Simplified Vibration Design for EC 5
With the RF‑/TIMBER Pro add-on module, it is possible to perform the vibration design known from DIN 1052 for the design according to EN 1995‑1‑1. In this design, the deflection under permanent and quasi-permanent action at the ideal one‑span beam may not exceed a limit value (6 mm according to DIN 1052). If you consider the relation between the natural frequency and the deflection for a hinged single-span beam subjected to a constant distributed load, a minimum natural frequency of about 7.2 Hz results from the 6 mm.
|l||Length of the beam|
|EI||Bending stiffness of the beam|
|l||Length of the beam|
|g||Acceleration of gravity|
If both equations are equated, the natural frequency of 7.2 Hz results in a deformation of 6 mm.
|fe, min, DIN||Minimum natural frequency according to DIN 1052|
|g||Acceleration of gravity|
If we take into account the fact that in most National Annexes of EC 5, a minimum natural frequency of 8.00 Hz is to be considered, we obtain a maximum deflection of about 5 mm.
|fe, min, EC5||Minimum natural frequency according to EN 1995-1-1|
If the structural system deviates from a hinged single-span beam (for example, continuous beams, cantilevers, restraints), this must be taken into account accordingly in the deflection limitation.
We analyze a three‑span beam in a dwelling house. To avoid discomfort caused by persons, the system shall have a minimum fundamental frequency of 8 Hz. In order to consider this in RF‑/TIMBER Pro, you can use the formula for three-span beams (see the PDF document below) to determine the maximum allowed deflection of the central span.
|wmax, 8Hz||Deflection limit to reach 8 Hz|
|kf||Correction factor (see PDF file)|
|l||Length of the middle field|
|lk||Length of the outer panels|
|fe, 8Hz||Minimum natural frequency|
In this case, the middle span may deform by -1 mm to comply with the frequency criterion. The actual deflection under permanent load (2.1 kN/m) is obtained as -0.683 mm. Thus, the design of the natural frequency is complied with, and the natural frequency of the beam is greater than 8 Hz. A check calculation results in a natural frequency of 9.76 Hz.
A more precise calculation with the RF‑/DYNAM Pro — Natural Vibrations add-on module results in a natural frequency of 9.86 Hz. The video shows the procedure.
Furthermore, it should be noted that further designs (stiffness criterion, vibration velocity, vibration acceleration) must be performed for the vibration design of apartment ceilings. Notes can be found in  or , for example.
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.
Do you have further questions or need advice? Contact us via phone, email, or chat or find suggested solutions and useful tips on our FAQ page available 24/7.
The effects due to snow load are described in the American standard ASCE/SEI 7-16 and in Eurocode 1, Parts 1 through 3. These standards are implemented in the new RFEM 6 program and the Snow Load Wizard, which serves to facilitate the application of snow loads. In addition to this, the most recent generation of the program allows the construction site to be specified on a digital map, thus allowing the snow load zone to be imported automatically. These data are, in turn, used by the Load Wizard to simulate the effects due to the snow load.
Lookout Tower Model (Left) and Deformation Image (Right) in RFEM (© Ingenieurbüro Braun GmbH & Co. KG)
Compared to the RF‑/TIMBER Pro add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Timber Design add-on for RFEM 6 / RSTAB 9:
- In addition to Eurocode 5, other international standards are integrated (SIA 265, ANSI/AWC NDS, CSA 086, GB 50005)
- Design of compression perpendicular to grain (support pressure)
- Implementation of eigenvalue solver for determining the critical moment for lateral-torsional buckling (EC 5 only)
- Definition of different effective lengths for design at normal temperature and fire resistance design
- Evaluation of stresses via unit stresses (FEA)
- Optimized stability analyses for tapered members
- Unification of the materials for all national annexes (only one "EN" standard is now available in the material library for a better overview)
- Display of cross-section weakenings directly in the rendering
- Output of the used design check formulas (including a reference to the used equation from the standard)
- How do I perform stability analysis to determine the critical load factor in RFEM 6?
- Where can I find the materials for the corresponding National Annexes in RFEM 6 and RSTAB 9?
- How does the "Orthotropic Plastic" material model work in RFEM?
- What is the meaning of the superposition according to the CQC rule in a dynamic analysis??
- Can I use RFEM to calculate a log house three-dimensionally?
- How do I display some results of all load cases in the printout report, but other results of the selected load cases only?
- I would like to carry out the flexural buckling design for timber components with imperfections and internal forces according to the second-order analysis. Is it sufficient to activate this in Details of the RF‑/TIMBER Pro add-on module or is it necessary to make additional settings?
- Can I design laminated veneer lumber with RFEM/RSTAB?
- How can I calculate a timber-concrete composite floor with cross-laminated timber?
- Is it possible to save the structures of the manufacturer-specific cross-laminated timber plates in the RF‑LAMINATE add-on module?