What is structural stability?
Structural stability is a structure’s ability to remain in equilibrium under every load: the building must not topple, lean, overturn or collapse. A good structure must be strong (not break), stiff (not deform too much) and stable (stay standing). Stability is mainly about resisting horizontal forces such as wind, out-of-plumb effects and vibration. Engineers often call the system that provides it the lateral stability or bracing system.
Individual members need to be stable too. A slender column can buckle and a deep, narrow beam can suffer lateral-torsional buckling (twist sideways), even when the material itself is nowhere near failing.
How a building becomes stable
A building is essentially a box. Loose walls, columns and floors are not stable on their own; they must be connected so that horizontal forces travel through stiff elements down to the foundation. Common means are:
- Shear walls or stiff cores, such as a concrete stair or lift core;
- Bracing (cross-bracing) in walls and roofs;
- Moment-resisting connections in portal frames;
- Floors acting as diaphragms that carry forces to the shear walls;
- Ties between walls, floors and roof.
Application
- Never just remove a wall. An internal wall that seems to carry nothing may be needed for stability. Have a structural engineer assess it first.
- Take care with large openings. A wide glazed opening in a facade or knocking two rooms together can weaken the stability.
- Keep it stable during construction. Walls and trusses are often not yet tied together while building. Prop and brace them until the structure is complete.
- Don’t forget the fixings. An extension or new roof must be properly tied to the existing structure and the foundation.
Common mistake: considering only vertical load (weight) and forgetting the wind. Lightweight structures like a carport or garden shed are more likely to blow over or lift than to fail under their own weight.
Related terms
- Shear wall
- Buckling
- Lateral-torsional buckling
- Portal frame
- Roof loads
- Brace
- Structural engineer
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