Evaluation of the Orientation of 90° and 180° Reinforcing Bar Hooks In

Research Note Hooks inWide Members of 90 Evaluation oftheOrientation RN-2009-2 Research Note crushing of concrete within the bend of thebar,of concrete withinthebend crushing against thesurroundingconcrete. tail as it bears stresses onthehook compressive the concretein the inner radiusof the hook, and en undertension,resulting inbearingagainst (90°) hookedbarstendtostraight Ninety-degree concrete. of thebaronenclosed bearing crete through bond alongthe bar surfaceand con and thesurrounding bars intension hooked Hook Behavior Background depicted inFigure3. tial limitationsofhooktiltinaconcretemember, behavior. The research also examined the poten ence of hook angletilt on hookperformance and influ the evaluate to Program Fellowship search study initiatedaspartoftheCRSIGraduateRe trated inFigures1and2. the hookisnolongervertical.Hooktiltingillus rotate the bar along its longitudinal axis, such that to is length hook the maintain and requirements one solutionusedinpracticetosatisfythecover bar, may exceed the member depth. In this case, the required concrete cover above and below the cordance withthe ACI 318-11 Code (2011), plus reinforced, thestandardhookheightinac heavily member thatis such asthecaseofashallow instances, In some be critical. can bars of hooked large, especially for large diameter bars, detailing quite be can sizes hook standard Because axis. major to themember’s (or normal) perpendicular corresponds withbeing tion, whichgenerally hooks areusuallyorientedintheverticaldirec hook. ends witha90°or180°standard These atdiscontinuous members areoftendeveloped Introduction Failure of both hooktypescan resultfrom Forces aretransferredbetween90°or180° results ofa This ResearchNotedescribes flexural in bars steel reinforcing Longitudinal ° and180 ° ------ReinforcingBar slab concrete in bar hooked a of Schematic ‒ 3 Figure solid for details bar slabs (CRSI2008) Recommended ‒ 2 Figure shown attheedgeofacantileverbalconyslab hooks bar reinforcing tilted of Example ‒ 1 Figure which may cause cracks to propagate to a nearby side Provisions for development of standard hooks in ten- face of the member. Splitting failure, originating within sion are provided in ACI 318-11, Section 12.5. The ten- the bar bend due to high stress concentrations, can also sion development length of deformed bars with standard occur within the plane of the hook. Cracking of the con- hooks ℓdh (determined in accordance with the Code) is crete behind the hook tail is possible, as well. a function of the reinforcing bar diameter, yield strength, presence of epoxy coating, concrete type, and speci- Code Requirements fied compressive strength of concrete. The development Hooks can be provided to develop reinforcing bars length can be reduced by various modification factors, in tension in locations where there is limited length to which account for the effects of excess reinforcement, develop a straight reinforcing bar. Standard hook dimen- confinement from stirrups or ties, and/or adequate con- sions including the minimum finished inside bend diame- crete cover. The parameters and factors that influence ter “D” and extension length “A” are given in ACI 318-11, the development length account for the magnitude of the Sections 7.1 and 7.2.1, and CRSI’s Design Handbook compressive stresses or the resistance to splitting. (2008), as shown in Figure 4. Summary of Study Scope and Objective The objective of this study was to evaluate the limits of reinforcing steel hook tilt from vertical to ensure ulti- mate performance of the member is not compromised. This was achieved experimentally by comparing the load-slip responses of modified beam-end specimens with different hooked bar orientations and configurations. Concrete reinforcement in this study included deformed reinforcing steel bars with standard hooks embedded in normal weight concrete. The test variables included hook tilt angle, hook bend type, reinforcing bar size, and group-effect. Four hook tilt angles were evaluated: 0° (horizontal), 22.5°, 45°, and 90° (vertical). Both 90° and 180° standard hooked reinforcing bars were in- vestigated. #5 and #8 bars were examined in this study since they are commonly used in practice. The effect of multiple bars was also examined to evaluate the effects of interaction of adjacent bars, as shown in Figure 1. Ad- ditionally, bar spacing and position were evaluated. The test specimen matrix is shown in Table 1.

