After this chapter, you should be able to
- Classify connection type, load direction and shear planes.
- Calculate embedment strength and fastener yield moment.
- Evaluate single- and symmetric double-shear Johansen modes.
- Check smooth-nail withdrawal and pull-through.
- Apply effective fastener-number rules.
- Lay out fasteners using end, edge and spacing requirements.
- Estimate connection slip and identify excluded specialist checks.
3.1 Purpose and learning outcomesSource §3.1
This chapter develops the transparent lecture-level design of dowel-type fasteners, fastener groups, smooth-nail withdrawal and serviceability slip.
3.2 Connection types and scopeSource §3.2
Identify whether the joint is timber-to-timber or steel-to-timber, the fastener type, shear planes and load direction. Proprietary connectors, glued joints and advanced semi-rigid modelling require their own declared or specialist methods.
3.3 Loading types, ULS and SLSSource §3.3
Separate lateral shear, axial withdrawal and combined demands. ULS resistance uses kmod and γM; SLS deformation uses connection stiffness appropriate to the load and assembly.
3.4 Fundamental design procedureSource §3.4
Define members and geometry, calculate embedment and yield properties, evaluate every applicable Johansen mode, convert to design resistance, apply group effects and verify spacing, splitting and slip.
3.5 Dowel action and shear planesSource §3.5
Dowel-type fasteners transfer lateral load by timber embedment and fastener bending. Resistance is reported per shear plane and may only be combined when the physical planes are symmetric and share load as assumed.
3.6 Member thickness and nail penetrationSource §3.6
Use actual member thicknesses and point-side penetration. The source lecture route requires minimum penetration and distinguishes head-side thickness from penetration into the receiving member.
3.7 Characteristic embedment strengthSource §3.7
Embedment depends on density, diameter, predrilling and load angle to grain. Predrilling is required by the source rules when density or diameter exceeds the stated limits.
Use d in millimetres and characteristic density in kg/m³; the source also records the non-predrilled and angled-to-grain routes.
3.8 Characteristic fastener yield momentSource §3.8
Fastener yield moment represents plastic-hinge resistance and depends strongly on diameter through the 2.6 exponent.
For the lecture nail examples fu is entered in N/mm² and d in millimetres to obtain Nmm.
3.9 Timber-to-timber single-shear resistanceSource §3.9
Evaluate embedment-only, combined embedment and yielding, and two-hinge modes. Select the minimum rather than assuming a preferred failure mechanism.
All applicable Johansen modes must be evaluated; permitted rope effect is taken as zero unless explicitly established.
3.10 Symmetric timber-to-timber double-shear resistanceSource §3.10
The double-shear source expressions give characteristic resistance per plane. Total fastener resistance requires identical planes and equal load sharing.
3.11 Basic steel-to-timber classificationSource §3.11
Classify the steel plate as thin or thick and locate it externally or internally before selecting the corresponding EC5 mode set; plate yielding and fastener detailing remain relevant.
3.12 Axially loaded smooth nailsSource §3.12
Check point-side withdrawal, head-side pull-through and any reduced-penetration factor. Wet installation can reduce the lecture strength values and the governing route is the minimum.
3.13 Multiple fastener connectionsSource §3.13
Fasteners in a row may not act with full physical count. Determine the effective number using spacing-dependent group rules and then assemble rows and shear planes without double counting.
The group exponent depends on the source spacing rules; physical fastener count is not automatically the effective count.
3.14 Spacing, end distances and edge distancesSource §3.14
Lay out fasteners relative to grain and load direction using minimum parallel/transverse spacing, loaded/unloaded end distance and loaded/unloaded edge distance.
3.15 Joint slip and connection stiffnessSource §3.15
Serviceability slip can materially affect trusses, built-up members and diaphragms. Use Kser for the stated member/fastener combination and include the joint deformation in the structural system.
Joint slip contributes to system deformation and connection stiffness must match the fastener/member arrangement.
3.16 Basic interactive calculator specificationSource §3.16
The source tool exposes lateral-fastener, group, axial-nail and joint-slip inputs. This approved implementation presents the WE-03A Johansen mode transparently and records the remaining design checks.
Fundamental Timber Connection Design Calculator
Lecture-level predrilled-nail single-shear calculation with all six Johansen modes, benchmarked to WE-03A.
- Inputs
- Fastener diameter and strength · Member densities and thicknesses · kmod · γM
- Outputs
- Embedment strengths · Yield moment · Governing Johansen mode · Characteristic and design resistance
- Status states
- PASS · FAIL · INVALID INPUT
- Validation
- Approved against the supplied worked-example results; project-specific verification remains required
Fundamental Timber Connection Design Calculator
Predrilled smooth-nail single-shear Johansen calculation reproducing WE-03A, including embedment, yield moment and all six source modes.
Johansen Mode (f) governs; design resistance is 1.14 kN per nail per shear plane.
