Load-bearing capacity of imperfection-sensitive timber members under combined bending and compression
Date
2026
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Göttingen : Cuvillier Verlag GmbH
Abstract
Diese Arbeit diskutiert das Tragverhalten und die Tragfähigkeit imperfektionsempfindlicher stabförmiger Holzbauteile mit kombinierter Biegung und Druck. Dabei werden die Ergebnisse der drei Forschungsprojekte DIBt - ZP 52-5-13.194, RP 7-1 des Exzellenzclusters IntCDC und IGF Nr. 21285 N zusammengeführt.
Die wesentlichen Ziele waren, eine Grundlage für ein umfassendes Verständnis des Stabilitätsverhaltens stabförmiger Holzbauteile zu legen und mechanisch sinnvolle, konsistente Nachweisverfahren für das Biegedrillknicken und Biegeknicken stabförmiger Holzbauteile mit kombinierter Biegung und Druck zu formulieren. Der Schwerpunkt lag dabei auf dem Phänomen des Biegedrillknickens. Da die Stabilitätsphänomene des Biegeknickens und des Biegedrillknickens jedoch fließend ineinander übergehen und eine strikte Trennung nicht zwingend mechanisch sinnvoll ist, wurde stets auch das Stabilitätsverhalten ganzheitlich betrachtet.
Für das Verständnis der realen Stabilitätsphänomene und die Generierung von Daten wurden Imperfektionsmessungen an 242 Holzträgern und 57 Holzstützen in 23 Gebäuden, Biegeknickversuche an 27 Buchenfurnierschichtholz GL75 Stützen und Biegedrillknickversuche an 19 Brettschichtholz GL 24h Trägern durchgeführt. Durch analytische Untersuchungen wurde das Wissen um die theoretischen Hintergründe des Stabilitätsverhaltens bei Biegung und Druck erweitert. Für die detaillierte Untersuchung der Einflüsse struktureller und geometrischer Imperfektionen und kombinierter Biegung und Druck wurden numerische Modelle entwickelt. Anhand dieser wurden zudem die experimentellen Ergebnisse durch umfangreiche numerische Parameterstudien und Monte-Carlo-Simulationen erweitert.
Durch das Zusammenführen von experimentellen, analytischen und numerischen Ergebnissen konnte die nichtlineare Nx,c-My,1-Interaktion der kc-km-Methode validiert werden und konsistente Ersatzimperfektionen für die Bemessung imperfektionsempfindlicher Holzträger und -stützen hergeleitet werden. Dabei zeigte sich, dass das Schub- und Druckplastizieren und die Querschnittsverwölbung infolge Schub einen signifikanten Einfluss auf die Tragfähigkeit (imperfektionsempfindlicher) Holzbauteile haben und in der Bemessung zu berücksichtigen sind.
Darauf aufbauend wurden Vorschläge zur Modifikation und Erweiterung der Nachweise imperfektionsempfindlicher stabförmiger Holzbauteile in FprEN 1995-1-1 entwickelt, die eine zuverlässigere, konsistentere und wirtschaftlichere Bemessung ermöglichen. Teile der Vorschläge, wie die Ersatzimperfektionen und die nichtlineare Nx,c-My,1-Interaktion des kc-km-Verfahrens, wurden bereits in FprEN 1995-1-1 integriert.
In dieser Arbeit werden erstmalig das Biegeknicken und Biegedrillknicken stabförmiger Holzbauteile auf Basis umfangreicher experimenteller, analytischer und numerischer in konsistenten Berechnungs- und Bemessungsmodellen miteinander verknüpft. Dieses tiefgreifende Verständnis bildet eine fundierte Grundlage, auf der nachfolgende Forschungen, z. B. zu Satteldachträgern und anderen Aspekten, aufbauen und diese erweitern können.
