Braced wall line

A structure of shear walls in the center of a large building—often encasing an elevator shaft or stairwell—form a shear core.

Shear walls resist in-plane loads that are applied along its height. The applied load is generally transferred to the wall by a diaphragm or collector or drag member. They are built in wood, concrete, and CMU (masonry).

Plywood is the conventional material used in wood (timber) shear walls, but with advances in technology and modern building methods, other prefabricated options have made it possible to inject shear assemblies into narrow walls that fall at either side of an opening. Sheet steel and steel-backed shear panels in the place of structural plywood in shear walls has proved to provide stronger seismic resistance.

A shear wall is stiffer in its principal axis than it is in the other axis. It is considered as a primary structure which provides relatively stiff resistance to vertical and horizontal forces acting in its plane. Under this combined loading condition, a shear wall develops compatible axial, shear, torsional and flexural strains, resulting in a complicated internal stress distribution. In this way, loads are transferred vertically to the building’s foundation. Therefore, there are four critical failure mechanisms; as shown in Figure 1. The factors determining the failure mechanism include geometry, loading, material properties, restraint, and construction.

The ‘slenderness ratio’ of a wall is defined as a function of the effective height divided by either the effective thickness or the radius of the gyration of the wall section. It is highly related to the ‘slenderness limit’ that is the cut-off between elements being classed ‘slender’ or ‘stocky’. The slender walls are vulnerable to buckling failure modes, including Euler in-plane buckling due to axial compression, Euler out-of-plane buckling due to axial compression and lateral torsional buckling due to bending moment. In the design process, structural engineers need to consider all these failure modes to ensure that the wall design is safe under various kinds of possible loading conditions.

In actual structural systems, the shear walls may function as a coupled system instead of isolated walls depending on their arrangements and connections. Two neighboring wall panels can be considered coupled when the interface transfers longitudinal shear to resist the deformation mode. This stress arises whenever a section experiences a flexural or restrained warping stress and its magnitude is dependent on the stiffness of the coupling element. Depending on this stiffness, the performance of a coupled section will fall between that of an ideal uniform element of similar gross plan cross-section and the combined performance of the independent component parts. Another advantage of coupling is that it enhances the overall flexural stiffness dis-proportionally to shear stiffness, resulting in smaller shear deformation.

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