Seismic Design & Assessment

Base isolation is a seismic protection strategy that decouples a structure from ground motion by inserting flexible isolators between the superstructure and its foundation. This shifts the structure's fundamental period to a long value, reducing seismic demands and protecting both the structure and its contents.

Capacity design is a seismic design philosophy in which ductile elements are deliberately chosen to yield first, while all other elements are protected by being designed with sufficient strength to remain elastic. It ensures that inelastic deformation occurs only in controlled, ductile locations.

A fragility curve is a probabilistic function that gives the likelihood of a structure or component reaching or exceeding a specific damage state as a function of a ground motion intensity measure. It is a fundamental tool in performance-based earthquake engineering and seismic risk assessment.

A moment frame is a structural system in which beams and columns are connected by rigid joints capable of transferring bending moments, providing lateral resistance through flexural action. Moment frames are among the most common lateral force-resisting systems in steel and reinforced concrete buildings.

Performance-based design (PBD) is a seismic design philosophy that explicitly defines performance objectives for a structure at multiple hazard levels and uses analytical procedures to demonstrate that the structure achieves them. It is the modern successor to prescriptive code-based design.

Pushover analysis is a nonlinear static analysis method in which a structure is subjected to a monotonically increasing lateral load pattern until a target displacement or collapse is reached. It provides insight into the structure's sequence of yielding, its lateral capacity, and its failure mechanism.

The response modification factor (R) is a code-based coefficient that reduces the elastic seismic design forces to account for the ductility, overstrength, and redundancy of a structural system. It reflects the structure's capacity to dissipate energy through inelastic behavior and is central to force-based seismic design.

Seismic retrofit is the modification of an existing structure to improve its resistance to earthquake loading. It is a critical practice for aging buildings, bridges, and infrastructure that were designed to outdated codes or no seismic provisions at all.

A shear wall is a vertical structural element designed to resist lateral forces — primarily wind and earthquake — by developing in-plane shear and flexural capacity. Shear walls are among the most efficient and widely used lateral force-resisting systems, particularly in reinforced concrete and masonry buildings.

A soft story is a building level that is significantly more flexible than the levels above it, typically due to tall ground-floor openings, lack of infill walls, or discontinuous lateral systems. Soft stories are a leading cause of earthquake collapse and a major target of retrofit programs worldwide.