Rebar and Structural Steel

Iranian reinforcing bars come in three main grades. A2, with a yield strength of 340 MPa, is semi-hard deformed bar used mostly for stirrups and transverse reinforcement. A3, at 400 MPa, is the standard longitudinal bar in beams, columns and foundations. A4, at 500 MPa, appears in special and pre-stressed structures. The difference is not only strength: ductility and bendability differ too. A4 bar is unsuitable for the tight bends of stirrups and will crack at the bend.

The weight per metre follows a simple rule: diameter squared divided by 162. A 16 mm bar therefore weighs about 1.58 kg/m. This is a practical check against underweight deliveries. If the weighbridge figure for a bundle falls more than 3 to 4 per cent below the calculated weight, the actual diameter is smaller than nominal and the steel area is less than the designer assumed. Standard bars are 12 m long and carry the mill name and grade rolled into the surface.

The most frequent execution error is swapping in a higher grade or different diameter without the structural engineer's approval. Seismic design relies on ductility, and stronger but less ductile steel can shift where the plastic hinge forms. Other recurring mistakes include shortening lap lengths, omitting spacers so the concrete cover is lost, and leaving stirrup hooks straight instead of bending them 135 degrees. All three reduce the frame's performance in an earthquake.

Light orange surface rust is harmless and even slightly improves bond, but flaking rust that peels off in layers means the section has lost material and the bar should be rejected. Do not store rebar directly on bare soil or in standing water.