I design a combined structure made of timber materials with different creeping parameters. How can I perform the serviceability limit state design according to EN 1995‑1‑1?


In RFEM and RSTAB, the simplified design from [1], Chapter 2.2.3, have been implemented for the automatic load combinations. This means that, strictly speaking, the structures concerning the final deformation may only be analyzed, in which the materials with identical creep behavior occur since the creep deformations are considered in a simplified way on the load side. If the structure is a combined structure made of timber with different creep behavior or in combination with steel, the final deformations must be determined according to [2] Amendment to 2.2.3 as follows:

"(4) If the structure consists of members or components having different creep behaviour, the long-term deformation due to the quasi-permanent combination of actions should be calculated using final mean values of the appropriate moduli of elasticity, shear moduli and slip moduli, according to The final deformation ufin is then calculated by the superposition of the instantaneous deformation due to the difference of the characteristic and quasi-permanent combinations of actions with the long-term deformation."

However, this requires the superposition of the results from different load combinations, which cannot be implemented automatically in RFEM and RSTAB. If the different creep behavior should be taken into account, it is necessary to create the load combinations manually, and reduce the stiffness according to the creep coefficient. The procedure is described on an example of a timber-concrete composite floor presented on the Info Day 2017. Below this FAQ, you can find the link for this video.


Creep coefficient Deformation coefficient Creep ratio Long-term deformations Final deformation


[1]   Eurocode 5: Design of timber structures - Part 1-1: General - Common rules and rules for buildings; EN 1995-1-1:2010-12
[2]   Eurocode 5: Design of timber structures - Part 1-1: General - Common rules and rules for buildings; EN 1995-1-1:2004/A2:2014


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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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