In this example, there are hexagonal head wood screws with a diameter of .47 in., used at a distance of 23.66 in. For softwood C24 according to Eurocode 5, this gives a spring constant of 156,598.98 psf. To comply with ANSI/AWC NDS, it is necessary to multiply the determined shift modulus by a factor of 0.5 according to Chapter 11.3.6, since the shift modulus is defined by the standard in consideration of two shear planes. Thus, the result in accordance with NDS is a spring constant of 190,919 lbf/ft². The figure shows a schematic distribution of bending and shear stress for "solid", "semi‑rigid", and "loose" coupling arranged from top to bottom.
Modeling Downstand Beam in Timber Structures 2: Shear Coupling
In order to represent the stiffness of the entire structure correctly, you can consider shear coupling between the ceiling and the downstand beam using the line release. This way, you can define a spring constant, thus avoiding the replacement system by using coupling members. The spring constant results from the shift modulus of the fastener, which can be determined according to EN 1995-1-1 or ANSI/AWC NDS, for example.
Author
Mr. Rehm is responsible for developing products for timber structures, and he provides technical support for customers.
Links
- Modeling Downstand Beam in Timber Structures 1: Torsion
- Modeling Downstand Beam in Timber Structures 2: Shear Coupling
- Modeling Downstand Beam in Timber Structures 3: Nonlinear Support Situation
- Structural Analysis & Design Software for Timber Structures
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Besides the standardized gamma method, you can display the semi-rigid composite beams also as a framework model.
For a timber connection as shown in Figure 01, you can take into account the torsional spring rigidity (spring stiffness for rotation) of the connections. You can determine it by means of the slip modulus of the fastener and the polar moment of inertia of the connection.
The previous article, titled Lateral-Torsional Buckling in Timber Construction | Examples 1, explains the practical application for determining the critical bending moment Mcrit or the critical bending stress σcrit for a bending beam's lateral buckling using simple examples. In this article, the critical bending moment is determined by considering an elastic foundation resulting from a stiffening bracing.
The article titled Lateral-Torsional Buckling in Timber Construction | Theory explains the theoretical background for the analytical determination of the critical bending moment Mcrit or the critical bending stress σcrit for the lateral buckling of a bending beam. This article uses examples to verify the analytical solution with the result from the eigenvalue analysis.
Using the "Beam Panel" thickness type, you can model timber panel elements in 3D space. You just specify the surface geometry and the timber panel elements are generated using an internal member-surface construct, including the simulation of the connection flexibility.
You have the option to perform the fire resistance design of surfaces using the reduced cross-section method. The reduction is applied over the surface thickness. It is possible to perform the design checks for all timber materials allowed for the design.
For cross-laminated timber, depending on the type of adhesive, you can select whether it is possible for individual carbonized layer parts to fall off, and whether you can expect increased charring in certain layer areas.
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Among others, the following cross-laminated timber manufacturers are available in the layer structure library:
- Binderholz (USA)
- KLH (USA, CAN)
- Kalesnikoff (USA, CAN)
- Nordic Structures (USA, CAN)
- Mercer Mass Timber
- SmartLam
- Sterling Structural
- Superstructures listed in Lignatec Edition 32 "Cross-Laminated Timber of Swiss Production"
By importing a structure from the layer structure library, all relevant parameters are adopted automatically. The library is continually updated.
The Timber Design add-on for RFEM 6 / RSTAB 9 is multi-purpose and combines a large number of additional elements. [*S16332764*] Timber Design Add-on for RFEM 6
Is it possible to create a second design case in RF‑LAMINATE?
How can I design dowel-laminated timber (DLT) or nail-laminated timber (NLT) in RFEM?
How can I perform a stability analysis for a tapered member?
How can I model a timber panel wall with RFEM?
Is it possible to perform fire resistance design of cross-laminated timber panels in RF‑LAMINATE?
How can I consider the flexibility of a continuous beam with slotted dowel connections?
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