Indeed past research showed that large-diameter reinforcing steel appeared to be weaker under fatigue loading conditions. Therefore, in some standards the stress range for testing fatigue of steel bars are reduced for increasing bar size for the same reason.
Moreover, fatigue performance of steel bars is also governed by stress concentrations at the root of ribs. Bar failure usually initiates from the root of ribs under fatigue loading. In this connection, any damage to ribs during bending process can lead to failure by fatigue.
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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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