Seismic design is the process of designing and verifying structures to withstand earthquake-induced ground motion without unacceptable loss of strength, stability, or serviceability.
The objective is not simply to make a structure stronger. Engineers need to understand how earthquake actions enter the structure, how forces and deformations are distributed through the structural system, and how members, connections, foundations, and other components behave under cyclic and dynamic loading.
The applicable seismic design requirements depend on the project location, site conditions, structural system, construction material, building or structure importance, and the governing code or industry standard.
This article explains the main principles of seismic design, commonly used seismic codes and standards, major seismic analysis methods, and considerations for buildings, bridges, offshore structures, and other engineered structures.
Turn FEA Results Into a Structured Verification Workflow
SDC Verifier helps engineers organize analysis results, build load combinations and envelopes, run structural checks against implemented standards, and generate calculation reports — without repeating the verification workflow manually.
Earthquake engineering covers the analysis, design, assessment, and strengthening of structures exposed to seismic actions.
During an earthquake, ground motion produces inertia forces within the structure. The resulting response depends on factors such as:
seismic hazard at the site;
soil and foundation conditions;
structural mass and stiffness;
natural periods and mode shapes;
damping;
structural configuration;
characteristics of the seismic-force-resisting system.
Seismic design therefore involves more than applying a horizontal force to a structural model. Depending on the governing standard and structure type, engineers may need to consider multiple earthquake directions, vertical seismic effects, torsion, modal response, deformation limits, stability, and the interaction of seismic effects with gravity and other loads.
The appropriate analysis method also depends on factors such as structural regularity, height, importance, seismic hazard, and expected nonlinear behavior.
Key Principles of Seismic Design
Ductility
Ductility is the ability of a structural component or system to undergo significant inelastic deformation under repeated load cycles while retaining sufficient load-carrying capacity.
This is important because many structures are not designed to remain completely elastic during the most severe design-level earthquake. Instead, selected parts of the structure may be allowed to yield and dissipate energy while brittle failure modes are avoided.
Ductility depends on the structural material, member proportions, local stability, reinforcement or connection detailing, and the behavior of the overall structural system.
Continuous Load Path and Redundancy
Earthquake-induced forces need a continuous load path through the structure and into the foundations.
Diaphragms, collectors, frames, braces, walls, members, connections, and foundations therefore need to work as an integrated system.
Redundancy can provide alternative load paths if individual components yield or are damaged. However, redundancy alone does not guarantee good seismic performance. Strength, stiffness, detailing, and interaction between structural components also matter.
Capacity Design
Capacity design is used to control where inelastic behavior is expected to occur.
Instead of allowing the weakest component to fail unpredictably, engineers identify the components or mechanisms intended to dissipate seismic energy and provide sufficient strength elsewhere in the load path to reduce the risk of brittle or undesirable failure modes.
This principle is central to many modern seismic design provisions.
Structural Regularity
Large discontinuities in stiffness, strength, mass, geometry, or load path can concentrate seismic demand.
Soft or weak stories, major setbacks, significant plan asymmetry, discontinuous lateral-force-resisting systems, and abrupt changes in stiffness or mass can therefore trigger additional code requirements or restrictions on simplified analysis procedures.
Drift and Deformation Control
Seismic design is not only a strength problem.
Excessive lateral deformation can damage structural and nonstructural components, increase second-order effects, affect equipment and services, and eventually compromise stability.
Seismic standards therefore commonly impose requirements related to story drift, total displacement, deformation capacity, and stability.
Seismic Hazard, Site Conditions, and Design Actions
Location is only the starting point for seismic design.
The engineer needs to translate the seismic hazard at the project site into design ground motion and structural demand.
Depending on the applicable standard, this may involve:
mapped ground-motion parameters or seismic zoning;
return periods or probability levels;
site or soil classification;
design response spectra;
structural importance or risk category;
damping;
structural periods;
behavior or response-modification factors.
