20 mm Reinforcing Bar - TCVN (Vietnam)
20 mm is a TCVN (Vietnam) reinforcing bar to TCVN 1651-2 / TCVN 5574. Its nominal diameter is 20 mm, giving a cross-section area As of 314.2 mm² and a mass of 2.466 kg/m. It is supplied in grade CB300-V / CB400-V / CB500-V with characteristic yield f_yk = 400 MPa. The tables below give the total steel area for 1-10 bars and the area per metre of width at common bar spacings.
| d | Nominal diameter | 20 mm |
| As | Cross-section area | 314.2 mm² |
| m | Mass per metre | 2.466 kg/m |
| u | Nominal perimeter | 62.8 mm |
| f_yk | Characteristic yield | 400 MPa |
| Bars | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| As (mm²) | 314 | 628 | 943 | 1,257 | 1,571 | 1,885 | 2,199 | 2,514 | 2,828 | 3,142 |
| s (mm) | 75 | 100 | 125 | 150 | 175 | 200 | 250 | 300 |
|---|---|---|---|---|---|---|---|---|
| As/m (mm²/m) | 4,189 | 3,142 | 2,514 | 2,095 | 1,795 | 1,571 | 1,257 | 1,047 |
Source: TCVN 1651-2 / TCVN 5574. Area = π/4 × d² for metric bars; ASTM areas are the standard's tabulated nominal values. Grades available: CB300-V, CB400-V, CB500-V.
Understanding these values
20 mm is a ribbed reinforcing bar to TCVN 1651-2 / TCVN 5574, the Vietnamese standard used with TCVN 5574 for concrete design. It is produced in the CB grade system - CB300-V / CB400-V / CB500-V - where the number in the grade name is the yield strength in MPa, so the grade you specify sets f_yk directly (400 MPa for the primary grade here). Its nominal diameter is 20 mm, which gives a cross-sectional area As of 314.2 mm² from pi/4 times the diameter squared, and a mass of 2.466 kg/m - so a 12 m length weighs about 29.6 kg. The nominal perimeter, used in bond and anchorage calculations, is 62.8 mm.
It is supplied in CB300-V, CB400-V, CB500-V, and unlike the European B500 system the number in a CB grade IS the yield strength - CB400-V means f_yk = 400 MPa. The primary grade here gives f_yk = 400 MPa, so changing grade changes the design strength directly rather than only the ductility class. The grade affects the strength you design to, not the geometry: the area of 314.2 mm² and the mass of 2.466 kg/m are the same whichever grade of TCVN (Vietnam) bar is specified.
For slabs and walls the number you need is area per metre width, which is the bar area times 1,000 divided by the spacing. At 150 mm centres 20 mm gives 2095 mm²/m, at 200 mm centres 1571 mm²/m, and at 250 mm centres 1257 mm²/m. Compare those against the As,req from your slab design, take the first arrangement that satisfies it, and then check the spacing against the maximum bar spacing TCVN 5574 allows for crack control - a larger bar at wider centres can meet the area and still fail that limit.
If you are working across standards, the nearest equivalents by area are EN / Eurocode 20 mm at 314.2 mm² (effectively identical), ASTM (US) #6 (No. 6) at 284 mm² (10% smaller), BS (UK) H20 (20 mm) at 314.2 mm² (effectively identical). Matching on area is the right first step, but it is not a code-sanctioned substitution: changing standard means re-checking anchorage length, lap length, bond and crack width, because those depend on bar surface geometry and the concrete, not on area alone.