Definition of spiral per ACI code

[stillfan1]

I have always been under the impression that if you have a continuous helix shaped transverse bar it was a spiral. Today I had an individual point out that the ACI318-14 R25.7.2.3 states that a circular continuously wound bar or wire is considered a spiral if it conforms to 25.7.3 (volumetric spiral ratio equation) otherwise, it is considered a tie. I thought spirals were ties? And if it is considered a tie, in a round pile, what is the longitudinal rebar spacing requirement. Is it the same as a rectilinear tie, with 6" spacing max unless additional transverse rebar is provided?

 

[HTURKAK]

Volumetric spiral ratio equation is one of the requirements and described 25.7.3.3. You must comply with the other requirements ..
25.7.3.1 thru 25.7.3.1 ...




Longitudinal bars is described in section 10.7.3.1 in ACI 318-14. For rectangular and square columns , minimum four bars at each corner specified. Circular columns could have 3 bars for triangular tie and 6 bars for circular ties.

There are other limitations for columns in a SMF ...the max. spacing of 14 in. is defined for SMF columns and 8 in. max. spacing for conditions given in Section 18.7.5.2(f) in ACI 318-14.

 

[stillfan1]

The code, is very vague when it comes to the lateral tie spacing vs longitudinal bar requirements. When you read Sokai and Sheikh 1989 publication I think it becomes very apparent that more direction is needed in this area. 16db in my case allows for 22" transverse spacing with 6" longitudinal spacing without additional ties with rectilinear tie. So what is the relationship between the lateral bars and the longitudinal bars with circular or hoops. I understand that the circular shape vs rectilinear provides different failure modes amd that the circular ties are going to provide more lateral support, but what is that relationship?

If the lateral bar spacing is decreased, how does that translate to the spacing of the longitudinal bars. For columns, it says that the longitudinal bars steel ratio should be 1-8%. Under section 10.3.1.2 you can reduce the bar area by 2 if the strength requirements are meet. Which means that your vertical bars need to meet a .5% to 4% area ratio. That is a pretty large tolerance and seems to me that it is left to the engineers judgement as to what ratio of rebar spacing they want to use.

I would appreciate it if someone would point me in the direction of any other literature out there that provides more guidance in respect to confinement and ductility based on transverse to longitudinal reinforcing parameter.

Thank you