Timber Nail

How it calculates

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 ≤ 1.0

Type 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 colour-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.