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Dipl.-Ing. (FH) Gerhard Rehm
2019-10-31

Stiffness Reduction Factors k33 and k88 in RF-LAMINATE

What are the stiffness reduction factors k33 and k88 in the Multilayer Surfaces Add-on?

Answer:

These factors reduce the torsional stiffness D33 as well as the shear stiffness D88 of the corresponding stiffness matrix elements of a surface. Since cross-laminated timber is generally not glued at the narrow side, no shear stresses can be transferred to the narrow sides of the timber. Thus, the stiffness would be overestimated in this case. For this reason, the stiffness must be reduced accordingly.

Some manufacturers provide us with these values when delivering layer structures. They result from internal analysis. The explanation for determining the correction factors is covered in [1]. An analysis of this work has also been included in the Austrian Annex to EN 1995‑1‑1 [2]. The result is shown in Image 02. The ratio of the timber width (a) to the timber thickness (ti) can be taken from the respective approval. Under "Downloads", you will find an Excel file with the formulas entered.

Library of Producers in Multilayer Surfaces Add-on
Library of Producers in Multilayer Surfaces Add-on
Determining Correction Factors According to [2]
Determining Correction Factors According to [2]
Author

Mr. Rehm is responsible for developing products for timber structures, and he provides technical support for customers.

References
  1. Gregor Silly: Numerische Studien zur Drill- und Schubsteifigkeit von Brettsperrholz (BSP). Technische Universität Graz: 2010
  2. Eurocode 5: Design of Timber Structures - Part 1-1: General - Common Rules and Rules for Buildings - National Specifications for the Implementation of OENORM EN 1995-1-1, National Comments and National Supplements; ÖNORM B 1995-1-1:2015-06-15
Downloads
Excel File for Stiffness Reduction of Cross-Laminated Timber
173.51 KB
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