NC STATE UNIVERSITY NC STATE High Performance Steel High Performance Steel Reinforcing Bars Reinforcing Bars Sami Rizkalla, Raafat El Sami Rizkalla, Raafat El - - Hacha Hacha C C onstructed onstructed F F acilities acilities L L aboratory ( aboratory ( CFL CFL ) ) N N orth orth C C arolina arolina S S tate tate U U niversity ( niversity ( NCSU NCSU ) ) and Salem Faza Salem Faza Concrete Reinforcement Technologies Concrete Reinforcement Technologies Detroit, April 22, 2002
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NC STATE UNIVERSITY NC STATE
High Performance Steel High Performance Steel Reinforcing Bars Reinforcing Bars
Shear strengthFatigue strengthTensile strength of bent barsBond strength and development lengthBehaviour as compression steel in reinforced concrete columns
NC STATE UNIVERSITY NC STATE
Mechanical Properties in Tension Mechanical Properties in Tension
Test method follow: ASTM A370, E8, and E111
Determine the stress-strain characteristics of three MMFX bar sizes (#4, #6, and #8)
Provide the following fundamental characteristics:Modulus of elasticity: EYield strength: fyUltimate stress: fu and corresponding strainUltimate strain: εsu
NC STATE UNIVERSITY NC STATE Results of Tension TestsResults of Tension Tests
Shear Strength Shear Strength Determine the Shear Strength of three bar sizes (#4, #6, #8) using five specimens for each size. The test specimen is subjected to double shear action
Shear strength is determined based on the failure load
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Results of Shear StrengthResults of Shear Strength#4MMFX Shear Strength
Determine the endurance limit for bar sizes #4 & #6
Determine the stress-number of cycles curve (S-N curve) for each bar size
The maximum tensile stress level varied: 90%, 80%, 75%, 70%, and 65% of the yield strengthThe minimum tensile stress level was set at 20% of the yield strength
NC STATE UNIVERSITY NC STATE
S-N Diagrams
0
20
40
60
80
100
120
10000 100000 1000000
Fatigue life, N, Cycles
Stre
ss (k
si)
#6MMFX
#4MMFX
SS--NN DiagramDiagram
NC STATE UNIVERSITY NC STATE
Tensile Strength of Bent BarsTensile Strength of Bent BarsExamine the bend effect on the strength of the MMFX reinforcing steel bent bars
Two different bar sizes (#4, and #6) were used
The radius of the bent is 90° (ACI 318-99)
20 Hydraulic Jack
Load Cell
#4 MMFX
18
Plastic tube
1212
Concrete BlockConcrete Block
NC STATE UNIVERSITY NC STATE
Bend Effect on Tensile StrengthBend Effect on Tensile Strength
Plastic tube for debonding
NC STATE UNIVERSITY NC STATE
Test SetTest Set--upup#4MMFX#4MMFX
Bend Effect on Tensile StrengthBend Effect on Tensile Strength
NC STATE UNIVERSITY NC STATE
Tensile Strength of Bent BarsTensile Strength of Bent Bars#4MMFX Reinforcing Steel Bars
0
20
40
60
80
100
120
140
160
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Strain (in/in)
Stre
ss (k
si)
165ksi
NC STATE UNIVERSITY NC STATE
#6MMFX Reinforcing Steel Bars
177 ksi
0
20
40
60
80
100
120
140
160
180
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
Strain (in/in)
Stre
ss (k
si)
Tensile Strength of Bent BarsTensile Strength of Bent Bars
NC STATE UNIVERSITY NC STATE
Bond Strength and Bond Strength and Development Length Development Length
Evaluate the bond strength and the development length of bar sizes #4, #6, and #8.
Different embedment length of 8db, 18db, 38db, 58db, 78db and 98db were examined for each selected size (db is the diameter of the bar).
NC STATE UNIVERSITY NC STATE
Bond Test SpecimenBond Test Specimen
12inLVDT
Load Cell
Jack
Elevation
Development length
Plan
NC STATE UNIVERSITY NC STATE
Bond SpecimensBond Specimens
Specially designed RC TSpecially designed RC T--sectionsection
Concrete T-section heavily reinforced with Grade 60 steel
Plastic tubesPlastic tubes
NC STATE UNIVERSITY NC STATE
Test SetTest Set--UpUp
self-reacting steel frame against the flange of the T-section
Jack Load Cell
NC STATE UNIVERSITY NC STATEResults of Bond TestsResults of Bond Tests
#4MMFX Embedment Length = 4in (8d)
2.2ksi, 0.0198in)
0
0.5
1
1.5
2
2.5
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Slip at the Free End (in)
Bon
d St
ress
(ksi
)
Axial stress = 70.6ksiMaximum Laod = 13830lb
NC STATE UNIVERSITY NC STATE
Results of Bond TestsResults of Bond Tests#6MMFX Embedment Length = 7in (9d)
(2.24ksi, 0.04975in)
0
0.5
1
1.5
2
2.5
0 0.04 0.08 0.12 0.16 0.2 0.24
Slip at Free End (in)
Bon
d St
ress
(ksi
)
Axial stress = 83.8ksiMaximum Laod = 36875lb
NC STATE UNIVERSITY NC STATE
Results of Bond TestsResults of Bond Tests4in 9in 19in 29.25in 39in 49in8d 18d 38d 58.5d 78d 98d