Experimental Program Test Specimens Modified beam-end specimens used in this study were modeled after previous tests reported in the literature (Minor 1971, Jirsa and Marques 1972, Minor and Jirsa 1975, Ehsani, et al. 1995) and in ASTM A944-10 (2010). The specimen was elongated so the reinforcing hook ex- tended beyond the reaction plates and the compression strut developing between the reactions. A PVC pipe bond breaker was provided along the straight portion of the bar to isolate the performance of the hooked portion of the bar.

Test specimen dimensions are summarized in Table 1. The specimen height was a function of the concrete above the hook extension (3 in.), the diameter (db), the length of the hook tail extension (12db), and the concrete cover (3db) of the test bar. The length of the specimen was the height plus the distance beyond the reaction plate. The distance beyond the reaction plate was the Figure 4 ‒ Hooked bar details for development of standard sum of 4 in., the diameter of the test bar, and 3 in. to ac- hooks (CRSI 2008) count for the cover of the tail extension of the bar. The width of the test specimens varied to accommodate the

2 Evaluation of the Orientation of 90° and 180° Reinforcing Bar Hooks in Wide Members [RN 2009-02] Table 1 ‒ Test Specimen Matrix Hook Angle of Standard Specimen1 Bar Size Tilt from Length (in) Width (in) Height (in) Hook Bend (°) Horizontal (°) BE-5-180-0 #5 180 0 17 1/2 17 3/8 9 7/8 BE-5-180-22.5 #5 180 22.5 17 1/2 16 5/8 9 7/8 BE-5-180-45 #5 180 45 17 1/2 14 1/2 9 7/8 BE-5-180-90 #5 180 90 17 1/2 8 5/8 9 7/8 BE-5-90-0 #5 90 0 22 1/2 27 3/8 14 7/8 BE-5-90-22.5 #5 90 22.5 22 1/2 25 7/8 14 7/8 BE-5-90-45 #5 90 45 22 1/2 21 1/2 14 7/8 BE-5-90-90 #5 90 90 22 1/2 8 5/8 14 7/8 BE-8-90-0 #8 90 0 30 39 22 BE-8-90-22.5 #8 90 22.5 30 36 5/8 22 (a) side view BE-8-90-45 #8 90 45 30 29 5/8 22 BE-8-90-90 #8 90 90 30 9 22 BE-5-90-0-G2A2 3-#5 90 0 22 1/2 67 3/8 14 7/8 BE-5-90-0-GA2 3-#5 90 0 22 1/2 47 3/8 14 7/8 BE-5-90-0-G0.5A2 3-#5 90 0 22 1/2 37 3/8 14 7/8 BE-5-90-22.5-G2A 3-#5 90 22.5 22 1/2 62 3/4 14 7/8 BE-5-90-22.5-GA 3-#5 90 22.5 22 1/2 44 3/8 14 7/8 BE-5-90-22.5-G0.5A 3-#5 90 22.5 22 1/2 35 1/8 14 7/8 BE-8-90-0-G2A2 3-#8 90 0 30 103 22 BE-8-90-0-GA2 3-#8 90 0 30 71 22 BE-8-90-0-G0.5A2 3-#8 90 0 30 55 22 BE-8-90-22.5-G2A 3-#8 90 22.5 30 95 3/4 22 BE-8-90-22.5-GA 3-#8 90 22.5 30 66 1/8 22 BE-8-90-22.5-G0.5A 3-#8 90 22.5 30 51 3/8 22 (b) end view Notes: Figure 5 ‒ Single bar specimens (90° hook 1. The following notation system is used to identify the variables of each specimen. The first term indicates the type of test: BE (Modified beam-end test).The sec- bar shown) ond term indicates the bar size: #5 or #8 standard. The third term is hook bend type: 90° or 180°. The fourth term is the angle of tilt from horizontal: 0°, 22.5°, 45° or 90°. Term G in the fifth term denotes specimens with multiple bars, and bar spacing is denoted as a multiple of bar extension length “A” defined in Figure 4.

