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FINITE ELEMENT MODELING, ANALYSIS AND VALIDATION OF THE SHEAR CAPACITY OF RC BEAMS MADE OF STEEL FIBER REINFORCED CONCRETE (SFRC)_ICACE 2014 CUET
The document presents research on modeling and analyzing the shear capacity of reinforced concrete beams made with steel fiber reinforced concrete (SFRC). Finite element models were created in ANSYS for plain reinforced concrete beams and SFRC beams. The models were validated against experimental test results. The following were found: 1) Experimental testing showed that the shear strength of beams increased by about 25%, 29%, and 18% for SFRC with steel fibers having aspect ratios of 40, 60, and 80, respectively, compared to plain reinforced concrete beams. 2) Finite element models created in ANSYS using solid elements for the concrete and link elements for reinforcement correlated well with experimental load-deflection curves and failure modes. 3) The
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FINITE ELEMENT MODELING, ANALYSIS AND VALIDATION OF THE SHEAR CAPACITY OF RC BEAMS MADE OF STEEL FIBER REINFORCED CONCRETE (SFRC)_ICACE 2014 CUET
- 1. AHSANULLAH UNIVERSITY OF SCIENCEAND TECHNOLOGY (AUST) FINITE ELEMENT MODELING, ANALYSIS AND VALIDATION OF THE SHEAR CAPACITY OF RC BEAMS MADE OF STEEL FIBER REINFORCED CONCRETE (SFRC) 1 Presented by: Md. Shahadat Hossain Department of Civil Engineering Ahsanullah University of Science and Technology (AUST), Dhaka-1208, Bangladesh Co-Authors: Md. Mashfiqul Islam Saiful Amin Zahidul Islam Mana Bala Md. Arman Chowdhury Ashfia Siddique Paper ID: SEE 075
- 2. 2 SFRC STEEL FIBER REINFORCEDCONCRETE
- 3. 3 OPC(Hydraulic cement & Admixtures) Fine &Coarse aggregates Dispersion of Short Discrete Steel Fiber SFRC components
- 4. 4 SFRC ADVANTAGES Enhancement of ductility and energy absorption capacitytransforms failure modes from brittle and dangerous shear failures into more ductile flexural failures Increase the flexural strength , direct tensile strength and fatigue strength. Enhance shear and torsional strength Shock resistance as well as toughness of concrete Increases stiffness , reduces deflections
- 5. 5 Applications of SFRC •industrial or factory pavements, highways, roads, parking areas , airport runways • tunnel linings, • pre-cast structures, structures in high seismic risk areas, bridge decks • off-shore platforms, water-retaining structures etc.
- 6.
- 7. Mechanism of SFRC Fibersdistribute randomly and act as crack arrestors. Resistance to crack extension provided near a crack tip(zone a) by the bond stress between fibers and concrete Increases the ductility by arresting crack and prevents the propagation of cracks by bridging fibers. 7 zone a: Free area of stress zone b: Fiber bridging area zone c: Micro-crack area zone d: Undamaged area When steel fibers are added to a concrete mix :
- 8. 8 To investigate the performanceof steel fiber with three different aspect ratio, i.e. 40, 60 and 80 To evaluate the shear capacities of SFRC RC beams due to aspect ratio of steel fibers. To examine failure patterns of RC beams made of SFRC. To construct FE models for plain reinforced concrete and SFRC in the FE platform of ANSYS 11.0 and also validate the models with the experimental results. Above all to provide the construction industry of Bangladesh with reliable experimental data and validated FE modeling about this engineering material.
- 9. 9 Experimental program andstrategy Experimental strategy Experimental program Specimen preparation Testing and Data Acquisition Investigation of failure pattern FE modeling through optimizing the basic engineering properties FE analysis applying experimental loading environment and displacement boundary conditions Validation of FE models and analyses with experimental results and failure modes
- 10. Strategy: Three different aspectratio of steel fibers are selected i.e. 40, 60 and 80 and prepared manually in the laboratory. The beams are designed with 2-12mmφ rebars(Figure-1) at bottom and without any web reinforcement(Figure-2). The Rebars are connected to provide anchorage at the end instead of making hook. The strategy is to estimate the shear capacity increament due to steel fiber in the concrete mix and also to evaluate the performance of fibers with respect to aspect ratio. 10
- 11. Figure1: Longitudinal reinforcement Figure 2:Experimental strategy on shear beams. 11
- 12. Materials Steel Fibers: Sourcetypes and shapes According to ASTM A 820/A 820M – 06, five general types of steel fibers are identified based upon the product or process used as a source of the steel fiber material, they are, Type I: cold-drawn wire, Type II: cut sheet, Type III: melt-extracted, Type IV: mill cut, Type V: modified cold-drawn wire and the fibers shall be straight or deformed. 12
- 13.
