Considering the Joint Slip in Parametric Timber Cross-Sections
Tips & Tricks
In timber design, beams are often built up of several timber elements. The individual elements can be connected by glue, nails, bolts, or dowels. A glued connection is to be assumed as rigid. In the case of dowel‑type fasteners, the joint is compliant (slip joint) and the cross‑section properties of the connected elements cannot be fully applied.
In RFEM 5 and RSTAB 8, it is possible to consider the compliance of the connections of built‑up members in the individual layers. This is done by entering the reduction factor gamma, which can be determined by means of the ‘gamma method’, for example according to EN 1995‑1‑1 (Annex B) or DIN 1052:2008 (8.6.2). This factor takes into account a reduction of the parallel axis theorem components of the cross‑section parts from which an effective bending stiffness results.
In addition, it is possible to assign different materials to the individual cross‑section. To do this, select the option ‘Hybrid’, and then select one of these materials as reference material to determine the ideal cross‑section properties.
Author
Dipl.-Ing. (FH) Gerhard Rehm
Product Engineering & Customer Support
Mr. Rehm is responsible for the development of products for timber structures, and provides technical support for customers.
Keywords
Composite timber cross-sections Flexibility Gamma method Composite beam
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Often, models are needed in several projects, like the purlin with columns and knee braces in this example. The dimensions can be changed directly in RFEM or RSTAB by shifting the nodes.
The cross-section resistance design analyzes tension and compression along the grain, bending, bending and tension/compression as well as the strength in shear due to shear force.
The design of structural components at risk of buckling or lateral-torsional buckling is performed according to the Equivalent Member Method and considers the systematic axial compression, bending with and without compressive force as well as bending and tension. Deflection of inner spans and cantilevers is compared to the maximal allowable deflection.
Separate design cases allow for a flexible and stability analysis of members, sets of members, and loads.
Design-relevant parameters such as the stability analysis type, member slendernesses, and limit deflections can be freely adjusted.
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