Overview
ConnForge is a calculation tool implementing EC5 (EN 1995-1-1) for timber connections. Calculations are deterministic and traceable to clause references. This page documents the engineering assumptions; for the current list of supported features and checks performed, see the live capabilities section at the bottom.
Applied actions
Lateral connections (ST, STS, TST, TT, TTT)
Applied actions: Vz,Ed and NEd are taken from the user's frame analysis at the connection location. The bolt group is offset from the line of action of Vz,Ed by a distance ex (measured from the load line to the bolt group centroid), which produces a local secondary moment My,ad = −Vz,Ed · ex. This auto-eccentricity moment is resisted by the bolt group via the polar moment method (each bolt takes a share proportional to its distance from the centroid). Shear Vz,Ed and axial NEd are distributed equally across all bolts. The local moment My,ad is automatically calculated and added because frame analysis cannot capture it: the lap is modelled as a pin in the global model, but the physical offset between the line of action and the bolt centroid is real and must be designed for at the connection level.
Moment connections (STM, STSM, TSTM, TTM)
Applied actions: My,Ed, Vz,Ed and NEd are taken directly from the user's frame analysis at the joint location. The moment My,Ed is resisted by the bolt group via the polar moment method (each bolt takes a share proportional to its distance from the centroid). Shear Vz,Ed and axial NEd are distributed equally across all bolts. No local lap eccentricity moment is added — the global frame moment already represents the full moment demand at this joint, and additional eccentricity from V acting on the bolt group is not relevant for moment-resisting connections where the joint is modelled as rigid in frame analysis.
Comparison
| Aspect | Lateral connections | Moment connections |
|---|---|---|
| Configurations | ST, STS, TST, TT, TTT | STM, STSM, TSTM, TTM |
| Frame model assumption | Pin joint at the lap | Rigid joint at the centroid |
| Inputs from frame analysis | Vz,Ed, NEd | My,Ed, Vz,Ed, NEd |
| Auto-eccentricity moment | Yes — My,ad = −Vz,Ed · ex, computed from geometry | No — frame moment already covers joint demand |
| Bolt force distribution | V and N equal share; My,ad via polar moment | V and N equal share; My,Ed via polar moment |
Geometric assumptions
- a4t calculated from member geometry, not user-input
- a3t,min = max(7d, 80 mm) for loaded end always
- For α = 0° to grain: a1,min = 4d, a2,min = max(7d, 80 mm), a3t,min = 3d, a4t,min = max(7d, 80 mm)
- For α = 90° to grain: a1,min = 4d, a2,min = 4d, a3t,min = max(7d, 80 mm), a4t,min = 4d
- Single bolt: nef = 1, no row reduction
- Circular pattern (moment connections): no nef reduction (all bolts equidistant from centroid)
Load cases
Each load case represents a single combination of design actions (M, V, N) acting simultaneously, with magnitudes and signs as entered by the user. Two load cases are supported per connection (LC1, LC2), and the design check is performed against whichever case governs.
ConnForge does not automatically envelope multiple sign combinations of the same load case (e.g. ±M paired with ±V). If the connection sees load reversal under different load combinations from frame analysis, the user is responsible for entering the worst-case sign combination — typically by running the most onerous combination as LC1 and a reversal as LC2, then comparing utilisations.
kmod
- Service class and load duration combined per EC5 Table 3.1
- Single kmod applied per connection — for combined load durations, user selects the shorter (more onerous) duration
Verification basis
ConnForge calculations are unit-tested against worked examples from Porteous & Kermani, Structural Timber Design to Eurocode 5 (2nd edition). Full reference list and methodology on the verification & references page.
Current capabilities
Connection types supported
- Lateral: ST, STS, TST, TT, TTT
- Moment: STM, STSM, TSTM, TTM
- Anchorage: Ledger to Masonry/Concrete
Fasteners
- Bolts: supported — grades 4.6, 5.6, 8.8, 10.9; diameters M8 to M30 (any integer mm; ISO 4014 stress areas tabulated for M6–M30)
- Dowels: supported
- Screws: not supported — Planned
Timber grades
- Glulam (EN 14080): GL20h, GL24h, GL28h, GL32h, GL36h
- Solid softwood (EN 338, C-class): C16, C18, C22, C24, C27, C30, C35, C40
- Solid hardwood (EN 338, D-class): D30, D40, D50, D60
Checks performed
- Fastener shear capacity via Johansen yield modes — EC5 Table 8.2 / 8.3
- Fastener group polar moment analysis — EC5 §8.3
- Embedment strength with Hankinson formula — EC5 §8.5.1.1, Eq 8.31–8.33
- Rope effect contribution (capped at 25%) — EC5 §8.2.2(2)
- Effective fastener reduction nef — EC5 §8.3.1.1, Eq 8.34
- Fastener spacing and edge distance limits — EC5 Tables 8.4 (bolts) and 8.5 (dowels)
- Splitting capacity (perpendicular to grain) — EC5 §8.1.4 (Eq. 8.4)(Eaves moment connection (T|T) only)Per-bolt envelope: full M+V+N vs M-only, both faces checked, worst case governs. Geometry-only formula — independent of timber grade.
- Steel plate bearing capacity — EC3 EN 1993-1-8
- Ledger shear — EC5 §6.1.7(Ledger anchorage only)
- Ledger bearing perpendicular to grain — EC5 §6.1.5(Ledger anchorage only)
- Anchor steel shear — EN 1992-4 §6.2.3(Ledger anchorage only)
- Anchor pryout — EN 1992-4 §6.3.3(Ledger anchorage only)
- Through-bolt steel shear — EN 1993-1-8(Ledger anchorage only)
Checks NOT performed
- Timber member design (bending, shear, compression, tension of the member itself)
- Block tear-out and row tear-out at the connection
- Fire resistance
- Long-term creep deformations
- Cyclic and fatigue loading
- Seismic detailing
- Connection slip and serviceability deflections
- Weld design
- Fastener corrosion class selection
- Anchor tension modes (pullout, cone, splitting, blowout)
- Wall capacity behind fixing
- Load eccentricity / moment on ledger
National annexes & partial factors
User-editable in Settings: yes. "No NA" applies plain EC5 recommended γM values per EN 1995-1-1 itself.
| National annex | γM,connection | γM,glulam | γM2,steel | Source clause |
|---|---|---|---|---|
| United Kingdom | 1.30 | 1.25 | 1.25 | NA to BS EN 1995-1-1:2004+A2:2014, Table NA.3 |
| Ireland | 1.30 | 1.25 | 1.25 | I.S. EN 1995-1-1/NA — see National Annex |
| Germany | 1.30 | 1.25 | 1.25 | DIN EN 1995-1-1/NA:2013 — see National Annex |
| France | 1.30 | 1.25 | 1.25 | NF EN 1995-1-1/NA — see National Annex |
| Netherlands | 1.30 | 1.25 | 1.25 | NEN-EN 1995-1-1+C1+A1/NB — see National Annex |
| Sweden | 1.30 | 1.25 | 1.25 | SS-EN 1995-1-1, BFS 2011:10 EKS — see National Annex |
| No NA (plain EC5) | 1.30 | 1.25 | 1.25 | EN 1995-1-1:2004+A2:2014, Table 2.3 (recommended values) |
γM,timber is split per EC5 Table 2.3 by material category. The column above shows γM,glulam (the default-grade case). C/D solid-timber grades use γM,solid; LVL/plywood/OSB grades use γM,lvl. All three values are user-editable in Settings.
Load cases
- 2 cases per connection (LC1, LC2)
- Envelope solving: no — user runs worst-case combination manually