Standard H-beams have an elongation of 15-25% in tensile tests. This measures the percentage increase in length before fracture: a 20% elongation means a 100mm sample stretches to 120mm before breaking. High elongation indicates ductility, allowing the beam to deform under stress without sudden failure-critical for absorbing impacts (e.g., earthquakes, collisions). Elongation is lower in high-strength grades (15-20%) compared to standard grades (20-25%), reflecting the strength-ductility trade-off. Specifications like ASTM A6 require minimum elongation values to ensure structural safety, with testing ensuring compliance.