Imperfection Measurements on Timber Members

Associated Project 11 (AP 11)



The increasing use of hardwoods and innovative hardwood products with significantly higher strengths has made it possible to achieve slimmer structures with larger spans in timber construction. However, this also means that individual timber members are more sensitive to in-plane flexural and lateral torsional buckling and therefore more sensitive to imperfections. The current imperfection approaches according to DIN EN 1995-1-1 vary greatly depending on the verification method (e.g. L/288 to L/1100 for BSH) and are not verified by measured values for members made of hardwood and members made of softwood that are subjected to bending.

An extensive measurement programme in collaboration with the Institute for Photogrammetry (IfP) of the University of Stuttgart on real members is intended to create a database of geometric imperfections of hardwood members (in particular laminated veneer lumber, LVL) and members made of softwood subjected to bending (in particular glulam). The measurements of geometric deviations (curvatures, inclinations, etc.) will be carried out by laser scanning the structure of wooden buildings. 15-20 timber buildings and at least 400 members will be measured.

The measured geometric imperfections, together with literature-based assumptions on structural imperfections, serve as input values for systematic analytical and numerical calculations of the load-bearing capacity of imperfection-sensitive timber members. The comparison of the numerically determined equivalent imperfections with the standard approaches allows an evaluation of the existing stability verification methods and the derivation of recommendations for improved differentiated approaches.

Finally, recommendations are given for the equivalent imperfections and buckling curves of imperfection-sensitive timber members, especially hardwood members, which allow economic design with EC5 verification methods at a uniform safety level. Due to the active participation of the applicant in the standardisation work, the results will also be included in the discussion on the revision of EC5.



Prof. Ulrike Kuhlmann
Institute of Structural Design (KE), University of Stuttgart


Janusch Töpler (KE)


Deutsches Institut für Bautechnik (DIBt)



  1. 2022

    1. Töpler, J., & Kuhlmann, U. (2022). In-plane buckling of beech LVL columns. In Proceedings of the 9th meeting of International Network on Timber Engineering Research (INTER) (Nos. 55-2–1; Issues 55-2–1).


  1. 2023

    1. Töpler, J., & Kuhlmann, U. (2023). Measurement data: Laser scanning of timber buidlings. DaRUS.
  2. 2022

    1. Töpler, J., & Kuhlmann, U. (2022). DIBt - ZP 52-5-13.194 - Imperfektionsmessungen an stabilitätsgefährdeten Holzbauteilen - Schlussbericht. /brokenurl#for:intcdc


  1. 2023

    1. Töpler, J., & Kuhlmann, U. (2023). Measurement data: Laser scanning of timber buidlings. DaRUS.


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