Optimization of the effective length method for timber members prone to lateral torsional buckling under combined compression and bending

For long-spanning load-bearing structures, bar-shaped components are usually used in timber construction, whereby the key to the economic efficiency of the constructions often lies in the slenderness of these timber components. Due to in-plane buckling and lateral torsional buckling, a so-called stability failure often occurs in these slender, bar-shaped timber components. For a combined loading of compression and bending, as occurs e.g. in the case of suspended beams or frames, the equivalent length method according to DIN EN 1995-1-1 is partly far on the safe side according to current investigations, which makes an economic and competitive design of such timber components considerably more difficult.  Furthermore, there are no measurement results from tests with cross-sectional dimensions common in building practice for the combined member verification, which could be used to verify the design method.

The aim of the research project is therefore to create the data basis for analytical and numerical investigations by means of experiments, on the basis of which the combined equivalent length method of lateral torsional buckling can be economically optimised and the moment-normal force interaction relationship for components at risk of lateral torsional buckling can be revised. Within the scope of the test programme, the influence of slenderness as well as the ratio of moment to normal force on the load-bearing behaviour of components at risk of lateral torsional buckling are to be investigated. Based on this, suitable analytical and numerical models will be developed, which can be verified on the basis of the test results. With these, additional parameters can be investigated and scatter can be taken into account, thus creating a comprehensive data basis for the revision of the verification with the effective length method.

The revised verification should enable planners as well as small and medium-sized timber construction companies to plan and erect more economical and competitive timber structures.

University of Stuttgart
Institute of Structural Design
Prof. Dr.-Ing. Ulrike Kuhlmann, Janusch Töpler

iVTH e.V. / AiF

January 1st, 2021 – December 31st, 2023