Constitutive Relationships of Prestressed Steel Fiber Reinforced Concrete in Tension Justin Mickey Softening Coefficients for Prestressed Steel Fiber Reinforced Concrete Thomas Kelleher NSF REU Summer Scholars University of Houston August, 2008
Overview of Today s Presentation Introduction Fabrication Testing Results Conclusions
Relevance Want to predict behavior of prestressed steel fiber reinforced concrete (SFRC) Applications include: Shear walls Box bridges Nuclear containment vessels Off-shore structures
Relevance Why steel fiber? Reduce or eliminate need for traditional shear reinforcement (stirrups) Less time and labor cost associated with stirrup pplacement and fabrication
Previous Research Researchers at UH have studied: Reinforced Concrete Steel Fiber Reinforced Concrete Prestressed Reinforced Concrete Currently studying behavior of prestressed Currently studying behavior of prestressed steel fiber reinforced concrete
Objectives For Prestressed SFRC: Constitutive relationship in tension Softening coefficients For both we want to: Calculate experimental Compare w/ previous theoretical Propose model
Mix Design Type I/II Cement Cement: Water ratio of 1:0.6 Target Compressive Strength of 6 ksi
Steel Fiber Reinforcement TEF-1: 0.5% by weight Dramix ZP305 1.2 x0.022 diameter fibers TEF-5: 1.5% by weight Dramix RC80/60 1.4 x0.03 diameter fibers
Steel Reinforcement Transverse Direction: 10 grade 60 #4 steel rebar Longitudinal Direction: TEF-1 1:10 10 TEF5:5 TEF-5 5 0.6 diameter grade 70 steel prestressing tendons 1 t 2
Form Layout Conduit Stirrups Ties
Casting Panels Mixing Slump Test 2 Batches Cylinder and Beam casting Vibrating
Cylinder and Beam Tests Cylinder Test: Compressive Strength Beam Test: Crack Strength
What is Prestressing? Improved tensile properties Residual compressive stress Stage T1 Tensile stress fcr σ c Not to scale Stage T2 Decompression ess o Compressive strain ε c ε cx ε cr ε c Tensile strain Stage UC ( i ci σ c Compressive stress σ ci, ε )
Prestressing Process Hydraulic Jack Specime Concrete Force per f ε σ pi Load Cell n ε ci σ ci Force Tendon TEF-1-0.000177-0.8620 ksi TEF-5-0.000099 (-0.4317 ksi) -330 kips 33 kips 152.1 ksi (-165.7 33.15 kips 152.7 kips) ksi ksi) kips) ksi ε pi 0.005244 0.005267 TEF-5: LVDTs
Plate Attachment Half Inch Steel Plates Prevent Cracking outside the measurable area Provide Bracing for imbedded steel Rebar
The Universal Element Tester 37 hydraulic in- plane jacks 100 tons capacity per jack Manual control Computerized control
Computerized Control System Custom control boxes by Gardner systems Capable of Load and Strain control
Load Control Load Cells Real time load readings Computer automatically adjusts hydraulic pressure e Useful preyielding
Strain Control LVDTs (Linear Variable Differential Transformer) Signal amplifier Pressure adjustments based on strain readings Allows for postyeilding data acquisition
Installation Yoke Attachment Pin Insertion Jack Alignment LVDT Mounting
Testing Sequential loading Tension in longitudinal direction Compression in transverse direction Purely axial loading Applied stresses = principle stresses
Testing Loading Sequence Test Segment Description Duration Tensile End Goal 1 Elastic Tensile 15 min. 15 kips 0 2 Release 5 min. 0 0 3 Elastic Compressive 15 min. 0 15 kips 4 Release 5 min. 0 0 5 Tensile 60 min. 45 kips 0 6 Tensile mode switch from load-control to strain-control 7 Tensile 60 min. 1.0% strain 0 8 Compressive 90 min. 1.0% strain 85 kips 9 Compressive ~60 min 1.0% strain Failure Compressive End Goal
Testing Monitor: Real time stress-strain curves Cracking Record crack width manually Hold tension when 3/8 in.
Results: Cylinder/Flexural Data Obtain properties of concrete 6 cylinders & 2 flexural specimens tested for each panel Panel f ' c ε 0 E c f r TEF-1 50.6 MPa (7.34 ksi) 0.00239 33.67 GPa (4883 ksi) 824 psi TEF-5 40.1 MPa (5.82 ksi) 0.00214 29.98 GPa (4348 ksi) 1668 psi
Results: Tensile Behavior TEF-1 TEF-1 Tension 1.6 1.4 1.2 1 Stress (ksi) 0.8 0.6 0.4 0.2 0-0.002 0 0.002 0.004 0.006 0.008 0.01 0.012-0.2 02 Strain
Results: Tensile Behavior TEF-5 TEF-5 Tensile 1.6 1.4 1.2 1 Stress (ksi) 0.8 0.6 0.4 0.2 0-0.002 0 0.002 0.004 0.006 0.008 0.01 0.012-0.2 02 Strain
Results: Tensile Behavior Embedded Steel Tendon Contribution f = E ε s ps E ps f ps = E ε ps E 5 psε s 1 + f pu s 1 5
Results: Tensile Behavior Prestressed Concrete Steel Fiber Concrete σ + c = Ec ( ε c ε ci ) σ ci σ = c E c ( ε c ε cx) σ = ( c E ε ) c ( c σ = c f cr 0.5 ( 0.4 0.3Wf ) ε cr ε cr σ c = f ε cr c ε c
Results: Tensile Behavior Proposed Equations: σ c = Ec ( ε c ε ci ) + σ ci σ c = Ec ( ε c ε ( cx ) σ = c f cr ε cr ε c ( 0.63 0.02* Wf )
Results: Tensile Behavior Graphical Comparison of Steel Tendons TEF-1 TEF-5 300 TEF-1 Steel Tension 300 TEF-5 Steel Tension 250 250 200 200 s (ksi) Stress 150 s s (ksi) Experimental 150 Theoretical Stres Experimental Theoretical 100 100 50 50 0-0.001 0.001 0.003 0.005 0.007 0.009 0.011 0.013 0.015 Strain 0-0.001 0.001 0.003 0.005 0.007 0.009 0.011 0.013 0.015 Strain
Results: Tensile Behavior Graphical Comparison of Concrete TEF-1 TEF-1 Concrete Tension TEF-5 TEF-5 Concrete Tension 0.9 0.9 0.7 0.7 0.5 0.5 k si) Stress (k 03 0.3 0.1 Theoretical Experimental (ksi) Stress 0.3 0.1 Theoretical Experimental -0.0010 0.0000 0.0010 0.0020 0.0030 0.0040 0.0050 0.0060-0.1-0.0010 0.0000 0.0010 0.0020 0.0030 0.0040 0.0050 0.0060 0.0070 0.0080-0.1-0.3-0.3-0.5 Strain -0.5 Strain