Seismic retrofit: strengthening existing structures against earthquakes

Common techniques and components

Retrofitting can involve many approaches depending on the type and condition of a building. Typical measures include:

• Strengthening of foundations and adding shear walls or bracing to resist lateral loads.
• Securing non-structural elements (e.g., mechanical systems, facades, and ceilings) to prevent falling hazards.
• Installing base isolators, energy dissipating dampers, or moment-resisting connections to control motion.
• Improving floor and roof diaphragms and tying them to walls and foundations.

Assessment and implementation

Successful retrofit begins with a seismic assessment: examining the building’s materials, structural system, soil conditions and intended use. Engineers develop a prioritized plan that balances performance objectives, budget and disruption. Typical project steps are:

1. Site and structural evaluation.
2. Design of retrofit measures and permits.
3. Construction, testing and final inspection.

Broader uses: While focused on earthquakes, many retrofit strategies also improve resistance to other hazards. For example, anchoring and reinforcement reduce damage from tornadoes, and improvements to connections and cladding help structures withstand strong winds and severe thunderstorms.

History and importance: Seismic retrofit practice evolved after major earthquakes demonstrated predictable failure modes in older construction. Modern codes and retrofit programs aim to reduce collapse risk in historic, residential, commercial and public buildings. While cost and disruption are considerations, retrofits deliver long-term benefits by saving lives, lowering repair costs after events, and preserving critical infrastructure.