2. Angle of tilt from horizontal is nominal. Actual angle is slightly larger than zero due to bar placement. tilt arc of the hooks on the bar ends. The cover distance on the side of the reinforcing steel hook was 4 in., based on ASTM A944-10.

Specimens were constructed with the reinforcing bar(s) on the bottom surface to mitigate the “top Figure 6 ‒ Multiple bar specimens – end view bar” effect; they were then later inverted for testing. Single bar specimens with 180° and 90° hooks are shown in Figure 5, and multiple bar specimens are shown in Figure 6. In the figures, ϴ is the angle of tilt Test Procedure from horizontal. The test setups for the single bar and multiple bar specimens are shown in Figures 7 and 8, respectively. Material Properties For the single bar specimens, a steel L-bracket ten- The reinforcing steel used in this study was ASTM sioned to the strong floor was used to provide the force A615, Grade 60. The measured yield strength of the #5 couple reaction created by the applied force to the bar and #8 reinforcing bars was 68.0 ksi and 67.5 ksi, re- and the horizontal reaction of the test specimen, depict- spectively. The concrete was normal weight, with a target ed in Figure 7. To resist overturning, a double channel compressive strength of 4,500 psi. The single bar test spreader beam was placed atop the specimen, creating specimens achieved an average compressive strength a distributed vertical reaction. This loading beam was of 6,450 psi, and the multiple bar specimens achieved held in position by two additional spreader beams ten- an average compressive strength of 4,850 psi; both sioned to the strong floor. To apply the force to the lead were measured at test date. The compressive strength end of the reinforcing bar, a center hole hydraulic jack of concrete (ƒ’c) and the splitting tensile strength of con- and load cell were placed on the bar, completed with an crete (ƒt) measured at test date for each specimen are end anchorage affixed to the bar end. provided in Table 2.

CRSI Research Note 3 Table 2 – Summary of Test Results For the multiple bar specimens,

Specimen f'c (psi) ft (psi) T1 (ksi) T1 (k) S1 (in) Failure Mode reactions for the horizontal force cou- BE-5-180-0 6580 490 60.7 18.8 0.002 Y ple were provided by two HSS tubes BE-5-180-22.5 6420 480 61.2 19.0 0.016 Y tensioned to the strong floor and a BE-5-180-45 5910 430 61.0 18.9 0.015 Y load frame tensioned to the strong BE-5-180-90 6690 410 61.3 19.0 0.050 Y floor, illustrated in Figure 8. The top BE-5-90-0 6150 450 60.3 18.7 0.034 Y BE-5-90-22.5 6130 420 60.9 18.9 0.014 Y beam reaction mechanism was simi- BE-5-90-45 6360 390 61.3 19.0 0.021 Y lar to the single bar specimens. Force BE-5-90-90 6590 460 59.0 18.3 0.004 Y to the lead end of the reinforcing bar BE-8-90-0 6570 440 62.1 49.0 0.028 Y Single Bar Specimens Bar Single was applied using a similar hydraulic BE-8-90-22.5 6610 410 60.8 48.0 0.065 Y jack and load cell arrangement placed BE-8-90-45 6610 400 60.1 47.5 0.007 Y BE-8-90-90 6480 440 59.5 47.0 0.012 Y on each reinforcing bar. The hydraulic Bar A 65.7 20.4 0.072 Y jack for each bar was manifolded in BE-5-90-0-G0.5A 4970 410 Bar B 67.3 20.8 0.108 Y parallel to ensure equal pressure from Bar A 62.4 19.4 0.074 Y BE-5-90-0-GA 5350 380 the pump; loads applied to each bar Bar B 66.4 20.6 0.068 Y were carefully monitored during test- Bar A 64.4 20.0 0.096 C BE-5-90-0-G2A 4840 380 ing to provide equal load distribution. Bar B 64.6 20.0 0.004 Y, C Bar A 67.4 20.9 0.071 Y BE-5-90-22.5-G0.5A 4840 420 Bar B 67.2 20.8 0.092 Y During testing, the applied force in Bar A 60.1 18.6 0.100 Y each bar was measured using a load BE-5-90-22.5-GA 4970 410 Bar B 63.8 19.8 0.081 Y cell. Slip was measured using linear Bar A 61.8 19.2 0.054 Y BE-5-90-22.5-G2A 4840 380 variable displacement transducers Bar B 66.7 20.7 0.052 Y (LVDTs) and displacement wires posi- Bar A 50.9 40.2 0.066 C BE-8-90-0-G0.5A 4470 410 tioned at the free end of the bar and Bar B 53.0 41.9 0.074 C Bar A 65.7 51.9 0.055 Y, C various locations along the embedded

