Development Length Calcs - Transverse Reinforcement

[littleherb]

According to ACI 318-14 Section 25.4.2.3, the development length of a bar can be reduced when considering the confining effects of transverse reinforcement. Does the code require this transverse reinforcement to be fully developed on both sides of the potential splitting plane?

The commentary discusses the removal of the transverse steel's yield strength from previous versions of the equation, as "tests demonstrate that transverse reinforcement rarely yields during a bond failure". This would imply that the transverse steel does not need to be fully developed, as it does not need to reach its full yield strength to be effective. But common sense says that it must have some embedment length or hook to provide some nominal amount of clamping force.

If it does need to be developed, can you reduce the length using the As,reqd/As,provided ratio? If so, is that based on the main bar's utilization or the transverse bar's? If the latter, how would you quantify that?

 

[r13]

If I am not mistaken, the transverse reinforcement is meant to strengthen the confining mechanism of the main reinforcement to be developed, the code is correct in that the transverse reinforcement is not likely to reach yield point. Didn't the code indicate acceptable form of the transverse reinforcement? If not, I think either stirrups, or hooked tie shall satisfy the requirement.

The reduction shall be based on the main reinforcement.

 

[Agent666]

Does the code require this transverse reinforcement to be fully developed on both sides of the potential splitting plane?

Yes, code does make this assumption and requires it. In most cases a spiral, rectangular ties, hoops or supplementary ties is assumed/implied to be used to count on the reduction in development length. If this reinforcement is not developed, it is assumed to not count towards taking that reduction in development length for the main bars. I'm surprised ACI318 does not make this clear, my own code loosely based on ACI makes it clear in the commentary.

The As,reg/As,provided ratio if applicable (i.e. not under seismic) applies to the main reinforcement only, not to ratioing effect of the confining reinforcement partially counting towards some reduction in development length of the main reinforcement.