- 14. Selection of shape Stress-straincurves for steel fiber reinforced mortars in tension (ACI 544.4R-88) 14
- 15. Fiber preparation The fibersare prepared manually in the laboratory. The cold drawn wires are cut from the coil as desired length to make the required aspect ratio. In this research the ends of the fibers are bended 120˚ to make enlarged ends which provide anchorage in the concrete matrix. Figure 3 shows the fiber preparation and images of the prepared fibers. 15
- 16. 16 Figure 3 :(a) Preparation of steel fibers (b) steel fibers of different aspect ratio. (a) (b)
- 17. 17 Three different typesof steel fiber aspect ratio (l/d) i.e. 40, 60 and 80 are selected to be made. Their corresponding measurements are given in the table-1 and shown in figure 4. Aspect ratio of steel fiber Diameter (mm) Effective length (mm) Original length (mm) Angle (Degree) 40 1.18 47.2 67.2 120 60 1.18 70.8 90.8 120 80 1.18 94.4 114.4 120 Aspect ratio: Table1: Steel fiber size and geometry
- 18. 18 (a) (b) Figure 4:(a) Size and geometry of steel fibers (b) image of fibers
- 19. 19 Aggregates Crushed stone areused as coarse aggregate in this research. Different types of aggregate are shown in Figure 5. Figure 5: (a) Stone aggregate (CA) and (b) Sand (FA) (a) (b)
- 20. 20 Cement type OPC(ordinary Portland cement) Coarse Aggregate Size 1 in passing and 3/4 in retain (50%) 3/4 in passing and 1/2 in retain (50%) C: FA: CA 1:1.5:3 W/C 0.5 Slump 1in (25mm) Fiber Volume 1.5% Fiber Aspect ratio 40, 60 and 80 Fiber type End enlarged Fiber Tensile strength 160000 psi (1100 MPa) Fiber cross section Circular Fiber dia 1.18 mm Concrete comp. strength 3700 psi (25.5 MPa) Type of coarse aggregate Stone Table 2: Mix design of plain reinforced concrete and SFRC Mix design
- 21. 21 Testing and DataAcquisition A digital universal testing machine (UTM) of capacity 1000 kN is used in this experiment. This is a displacement controlled machine. Load and displacement value can be measured from this UTM. In this experiment displacement rate of 0.5mm per minute is applied. Lateral displacements/strain are measured by analyzing the image histories obtained from high definition video camera(Figure 6&7) and employing an image analysis technique which is called Digital Image Correlation Technique (DICT).
- 22. 22 Figure 7: Horizontaldata acquisition system via DICT. Figure 6: Experimental setup for shear critical beam in the UTM.
- 23. 23 Images of ExperimentalTesting of Simply Supported Beam
- 24. 24 0 1000 2000 3000 4000 5000 0 0.005 0.010.015 CSCCON CSC40 CSC60 CSC80 Compressivestress(psi) Compressive strain 0 7 14 21 28 35 Compressivestress(MPa) 2691 psi (19 MPa) 3741 psi (26 MPa) 4400 psi (30 MPa) 3733 psi (25.7 MPa) Fig. 8: Experimental results of plain concrete and SFRC cylinder (a) compression (b) splitting tension 0 200 400 600 800 1000 1200 1400 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 CSTCON CST40 CST60 CST80 Tensilestress(psi) Tensile strain 0 1.4 2.8 4.2 5.6 7.0 8.4 9.8 Tensilestress(MPa) (a) (b)
- 25. 25 (a) Fig. 9: Experimentalresults of plain reinforced concrete and SFRC beam (a) load deflection behaviour of beams. 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 CSBSCCON CSBSC40 CSBSC60 CSBSC80 Load(kip) Mid point deflection (in) 0 12.7 25.4 38.1 50.8 Mid point deflection (mm) 0 22 44 66 88 110 Load(kN) 132 154
- 26. 26 FE modeling * Suitableelement type * Adequate mesh size * Optimized material properties * Appropriate boundary conditions * Realistic loading environment * Proper time stepping
- 27. 27 SOLID65 is usedin ANSYS 11.0 to model the concrete and also SFRC, which is a three dimensional (3D) solid element having eight nodes with three degrees of freedom at each node, i.e., translational in the nodal x, y, and z directions. The element is capable of plastic deformation, cracking in tension, crushing in compression and is also applicable for reinforced composites (ANSYS 2005), such as, fibreglass, SFRC etc. The flexural reinforcement is modelled using LINK8 element, which is a 3D spar element as well as a uniaxial tension-compression element with three degrees of freedom at each node same as SOLID65. The geometry and node locations for SOLID65 and LINK8 elements are shown in Fig. FE element:
- 28. 28 FE models (a) (b) Figure 9:Typical diagram of FE model of Shear-critical RC beam in ANSYS 11.0 (a) volume and (b) after meshing.
