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.

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 Connection

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

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