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Evaluation of the Orientation of 90° and 180° Reinforcing Bar Hooks in Wide 

Members

By: 

Nichole Podhorsky, M.S. Student

Lesley Sneed, Ph.D., P.E., Missouri S&T

Outline

I. IntroductionII. ObjectiveIII. Experimental Program1. Test Setup2. Beam‐end Specimens3. Instrumentation

IV. Test Specimen ConstructionV. ProcedureVI. Material PropertiesVII. Preliminary Results

Introduction

Bond of Reinforced Concrete is influenced by:

Bond is influenced by:• Steel properties• Concrete properties• Structural characteristics

Bond Transfer forces:• Friction forces• Chemical adhesion• Mechanical anchorage

Minor, John, and James O. Jirsa. "Behavior of Bent Bar Anchorages." ACI Journal 1975

l

Introduction

Bond transfer forces:  Deformed (ribbed) bar

ACI Committee 408. “Bond and Development of Straight Reinforcing Bars in Tension." American Concrete Institute (2003)

Introduction

Hooked Bar in Concrete:

Park, Robert, and Thomas Paulay. Reinforced Concrete Structures. New York, NY: J. Wiley and Sons, 1975.

Introduction

Evaluation of 90° and 180° bar hooks• Transverse reinforcement• Hook is usually in the vertical direction

Construction site photos(heavily reinforced shallow member)

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Objective

Evaluation of 90° and 180° bar hooks• Evaluate the limits of hook tilt• If possible, recommend limitations of hook tilt

Schematic of a hooked bar in a concrete slab

Experimental Program

Test Setup:• Pullout test (a)• Beam‐end test (b)• Beam anchorage test (c)g ( )

ACI Committee 408. “Bond and Development of Straight Reinforcing Bars in Tension." American Concrete Institute (2003)

Experimental Program

Beam‐end Test:

Minor and Jirsa beam‐end specimen Ehsani et al beam‐end specimen

Experimental Program

Beam‐end Test ‐ Reactions

Experimental Program

Beam‐end Specimen Design:Modified for compression strut

Compression strut from ACI 318‐08Modified beam‐end specimen

Experimental Program

Beam‐end Specimen Design:

Height• Concrete cover over tail extension, 3”• Tail length of the bar per ACI• Diameter of the bar, db• Cover over bar, 3db

Length• Height• 4” out of compression strut• Diameter of the bar, db• Concrete cover, 3”

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Experimental Program

Specimen Design: Width

Single‐Bar Specimen Group‐Effect Specimen

Side view

Experimental Program

Single‐Bar Specimen Design: Width• Based on ASTM A944 modified, 4” side cover

Width increase for aincrease for a 90° hook tilted

Width increase for a 180° hook tilted

Experimental Program

Group‐Effect Specimen Design: Width

• Spacing:  0.5A, A and 2A spacing (A dimension is defined by CRSI)

CRSI Design Handbook. Schaumburg, IL: Concrete Reinforcing Steel Institute, 2008

Experimental Program

Group‐Effect Specimen Design: Width

Width increase for a 0.5 A spacing 

Width increase for a A spacing

Width increase for a 2A spacing

Experimental Program

Specimen1 Bar Size Standard Hook Bend (º)Hook Angle of Tilt From

Horizontal (º)

BE-5-180-0 No.5 180 0

BE-5-180-22 5 No 5 180 22 5

Single‐Bar Specimen Test Matrix:

BE 5 180 22.5 No.5 180 22.5

BE-5-180-45 No.5 180 45

BE-5-180-90 No.5 180 90

BE-5-90-0 No.5 90 0

BE-5-90-22.5 No.5 90 22.5

BE-5-90-45 No.5 90 45

BE-5-90-90 No.5 90 90

BE-8-90-0 No.8 90 0

BE-8-90-22.5 No.8 90 22.5

BE-8-90-45 No.8 90 45

BE-8-90-90 No.8 90 90

Experimental Program

Group‐Effect Specimen Test Matrix: 3 bar

Specimen1 Bar SizeStandard Hook

Bend (º)Hook Angle of Tilt From Horizontal (º)

BE-5-90-0-G2A2 3-No.5 90 0

BE-5-90-0-G1A2 3-No.5 90 0

BE-5-90-0-G0.5A2 3-No.5 90 0

BE-5-90-22.5-G2A 3-No.5 90 22.5

BE-5-90-22.5-G1A 3-No.5 90 22.5

BE-5-90-22.5-G0.5A 3-No.5 90 22.5

BE-8-90-0-G2A2 3-No.8 90 0

BE-8-90-0-G1A2 3-No.8 90 0

BE-8-90-0-G0.5A2 3-No.8 90 0

BE-8-90-22.5-G2A 3-No.8 90 22.5

BE-8-90-22.5-G1A 3-No.8 90 22.5

BE-8-90-22.5-G0.5A 3-No.8 90 22.5

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Instrumentation

DisplacementString 

Potentiometer• 4 slip wires per bar                       2H, 3H, 3V, 4V or 4H2H, 3H,  3V, 4V or 4H

DCVT • 1 per bar                            1H

StrainStrain Gages

• 3 per bar                     Lead, Fore, Aft

Minor, John, “A Study of Bent-Bar Anchorages in Concrete,” PhD Thesis, Rice University, Houston TX, January 1971