Global seismic hazard map showing peak ground acceleration (PGA) distribution worldwide. A regional hazard map is only a starting point; project-specific seismic design also depends on site conditions and the requirements of the applicable code. GEM Global Seismic Hazard Map v2023.1 PNG/poster під CC BY-SA 4.0
Local ground conditions can significantly modify the motion experienced by a structure. Soft soil deposits can amplify motion over certain frequency ranges, while liquefaction, slope instability, fault displacement, and other geotechnical hazards can require separate assessment.
The structural engineer should therefore use the site-specific or code-defined seismic parameters and geotechnical information applicable to the project rather than relying on a broad geographical classification alone.
Major Seismic Codes and Standards
There is no single global seismic design code. Requirements vary by jurisdiction, structure type, material, and industry.
Major seismic design codes and standards including ASCE 7, AISC 360, Eurocode 8, NZS 1170.5, IS 1893, GB/T 50011, ISO 3010, and ISO 19901-2.
Standard
Region / Application
Role
ASCE/SEI 7-22
United States
Seismic loads, analysis criteria, Seismic Design Categories, structural-system requirements, drift, and related design provisions
ANSI/AISC 360-22
United States
General strength and design requirements for structural steel members and connections
ANSI/AISC 341-22
United States
Seismic provisions for structural steel and composite steel-concrete seismic-force-resisting systems
ANSI/AISC 358-22
United States
Prequalified connections for special and intermediate steel moment frames
ACI CODE-318-25
United States / international use
Latest ACI structural-concrete code; adoption depends on the governing building code
Eurocode 8 / EN 1998
Europe
Seismic actions and earthquake-resistant design rules, including material-specific seismic provisions
NZS 1170.5:2004 / SNZ TS 1170.5:2025
New Zealand
Earthquake actions and seismic design requirements
IS 1893 (Part 1):2016
India
Seismic zoning and general earthquake-resistant design criteria
GB/T 50011-2010, 2024 edition / GB 55002-2021
China
Seismic design of buildings and mandatory seismic precaution requirements
ISO 3010:2017
International
General principles for seismic actions on structures
ISO 19901-2:2026
Offshore
Seismic design and assessment of offshore structures
The latest published edition is not automatically the edition applicable to every project. Local legislation, adopted building codes, National Annexes, contracts, authorities having jurisdiction, and project specifications can require a different edition.
Seismic Design Codes in the United States
For most US building projects, seismic requirements are applied through the building code adopted by the relevant jurisdiction, commonly an edition of the International Building Code.
The 2024 IBC referencesASCE/SEI 7-22 for structural loads and seismic design criteria.
For steel structures, ANSI/AISC 360-22 provides the general requirements for structural steel design, while ANSI/AISC 341-22 adds seismic-specific requirements for seismic-force-resisting systems. ANSI/AISC 358-22 provides prequalified connections for special and intermediate steel moment frames.
For concrete, ACI CODE-318-25 is ACI’s latest published Building Code for Structural Concrete. However, the 2024 IBC continues to reference ACI 318-19.
Engineers should therefore use the edition referenced by the building code or other regulatory framework applicable to the project rather than assuming that the latest publication automatically governs.
Eurocode 8
Eurocode 8, EN 1998, Design of structures for earthquake resistance, is the European family of standards for seismic design.
Eurocode 8 includes both seismic actions and material-specific rules for earthquake-resistant structural design. The relevant material Eurocodes, such as Eurocode 2 for concrete and Eurocode 3 for steel, still provide the underlying resistance models used together with the seismic provisions.
Second-generation Eurocode 8 parts include EN 1998-1-1:2024 and the building-specific EN 1998-1-2:2026.
National implementation remains transitional. Engineers therefore need to check the applicable National Annex, national implementation status, project requirements, and transition provisions before selecting the governing Eurocode edition.
New Zealand: NZS 1170.5 and SNZ TS 1170.5
NZS 1170.5:2004 remains the earthquake-action standard referenced by the New Zealand Building Code.
SNZ TS 1170.5:2025, Structural design actions — Part 5: Earthquake actions — New Zealand, incorporates the 2022 National Seismic Hazard Model and more recent engineering practice.
It can be used for new buildings as an Alternative Solution under the New Zealand Building Code, but it does not simply replace NZS 1170.5:2004 for every project.