- Embedment fh,1,k
- 48.81 N/mm²
- Embedment fh,2,k
- 48.81 N/mm²
- Embedment ratio β
- 1.000
- Yield moment My,Rk
- 6617 Nmm
- Governing characteristic Fv,Rk
- 1.848 kN
- Design resistance Fv,Rd
- 1.14 kN
Show source calculation trail
fh,k = 0.082(1 - 0.01d)ρkMy,Rk = 0.3 fu d2.6 = 6617 NmmFv,Rk = min(Fa … Ff) = 1848 NFv,Rd = kmod Fv,Rk / γM = 1.14 kN
3.17 Worked Example WE-03A — single nail in a timber spliceSource §3.17
The first source example establishes embedment, fastener yield and the governing single-shear mode.
WE-03A · Single nail in a timber splice
A 4 × 60 mm smooth nail joins D50 members in single shear under SC2 medium-term loading.
- Penetration
t2 = 60 − 25 = 35 mm > 8d = 32 mm
Penetration satisfied - Embedment
fh,k = 0.082[1 − 0.01(4)](620)
fh,k = 48.81 N/mm2 - Yield moment
My,Rk = 0.3(600)(42.6)
My,Rk = 6,617 Nmm - Johansen modes
Fv,Rk = min(4,881; 6,833; 2,483; 1,975; 2,586; 1,848)
Mode (f): 1.848 kN - Design resistance
Fv,Rd = 0.8(1.848) / 1.3
Fv,Rd = 1.14 kN
Result. One nail provides approximately 1.14 kN per shear plane; Mode (f) governs.
3.18 Worked Example WE-03B — single bolt in double shearSource §3.18
The double-shear example uses different outer and middle-member densities and reports resistance per shear plane.
WE-03B · Single bolt in double shear
A 12 mm bolt connects D70 outer members to a D50 middle member with load parallel to grain.
- Embedment
fh,1,k = 64.94; fh,2,k = 44.74 N/mm2
β = 0.69 - Yield moment
My,Rk = 0.3(400)(122.6)
My,Rk = 76,745 Nmm - Double-shear modes
min(Fg, Fh, Fj, Fk) = min(19.483, 20.133, 8.981, 11.360)
Fv,Rk = 8.98 kN per plane
Result. Mode (j) governs at 8.98 kN per shear plane; doubling is valid only for symmetric, equally shared planes.
3.19 Worked Example WE-03C — axially loaded smooth nailSource §3.19
The withdrawal example combines wet-installation reduction, penetration, head pull-through and the source reduced-penetration factor.
WE-03C · Axially loaded smooth nail
A 2.65 × 40 mm smooth nail connects D24 plank to D40 stud after wet installation in SC3 short-term loading.
- Penetration
tpen = 40 − 15 = 25 mm > 8d = 21.2 mm
Minimum penetration satisfied - Reduced strengths
fax,k = 4.05; fhead,k = 11.03; fax,k,h = 3.15 N/mm2
Wet-installation reduction applied - Characteristic routes
Fax,Rk,1 = 268 N; Fax,Rk,2 ≈ 517 N
Withdrawal governs - Reduced penetration
kpen = 25/[4(2.65)] − 2 = 0.36
Fax,Rk,red = 96.5 N - Design resistance
Fax,Rd = 0.7(96.5) / 1.3
Fax,Rd ≈ 52 N
Result. The design axial resistance is approximately 52 N per nail.
3.20 Worked Example WE-03D — number and layout of nailsSource §3.20
Group effectiveness changes with parallel spacing, so an arrangement with enough physical nails may still need a layout revision.
WE-03D · Number and layout of nails
Design a nail group for FEd = 12.75 kN using the WE-03A resistance of 1.14 kN per nail per shear plane.
- Initial count
napprox = 12.75 / 1.14
Try 12 nails - First spacing
a1 = 10d; kef = 0.85; nef = 20.85
Fgroup,Rd = 12.33 kN — inadequate - Revised spacing
a1 = 60 mm > 14d; kef = 1.0
Fgroup,Rd = 13.68 kN
Result. The revised 12-nail arrangement is adequate, subject to all end, edge and transverse spacing rules.
3.21 Common mistakes and design decisionsSource §3.21
Common errors are using one mode only, confusing per-plane and total resistance, omitting predrilling/penetration, counting every fastener as fully effective, and ignoring splitting, spacing or SLS slip.
3.22 Chapter summarySource §3.22
A defensible timber connection calculation links material embedment, fastener yielding, geometry, all applicable failure modes, group layout and serviceability stiffness.
Key points
- Classify the joint and shear planes before calculation.
- Embedment strength depends on density, diameter and grain direction.
- Evaluate all applicable Johansen modes.
- Group capacity uses effective—not merely physical—fastener count.
- Spacing, splitting, axial resistance and joint slip remain explicit checks.
Source references recorded by the supplied chapter
- University of Moratuwa timber connection lectures.
- EN 1995-1-1:2004+A2:2014, connection rules.
- IStructE/TRADA Manual connection sections.
- Porteous & Kermani connection design chapters.
- Swedish Wood connection design examples.