Reinforced-concrete (shear) wall

A load-bearing reinforced-concrete wall cast in place, continuous and monolithic: besides enclosing the space, it is structure. For its in-plane stiffness it is the element that braces the building against wind and earthquake — the «shear wall» or stair/lift «core» — and, below ground, it acts as a watertight retaining wall. It is built with formwork, reinforcement and a pour, and must be designed for the vertical loads and for the horizontal actions in its own plane.

The reinforced-concrete shear wall is a wall that works as structure. Unlike an infill or a masonry wall, it is cast in place continuously with the floors and foundations, forming with them a single stiff organism. It is used where strength and, above all, stiffness are needed: stair and lift cores, basement retaining walls, the shear walls that brace tall buildings.

A wall is enormously stiffer in its own plane than out of plane. It is this stiffness that makes it the ideal brace: it takes the horizontal actions — wind, and above all earthquake — and carries them down, keeping the building from swaying or deforming too much. Arranged symmetrically in plan, the walls «govern» the seismic behaviour; badly distributed, they introduce harmful torsion. Their position is a structural choice, not only an architectural one.

Underground the wall also acts as a retaining wall: it holds back the thrust of the soil and the groundwater. It then becomes a tank, and must be waterproofed — with membranes, bentonite barriers or watertight concretes — and drained, detailing the construction joints with water-stops. The cover toward the soil must be generous to protect the reinforcement from the aggressive environment.

The wall is built by placing the reinforcement between two forms and pouring the concrete, which is vibrated to fill every corner without segregating. Quality is born in the details: cover guaranteed by spacers, clean and reinforced construction joints, tight, well-propped forms to resist the thrust of the fresh concrete. Fair-faced concrete needs very careful forms and pour; otherwise it is finished with plaster or, externally, with an insulation system.