Design code guide
Eurocode 2 strut-and-tie — §6.5 (2004) is now §8.5 (2023)
If you learned Eurocode 2 strut-and-tie from the 2004 text, you learned §6.5 and the fixed factor ν' = 1 − fck/250. The second-generation EN 1992-1-1:2023 moved the method to §8.5 and replaced that factor: the strength reduction now depends on the angle between the strut and the ties crossing it — a geometric proxy for the strain state that cracks the strut.
AStrutTie implements the 2023 rules. This page is written so you can see what carried over and what did not.
Strut strength (§8.5.2)
The design stress in a strut is limited to a fraction of the design concrete strength:
| Minimum angle θ_cs between strut and crossing tie | ν |
|---|---|
| 20° ≤ θ_cs < 30° | 0.40 |
| 30° ≤ θ_cs < 40° | 0.55 |
| 40° ≤ θ_cs < 60° | 0.70 |
| 60° ≤ θ_cs ≤ 90° | 0.85 |
| No transverse cracking — declared per 8.120 (no crossing tie, or transverse compression) | 1.00 |
- A shallow strut crossed by a tie at 25° keeps less than half the strength of one crossed at 70°. Model geometry now moves capacity directly.
- η_cc is the other change to watch: above 40 MPa it starts cutting the design strength — 0.928 at fck = 50 MPa, 0.794 at 80 MPa. High-strength concrete gives less than the nominal number suggests.
- AStrutTie takes ν = 0.40 when neither an angle nor a 8.120 declaration is available — with no basis, it gives the least favourable band rather than assuming the best case.
Nodes (§8.5.4)
In the 2023 text the node rules are unified with the strut rules rather than carrying their own separate table of factors.
- CCC — ν = 1.00; the node is governed by the struts framing into it, and a separate check can be dispensed with.
- CCT and CTT — ν comes from the same angle expression as the struts, on the basis of ties anchored inside the node.
Ties (§8.5.3)
Eurocode is a partial-factor code: safety sits in γ_C and γ_S rather than in a single resistance factor φ. AStrutTie keeps that structure — the tie factor is 1/γ_S and the concrete factor 1/γ_C — so the printed derivation matches the code's own form instead of being folded into one number.
- Steel input is taken as the characteristic value fyk. Treating it as a design value would under-provide steel by about 13% — an unsafe-side error, so the distinction is enforced.
What changed from 2004
The practical consequence: a model that passed on the 2004 rules is not automatically a pass on 2023, and the direction of the change depends on your geometry. Shallow struts get worse; well-angled struts with declared uncracked regions can get better.
| Item | 2004 | 2023 |
|---|---|---|
| Clause | §6.5 | §8.5 |
| Strength reduction | ν' = 1 − fck/250, fixed | ν from strut-to-tie angle (0.40–0.85), or 1.00 if no transverse cracking is declared |
| High-strength concrete | covered by ν' alone | additional η_cc = (40/fck)^(1/3) ≤ 1.0 on fcd |
| Nodes | separate factors per node type | unified with the strut ν expression (CCC = 1.00) |
What AStrutTie checks for you
The report shows which ν band applied, the angle it came from, and the partial factors used.
- Strut stress against ν · fcd with the θ_cs band named
- η_cc applied above 40 MPa, shown as its own term
- Node checks on the unified 2023 basis (CCC governed by struts)
- Tie steel from fyd = fyk / γ_S, with γ_S = 1.15 stated
- The conservative ν = 0.40 fallback whenever no angle and no 8.120 declaration exists
Try it on your own D-region
Switch the design code on the same model and watch which checks change — the fastest way to see what the 2023 revision does to your work.
This page summarises how the code is applied in AStrutTie; it is not a substitute for the code itself. Clause and equation numbers refer to EN 1992-1-1:2023 §8.5. National Annex values may differ from the recommended values shown.