Service overview
Infrastructure, earthquake analysis, geotechnics, transportation, water resources, construction materials. This service is part of that division and is scoped individually around what you need to learn, decide or publish.
Earthquakes subject structures to dynamic loads of short duration, high intensity and great uncertainty. A structure that behaves well under static loads can fail under seismic shaking because of its flexibility, irregularity or lack of ductility. Seismic analysis evaluates how a structure will respond and whether its performance is acceptable, in terms of strength, drift, damage and, in research, probability of exceeding performance levels.
Methods range from simple equivalent static procedures to nonlinear time-history analysis with recorded or simulated ground motions. The more sophisticated the method, the more it depends on assumptions about modelling, material behaviour and the selection of ground motions. Credible seismic research therefore reports not only the results but the choices behind them, and tests how sensitive the conclusions are to those choices.
If you plan to publish the outcome, see manuscript & publication support, for example computational & simulation manuscripts or original research article writing.
What this service covers
Problems this service can address
- Uncertain ground-motion input for analysis
- Nonlinear behaviour in members and connections
- Interpreting performance relative to damage states
Methods and analytical approaches
- Equivalent static and response-spectrum analysis
- Nonlinear static (pushover) and time-history analysis
- Ground-motion selection and scaling concepts
- Fragility and performance-level evaluation
Applications
- Seismic assessment of buildings and bridges
- Base-isolation and retrofit studies
- Parametric studies for research papers
Relevant engineering disciplines
Scope, inputs and deliverables
Scope of work
- Definition of the technical question, system boundary and success criteria
- Analysis, modelling or data work appropriate to your inputs
- Results with stated assumptions and limits of validity
- Documentation in a form suitable for reports or publication
- Feasibility check on: structural description and material data
Typical inputs required from you
- Structural description and material data
- Site or ground-motion information
- Criteria for acceptable performance
Deliverables
- Seismic analysis report
- Response and damage indicators
- Assumption and limitation register
Highly specialised requests are first checked for feasibility from this information. Please do not send confidential data through the public form; describe it first and agree secure transfer afterwards.
Project workflow and method
- 01Enquiry and requirement assessment
- 02Technical scoping and proposal
- 03Execution
- 04Quality review and delivery, with an agreed round of revisions
Read the full project workflow.
In depth: how the work is done
Equivalent static and response-spectrum analysis
Equivalent static methods represent seismic loading by lateral forces derived from a design spectrum and the structure's period and mass. Response-spectrum analysis combines the contributions of several vibration modes using the spectrum, and modal combination rules. Both assume linear behaviour with reduction factors that account for expected ductility. They are suitable for regular structures and for preliminary evaluation, with known limitations when nonlinearity or irregularity is significant.
Nonlinear static (pushover) analysis
Pushover analysis applies an increasing lateral load pattern to a nonlinear model until a target displacement or collapse mechanism is reached, producing a capacity curve. Comparison of capacity with seismic demand, for example via the capacity-spectrum or displacement-coefficient approaches, indicates performance. It reveals weak storeys and sequence of yielding. Its limitation is that it assumes a fixed load pattern and mainly first-mode response, so for tall or irregular structures time-history analysis is preferable.
Time-history analysis and ground motion selection
Nonlinear time-history analysis integrates the equations of motion under ground-motion records, capturing cyclic degradation, higher modes and duration effects. Records are selected and scaled to match a target spectrum or scenario, with attention to magnitude, distance, site conditions and spectral shape. The number of records influences the reliability of mean response estimates, and record-to-record variability is part of the answer rather than a nuisance.
Modelling choices: nonlinearity, damping and soil-structure interaction
Results depend on how members are modelled: plastic hinges or fibre sections, degradation of stiffness and strength, joint behaviour and the contribution of non-structural elements. Damping assumptions, particularly Rayleigh damping, can distort response if poorly chosen. Soil-structure interaction can lengthen period and change demand and is significant for stiff structures on soft soil. We document choices and test sensitivity.