A seventh revision was published in 2025 but withdrawn in March 2026. The 2016 edition therefore remains current.
Other parts of the IS 1893 series cover particular structure types, so engineers should identify the relevant part for the project rather than treating Part 1 as the complete seismic design specification for every structure.
China: GB/T 50011 and GB 55002
China’s seismic framework includes GB/T 50011-2010, Standard for Seismic Design of Buildings, as partially revised in 2024, together with the mandatory GB 55002-2021, General Code for Seismic Precaution of Buildings and Municipal Engineering.
The 2024 revision of GB/T 50011 became effective on 1 August 2024. Its designation as GB/T identifies it as a recommended national standard, while GB 55002 forms part of the mandatory general-code framework.
Engineers should verify the documents and provisions applicable to the specific project and jurisdiction.
ISO 3010
ISO 3010:2017, Bases for design of structures — Seismic actions on structures, remains the current published edition.
It provides general principles for determining seismic actions and can serve as a source document for national standards and regulations rather than functioning as a legally binding building code by itself.
A revision of ISO 3010 is under development.
Its direct scope also has important limits. ISO 3010 does not apply to bridges, dams, geotechnical works, tunnels, or nuclear power plants.
ISO 19901-2 for Offshore Structures
ISO 19901-2:2026, Specific requirements for offshore structures — Part 2: Seismic design, provides requirements and recommendations for seismic design and assessment of offshore structures.
The 2026 edition supersedes the 2022 edition.
It addresses seismic actions and structural assessment together with associated geological hazards, including liquefaction, slope instability, fault displacement, and tsunamis.
Seismic Design of Concrete Structures
Seismic design of reinforced concrete requires more than providing sufficient resistance for calculated forces.
Earthquake-resistant concrete design also depends on:
reinforcement detailing;
confinement;
shear resistance;
anchorage and development;
beam-column joint behavior;
deformation capacity;
the intended hierarchy of strength.
In the United States, seismic demands and overall seismic criteria are established through the adopted building code and ASCE 7, while ACI 318 provides concrete-specific design and detailing requirements.
In Europe, EN 1998 defines the seismic action and seismic-specific requirements for concrete buildings, including rules related to ductility and capacity design, while EN 1992 provides the underlying concrete resistance provisions.
The relationship between the seismic standard and material standard therefore depends on the regulatory framework being used.
Seismic Design of Steel Structures
Steel structures can provide substantial ductility and energy-dissipation capacity, but only when the structural system, members, local stability, connections, and detailing are designed consistently with the intended seismic behavior.
Seismic design framework for steel structures in the US and Europe. A standard steel strength check does not by itself demonstrate full seismic-code compliance.
For US building design, ASCE 7, AISC 360, AISC 341, and where applicable AISC 358 perform different but connected roles.
AISC 360 provides general member and connection resistance requirements, while AISC 341 adds seismic-specific requirements for the seismic-force-resisting system. AISC 358 provides prequalified moment-frame connections where applicable.
For European projects, EN 1998 defines seismic action and steel-specific seismic rules such as ductility requirements, dissipative behavior, and capacity-design provisions, while EN 1993 supplies the general member and connection resistance models.
A normal steel strength check under a seismic load combination should therefore not be confused with verification of all seismic-specific requirements of the governing code.
The analysis method required or permitted by a seismic standard depends on the structural system, dynamic characteristics, regularity, seismic demand, and other code-defined conditions.
Equivalent Lateral Force Analysis
Equivalent lateral force analysis, also referred to as the lateral force method in some standards, represents earthquake effects using static lateral forces distributed through the structure.
It can provide an efficient method for structures that satisfy the relevant code limits, but it does not explicitly capture the contribution of multiple vibration modes in the same way as modal analysis.
Modal Response Spectrum Analysis
Modal response spectrum analysis evaluates the dynamic response of a structure using its natural modes and a design response spectrum.
A response spectrum represents the peak response of single-degree-of-freedom systems with a given damping ratio over a range of natural periods.
Design codes typically provide smoothed spectra representing seismic hazard and site conditions rather than the response to a single earthquake record.
