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NZS 3603:1993Australia

Timber Column

Column loads link from beam reactions above to footing calculations below automatically - change a load once and the whole load path updates. Design timber columns and studs to NZS 3603:1993 with checks for axial compression capacity, combined moment-compression interaction, biaxial stability (Cl 2.10), and shear about both axes.

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What it calculates

The Calcs.com timber column calculator to NZS 3603 enables the fast and accurate design of timber columns and studs to New Zealand standards. With support for dynamic load linking between beams and columns, easily design accurate and quality engineered columns.

Code standards

  • NZS 3603:1993

How it calculates

Structural model and load combinations

The calculator models the timber column as a member under combined axial compression and biaxial bending. Loads are entered by type - dead (G), live (Q), wind (W) - and governing strength and serviceability combinations are generated per NZS 1170.0/1170.1. Bending moments can be entered directly or received from linked beam calculations above.

Axial compression capacity (NZS 3603:1993 Cl 3.2.5 and Cl 2.10)

Factored axial compression capacity phi × N_n is computed from the characteristic compressive strength, adjusted by duration-of-load, moisture, and stability factors. The stability factor for compression buckling (Cl 2.10) is derived separately for the major and minor axes using the respective effective lengths and slenderness ratios (Cl 3.2.5). The lower stability factor governs, and controls how much of the full compressive resistance is available.

For grouped or laminated members, the group modification factor per Cl 2.9 is applied to account for load sharing between individual plies.

compression utilization = N* / phi × N_n ≤ 1.0

Moment capacity about each axis (NZS 3603:1993 Cl 3.2.4)

Factored moment capacity phi × M_n is computed for both the major and minor axes from the characteristic bending strength adjusted by duration-of-load, moisture, and the lateral stability factor (Cl 2.10). The stability factor for bending accounts for lateral buckling of the compression face based on the major-axis effective length.

Combined moment-compression interaction (NZS 3603:1993 Eqns 3.22-24)

When both axial compression and bending moments are present, the calculator checks the combined interaction per NZS 3603:1993 Eqns 3.22-24. Stability factors for compression buckling about each axis and for bending enter the interaction equations, which must satisfy:

interaction utilization = N*/phi×N_n + M_x*/phi×M_nx + M_y*/phi×M_ny ≤ 1.0

Shear capacity (NZS 3603:1993 Cl 3.2.3.1 and Cl 8.7.1-2)

Shear is checked about both the major and minor axes, using the characteristic shear strength and appropriate adjustment factors. For glulam members, Cl 8.7.1-2 provisions apply.

Deflection and extension checks

Three deflection limits are verified independently per span: short-term, long-term (including creep), and imposed-load deflection. For columns subject to tie-down or uplift, axial extension limits (short-term, long-term, and imposed-load) are also checked against user-defined absolute limits.

Service condition and moisture content

Moisture adjustment factors per Cl 6.3.3 are applied when the expected moisture content over a 12-month period exceeds the threshold for dry service. This reduces both strength and stiffness properties consistently across all checks.

Load linking

The column's base reaction is exported as a linked output to connected footing calculations. Axial load at the top can be linked from beam reactions above, completing the full load path from beam to column to footing automatically.

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Frequently asked questions

What design standard does this calculator use?
The calculator designs timber columns and studs to NZS 3603:1993 (Amendment 4). Stability factors for bending and compression buckling follow Cl 2.10. Effective lengths for buckling about each axis reference Cl 3.2.5. Load combinations follow NZS 1170.0 and AS/NZS 1170.1.
What are the key inputs?
Key inputs include the timber section (species, grade, and product type - or a custom section), column height, effective length factors for both major and minor axes, number of members in a group or laminate, service condition (dry or wet), and axial load plus bending moments about both axes. Loads can be entered directly or linked from beam calculations above.
What checks and outputs does it produce?
The calculator checks axial compression capacity, moment capacity about both major and minor axes (NZS 3603:1993 Cl 3.2.4), combined moment-compression interaction (Eqns 3.22-24), shear capacity about both axes (Cl 3.2.3.1), and three deflection limit states: governing short-term deflection, long-term deflection, and imposed-load deflection. Extension (axial shortening/elongation) limits are also checked for tie-down or foundation applications.
How does the combined moment-compression interaction work?
When axial compression and bending moments are both present, the calculator checks the combined interaction equations per NZS 3603:1993 Eqns 3.22-24. Stability factors for compression buckling about each axis (Cl 2.10) are computed from the effective lengths and slenderness. The interaction check ensures the combined demand does not exceed capacity when both loads act simultaneously.
Can it handle laminated and glulam columns?
Yes. Multiple members in a group or laminate are supported, with the group modification factor per Cl 2.9 applied automatically. Glulam lamination checks reference Cl C8.7.2. Effective lengths for buckling about each axis are specified independently, allowing different bracing conditions in each plane - common for wall studs with blocking in one direction only.
Does this calculator support load linking with beam and footing calculations?
Yes - axial load at the column top can be linked directly from beam reactions above, and the column's base reaction links to connected footing calculations. The full load path - beam to column to footing - updates automatically whenever any upstream input changes.

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