Instrumentation

String Potentiometers (4 slip wires per bar):

90° bar with slip wires180° bar with slip wires

Instrumentation

String Potentiometers (4 slip wires per bar):

String potentiometers mounted on wooden support

Group effect with slip wires coming out the back face of concrete

Instrumentation

DCVT (1 per bar):

Single‐Bar SpecimenGroup‐Effect Specimen

Instrumentation

Strain Gages (3 per bar):

180° reinforcing bar 90° reinforcing bar

Test Specimen Construction

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Test Specimen Construction Test Specimen Construction

Procedure

Test Setup:

Single‐Bar Specimen

Procedure

Single‐Bar Specimen Test Setup:

Elevation of test setup Anchorage system, loading cell, and hydraulic jack

Procedure

Group‐Effect Specimen Test Setup:

Elevation of test setup Anchorage system, loading cell, and hydraulic jack

Procedure

Testing Procedure:Monotonic Loading every 2 minutes • Allows stabilization of condition• Allows for recording of data

No. 5 Bar:• Loaded in 500 lb increments • (36 load stages before yield of 60ksi bar)

No. 8 Bar:• Loaded in 1300 lb increments • 36 load stages before yield of 60ksi bar)

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Procedure

Loading Specimen:

3 Hydraulic Jack Setup

Hand Pump

Procedure

Test END Modes:Bar Slip:• More than  0.12 inches of slip (slip wires)

Concrete Cracking:• Any cracking of concrete (visual/auditory)

Yield of Bar:• Reinforcing bar yields (strain gage/slip wires)

Procedure

Concrete cracking Steel Yielding

Material Properties

Steel: No. 8 bars No. 5 bars

Material Properties

100,000

120,000Steel Properties

ULTIMATE

NO. 5 NO. 8 NO. 5 NO. 8

105103 103

101

0

20,000

40,000

60,000

80,000

Load (p

si) YIELD

NO. 5 NO. 8 NO. 5 NO. 8

Coupon Tensile Test

Coupon Tensile Test

Steel Manufacturer

Steel Manufacturer

68.0 67.5 66.0 67.5

Material Properties

Concrete:  Moist‐cure

Wet burlap and plastic moist‐cure in the Missouri S&T High Bay Structures Lab

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Material Properties

Concrete:Compression cylinder 4”x8”               Split cylinder 4”x8”

Material Properties

Concrete:  Single‐Bar Specimens:

Compression Cylinder 4”x8”  Split Cylinder 4”x8”Average strength = 6400 psi Average strength = 450 psiAverage strength   6400 psi  Average strength   450 psi

Group‐Effect Specimens:

Compression Cylinder 4”x8”  Split Cylinder 4”x8”Average strength = 4850 psi Average strength = 400 psi

Preliminary Results

50,000

60,000

70,000

si)

No.8_90_0

0

10,000

20,000

30,000

40,000

,

Lead

 Bar Stress (p

Slip (in)

1H 2H 3H 3V 4V

0.02 in

Preliminary Results

45 000

50,000

55,000

60,000

65,000

70,000

(psi)

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

0 0.02 0.04 0.06 0.08 0.1 0.12

Lead

 Bar Stress 

Slip (in)

No.8_90_22.5 1H

No.5_90_22.5 1H

60

70

80

i)

BE‐5‐90‐0‐2A Bar A

Preliminary Results

0

10

20

30

40

50

60

Lead

 Bar Stress (ks

1H 2H 3H 3V 4V

0.1 inch

60

70

80

BE‐5‐90‐22.5‐2A Bar A

60

70

80BE‐5‐90‐22.5‐2A Bar A

Preliminary Results

0

10

20

30

40

50

60

Lead

 Bar Stress (ksi)

1H 2H 3H 3V 4V

0.1 inch

0

10

20

30

40

50

Lead

 Bar Stress (ksi)

1H 2H 3H 3V 4V

0.1 inch

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Preliminary Results

Discussion:• The bar slip was greatest at the lead end of the bar

• In specimens with No. 5 bars, most of the slip occurs at the bent region of the bar, little slip was measured at thethe bent region of the bar, little slip was measured at the tail end of the bar

• Specimens with No. 8 bars showed more slip than the No. 5 bars at the tail end of the hook

• In specimens with No. 8 bars, the maximum load was the least in the horizontal direction and increased with increased tilt

• In specimens with No. 5 bars, the maximum load was similar for all angles of tilt

Preliminary Results

Discussion:• In the group‐effect specimens, the No.5 bars yielded, no matter the tilt angle or spacing.

• The No. 5 bars also had similar graphs, with the same stiffness and failure mode.

• In the group‐effect specimens, the No. 8 bar had more cracking as a test end mode although some yielding did occur.

• Data analysis is ongoing.

Acknowledgements

Center for Transportation Infrastructure and Safety A National University Transportation 

Center at Missouri S&T

Concrete Reinforcing 

Steel Institute

Jon Knapp & Ambassador Steel CorporationGateway Building Products

Questions

Thank You from:

Lesley Sneed, Ph.D., P.E. Missouri S&T Professor

Comments

Nichole PodhorskyMissouri S&T Student

Procedure

Group‐Effect Specimen Test Setup: