AustraliaAS 1720.1:2010
Design rectangular nail groups to AS 1720.1:2010. Checks direct shear capacity (Cl 4.2.3.2), in-plane moment capacity (Cl 4.2.3.3), and withdrawal capacity (Cl 4.2.3.4) for timber-to-timber and timber-to-steel connections.
Method & scope
Calculation method
Joint type and nail position
The first input is joint type and nail position, which sets two key modification factors from AS 1720.1:2010 Figures 4.2 and 4.4:- Type 1 (shear) joints, nails are loaded laterally. Side grain positions use k_13 = 1.0; end grain positions use k_13 = 0.6. Single shear gives k_14 = 1.0; double shear gives k_14 = 2.0.
- Type 2 (tension) joints, nails are loaded axially in withdrawal. Side grain uses k_13 = 1.0; end grain uses k_13 = 0.6.
Characteristic fastener capacity
For the selected nail diameter and the joint group of the receiving timber member, the calculator looks up the characteristic lateral capacity Q_k (Type 1) or the characteristic withdrawal capacity Q_wk per unit penetration (Type 2) from AS 1720.1:2010 Section 4.2 tables. Joint group is determined by the timber species and seasoning condition, a seasoned hardwood such as F17 carries a higher joint group rating than a softwood such as MGP10.Load combinations and load duration factor k_1
Applied loads (dead, live, wind, earthquake, etc.) are entered per load type. The calculator assembles AS/NZS 1170.0 strength load combinations and identifies the governing combination. The load duration factor k_1 is applied to the demand side, it reflects the characteristic strength reduction for sustained loads and takes values of 0.57 for permanent actions, 0.69 for floor live, 0.77 for roof live, 0.94 for wind, and 1.14 for earthquake.Rectangular pattern capacity, Type 1 (shear) joints
For a rectangular pattern of n_x columns and n_y rows with spacings s_x and s_y, the calculator derives: Direct shear capacity (Cl 4.2.3.2): V_d,j = joint_category_factor × k_13 × k_14 × n × Q_k where n = n_x × n_y is the total nail count. In-plane moment capacity (Cl 4.2.3.3): The polar second moment of area of the nail pattern about its centroid is computed from the spacings. The moment capacity M_d,j corresponds to the most critically loaded nail at maximum distance from the centroid, scaled by the same characteristic fastener capacity. The combined utilization for simultaneous shear and moment loading: (V* / V_d,j)² + (M* / M_d,j)² ≤ 1.0Type 2 (tension/withdrawal) joints
The withdrawal capacity per nail is derived from the characteristic withdrawal capacity Q_wk and the penetration depth t_p into the receiving member. For the full pattern: N_d,j = joint_category_factor × k_13 × n × Q_wk × t_p The demand N* is compared against N_d,j (Cl 4.2.3.4) and the utilization ratio is reported.Joint category factor
The joint category (Category 1 to 4 per AS 1720.1 Table 2.5) applies a capacity reduction factor reflecting structural risk and inspection level. Category 1 (house construction) uses base characteristic values; higher categories apply increasing reduction factors to the calculated capacity.Outputs and pattern diagram
The calculator displays a visual cross-section diagram of the nail pattern, updating in real time as geometry inputs change. Output utilization ratios are color-coded: green for pass, red for fail. Each check, Shear, Moment, and Tension, shows the demand, capacity, and utilization ratio with the corresponding AS 1720.1 clause number, making outputs directly traceable to the standard for documentation and peer review.How to use it
1
Open the calculator
Open it from Run calc in the About this calculator panel above.
2
Enter your inputs
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See Checks, References, Conditions and Assumptions.
3
Review the results and export
Check the utilization of each governing check in the summary, then export a PDF report. See Views and Export.
Common questions
What design standard does this calculator use?
What design standard does this calculator use?
AS 1720.1:2010 (Timber Structures). The calculator applies Section 4.2 of that standard to determine the design capacity of nailed connections, using characteristic values for lateral (shear) and withdrawal capacity, combined with joint category factors and load duration factor k_1.
What are the key inputs?
What are the key inputs?
Joint type and nail position (side grain or end grain; single or double shear for Type 1, or withdrawal for Type 2), nail size and type, timber species and joint group, rectangular pattern geometry (n_x nails in X, n_y in Y, spacings s_x and s_y), penetration depth t_p, joint category, and applied shear/moment or tension loads with load types for AS/NZS 1170 load combinations.
What does the calculator check and output?
What does the calculator check and output?
For Type 1 (shear) joints, the calculator outputs direct shear demand V* and capacity V_d,j (AS 1720.1 Cl 4.2.3.2), and in-plane moment demand M* and capacity M_d,j (Cl 4.2.3.3), each with a utilization ratio. For Type 2 (tension/withdrawal) joints it outputs withdrawal demand N* and capacity N_d,j (Cl 4.2.3.4). The governing utilization ratio is flagged in the calculation header.
Does the calculator support combined shear and withdrawal loading?
Does the calculator support combined shear and withdrawal loading?
The calculator supports Type 1 (lateral shear) and Type 2 (withdrawal) joints as separate modes per AS 1720.1 Figures 4.2 and 4.4. Select the joint type that matches your connection, Type 1 for nails loaded laterally in side grain or end grain, Type 2 for nails loaded axially in withdrawal. Combined shear-withdrawal is not evaluated within a single check.
Does the calculator verify nail spacing, edge distances, and detailing requirements?
Does the calculator verify nail spacing, edge distances, and detailing requirements?
The calculator checks pattern capacity under the specified load case. Minimum spacing, end distance, and edge distance requirements per AS 1720.1 Table 4.5 must be verified separately, the calculation notes this assumption explicitly. The pattern geometry diagram updates in real time as you adjust n_x, n_y, s_x, and s_y.
Next steps
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