The response of relevant structural modes is calculated and then combined using the modal-combination procedure required by the applicable methodology, such as SRSS or CQC.
Because modal response-spectrum results represent peak responses, they do not retain a unique physical algebraic sign in the same way as ordinary static results. This becomes important when seismic effects are combined with gravity loads or earthquake actions from other directions.
Response-History Analysis
Response-history analysis determines structural response over time using earthquake ground-motion histories.
The analysis may be linear or nonlinear depending on the engineering objective and governing requirements.
Nonlinear response-history analysis can represent inelastic structural behavior in substantially greater detail, but it also requires more rigorous assumptions concerning ground-motion selection and scaling, nonlinear component behavior, damping, numerical convergence, and interpretation of results.
A more sophisticated analysis method is not automatically a better method. The method needs to be appropriate for the structure, available input data, engineering objective, and governing standard.
Some seismic standards also permit nonlinear static, or pushover, analysis for particular applications.
Seismic Design for Bridges, Offshore, and Other Structures
Seismic requirements for one structural category should not automatically be transferred to another.
Bridges
Bridge seismic design can involve:
site-specific seismic hazard;
foundation and soil-structure interaction;
pier ductility;
bearing and joint behavior;
unseating prevention;
isolation or energy-dissipation systems;
displacement demand;
post-earthquake functionality.
Dedicated bridge standards should be used where required. General seismic standards do not necessarily apply directly to bridge design.
Offshore Structures
Offshore seismic design introduces additional interactions between structural response, foundations and pile-soil behavior, and the hydrodynamic added mass of the surrounding water.
ISO 19901-2:2026 covers seismic design and assessment of offshore structures and includes recommendations for floating structures.
It also addresses relevant geological hazards such as liquefaction, slope instability, fault displacement, and tsunamis.
For structures in high-seismic areas or with high consequence levels, seismic assessment can also require site-specific probabilistic seismic hazard analysis.
Industrial and Special Structures
Industrial structures can differ substantially from ordinary buildings in geometry, mass distribution, equipment loads, support conditions, and required performance.
Examples include:
process structures;
pipe racks;
towers and chimneys;
storage structures;
power-generation structures;
mining and heavy industrial structures.
The governing seismic framework should therefore be established for the actual structure type before selecting analysis procedures and verification criteria.
General building provisions may be part of that framework, but industry-specific or structure-specific standards can also apply.
Structural Verification in SDC Verifier
Seismic analysis and structural verification are related but separate stages of the engineering workflow.
For models analyzed in Ansys Mechanical, Femap, or Simcenter 3D, SDC Verifier can work with supported result cases from the host solver. These results can then be organized as Individual Loads for post-processing and structural verification.
In Ansys, an Individual Load can represent an imported step or substep result. In Femap, an existing Output Set can be used. In Simcenter 3D, an existing Result Case can be converted into an Individual Load.
SDC Verifier Standalone can also create Individual Loads from existing Output Sets or calculate supported analyses using its built-in solver.
Its built-in analysis types include linear static, nonlinear static, linear buckling, normal modes, and custom jobs. Response-spectrum analysis is not among them.
Working with Seismic Result Cases
When seismic analysis results are already available, SDC Verifier can organize them together with other result cases for subsequent structural verification.
A Standard Load Set is a factored linear combination of Individual Loads.
For analyses where linear superposition is valid, this allows available seismic result cases to be combined with gravity and other applicable load cases without solving every linear combination as a separate FEA run.
Logic Factors can generate combinations with alternative factors, including opposite signs. This can be useful when verification combinations require positive and negative factors or alternative directional factors.
This functionality is part of the post-processing and verification workflow rather than the seismic dynamic analysis itself.
Modal analysis, response-spectrum calculation, modal combination, and the appropriate treatment of modal signs remain part of the seismic analysis methodology and solver workflow.
Applying a positive or negative factor to an imported response-spectrum result does not reconstruct the physical sign correlation between individual modal responses.
Results from nonlinear analyses cannot generally be recombined using linear superposition. Where nonlinear interaction between loads matters, the combined loading needs to be represented in the nonlinear analysis itself.
