Percentage Elongation of Reinforcement Bars

After a bar fractures during the tensile test, the two broken pieces are fitted back together and the distance between the original gauge marks is re-measured. The increase in length, expressed as a percentage of the original gauge length, is the percentage elongation.

This is the key ductility measure for reinforcement — IS 1786 sets minimum elongation values for each grade, higher for the ductility-graded bars (Fe 500D, Fe 550D) used in seismic design, since ductile bars can redistribute load and deform visibly before failure.