Timber Column

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 - permanent (G), variable (Q), wind (W) - and EN 1990:2002 governing ULS combinations are generated automatically. Bending moments can be entered directly or received via load linking from beam calculations above. Deformation checks use serviceability combinations.

Material partial factor and k_mod

Characteristic strengths are divided by the material partial factor gamma_M and modified by k_mod based on service class (1, 2, or 3) and load duration class. The combination that produces the worst utilization governs.

design strength = f_k × k_mod / gamma_M

Cross-section compression (EN 1995-1-1:2004 Cl 6.1.4)

Design compressive stress sigma_c,0,d = N_d / A is checked against the design compressive strength f_c,0,d.

compression utilization = sigma_c,0,d / f_c,0,d ≤ 1.0

Bending strength about each axis (EN 1995-1-1:2004 Cl 6.1.6)

Bending stresses about the Y-axis and Z-axis are each checked against their respective design bending strengths. For rectangular sections, the same characteristic bending strength applies to both axes, adjusted by k_mod and gamma_M.

Shear strength about each axis (EN 1995-1-1:2004 Cl 6.1.7)

Shear stresses induced by forces in each plane are checked against the design shear strength f_v,d. The effective shear area accounts for the cross-section geometry.

Cross-section bending and compression interaction (EN 1995-1-1:2004 Eq 6.19 and 6.20)

When axial compression and biaxial bending are combined, the cross-section interaction is checked through two simultaneous equations (Eq 6.19 and 6.20) that weight the demands by the km factor:

interaction = sigma_c,0,d/f_c,0,d + sigma_m,y,d/f_m,y,d + km × sigma_m,z,d/f_m,z,d ≤ 1.0 interaction = sigma_c,0,d/f_c,0,d + km × sigma_m,y,d/f_m,y,d + sigma_m,z,d/f_m,z,d ≤ 1.0

Flexural buckling interaction (EN 1995-1-1:2004 Cl 6.3.2, Eq 6.23 and 6.24)

Compressive resistance is reduced by the buckling factor k_c,y (about Y-axis) and k_c,z (about Z-axis), each derived from the relative slenderness lambda_rel,c for that axis. The combined flexural-buckling and bending interaction is checked as:

interaction = sigma_c,0,d / (k_c,y × f_c,0,d) + sigma_m,y,d/f_m,y,d + km × sigma_m,z,d/f_m,z,d ≤ 1.0 interaction = sigma_c,0,d / (k_c,z × f_c,0,d) + km × sigma_m,y,d/f_m,y,d + sigma_m,z,d/f_m,z,d ≤ 1.0

Lateral torsional buckling interaction (EN 1995-1-1:2004 Cl 6.3.3, Eq 6.35)

When the compression face of the column is unrestrained against lateral movement, lateral torsional buckling is checked. The stability factor k_crit is applied to the major-axis bending strength, and the interaction with axial compression is checked per Eq 6.35:

interaction = (sigma_m,y,d / (k_crit × f_m,y,d))² + sigma_c,0,d / (k_c,z × f_c,0,d) ≤ 1.0

Deformation checks (EN 1995-1-1:2004 Cl 2.2.3)

Governing instantaneous and final (creep-adjusted) deformations are computed for bending about each axis independently. All four combinations (instantaneous Y, instantaneous Z, final Y, final Z) are checked against span-ratio limits from EN 1995-1-1:2004 Table 7.2 and any user-defined absolute limits.

Load linking

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