Superposition of axial stress and bending stress on a section — the maximum fiber stress a beam-column or eccentrically loaded member sees.
Standard method — stated scope limits apply
Loads & Section
Enter loads and section properties.
About This Calculation
A structural member under BOTH axial load (compression or tension) and bending moment simultaneously experiences combined stress — the two stress contributions superimpose directly (axial stress is uniform across the section, bending stress varies linearly from maximum compression on one face to maximum tension on the other), meaning the actual peak stress at the extreme fiber can be significantly higher than either effect analyzed alone would suggest. Checking combined stress against allowable stress is essential for any column or beam-column that carries genuine eccentric or off-axis loading, not just pure axial or pure bending members.
Frequently Asked Questions
Why do axial and bending stress simply add together, rather than combine some other way?
Both are normal stresses acting perpendicular to the same cross-section — by basic mechanics of materials, normal stresses from independent load effects on the same section superimpose algebraically (with appropriate sign for tension/compression), which is why the combined stress formula is a straightforward sum rather than a more complex interaction.
Why does eccentric axial loading create bending, even with no separate applied moment?
Any axial load applied off the section’s centroidal axis creates a moment equal to load times eccentricity, exactly as if that moment had been applied directly — a column loaded even slightly off-center is genuinely experiencing combined axial-plus-bending stress, not pure axial stress, which is a common real-world loading condition rather than an edge case.
Does combined stress checking replace a full column buckling (slenderness) check?
No — combined stress checks the SECTION’s material stress capacity at a given load, while buckling is a separate STABILITY failure mode governed by the member’s slenderness ratio, which can cause failure at a load well below what the material stress alone would allow for a sufficiently slender column; both checks are needed independently.