔ middle spandisplacementεcmax ultimatestrain(compression)l beam span
High Performance Structures and Materials VTFS1TS1Figure 10:Load-mid span deflection, bending testing.Table 20.450.491.000.320.560.710.751.00Shear tests results.Wcrmax[mm]0.10.20.30.40.10.20.30.5-NotesP forcePmax maximum forceWcrmax maximum inclined crackwidtha/d 1 (shear slenderness ratio)PF0,1/ PFF0,1 3.2PFu/ PFFu 2.04(a)Figure 11:(b)(a) Failure of TSF1; (b) failure of TS1TFS2TS2Figure 12:Load-mid span deflection, shear testing.WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)87
88 High Performance Structures and Materials V(a)Figure 13:(b)(a) Failure of TS2; (b) failure of TSF2. 10mm, s 100mm, steel Bst500S). The same crack opening of 0.1mm isproduced at P/ Pu 0.32 for the steel fiber reinforced beam (without stirrups). Byadding fiber in concrete composition the rupture force is 2.04 times higher thanfor concrete without fibers.Load-mid span deflection curves are displayed in Figure 12.The failure of the beams is presented in Figure 13.4 ConclusionsThe paper presents the mechanical properties of ultra high performance concrete.The influence of steel fiber reinforcement, age, geometry of the specimensand environmental conditions was evaluated.Fiber reinforcement influence was analyzed in terms of mechanical propertiesand behavior of concrete beams in shear and bending. Thermal treatmentimproved mechanical strengths. Fiber addition improved the compressivestrengths, but the most significant influence was on the tensile strengths and onthe element behavior.Smaller specimens exhibited higher flexural strength.Splitting tensile strength of UHPFRC is about 2.2 times higher than that ofUHPC.It was observed a ductile post peak behavior for UHPFRC with 2% steelfibers by concrete volume.For about 85-95% of the peak load, UHPC and UHPFRC displayed a quasilinear behavior when tested in flexure.Regarding shear and bending tests on beams, the steel fibers additionimproved the behavior and loading capacity for the tested beams.The tests suggested that fiber reinforcement is extremely efficient and cansuccessfully replace steel stirrups. This aspect is very important for both timeand money saving. Moreover, ultra high performance concrete requires smallcross sections and, bearing in mind the compressive strength of this concrete, itis quite impossible to use only stirrups as shear reinforcement.AcknowledgementsThis research was conducted within a PCE-PN II-IDEI Program, code1053/2007, financed by National Scientific Research Council for HigherWIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
High Performance Structures and Materials V89Education (CNCSIS), Romania. The authors would like to express their gratitudeto CNCSIS.References[1] Rossi P. (2001) Ultra-High-Performance Fiber-Reinforced Concrete-AFrench Perspective on approaches used to produce high-strength, ductilefiber reinforced concrete, Concrete International, December, 46-52[2] Magureanu C., Sosa I. (2008) Ultra High Performance Concrete. Reinforcedand Prestressed concrete Structures Roads. Bridges and railways.Proceedings of the International Conference: Construction 2008, ClujNapoca. 127-132.[3] Magureanu C., Heghes B., Corbu O, Szilagy H., Sosa I. (2008) Behavior ofHigh and Ultra High Fiber Reinforced Concrete. 8th InternationalSymposium on Utilization of High-Strength and High-PerformanceConcrete, Tokyo. 353-356.[4] Magureanu C., Heghes B., Negrutiu C. (2009) Ultra High PerformanceConcrete with and without steel fiber. Concrete 21 Century Super Hero,London.[5] Benjamin A. Graybeal, (2007) Compressive behavior of Ultra HighPerformance Fiber-Reinforced Concrete. ACI Materials Journal, MarchApril, 316-319.[6] Sugamata T., Sugiyama T, Okazawa S. (2002) Study on the fresh andhardened properties of concrete containing superplasticizers for Ultra HighStrength Concrete, Proceedings of the 1st fib Congress, Session 9, 87-96.WIT Transactions on The Built Environment, Vol 112, 2010 WIT Presswww.witpress.com, ISSN 1743-3509 (on-line)
Ultra high performance fiber reinforced concrete (UHPFRC) stands for concretes with compressive strengths exceeding 150 MPa [1]. The concrete composition includes high cement content, mineral admixture (usually silica fume), steel fibers and a very low water/binder ratio, ensured by the use of last generation
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a bending moment acting on the cross section of the bar. The shear force and the bending moment usually vary continuously along the length of the beam. The internal forces give rise to two kinds of stresses on a transverse section of a beam: (1) normal stress that is caused by bending moment and (2) shear stress due to the shear force.
Air bending is suitable for prototype development, part production and small batch production due to flexibility, lesser numbers of changes and low cost of tooling. Air bending is falsely judged as an easily understandable process. Bending behavior of metal sheet in air bending process is complex for sheet material, tool and process [4].
Statically Indeterminate axially Load member Thermal Stress TEST 1 (Tentative date: 9/17) 5. Torsion Angle of Twist 6. Indeterminate torque-loaded Member Shear and Moment 7. Shear and Moment Diagrams Graphical method for constructing Shear and Moment Diagram 8. Bending Stress Flexure formula Unsymmetrical Bending 9. Shear Stress The shear formula
Shear Stress vs Shear Displacement 0 20 40 60 80 100 0 2040 6080 100 Shear Displacement (mm) Shear Stress (kPa) Normal Stress - 20.93 kPa Field id: MID-AAF-0002-1 Measured Cohesion 14.99 Water Content 5.62 Shear box size 5.08 Peak Shear Stress 31.34 Intrinsic Cohesion 14.45 Wet Density 2240 Matri
