Continuous tie down systems in wood shearwalls

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The deflection limit state often controls the design of wood shearwalls. At each story, the lateral drift must be verified and must be within the limit prescribed by the design code applicable. For multi-story stacked shearwall constructions, the deflection verification is even more important.

To enhance productivity and the ease of use of the GSE Timber software, an additional type of wood shearwall anchorage has been added. Continuous tie down systems and their effects on the shearwall properties are now available in the GSE Timber software. Standard libraries of continuous tie down rods are also readily available. With this function, GSE users can efficiently generate, verify, and design multi-story wood shearwalls.
Continuous tie down systems in wood shearwalls

In the GSE Timber software, the wood shearwalls are automatically generated according to the various inputs defined by users in the Wood shearwalls menu. In that menu, the chord members sections are defined.

In previous versions of the GSE, only regular wood sections were available. Now, a new type of section may be created and selected. The new cross-section is composed of two main components, the wood members and a steel rod. The wood members may be built-up sections made of regular sawn lumber.

Continuous tie down systems in wood shearwalls

Shearwalls are specifically used to resist lateral loads. Under a lateral loading case, the chord members will resist the tension and compression forces generated by the overturning bending moment. The wood members act as compression only members and the steel rods act as a tension only members. As the tension chord and compression chord are not symmetric, the transformed moment of inertia of the shearwall has to be calculated (Newfield, 2013)1. The steel rod area is calculated as an equivalent wood section.

Itr = At,tr * ytr2 + Ac * (Lc - ytr )2

The calculated transformed inertia directly affects the shearwall stiffness and thus, the calculated deflections. The modified wall properties are automatically calculated in the software.

1. Newfield, G., Ni, C., Wang, Wang, J. 2013. A mechanics-based approach for determining deflections of stacked multi-storey wood-based shearwalls. FPInnovations, Vancouver, B.C and Canadian Wood Council, Ottawa, Ont.

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The GSE General Structural Engineering software is a fully integrated analysis and design software for structural engineering. The software accounts for steel, cold-formed steel, concrete, automated slab design, timber, light frame wood and aluminum.

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