Concrete · Precast & tilt-up
Grouted duct anchorage and panel joint shear friction calculator
Starter bars from a footing or slab grouted into corrugated ducts in a precast panel. The embedment must develop the bar in the grout (development length using the grout strength, confined by the duct) and transfer the force from the duct to the surrounding concrete. The horizontal joint is checked for shear friction (clamping by the bars plus the permanent compression, coefficient μ for the joint surface).
Standard: Development of a bar in grout (AS 3600 Cl 13.1.2 basic length with grout strength, k3 = 0.7 confined) · duct–concrete bond · AS 3600 Cl 8.4 shear friction across the joint
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Bar diameter | 20 | mm |
| fsy | 500 | MPa |
| Grout strength | 60 | MPa |
| Duct internal diameter | 50 | mm |
| Panel concrete f′c | 40 | MPa |
| Embedment provided | 600 | mm |
| Bars across the joint | 4 | |
| Joint length (panel width) | 2.4 | m |
| Panel thickness | 200 | mm |
| Joint surface | Smooth / grouted bed (μ = 0.6) | |
| Design shear across the joint | 250 | kN |
| Permanent compression across the joint | 150 | kN |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| k2 = (132 − db)/100 | 1.12 | |
| Development length in grout (k3 = 0.7) | 580 | mm |
| Bar force As·fsy | 157.1 | kN |
| Duct–concrete bond stress 0.5√f′c | 3.16 | MPa |
| Length to transfer from duct to concrete | 316 | mm |
| Required embedment | 580 | mm |
| Joint shear stress v* | 0.521 | MPa |
| Shear friction strength vuf | 0.973 | MPa |
| Joint capacity φVuf | 327 | kN |
- ✓ Embedment ≥ required — 600 vs 580 mm
- ✓ Joint shear ≤ φVuf — 76 %
- ✓ Duct ≥ 2.5db for grouting tolerance
Method, formulas and assumptions
- Bar in grout: Lsy.tb = 0.5k1k3·fsy·db/(k2√f′cg) with k3 = 0.7 for the duct confinement, not less than 0.058fsy·db (AS 3600 Cl 13.1.2.2 form). Use the grout supplier's or duct manufacturer's tested values where available.
- Duct to concrete: bond 0.5√f′c on the duct's outer perimeter (approximate).
- Shear friction (Cl 8.4): vuf = μ(Asf·fsy + gp)/A ≤ 0.2f′c and 10 MPa, φ = 0.7; bars must be anchored on both sides of the joint.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.