Fragility and performance-level evaluation
Fragility curves give the probability of exceeding a damage state as a function of ground-motion intensity. They can be derived from analysis results using incremental dynamic analysis or other approaches, with uncertainty from both ground motion and modelling. Performance levels, such as immediate occupancy or collapse prevention, are linked to limits on drift or other measures. The assumptions linking response to damage are stated, since they carry considerable uncertainty.
Quality control and good practice
Quality-control approach
- Models and analyses are checked against hand calculations, published benchmarks or your data where available.
- Assumptions, boundary conditions and sources are listed in the deliverable.
- Units, symbols and terminology are checked for consistency.
- Limits of validity are stated; the work is research-level analysis, not certification.
Common pitfalls this service helps avoid
- Too few ground motions. A small record set gives unreliable estimates of mean response and its variability.
- Using a pushover for irregular tall structures. Higher-mode and torsional effects may invalidate a fixed-pattern pushover.
- Arbitrary damping assumptions. Poorly chosen Rayleigh damping can artificially damp or amplify response.
- Ignoring model uncertainty. Fragility derived from a single deterministic model understates total uncertainty.
What good reporting looks like
A seismic analysis report describes the structure and model, the material and component behaviour, the seismic hazard or design spectrum and ground-motion selection, the analysis methods, results such as drift, forces, capacity curves and damage indicators, sensitivity to modelling choices, fragility or performance evaluation if applicable and limitations. It is research-level analysis and is not a substitute for a seismic assessment required by regulations, which must be carried out by licensed engineers following applicable codes.
An illustrative scenario
Hypothetical example written for explanation. It is not a client case, a result or a testimonial.
Suppose a researcher is evaluating a mid-rise frame structure with a soft ground storey. A response-spectrum analysis suggests acceptable drift, but a pushover analysis shows a concentration of deformation in the first storey and a mechanism at modest load. A set of time-history analyses with scaled records confirms large drift demand at the first storey in several records. The report presents the median and dispersion of drift, notes the sensitivity to damping and recommends a retrofit concept to be studied further.
Questions to settle before you begin
- Which seismic hazard level or scenario am I considering?
- How will I select and scale ground motions?
- Which nonlinear member behaviours must I model?
- How uncertain are my modelling assumptions?
- Which performance criteria will I use to judge the structure?
Key terms
- Response spectrum
- A plot of peak response of single-degree-of-freedom systems of varying period to a ground motion.
- Pushover analysis
- A nonlinear static analysis under increasing lateral load.
- Ductility
- The ability of a structure or member to deform inelastically without losing capacity.
- Fragility curve
- A function giving the probability of exceeding a damage state versus intensity.
- Inter-storey drift
- The relative lateral displacement between adjacent floors.
Working together on Civil, Structural & Infrastructure Engineering projects
Civil, structural and infrastructure research engagements start with a description of the structure or system, the loads and environment, the codes or standards that provide context and the questions the research must answer. We ask for drawings or descriptions, material data, monitoring data where they exist and any previous analyses. The work provides research analysis, literature-based assessment and documentation. It does not replace the design responsibility of licensed engineers, code compliance checks or site-specific professional judgement, and it states clearly where those are required.
Frequently asked questions
Is a seismic study a safety certification?
No. It is an analysis in support of research or engineering evaluation, not a certification of safety.
Do you perform code-compliant seismic design?
No. Code-based design and assessment of real buildings must be carried out by licensed professionals.
Can you help with ground motion selection?
Yes. Selection and scaling concepts and their influence on results can be discussed and documented for research use.
Can you model base isolation or retrofit?
Research-level modelling of isolation and retrofit options is possible with suitable inputs.
Do you provide experimental testing?
No. We analyse and model using data you supply.
How is this service scoped and priced?
After your enquiry we review what you need, ask for missing information and send a written scope and quotation. Price depends on complexity, deliverables and timeline. See the project workflow.