4/12/2011. Outline. Introduction. Introduction. Introduction. Introduction

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1 Evaluation of the Orientation of 9 and 18 Reinforcing Bar Hooks in Wide Members By: Nichole Podhorsky, M.S. Student Lesley Sneed, Ph.D., P.E., Missouri S&T Outline I. Introduction II. Objective III. 1. Test Setup 2. Beam end Specimens 3. IV. Test Specimen Construction V. VI. VII. Introduction Bond of Reinforced Concrete is influenced by: Introduction Bond transfer forces: Deformed (ribbed) bar 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 ACI Committee 48. Bond and Development of Straight Reinforcing Bars in Tension." American Concrete Institute (23) Introduction Hooked Bar in Concrete: Introduction Evaluation of 9 and 18 bar hooks Transverse reinforcement Hook is usually in the vertical direction Construction site photos (heavily reinforced shallow member) Park, Robert, and Thomas Paulay. Reinforced Concrete Structures. New York, NY: J. Wiley and Sons,

2 Objective Evaluation of 9 and 18 bar hooks Evaluate the limits of hook tilt If possible, recommend limitations of hook tilt Test Setup: Pullout test (a) Beam end test (b) Beam anchorage test () (c) Schematic of a hooked bar in a concrete slab ACI Committee 48. Bond and Development of Straight Reinforcing Bars in Tension." American Concrete Institute (23) Beam end Test: Beam end Test Reactions Minor and Jirsa beam end specimen Ehsani et al beam end specimen Beam end Specimen Design: Modified for compression strut 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 Modified beam end specimen Compression strut from ACI Length Height 4 out of compression strut Diameter of the bar, db Concrete cover, 3 2

3 Specimen Design: Single Bar Specimen Group Effect Specimen Single Bar Specimen Design: Based on ASTM A944 modified, 4 side cover 9 hook tilted Side view 18 hook tilted Group Effect Specimen Design: Spacing:.5A, A and 2A spacing (A dimension is defined by CRSI) Group Effect Specimen Design:.5 A spacing A spacing 2A spacing CRSI Design Handbook. Schaumburg, IL: Concrete Reinforcing Steel Institute, 28 Single Bar Specimen Test Matrix: Hook Angle of Tilt From Specimen1 Bar Size Standard Hook Bend (º) Horizontal (º) BE No.5 18 BE No BE No BE No BE-5-9- No.5 9 BE No BE No BE No BE-8-9- No.8 9 BE No BE No BE No Group Effect Specimen Test Matrix: 3 bar Standard Hook Bar Size Hook Angle of Tilt Specimen1 Bend (º) From Horizontal (º) BE-5-9--G2A2 3-No.5 9 BE-5-9--G1A2 3-No.5 9 BE-5-9--G.5A2 3-No.5 9 BE G2A 3-No BE G1A 3-No BE G.5A 3-No BE-8-9--G2A2 3-No.8 9 BE-8-9--G1A2 3-No.8 9 BE-8-9--G.5A2 3-No.8 9 BE G2A 3-No BE G1A 3-No BE G.5A 3-No

4 Displacement String Potentiometer 4 slip wires per bar 2H, 3H, 3V, 4V or 4H DCVT 1 per bar 1H String Potentiometers (4 slip wires per bar): Strain Strain Gages 3 per bar Lead, Fore, Aft Minor, John, A Study of Bent-Bar Anchorages in Concrete, PhD Thesis, Rice University, Houston TX, January bar with slip wires 9 bar with slip wires String Potentiometers (4 slip wires per bar): DCVT (1 per bar): Group effect with slip wires coming out the back face of concrete String potentiometers mounted on wooden support Group Effect Specimen Single Bar Specimen Strain Gages (3 per bar): Test Specimen Construction 18 reinforcing bar 9 reinforcing bar 4

5 Test Specimen Construction Test Specimen Construction Test Setup: Single Bar Specimen Test Setup: Elevation of test setup Anchorage system, loading cell, and hydraulic jack Single Bar Specimen Group Effect Specimen Test Setup: Testing : Monotonic Loading every 2 minutes Allows stabilization of condition Allows for recording of data Elevation of test setup Anchorage system, loading cell, and hydraulic jack No. 5 Bar: Loaded in 5 lb increments (36 load stages before yield of 6ksi bar) No. 8 Bar: Loaded in 13 lb increments 36 load stages before yield of 6ksi bar) 5

6 Loading Specimen: Test END Modes: Bar Slip: More than.12 inches of slip (slip wires) Concrete Cracking: Any cracking of concrete (visual/auditory) Yield of Bar: Reinforcing bar yields (strain gage/slip wires) 3 Hydraulic Jack Setup Hand Pump Concrete cracking Steel Yielding Steel: No. 8 bars No. 5 bars 12, 1, Steel Properties ULTIMATE NO. 5 NO. 8 NO. 5 NO. 8 Concrete: Moist cure Load (psi) 8, 6, 4, YIELD NO. 5 NO. 8 NO. 5 NO. 8 2, Wet burlap and plastic moist cure in the Missouri S&T High Bay Structures Lab Coupon Tensile Test Steel Manufacturer Coupon Tensile Steel Test Manufacturer 6

7 Concrete: Compression cylinder 4 x8 Split cylinder 4 x8 Concrete: Single Bar Specimens: Compression Cylinder 4 x8 Split Cylinder 4 x8 Average strength = 64 psi Average strength = 45 psi Group Effect Specimens: Compression Cylinder 4 x8 Average strength = 485 psi Split Cylinder 4 x8 Average strength = 4 psi Lead Bar Stress (p si) No.8_9_ 7, 6, 5, 4, 3, 2, 1,.2 in 1H 2H 3H 3V 4V Slip (in) Lead Bar Stress (psi) 7, 65, 6, 55, 5, 45, 4, 35, 3, 25, 2, 15, 1, 5, Slip (in) No.8_9_22.5 1H No.5_9_22.5 1H i) Lead Bar Stress (ks BE 5 9 2A Bar A Lead Bar Stress (ksi) BE A Bar A inch 1H 2H 3H 3V 4V 1.1 inch 1H 2H 3H 3V 4V 7

8 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 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 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 Questions Thank You from: Concrete Reinforcing Steel Institute Center for Transportation Infrastructure and Safety A National University Transportation Center at Missouri S&T Jon Knapp & Ambassador Steel Corporation Gateway Building Products Comments Lesley Sneed, Ph.D., P.E. Missouri S&T Professor Nichole Podhorsky Missouri S&T Student Group Effect Specimen Test Setup: 8