Verification Against Implemented Standards
SDC Verifier does not provide predefined verification according to the seismic design codes discussed in this article, such as ASCE 7, AISC 341, AISC 358, Eurocode 8, NZS 1170.5, IS 1893, or GB/T 50011.
It also does not provide predefined concrete design verification according to ACI 318 or Eurocode 2.
Instead, seismic analysis results can be used as input to structural checks that are implemented in SDC Verifier.
For example, where applicable to the project, structural steel members subjected to seismic load combinations can be checked according to AISC 360-22.
This verifies the relevant AISC 360 member requirements. It does not by itself demonstrate compliance with the seismic-specific requirements of AISC 341 or ASCE 7.
The same distinction applies to other structural checks.
Passing any structural check in SDC Verifier under a seismic result combination does not by itself demonstrate compliance with the complete seismic design standard.
Requirements such as capacity design, seismic-system restrictions, ductility-related detailing, overstrength provisions, prequalified seismic connections, and drift limits remain part of the engineer’s seismic design process unless a specific requirement is explicitly covered by the verification being performed.
Custom Checks
Where a required criterion is not available as a predefined check, Custom Checks can extend the verification workflow using user-defined formulas.
Custom Checks can use available FEA results, material and property variables, constants, classifications, standard tables, mathematical functions, and results from other checks.
Available result variables include stresses and strains, beam forces and moments, and plate or shell forces and moments.
This makes Custom Checks suitable for user-defined criteria such as:
stress-based utilization;
member force-to-capacity ratios;
capacity or overstrength formulas where the necessary inputs are available;
calculations combining FEA demand with section, material, or project-specific parameters;
logical pass/fail criteria.
Custom Checks are not a substitute for a complete seismic code or seismic design workflow, and they do not provide a general workflow for interstory drift or global structural-irregularity assessment.
Reviewing Governing Results
A Load Group creates an envelope over Individual Loads, Load Sets, or other Load Groups and can identify minimum, maximum, and absolute values for quantities such as stresses, displacements, and forces.
This allows engineers to review governing results across large sets of analysis cases and verification combinations rather than inspecting every case independently.
The resulting analyses, checks, combinations, model information, result tables, plots, and supporting calculation data can then be organized into SDC Verifier reports.
Need Support With Structural Verification?
For complex engineering projects, SDC Verifier’s engineering team can support structural calculations, standards-based checks, verification workflows, optimization, and technical reporting using your FEA model and project requirements.
Seismic design is the process of analyzing, designing, detailing, and verifying a structure so that it can satisfy the required performance and safety criteria when subjected to earthquake-induced ground motion.
It includes seismic hazard definition, structural analysis, selection and detailing of the seismic-force-resisting system, deformation control, and verification according to the applicable codes and standards.
Which codes govern seismic design in the United States?
For most US buildings, governing requirements come from the building code adopted by the relevant jurisdiction, commonly an edition of the International Building Code.
The 2024 IBC references ASCE/SEI 7-22 for seismic loads and design criteria, ANSI/AISC 360-22 and ANSI/AISC 341-22 for applicable structural steel design, and ACI 318-19 for structural concrete.
ANSI/AISC 358-22 provides prequalified connections for special and intermediate steel moment frames.
What is a Seismic Design Category?
Within the ASCE 7 framework, a Seismic Design Category is a classification used to determine the seismic design requirements applicable to a building or structure.
Its determination depends on parameters defined by the standard, including seismic hazard and the risk category of the structure.
The resulting category affects requirements for analysis, structural systems, detailing, structural irregularities, and other aspects of earthquake-resistant design.
What is the difference between seismic analysis and seismic design?
Seismic analysis determines how a structural model responds to earthquake actions, producing quantities such as forces, stresses, accelerations, reactions, and displacements.
Seismic design is broader. It uses those analysis results together with code requirements to select the structural system, design and detail components and connections, control deformation and failure mechanisms, and verify that the complete structure satisfies the required seismic criteria.
Analysis provides the structural response. Design determines how that response is used to achieve the required performance.