This thesis discusses the load-bearing behaviour and capacity of imperfection-sensitive timber members under combined bending and axial compression. It combines the results of three research projects: DIBt - ZP 52-5-13.194, RP 7-1 of the Cluster of Excellence IntCDC, and IGF No. 21285 N. The main objectives were to establish the basis for a comprehensive understanding of the buckling behaviour of timber members and to formulate mechanically sound, consistent verification methods for the buckling of timber members with combined bending and axial compression. The focus was on the lateral torsional buckling phenomenon. However, as there is a fluent transition between the stability phenomena of flexural buckling and lateral torsional buckling and a separation is not necessarily mechanically reasonable, the stability phenomena were always studied holistically. For a better understanding of the stability phenomena and generation of a database, imperfection measurements on 242 timber beams and 57 timber columns in 23 buildings, flexural buckling tests on 27 beech LVL GL75 columns, and lateral torsional buckling tests on 19 GL 24h beams were conducted. Through analytical investigations, the knowledge of the theoretical background of the stability behaviour at bending and axial compression was broadened. For the detailed study of the influences of structural and geometrical imperfections and combined bending and axial compression, numerical models were developed. Based on these, the experimental results were extended by extensive numerical parameter studies and Monte Carlo simulations. By combining experimental, analytical, and numerical results, the nonlinear Nx,c-My,1-interaction of the kc-km-method was validated, and consistent equivalent imperfections were derived for the design of imperfection-sensitive timber beam-columns. Additionally, the results demonstrated that the shear and compressive plasticising and the cross-sectional warping due to shear have a significant influence on the load-bearing capacity of (imperfection-sensitive) timber members and should be taken into account in the design. On this basis, proposals were developed for a modification and extension of the verifications of imperfection-sensitive timber members in FprEN 1995-1-1, which allow for a more reliable, consistent, and economical design. Parts of the proposals, such as the equivalent imperfections and the nonlinear Nx,c-My,1-interaction of the kc-km-method, have already been incorporated into FprEN 1995-1-1. For the first time, by means of comprehensive experimental, analytical, and numerical investigations, this thesis was able to combine flexural buckling and lateral torsional buckling in consistent analysis and design models. This in-depth understanding provides a sound foundation on which subsequent research, e.g. on double-tapered beams and other aspects, can build and expand.
This thesis discusses the load-bearing behaviour and capacity of imperfection-sensitive timber members under combined bending and axial compression. It combines the results of three research projects: DIBt - ZP 52-5-13.194, RP 7-1 of the Cluster of Excellence IntCDC, and IGF No. 21285 N. The main objectives were to establish the basis for a comprehensive understanding of the buckling behaviour of timber members and to formulate mechanically sound, consistent verification methods for the buckling of timber members with combined bending and axial compression. The focus was on the lateral torsional buckling phenomenon. However, as there is a fluent transition between the stability phenomena of flexural buckling and lateral torsional buckling and a separation is not necessarily mechanically reasonable, the stability phenomena were always studied holistically. For a better understanding of the stability phenomena and generation of a database, imperfection measurements on 242 timber beams and 57 timber columns in 23 buildings, flexural buckling tests on 27 beech LVL GL75 columns, and lateral torsional buckling tests on 19 GL 24h beams were conducted. Through analytical investigations, the knowledge of the theoretical background of the stability behaviour at bending and axial compression was broadened. For the detailed study of the influences of structural and geometrical imperfections and combined bending and axial compression, numerical models were developed. Based on these, the experimental results were extended by extensive numerical parameter studies and Monte Carlo simulations. By combining experimental, analytical, and numerical results, the nonlinear Nx,c-My,1-interaction of the kc-km-method was validated, and consistent equivalent imperfections were derived for the design of imperfection-sensitive timber beam-columns. Additionally, the results demonstrated that the shear and compressive plasticising and the cross-sectional warping due to shear have a significant influence on the load-bearing capacity of (imperfection-sensitive) timber members and should be taken into account in the design. On this basis, proposals were developed for a modification and extension of the verifications of imperfection-sensitive timber members in FprEN 1995-1-1, which allow for a more reliable, consistent, and economical design. Parts of the proposals, such as the equivalent imperfections and the nonlinear Nx,c-My,1-interaction of the kc-km-method, have already been incorporated into FprEN 1995-1-1. For the first time, by means of comprehensive experimental, analytical, and numerical investigations, this thesis was able to combine flexural buckling and lateral torsional buckling in consistent analysis and design models. This in-depth understanding provides a sound foundation on which subsequent research, e.g. on double-tapered beams and other aspects, can build and expand.
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