Muiltiple Bar Specimens BE-8-90-0-GA 4850 450 Bar B 61.9 48.9 0.027 Y, C hook. Strain in the bar was measured Bar A 63.8 50.4 0.050 C BE-8-90-0-G2A 5020 420 at the free end and various positions Bar B 64.6 51.0 0.036 C along the embedded hook with elec- Bar A 62.9 49.7 0.201 S BE-8-90-22.5-G0.5A 4260 450 tronic strain gages affixed to the bar. Bar B 67.9 53.7 0.230 S Bar A 63.3 50.0 0.081 Y The load was applied incrementally, BE-8-90-22.5-GA 5310 410 Bar B 66.9 52.8 0.070 Y which typically resulted in 36 load Bar A 33.5 26.5 0.077 C stages for the both #5 and #8 bars BE-8-90-22.5-G2A 4450 410 Bar B 36.7 29.0 0.057 C based on a nominal yield strength of 60 ksi. At each load stage, the load

(a) side view (a) side view

(b) top view (b) top view

Figure 7 ‒ Single bar specimen test setup Figure 8 ‒ Multiple bar specimen test setup

4 Evaluation of the Orientation of 90° and 180° Reinforcing Bar Hooks in Wide Members [RN 2009-02] was applied and held constant. Table 3 – Specimen Groups and Results

Once the load stabilized, elec- / Specimen f'c,avg (psi) , T1 (ksi) T1* (ksi) S1 (in) Failure Mode ′ ′ tronic data were recorded. Be- BE-5-180-0 𝒇𝒇 𝒄𝒄0.99𝒂𝒂𝒂𝒂𝒂𝒂 𝒇𝒇 𝒄𝒄 60.7 59.9 0.002 Y BE-5-180-22.5 1.00 61.2 61.1 0.016 Y havior of the specimens such 6400 BE-5-180-45 1.04 61.0 63.5 0.015 Y as cracking, bar slip, and failure Group 1 BE-5-180-90 0.98 61.3 60.0 0.050 Y was observed and documented BE-5-90-0 1.01 60.3 61.1 0.034 Y at each load stage. BE-5-90-22.5 1.01 60.9 61.7 0.014 Y 6307 BE-5-90-45 1.00 61.3 61.1 0.021 Y Group 2 All specimens were tested BE-5-90-90 0.98 59.0 57.7 0.004 Y BE-8-90-0 1.00 62.1 62.1 0.028 Y to failure. Failure was de- Single Bar Specimens BE-8-90-22.5 1.00 60.8 60.6 0.065 Y fined as one of three test-end 6567 BE-8-90-45 1.00 60.1 59.9 0.007 Y Group 3 modes: reinforcing bar yield- BE-8-90-90 1.01 59.5 59.9 0.012 Y ing, excessive concrete crack- BE-5-90-0-G0.5A Bar A 0.99 65.7 65.3 0.072 Y 4905 ing, or reinforcing bar slip. The Grp 16 BE-5-90-22.5-G0.5A Bar A 1.01 67.4 67.8 0.071 Y reinforcing bar yield mode was BE-5-90-0-GA Bar A 0.98 62.4 61.3 0.074 Y 5160 characterized by a plateau in Grp 17 BE-5-90-22.5-GA Bar A 1.02 60.1 61.2 0.100 Y BE-5-90-0-G2A Bar A 1.00 64.4 64.4 0.096 C the force - displacement or 4840 force - strain plot monitored Grp 18 BE-5-90-22.5-G2A Bar A 1.00 61.8 61.8 0.054 Y BE-8-90-0-G0.5A Bar A 0.99 50.9 50.3 0.066 C during testing. Concrete crack- 4365 ing was monitored visually and Grp 19 BE-8-90-22.5-G0.5A Bar A 1.01 62.9 63.6 0.201 S BE-8-90-0-GA Bar A 1.02 65.7 67.3 0.055 Y, C audibly during testing; cracking 5080 Multiple Bar Specimens - Bar A typically destroyed the con- Grp 20 BE-8-90-22.5-GA Bar A 0.98 63.3 61.9 0.081 Y BE-8-90-0-G2A Bar A 0.97 63.8 62.0 0.050 C crete confinement in the hook 4735

