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In BS4449:1997 it species a re-bend test of steel reinforcement where
reinforcing steel is bent 45o at 100oC for an hour and then bent back by 23o.
The purpose of re-bend test is to measure the effect of strain ageing on steel. Strain ageing has embrittlement effect which takes place after cold deformation by diffusion of nitrogen in steel. Hence, there is limitation stated in some design codes to restrict the nitrogen content of steel to 0.012%.