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# Fatigue stress limit for a bar with end cogs -AS 5100.2-2017

## Fatigue stress limit for a bar with end cogs -AS 5100.2-2017

(OP)
In AS5100.2-2017 Table 2.2.5 "Permissible Tensile Fatigue Stress Ranges in Steel" provided for reinforcement an equation "150 (0.35 + 0.0026 d_1/d_b)", with d_b defined as the diameter of rebar and d_i defined as the nominal internal diameter of reinforcement bend or hook. It is not clear whether the intention of this clause is to restrict the stress range of the entire bottom rebar end-anchored by cogs to 72 MPa. Or whether the 72MPa restriction applies only to the the bent portion of the cogs. Please discuss.

Also, this equation does not place a upper limit to the bracketed-term factor applied to 150. For a straight bar, d_i approaches infinity and this implies that the stress range allows is infinity which is clearly not correct. For a straight bar, it should be 150 MPa as per the value in the previous version of this standard.

### RE: Fatigue stress limit for a bar with end cogs -AS 5100.2-2017

My understanding is

Only apply a reduction within the bent portion of the bar, I.e where the damage is.

Re the Upper limit, Yes it is an error.
It is a reduction factor, so value of the multiplier should not be greater than 1.0.

### RE: Fatigue stress limit for a bar with end cogs -AS 5100.2-2017

(OP)
Thank you Rapt for your comment. A follow on question is how to determine the elastic stress in the curved portion of a bar at a closing corner of a frame since the corner is a disturbed region and plane section remains plane does not apply.

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