Grp 21 BE-8-90-22.5-G2A Bar A 1.03 33.5 34.5 0.077 C vicinity, which usually led to bar BE-5-90-0-G0.5A Bar B 0.99 67.3 66.8 0.108 Y pullout. Excessive slip of the re- 4905

Grp 32 BE-5-90-22.5-G0.5A Bar B 1.01 67.2 67.6 0.092 Y inforcing bar was characterized BE-5-90-0-GA Bar B 0.98 66.4 65.2 0.068 Y by large movement recorded in 5160 Grp 33 BE-5-90-22.5-GA Bar B 1.02 63.8 65.0 0.081 Y the lead bar LVDT, and defined BE-5-90-0-G2A Bar B 1.00 64.6 64.6 0.004 Y, C 4840

as slip greater than 0.12 in. Grp 34 BE-5-90-22.5-G2A Bar B 1.00 66.7 66.7 0.052 Y

BE-8-90-0-G0.5A Bar B 0.99 53.0 52.4 0.074 C 4365

Results Grp 35 BE-8-90-22.5-G0.5A Bar B 1.01 67.9 68.8 0.230 S BE-8-90-0-GA Bar B 1.02 61.9 63.3 0.027 Y, C General – A summary of 5080 Multiple Bar Specimens - Bar B

Grp 36 BE-8-90-22.5-GA Bar B 0.98 66.9 65.4 0.070 Y the test results is provided in BE-8-90-0-G2A Bar B 0.97 64.6 62.7 0.036 C Table 2 with the failure mode 4735

Grp 37 BE-8-90-22.5-G2A Bar B 1.03 36.7 37.8 0.057 C of each specimen identified by yielding (Y) of the bar, concrete cracking (C), and/or slip (S) of the reinforcing bar. The failure mode of all single bar stress (T1) was normalized to the average group bar specimens was by bar yielding, while the failure concrete compressive strength by the factor √ƒ’c,avg ̸ƒ’c mode of the multiple bar specimens varied. As shown to account for the minor differences in measured con- in Table 2, the maximum bar stress or force is termed crete compressive strength (Ehsani, et al. 1995). T1, and the corresponding displacement at the bar end is denoted S1. Note the values of S1 were corrected to Effect of Hook Tilt Angle – For the single bar spec- account for bar elongation. For the multiple bar speci- imens, all bars at the four tilt angles were able to de- mens, Bar A refers to the exterior bar closest to the velop yielding at approximately 60 ksi, irrespective of side edge, and Bar B refers to the interior bar. tilt angle as shown in Figure 9. For the concrete compressive strength at testing, the tilt angle did not have The influence of the different test variables was an effect on the displacements of the reinforcing bar. evaluated by comparing the reinforcing bar stress-displacement relationships for different groups of speci- The graphs in Figures 10 and 11 show that the mens. Specimens were grouped to isolate a single maximum normalized bar stress was similar among all test variable, either hook tilt angle, bar size, hook type, multiple-bar specimens, at approximately 60 ksi, ex- number of bars, or bar position, while holding other cept for a few that cracked before yielding. The data test variables constant. Table 3 presents the specimen showed that the #5 bars generally yielded, while the #8 groups discussed in this research note; full results are bars exhibited one of the three failure modes. The dif- discussed in Podhorsky (2011). To compare the per- ferent failure modes were likely due to the higher force formance of specimens within a group of either single transfer to the concrete in bond required in order to bar specimens or multiple bar specimens, maximum yield the #8 bars versus the #5 bars. Even though the

