Column tie requirements 3

[struct_eeyore]

Shameless follow up on my previous post about tie spacing requirements in columns.

Looking at the new 318 - Section 10.7.6.1.2 directs to 25.7.2, which gives the typically known (to me) spacing of 16db long/48db tie/ least column dimension.
However, reading further, Section 10.7.5.6.1 states that " if required shear reinforcing shall be provided using ties hoops, or spirals"
It then goes on to provide a table for spacing, which seems like an additional criteria to what's in 25.7.2 - but that's beside the point.

Does 10.7.5.6.1 say that columns can be designed w/o ties if the shear is low enough? Am I missing something here?

 

[bugbus]

I'm not that familiar with ACI 318 so the below is just my general understanding / basic principles.

Even if the shear force is small, column ties are always required to (1) restrain the vertical bars against buckling and (2) confine the core concrete to improve ductility as overload is approached (and in some cases enhance the compressive strength of the concrete).

 

[ProgrammingPE]

Ties are required in concrete columns in order to laterally support the longitudinal reinforcement per Section 10.7.6.1.4. (This is what directs you to Section 10.7.6.1.2 in the first place, which then points you to Section 25.7.2 for the tie spacing of 16*db,long and 48*db,tie.)

Section 10.7.6.5 includes the requirements for shear reinforcing. It says "if required" since Section 10.6.2.1 says that a minimum area of shear reinforcement is required in regions where Vu > 0.5ΦVc. This means the requirements of Table 10.7.6.5.2 are only necessary if shear reinforcement is required.

(Chapter 9 on Beams does essentially the same thing for shear reinforcing with Section 9.6.3.1 specifying when minimum shear reinforcing is required and Table 9.7.6.2.2 setting the maximum spacing "if required".)

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