Ties Spacing

[ASultani]

What is the spacing between ties at the start and end of the column as we used to say at the critical length of columns?

 

[JAE]

If there's a lot of bending and therefore shear, you design them the same as you would beam shear. Elsewise design them as containment reinforcement for your vertical bars and maybe add a couple extra at the top and bottom.

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[ASultani]

Bit I studied that vertical spacing shall not exceed 16 longitudinal bar diameter is this good.

 

[JAE]

1. Ties need to be placed to the maximum spacing required by the code you are designing under.
2. Ties need to be placed to the maximum spacing required based on the applied shear and on the shear capacity of the concrete with the ties.

So these two items above control your tie spacing. Whichever is a smaller spacing controls.

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[ASultani]

At the start and end the spacing shall be less and at middle when we design. The spacing should be max regarding to the code there we have codes from ACI THAT it should not exceed more that 16 longitudinal bar diameter and 48 wire diameter or least dimension of compression member but this code is for the part of colum where buckling happens and the column support is fix from both side then how to design ties at the start?

 

[jayrod12]

We can't make this any easier.

Analyze your structure. Determine the shear diagram for your column in question.

Provide ties to resist this shear.

If your applied shear does not require ties then you must provide enough to be considered confinement reinforcing which is as you've described above 16*longitudinal bar diameter or 48*tie diameter or least dimension of your column.

If you can't choose you tie spacing after this then you likely shouldn't be working on this project

 

[JFarrar]

In addition to what jayrod12 wrote above, per ACI 318-08 7.10.5.4, provide ties not more than half a tie spacing above top of footing or slab and not more than half a tie spacing below lowest horizontal reinforcing in slab, drop panel or shear cap above.

For columns with beams framing from 4 directions, per ACI 7.10.5.5, provide ties not more than 3 inches below lowest reinforcement in shallowest beam.

 

[shaneelliss]

If you are wondering about seismic cases, where chapter 21 applies, you need ties sized and spaced as dictated by the probable shear that the column will see, assuming the shear strength of concrete is zero, and based on the equation: (probable moment strength at top + probable moment strength at the bottom) / length of column, where the probable moment strength is Mn using phi=1 and Fy=1.25Fy. The max spacing is based on (smallest dimension of column / 4) or (6x diameter of longitudinal bars) or the equation (4 + ((14-hx)/3)), where hx is the smallest dimension on the confined core (inside hoops or ties). But in all cases, the spacing for the bar can't be greater than 6" or less than 4". This applies to the length of the largest of the minimum dimension of the column or overall length / 6 or 18".

 

[ASultani]

JFarrer and shaneeliss tnx I was searching the answer you guys wrote here tnx