CRSI Research Note 5 Figure 9 ‒ Influence of tilt angle on maximum normalized bar stress for Groups 1 to 3 (single bar specimens)

Figure 10 ‒ Influence of tilt angle on maximum normalized bar stress for Groups 16 to 21 (multiple bar specimens – Bar A, exterior bar) stresses were similar, the displacements were much Effect of Bar Size – The testing showed that the different. The displacements of the multiple bar speci- maximum normalized bar stress was similar for both mens were generally higher than the displacements of the #5 and #8 bars. The bar displacements varied for the single bar specimens. the single bar specimens, but not enough of a data trend could be established.

6 Evaluation of the Orientation of 90° and 180° Reinforcing Bar Hooks in Wide Members [RN 2009-02] Figure 11 ‒ Influence of tilt angle on maximum normalized bar stress for Groups 32 to 37 (multiple bar specimens – Bar B, interior bar)

In the multiple bar specimens, the testing showed When the single and multiple bar tests were com- the maximum normalized bar stress was similar among pared, the testing revealed closer spacing of multiple all specimens, except for those tests for which con- bars results in an increase in reinforcing bar slip or crete cracking was the failure mode. The data showed displacement relative to the concrete. At a close spac- the #5 bars generally yielded, while the #8 bars exhib- ing, one reinforcing bar and its bond behavior with the ited different failure modes. As addressed previously, concrete clearly has an effect on the adjacent rein- the different failure modes were likely due to the higher forcing bar and its bond behavior. This adjacent bar force that must be transferred to the concrete in bond influence was shown to increase with a closer spacing in order to yield the #8 bars versus the #5 bars. of reinforcing bars. For the larger bar spacings, the normalized, single bar displacements were similar to Effect of Hook Type – This variable was studied those of the multiple bar specimens with an A or 2A only in the single bar specimens. Test results revealed spacing (wide spacing). This indicates the bars were that there was little difference between the 90° and spaced sufficiently apart to avoid the overlap of the 180° hooks studied. This observation corroborates bond stresses. similar conclusions from various testing programs conducted at the University of Texas. Conclusions and Recommendations Multiple Bar Spacing – A variable spacing of the This study was conducted to investigate the poten- three reinforcing bars was studied, with the spacing tial influence of hook tilt angle on the performance of based on the standard reinforcing hook geometry: reinforcing bars hooks. This was approached experi- 0.5A, A and 2A. Generally all multiple bar specimens mentally by comparing the bar stress-displacement reached similar maximum normalized bar stress, ex- responses in 24 modified beam-end specimens with cept for when the cracking failure mode governed. For different hooked bar orientations and configurations. the exterior bar (Bar A), the #5 bar size exhibited no Twelve specimens included a single bar, and 12 speci- influence regarding bar spacing. On the contrary, the mens included three bars. To isolate the performance #8 exterior located bars exhibited increased lead bar of the bar hook, only the hooked portion of each bar slip with a closer bar spacing. Johnson and Jirsa’s was bonded to the surrounding concrete. (1981) study also reported this trend. For the single interior bar (Bar B), both the #5 and #8 bars exhibited All single bar specimens were able to achieve bar increased lead bar slip with closer bar spacing. yielding, and no concrete crushing was observed in the test specimens after failure. On the other hand, the multiple bar specimens, which had a lower average concrete

