Reinforcement and Prestressing
Reinforcement and Prestressing
This domain tests whether the reinforcement shown on the drawings is actually in place, correctly detailed and properly spliced, plus the special verification tasks on prestressed members.
Bars, grades and identification
- Soft-metric designations follow nominal diameter: No. 10 = 9.5 mm, No. 13 = 12.7 mm, No. 16 = 15.9 mm, No. 19 = 19.1 mm, No. 25 = 25.4 mm, No. 36 = 35.8 mm, No. 43 = 43.0 mm.
- Common grades are 420, 520 and 550 MPa (ASTM A615). A706 low-alloy bar is used where welding or seismic ductility is required; epoxy coating is per ASTM A775.
- Check tags and mill certificates against the approved submittal, and repair coating damage with the approved patching material.
Hooks, laps and splices
- 90° standard hook tail = 12db; 180° hook tail = 4db but not less than 65 mm; stirrup and tie hooks = 6db at 90° or 135°, not less than 75 mm.
- Tension lap splices: Class A = 1.0ld and Class B = 1.3ld. Class A needs As,provided/As,required ≥ 2 and no more than half the bars spliced at one location; otherwise use Class B.
Prestressing
- Seven-wire strand is typically Grade 1860 MPa low-relaxation to ASTM A416.
- Verify force by gauge pressure and measured elongation; elongation differing from the calculated value by more than about 7% must be investigated before acceptance.
- No welding, flame cutting or arc strikes on strand. Bonded tendons are grouted after stressing.
Worked example
A beam has four No. 25 bars where three would satisfy As,required, and all four are spliced in the same section. As,prov/As,req = 4/3 = 1.33, which is less than 2, and 100% of the bars are spliced at one location, so the splice must be Class B: 1.3ld. With ld = 1200 mm, the minimum lap is 1560 mm.
Traps
- Assuming Class A because there are extra bars, without checking both conditions.
- Using the 12db standard-hook tail for stirrups.
- Accepting a prestressing record that shows elongation but no gauge pressure.