How Ductility and Stiffness Determine Building Performance in Quakes

22 September 2026 / 3 min read

When engineers assess how well a building can endure strong lateral motion from ground shaking in an earthquake, one critical factor is ductility: the extent to which a material (or structure) can undergo large deformations without failing. The term is used in earthquake engineering to designate how well a building will endure large lateral displacements imposed by ground shaking.

Another key measure is stiffness, or how much force is required to displace a building by a certain amount. A building that requires more force to shift is considered stiffer, which can help mitigate damage by allowing less deformation under earthquake stresses.

However, a structure that’s too stiff and fragile (often referred to as brittle) will be prone to failure under relatively small movements. An example of a brittle structure is an unreinforced masonry building, which will tolerate very little displacement before damage and failure begin.

building-in-ruins

A ductile structure’s ability to contort and dissipate energy during an earthquake is therefore also helpful, as it will allow more deformation without reaching ultimate failure or collapse. An example of a ductile structure is a properly detailed steel frame with enough elasticity to withstand large deformations before it begins to fail. Ductility doesn’t make buildings “damage-proof,” but it makes sudden collapse less likely and enhances life safety. It may also support safer evacuation and facilitate post-earthquake inspection and repair.

Building codes

Prior to 1975, building codes and construction standards in the U.S. didn't have explicit ductility requirements. As a result, most pre-1975 buildings that haven’t been seismically upgraded are believed to be non-ductile. Many such structures demonstrated brittle failures during past earthquakes, such as the 1971 San Fernando earthquake.

Only after 1975 did seismic design codes and construction standards begin to establish ductility requirements for buildings in areas of high seismic risk. As engineering knowledge advanced, improvements in the construction standards of ACI-318-2011 (Building Code Requirements for Structural Concrete and Commentary) and AISC-341-2010 (Seismic Provisions for Structural Steel Buildings) were integrated directly into seismic design codes.

For steel structures, AISC-341-2010 required more stringent detailing for welded connections in steel moment-resisting and braced frames, as well as for composite structures in which concrete elements are reinforced with structural steel sections. Similarly, ACI-318-2011 improved the requirements for steel confinement in the most critical sections of concrete columns and walls. More recent construction standards ACI-318-2019 and AISC-341-2022 have required high-ductility materials and added tightened requirements for continuity and smooth load paths to prevent brittle failure.

Ductility in the Verisk U.S. Earthquake Model

Through studying the evolution of design and construction standards for steel and reinforced concrete structures, Verisk engineers have been able to assign ductility classes for different regions and time periods in the U.S. This understanding of how ductility detailing requirements have changed allows the vulnerability of more ductile structures to be modified appropriately to reflect the impact of both reduced initial stiffness and increased deformation capacity.

The current Verisk Earthquake Model for the U.S. implicitly accounts for ductility in assigning code levels related to the design seismic base shear demand at a given location during a particular period. Verisk’s updated U.S. Earthquake Model explicitly accounts for ductility in the damage functions for steel and reinforced concrete buildings.

The Verisk U.S. Earthquake Model leverages local and regional expertise to represent the most advanced understanding of seismic hazard and building vulnerability.

Learn more

Ductility and Stiffness—What They Are and Why They Matter in an Earthquake

Building codes

Ductility in the Verisk U.S. Earthquake Model