Materials and Structures

, Volume 38, Issue 5, pp 507–513 | Cite as

Bending moment and axial force interacting on solid timber beams

  • R. Steiger
  • M. Fontana
Scientific Reports


This paper describes the results of bending moment (M) and axial force (N) interaction tests on 220 solid spruce specimens with cross-section 80×160 mm. Depending on the timber strength, existing design models for M/N-interaction are fitted to the test results and different analytical approaches for the magnification or reduction of the initial moment due to beam deflections are evaluated. Interaction graphs of timber columns subjected to simultaneous action of bending moment and axial force exhibit convex curvilinearity viewed from the basis of the diagram. The degree of convexity depends on the slenderness of the column and on the strength of the timber. In the case of stocky columns subjected to high bending moments and small axial forces, the highest deviation from linearity can be observed. Design models published in standards and in literature describe the non-linearity of the interaction curve on the basis of an elastic stress-strain relationship in the tension portion of the cross-section and by a non-linear, “plastic” behaviour of the compression zone. Majority of former tests were performed on timber beams with small cross-section. For the case of interaction of bending and tension stress, only a limited number of results are available, because of the difficulty to apply high tension forces.


Timber Axial Force Tangent Modulus Magnification Factor Compression Zone 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Cet article présent les résultats de 220 essais vérifiant l'effet de l'interaction entre un moment de flexion (M) et un effort normal (N) agissant en même temps sur des poutres du bois massif d'épicéa de section 80×160 mm. Les résultats sont comparés avec des modèles de dimensionnement en cas d'interaction M/N et différentes estimations de l'amplification ou de la réduction du moment de flexion initial, provoquées par les déformations de la poutre, sont évaluées. Les courbes d'interaction M/N sont convexes par rapport à l'origine des axes, avec une déviation du modèle linéaire en particulier dans le cas de grands momments et petits efforts normaux. L'ampleur de cette convexité dans la courbe d'interaction dépend de l'élancement de la poutre et de la qualité du matériau. Les modèles de dimensionnement qui résultent des essais considèrent la non linéarité des courbes d'interaction à l'aide d'un comportement élastique en traction et plastique en compression. Beaucoup d'essais décrits dans la littérature se basent sur des éprouvettes de petites dimensions. En plus il y a très peu de données pour le cas de flexion avec traction, car l'application de grands efforts de tractions est difficile.


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Copyright information

© RILEM 2005

Authors and Affiliations

  • R. Steiger
    • 1
  • M. Fontana
    • 2
  1. 1.Empa, Swiss Federal Laboratories for Materials Testing and Research, Wood LaboratoryDübendorfSwitzerland
  2. 2.Swiss Federal Institute of TechnologyETHZZurichSwitzerland

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