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In my experience, nearly all engineers including myself point the toe of the bars away from each other - not following the CRSI recommendation. It is the traditional method and one would expect that if it was inadequate, the literature would be filled with failures due to this method of placing reinforcement, but I have never come across such a situation either first hand or documented in a report. It is not out of the question that such reports exist and they have not come to my attention. More to the point, if the toe pointing away method does not sufficiently develop reinforcement, then it impugns the development length formula in ACI 318. Either you have enough embedment to develop a bar or you don't!

My suggestion is that until ACI committee 318 specifically amends the embedment length requirements for this situation, bar toes pointing away from each other remains a valid way to detail retaining walls.

Reinforcement detailing at the bottom of retaining walls and in knee-joints (a beam-column joint where both beam and column terminate at the joint) is still a subject of discussion among researchers. A famous study by Nilsson and <g class="gr_ gr_32 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" id="32" data-gr-id="32">Losberg</g> in 1976 [1] demonstrated the proper orientation of reinforcing bars in such joints. Figures (a) and (b) from Darwin et al. (2016) [2] after Nilsson and Losberg (1976) [1] below show two different reinforcement configurations at the joint. The joint on the left (Figure a) can reach only 24-40% of the nominal flexural strength of the connecting members, while the joint on the right (Figure b) can reach 82-110% of the nominal flexural strength of the connecting members. The efficiency in each joint depended on the reinforcement ratio.

Bar bent inward (Figure b) performs better because it is continuously either in tension or in compression when the joint is subjected to bending moment, as shown in Figures (c) and (d). This is, however, not the case in Figure (a); the hooked bar bent outward is in tension (or in compression) at the outer face of the flange and is in compression (or in tension) at the outer face of the web (Figures c and d). Such alternate compression and tension stresses along the same bar makes it ineffective in arresting cracks resulting in reduced joint efficiency.

An additional bar placed diagonally from the outer face of the flange to the outer face of the web further enhances the joint efficiency by arresting the cracks radiating inward from the corner.

Figures (c) and (d): T-joint behavior subjected to moment: (a) bending moment and resulting shear forces; (b) strut-and-tie model. (Darwin et al. 2016 [1])

[1] Nilsson, I. H. E., and <g class="gr_ gr_44 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" id="44" data-gr-id="44">Losberg</g>, A., 1976, "Reinforced Concrete Corners and Joints Subjected to Bending Moment," ASCE Structural Division, Vol. 102, No. ST6, pp. 1229-1254.

[2] Darwin, D., Dolan, C. W., and Nilson, A. H., 2016, Design of Concrete Structures, McGraw-Hill, New York, pp. 776.

Krishna,

Please, verify for the Fig.(b) of <g class="gr_ gr_86 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins replaceWithoutSep" id="86" data-gr-id="86">first</g> diagram, the "U" frame is not proper design. No matter what type of concrete is used.

Reinforcement detailing at the bottom of retaining walls and in knee-joints (a beam-column joint where both beam and column terminate at the joint) is still a subject of discussion among researchers. A famous study by Nilsson and <g class="gr_ gr_94 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" id="94" data-gr-id="94">Losberg</g> in 1976 [1] demonstrated the proper orientation of reinforcing bars in such joints. Figures (a) and (b) from Darwin et al. (2016) [2] after Nilsson and Losberg (1976) [1] below show two different reinforcement configurations at the joint. The joint on the left (Figure a) can reach only 24-40% of the nominal flexural strength of the connecting members, while the joint on the right (Figure b) can reach 82-110% of the nominal flexural strength of the connecting members. The efficiency in each joint depended on the reinforcement ratio.

Bar bent inward (Figure b) performs better because it is continuously either in tension or in compression when the joint is subjected to bending moment, as shown in Figures (c) and (d). This is, however, not the case in Figure (a); the hooked bar bent outward is in tension (or in compression) at the outer face of the flange and is in compression (or in tension) at the outer face of the web (Figures c and d). Such alternate compression and tension stresses along the same bar makes it ineffective in arresting cracks resulting in reduced joint efficiency.

An additional bar placed diagonally from the outer face of the flange to the outer face of the web further enhances the joint efficiency by arresting the cracks radiating inward from the corner.

Figures (c) and (d): T-joint behavior subjected to moment: (a) bending moment and resulting shear forces; (b) strut-and-tie model. (Darwin et al. 2016 [1])

[1] Nilsson, I. H. E., and <g class="gr_ gr_85 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" id="85" data-gr-id="85">Losberg</g>, A., 1976, "Reinforced Concrete Corners and Joints Subjected to Bending Moment," ASCE Structural Division, Vol. 102, No. ST6, pp. 1229-1254.

[2] Darwin, D., Dolan, C. W., and Nilson, A. H., 2016, Design of Concrete Structures, McGraw-Hill, New York, pp. 776.