- 29. 29 FE governing parameters Modulusof elasticity Stress-strain behaviour Poisson’s ratio Density Willum and Warke (1975) criterion Shear transfer coefficient for open crack Shear transfer coefficient for close crack Tensile strength Compressive strength
- 30. 30 Properties for FE model Beamspecimen (SOLID65) Rebar (LINK8) CSBSCCON CSBSC40 CSBSC60 CSBSC80 Modulus of elasticity 3000000 psi 1870000psi 1400000psi 1400000psi Density 2.69g/cm3 2.77g/cm3 2.72g/cm3 2.74g/cm3 7.8g/cm3 Tensile strength 4 Mpa 6 MPa 8 MPa 6.3 MPa - Poisson’s ratio 0.325 0.325 0.325 0.325 0.3 Displacement boundary condition (-y direction) 0.5mm 0.5mm 0.5mm 0.5mm Shear transfer co- efficient: closed crack 0.25 0.5 0.5 0.5 - Open crack 0.3 0.3 0.3 0.3 - Yield stress - - - - 420 MPa Table 3: FE input data for SOLID65 and LINK8 element
- 31. 31 0 5 10 15 20 25 30 35 0 0.5 11.5 2 ANSYS CSBSCCON CSBSCCON Load(kip) Mid point deflection (in) 0 12.7 25.4 38.1 50.8 Mid point deflection (mm) 0 22 44 66 88 110 Load(kN) 132 154 Fig. 4: Evaluation of load deflection behaviour FE and experimental SC beams a) CSBSCCON i.e. control beam b) CSBSC40 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 ANSYS CSBSC40 CSBSC40 Load(kip) Mid point deflection (in) 0 12.7 25.4 38.1 50.8 Mid point deflection (mm) 0 22 44 66 88 110 Load(kN) 132 154 (a) (b)
- 32. 32 Fig. 4: Evaluationof load deflection behaviour FE and experimental SC beams a) CSBSC60 b) CSBSC80. 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 ANSYS CSBSC80 CSBSC80 Load(kip) Mid point deflection (in) 0 12.7 25.4 38.1 50.8 Mid point deflection (mm) 0 22 44 66 88 110 Load(kN) 132 154 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 ANSYS CSBSC60 CSBSC60 Load(kip) Mid point deflection (in) 0 12.7 25.4 38.1 50.8 Mid point deflection (mm) 0 22 44 66 88 110 Load(kN) 132 154 (a) (b)
- 33. 33 Fig. 6: Experimentaland FE failure pattern (a) CSBFCCON (b)CSBFC40 (a) (b)
- 34. 34 Fig. 6: Experimentaland FE failure pattern (a) CSBFC60 (b) CSBFC80. (b)(a)
- 35. 35 Shear strength ofSC beams increased about 25%, 29% and 18% for the SFAR 40, 60 and 80 respectively compared to control specimen.The ductility is enhanced 1.33, 1.58 and 1.17 times respectively. The FE models showed similar analyses result compared to experimental outcomes which ensures good agreements The failure patterns are also similar which also validated the FE models. FE models showed conservative results which ensure adequate factor of safety as well as reliability of FE modeling and analyses. Further investigation shows the capability of the models to predict capacity enhancements due to SFRC which ensures reliability of FE models.