Shear Walls & Bracing Systems Notes

Last reviewed 16 Sept 2026 · 8 min read

Lateral load resisting systems

System	Behaviour	Typical use
Moment resisting frame (MRF)	Beams and columns with rigid joints resist lateral loads by bending — flexible, shear-type deflection	Low- to mid-rise buildings; architectural freedom
Shear wall system	Stiff RC walls act as vertical cantilevers — flexural-type deflection	Mid- to high-rise; residential towers
Braced frame	Diagonal members form trusses — axial forces resist lateral load	Steel buildings, industrial structures
Dual system	Shear walls/braces + moment frames sharing lateral load (frames designed for a minimum share)	High-rise buildings
Core system	Central core walls (lifts, stairs)	Office towers
Outrigger and belt truss	Stiff arms link the core to perimeter columns, reducing core overturning moment and drift	Tall buildings
Tube systems	Closely spaced perimeter columns act as a hollow tube; tube-in-tube, bundled tube, braced tube	Very tall buildings
Flat slab with shear walls	Flat slabs carry gravity; walls carry lateral load	Buildings needing flexible floor plans

Shear walls

Shear walls (structural walls) are vertical plate-like RC (or masonry/steel) elements that resist in-plane lateral forces — shear and overturning moment — and provide high lateral stiffness, controlling drift.

Advantages

High stiffness and strength — small drifts; reduced non-structural damage.
Good seismic performance when properly detailed (few collapses of well-designed shear wall buildings in past earthquakes).
Economical for taller buildings compared with increasing frame member sizes.

Behaviour by aspect ratio

Wall type	Height/length ratio	Behaviour
Slender (flexural) walls	Large (commonly > 2)	Flexure dominates; ductile plastic hinge at base; behave like cantilever beams
Squat (short) walls	Small (commonly < about 1–1.5)	Shear dominates; diagonal cracking; less ductile
Intermediate	1.5–2	Combined flexure and shear

Types of walls

Cantilever (isolated) walls — solid rectangular, flanged (T, L, I, C) sections.
Coupled walls — two or more walls connected by coupling beams at floor levels through openings (doors/windows); coupling beams yield and dissipate energy; deep coupling beams use diagonal reinforcement.
Core walls — closed or partially closed sections around lifts and stairs; high torsional stiffness.
Walls with openings — openings located in a regular pattern; trimming bars around openings.
Boundary elements — thickened or specially confined wall ends carrying large compressive stresses (see Ductility & Ductile Detailing).

Placement of shear walls

Walls in both principal directions.
Symmetric arrangement to avoid torsion; placing walls near the perimeter increases torsional resistance.
Continuous from foundation to top — no discontinuities (avoid walls stopping at lower floors, which create soft storeys).
Openings aligned vertically.
Adequate foundations to resist overturning.

Stiffness and distribution of lateral forces

FormulaStiffness of a cantilever wall (top point load)

Δ = \frac{P H ^{3}}{3 E I} + \frac{1.2 P H}{G A}, k = \frac{1}{\frac{H ^{3}}{3 E I} + \frac{1.2 H}{G A}}

For slender walls, flexural deformation dominates → $k \propto E I / H^{3} \propto t L^{3}$ (for rectangular walls of length $L$ and thickness $t$ ).
For squat walls, shear deformation is significant.

FormulaDistribution with rigid floor diaphragm (no torsion)

V_{i} = V \frac{k _{i}}{\sum k _{j}}

Centre of rigidity (walls parallel to y at positions $x_{i}$ ):

x_{C R} = \frac{\sum k _{y i} x _{i}}{\sum k _{y i}}

Eccentricity $e = x_{C M} - x_{C R}$ causes torsional moment $T = V e_{d}$ (with design eccentricity), producing additional forces in walls proportional to $k_{i} r_{i}$ where $r_{i}$ is distance from the CR:

V_{i, t or s i o n} = \frac{T k _{i} r _{i}}{\sum ( k _{x} y ^{2} + k _{y} x ^{2} )}

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