CRSI Research Note 7 compressive strength than the single bar specimens, ex- Concrete Reinforcing Steel Institute - CRSI (2008), hibited different modes of failure including bar yielding, CRSI Design Handbook, Schaumburg, Illinois, 788 pp. concrete cracking, and excessive slip. Ehsani, M.R., Saadatmanesh, H., and Tao, S. Results showed no clear relationship between hook (1995), “Bond of Hooked Glass Fiber Reinforced Plas- tilt angle and hook performance, and for the specimens tic (GFRP) Reinforcing Bars to Concrete,” ACI Materi- tested in this study, hook tilt angle did not appear to have als Journal, Vol. 92, No. 4, American Concrete Insti- an effect on the maximum stress or displacement of the tute, July-August, pp. 391-400. reinforcing bar. Similar to results found in previous stud- ies, results generally indicated that bar slip (displace- Jirsa, J.O. and Marques, J.L.G. (1972), “A Study ment) increased with closer bar spacing in specimens of Hooked Bar Anchorages in Beam-Column Joints,” with multiple bars. Final Report, Project 33, Reinforced Concrete Re- search Council, Department of Civil Engineering, Acknowledgements Structures Research Laboratory, University of Texas at Austin, 79 pp. This research was conducted by Missouri University of Science and Technology (Missouri S&T) with the spon- Marques, J.L.G. (1973), “Study of Anchorage Ca- sorship of the Concrete Reinforcing Steel Institute (CRSI) pacities of Confined Bent-Bar Reinforcement,” Ph.D. and the National University Transportation Center at Mis- Thesis, Rice University, Houston, Texas, 215 pp. souri S&T. Longitudinal reinforcing steel and bar supports used in this work were generously provided by Ambas- Marques, J.L.G. and Jirsa, J.O. (1975), “A Study of sador Steel Corporation and Gateway Building Products. Hooked Bar Anchorages in Beam-Column Joints,” ACI Journal, Proceedings, Vol. 72, No. 5, May, pp. 198-209. References Minor, J. and Jirsa, J.O. (1975), “Behavior of Bent American Concrete Institute - ACI Committee Bar Anchorages,” ACI Journal, Proceedings, Vol. 72, 318 (2011), Building Code Requirements for Struc- No. 4, April, pp. 141-149. tural Concrete (ACI 318-11) and Commentary (ACI 318R-11), Farmington Hills, Michigan, 503 pp. Minor, J. and Jirsa, J.O. (1971), “A Study of Bent Bar Anchorages,” Rice Structural Research Report ASTM International - ASTM A944 (2010), Stan- No. 9, Department of Civil Engineering, Rice Univer- dard Test Method for Comparing Bond Strength of sity, Houston, Texas, 65 pp. Steel Reinforcing Bars to Concrete Using Beam-End Specimens, ASTM A944 - 10, ASTM International, Podhorsky, N.L. (2011), “Evaluation of the Orien- West Conshohocken, PA, 4 pp. tation of 90° and 180° Reinforcing Bar Hooks,” M.S. Thesis, Missouri University of Science and Technol- ogy, Rolla, Missouri, 174 pp.

Contributors: The principal authors on this publication are Nicole L. Witushynsky (née Podhorsky) and Lesley H. Sneed, Ph.D., PE, of Missouri University of Science & Technology. This document represents a summary of their CRSI research project on the subject topic; the final report should be referenced for more information on the topic research.

Keywords: Development length, standard hook, tilt, deformed bar, reinforcement, reinforced concrete

Reference: Concrete Reinforcing Steel Institute-CRSI [2013], “Evaluation of the Orientation of 90° and 180° Reinforcing Bar Hooks in Wide Members,” CRSI Research Note RN 2009-2, Schaum- burg, Illinois, 8 pp. 933 North Plum Grove Rd. Note: This publication is intended for the use of professionals competent to evaluate the signifi- Schaumburg, IL 60173-4758 cance and limitations of its contents and who will accept responsibility for the application of the p. 847-517-1200 • f. 847-517-1206 material it contains. The Concrete Reinforcing Steel Institute reports the foregoing material as a www.crsi.org matter of information and, therefore, disclaims any and all responsibility for application of the stated principles or for the accuracy of the sources other than material developed by the Institute. Regional Offices Nationwide A Service of the Concrete Reinforcing Steel Institute The opinions and findings expressed in this Research Note are those of the researchers and do not ©2013 This publication, or any part thereof, may not be necessarily reflect the opinions or recommendations of the Concrete Reinforcing Steel Institute. reproduced without the expressed written consent of CRSI.

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