Overview
ConnForge calculations are verified by direct comparison against published worked examples from established structural timber engineering textbooks. Each connection type has unit tests asserting key intermediate values (embedment strength, yield modes, design capacity) against published reference values. When discrepancies are found between ConnForge and a reference source, they are investigated and either resolved or documented.
Reference standards
| Standard | Title | Role |
|---|---|---|
| EN 1995-1-1:2004 + A2:2014 | Design of timber structures: General — Common rules and rules for buildings | Primary calculation standard |
| UK NA, IS NA, DIN NA, NF NA, NEN NA, SS NA | National Annexes to EN 1995-1-1 | Country-specific partial factors and modifications |
| EN 1993-1-8:2005 | Design of steel structures: Design of joints | Steel plate bearing capacity equations |
| EN 14080:2013 | Glued laminated timber and glued solid timber — Requirements | Glulam grade properties (densities, characteristic strengths) |
| EN 338:2016 | Structural timber: Strength classes | Solid timber grade properties |
| EN 14399 / ISO 4014 | Bolt geometry and grade specifications | Fastener properties |
Verification approach
Calculations are unit-tested at the level of pure formula primitives — embedment strength fh,0,k, the k90 factor, the Hankinson formula for angled embedment, and the characteristic yield moment My,Rk. These primitives have closed-form solutions in EC5 and any drift in implementation is caught immediately by a failing test.
Higher-level outputs — yield modes, polar moment bolt force distribution, full design capacity Fv,Rd — are tested against published worked examples. When a published example uses a different convention (e.g. an older washer-diameter rule, or excludes auto-eccentricity), the test is set up to isolate the matching components and document the divergence.
Reference textbooks
Porteous & Kermani — Structural Timber Design to Eurocode 5 (2nd edition)
Primary reference for connection design worked examples. ConnForge has tests covering:
- Example 12.8.1 — Steel-to-timber moment connection, 3×3 M12 grade 4.6 bolts in C24, combined moment, shear and axial loading. ConnForge matches the published utilisation of 53.3%.
- Example 10.13.3 — 5-member overlap bolted joint, M12 grade 4.6 bolts in C18 timber. The 5-member topology has no direct TTT equivalent, so the TTT regression suite asserts only the EC5 primitives independent of joint topology: k90, fh,0,k, Hankinson at 0°/30°/60°/90°, My,Rk, β ratios, and Johansen modes g/h/j/k for sub-joint 1-2-1 (EC5 Eq. 8.7). ConnForge reproduces all four published Johansen mode values. The book's reported Fv,Rk,4 = 13.11 kN adds the full Fax,Rk uncapped to mode (k), which conflicts with the 25% rope cap of EC5 §8.2.2(2) — ConnForge follows EC5 (likely a book error). The fastener-specific rope-effect contract (zero for dowels, capped per EC5 for bolts) is also asserted.
Cross-checks against commercial software
ConnForge results have been compared against established commercial timber connection design tools. In most cases results agree closely. Where ConnForge differs, the discrepancy is investigated. Documented cases where ConnForge is the more conservative or more correct value:
- Bolt group load distribution under combined shear, axial, and moment: some tools use a simplified scalar summation that does not vectorially resolve shear and axial components against the moment-induced bolt force. ConnForge uses a full vector sum at each bolt position.
- k90 calculation: ConnForge implements EC5 Eq 8.33 strictly; some tools use approximations that differ slightly at smaller bolt diameters.
- Single-shear yield mode (c) of EC5 Table 8.2: a probable unit-handling discrepancy was identified in one cross-check tool where the characteristic yield moment was treated inconsistently between equation steps. ConnForge handles units consistently.
These notes are included for transparency, not to disparage other tools — every implementation makes interpretation choices, and an engineer using two tools should expect occasional disagreement. The goal is that when ConnForge differs, the reasoning is visible.
Reporting issues
If you find a calculation result that disagrees with a published worked example, hand calculation, or another verified tool, please report it via the in-app feedback button. Include the connection geometry, applied loads, expected value, and source of the expected value. Discrepancies are taken seriously and investigated — the verification record is kept honest by user reports.