1. Design action and bolt
Strength limit state action effect in shear.
Bolt diameter used for φ, k16 qualification, spacing guidance and washer guidance.
Table 2.2
Clause 2.4.1.1 / Table 2.3
2. Timber condition and side plates
Table 4.12
beff is the timber thickness that is actually effective in developing the bolt-bearing capacity at the shear interface. It is not always the total physical thickness of all connected timber pieces.
Clause 4.4.3.2 / Figure 4.7
Clause 4.4.2.4 / Tables 4.9 & 4.10
What does effective timber thickness beff mean in real construction?
Imagine looking through the connection along the bolt. The bolt passes through one or more timber members, and the load is transferred across one or more shear interfaces. AS 1720.1 does not always use the total bolt grip length as the timber thickness for capacity. Instead, beff represents the thickness of timber that is effective at the relevant interface for the particular joint configuration.
For load parallel to grain — Table 4.9(A):
• Two-member joint: beff = the smaller of t1 and t2.
• Three-member joint: beff = the smaller of t2 and 2t1.
• Multiple-member joint: beff is determined separately at each interface from the adjacent member thicknesses shown in Table 4.9(A).
For load perpendicular to grain — Table 4.10(A):
beff is defined differently and depends on the connection configuration. For example, for the two-member configuration shown in Table 4.10(A), beff = 2t1.
Simple physical example: if two timber members are 45 mm and 70 mm thick and the load is parallel to grain, the two-member rule gives beff = min(45, 70) = 45 mm. The extra thickness of the 70 mm member does not increase the single-interface capacity beyond the effective thickness defined by the Standard.
Tables 4.9(A) and 4.10(A)
Imagine looking through the connection along the bolt. The bolt passes through one or more timber members, and the load is transferred across one or more shear interfaces. AS 1720.1 does not always use the total bolt grip length as the timber thickness for capacity. Instead, beff represents the thickness of timber that is effective at the relevant interface for the particular joint configuration.
For load parallel to grain — Table 4.9(A):
• Two-member joint: beff = the smaller of t1 and t2.
• Three-member joint: beff = the smaller of t2 and 2t1.
• Multiple-member joint: beff is determined separately at each interface from the adjacent member thicknesses shown in Table 4.9(A).
For load perpendicular to grain — Table 4.10(A):
beff is defined differently and depends on the connection configuration. For example, for the two-member configuration shown in Table 4.10(A), beff = 2t1.
Simple physical example: if two timber members are 45 mm and 70 mm thick and the load is parallel to grain, the two-member rule gives beff = min(45, 70) = 45 mm. The extra thickness of the 70 mm member does not increase the single-interface capacity beyond the effective thickness defined by the Standard.
Tables 4.9(A) and 4.10(A)
3. Bolt arrangement — automatic n and na
Grain direction →
→
↓
Rows counted parallel to the load direction for na.
Use only when your na is not one of the explicitly tabulated values or your engineering basis requires it.
Table 4.12: na = total number of rows of fasteners per interface. For a 3 × 2 grid:
horizontal load gives na = 3; vertical load gives na = 2. Total bolts remain n = 6.
4. Characteristic single-bolt system capacity Qsk
Derive from Table 4.9(A) using Qkl from Table 4.9(B)/(C), as applicable.
Derive from Table 4.10(A) using Qkp from Table 4.10(B)/(C), as applicable.
Clause 4.4.2.4: this calculator allows only the two principal directions requested: Qsk = Qskl for load parallel to grain and Qsk = Qskp for load perpendicular to grain.
This calculator intentionally does not reproduce the full Tables 4.9(B)/(C) and 4.10(B)/(C). Enter the characteristic values from your licensed copy of AS 1720.1 for the selected joint group, effective thickness and bolt diameter.
5. Detailing inputs
Clause 4.4.4.2
For the parallel-to-grain arrangement, Figure 4.9(a) shows 5D between bolts along the load direction.
Check Figure 4.9 for the selected load-to-grain orientation.
Spacing, edge and end distances are governed by Clause 4.4.4 and Figure 4.9. The calculator performs only the direct checks that can be assigned unambiguously from the selected inputs; always review the figure for the complete geometry.
6. Result
φ
—
k1
—
k16
—
k17
—
n bolts
—
na rows/interface
—
Qsk
—
Nd,j
—
7. Step-by-step calculation and clause traceability
8. Reference map used by this calculator
Item
AS 1720.1 reference
Calculator use
Type 1 bolt capacity
Clause 4.4.3.2, Eq. 4.4(3)
Nd,j = φ k1 k16 k17 n Qsk
Capacity factor φ
Clause 2.3 / Table 2.2
Selected from bolt size (≤M16 or >M16) and joint category.
Duration factor k1
Clause 2.4.1.1 / Table 2.3
Uses the laterally loaded fastener column.
Metal side-plate factor k16
Clause 4.4.3.2 / Figure 4.7
1.2 only when the stated metal side-plate, close-fit and beff/D conditions are satisfied; otherwise 1.0.
Multiple-fastener factor k17
Table 4.12
Depends on timber condition and na, the total number of fastener rows per interface.
Characteristic system capacity Qsk
Clause 4.4.2.4; Tables 4.9 and 4.10
Parallel-to-grain or perpendicular-to-grain system capacity, as selected by the user.
Spacing/end/edge distances
Clause 4.4.4 / Figure 4.9
Detailing check; bolt spacings are centre-to-centre.
Washers
Clause 4.4.5 / Table 4.11
Minimum washer guidance for timber-to-timber structural bolted joints.
Engineering note: this tool addresses the AS 1720.1 Type 1 timber-joint capacity expression only. It does not replace checks for connected-member net section, splitting, eccentricity, steel plate strength, bolt steel strength where relevant, durability/corrosion, fire, serviceability, or project-specific load combinations.