A code like B420C on a drawing specifies exact strength and ductility properties, not just a generic grade of steel. Misreading it changes how a structure actually performs under load.
What the letters and numbers mean
In reinforcement steel codes such as B420C, B identifies it as reinforcing bar, 420 states the characteristic yield strength in megapascals, and the final letter, typically A, B or C, indicates the ductility class, with C representing the highest ductility, most relevant in seismic design where the steel needs to deform without fracturing under repeated load reversal.
Structural steel grades for plate and section work, such as S355, follow a related but separate convention, where S identifies structural steel and the number states the minimum yield strength in megapascals.
Why the ductility class matters in seismic zones
In earthquake resistant design, the ductility class is not a secondary detail but a governing parameter, since a structure's ability to absorb seismic energy without brittle failure depends directly on the reinforcement's capacity to yield and deform predictably rather than snap.
Turkish seismic design codes specify minimum ductility class requirements for critical structural elements, and substituting a lower class steel because it happens to be available is a code compliance failure, not a minor material swap.
Confirming what actually arrives on site
Mill certificates accompanying a steel delivery state the actual grade and ductility class of that specific batch, and checking this against the drawing's specification before the steel is placed, not after, is the only way to confirm the material on site actually matches what was designed.