Langford Analytic · Knowledge Base
Seismic Analysis & Qualification
Seismic qualification requires more than applying an acceleration value to a structural model. Structural response depends on the frequency content of the input motion, system dynamics, damping, modal participation, support conditions, mass distribution, load combinations and the way peak responses are combined. This section covers the complete engineering workflow from seismic input definition and response-spectrum analysis through equipment qualification, anchorage, test correlation and defensible reporting — organised into twelve technical groups: seismic fundamentals, response spectra, modal response spectrum analysis, directional response, stress and force recovery, structural modelling, equipment and cabinet qualification, anchorage and supports, qualification by analysis and test, nonlinear and advanced methods, software implementation, and verification, review and reporting.
Seismic Fundamentals
Seismic Analysis FundamentalsHow earthquake ground motion becomes structural response — the complete chain from seismic input through dynamic amplification to engineering assessment.Earthquake Ground Motion FundamentalsHow seismic ground motion is characterised — amplitude, frequency content, duration, phase and the difference between ground motion and structural response.Ground Response vs Floor ResponseThe critical distinction between ground motion at the base of a structure and the amplified, filtered motion at upper floors — and why equipment qualification depends on it.Acceleration, Velocity and Displacement in Seismic ResponseHow acceleration, velocity and displacement each reveal different aspects of seismic response — and why all three matter for structural assessment.Frequency, Period and Structural ResponseHow the frequency content of seismic input and the natural period of a structure combine to determine dynamic amplification — the foundation of response-spectrum analysis.Resonance in Seismic LoadingHow seismic input frequencies near structural natural frequencies produce resonant amplification — and why seismic resonance differs from harmonic excitation resonance.Rigid vs Flexible Equipment BehaviourWhy the distinction between rigid and flexible equipment is fundamental to seismic qualification — and how it determines whether equipment sees static acceleration or dynamic amplification.Base Excitation FundamentalsHow seismic ground motion enters a structure as base excitation — the support motion formulation and its implications for modal response spectrum analysis.Seismic Mass and Inertial LoadingHow seismic acceleration converts to inertial loading through mass distribution — and why mass modelling decisions govern seismic response prediction.Centre of Gravity and Mass Distribution EffectsHow the location of the centre of gravity and the distribution of mass affect seismic response — eccentricity, torsion and overturning moments.
Response Spectra
Response Spectrum FundamentalsWhat a response spectrum represents — the peak response of single-degree-of-freedom oscillators across a range of frequencies — and why it is the central tool of seismic analysis.Design Response SpectraHow design response spectra are constructed — codified, smoothed spectra representing seismic hazard for a site, and how they differ from specific ground motion spectra.Floor Response SpectraHow floor response spectra capture the amplified, filtered motion at structural floors — and why they are the primary input for equipment seismic qualification.Ground Response SpectraHow ground response spectra characterise seismic motion at the ground or foundation level — and how they differ from floor response spectra.Acceleration Response SpectraHow acceleration response spectra are constructed and interpreted — the most commonly used spectral form for structural seismic assessment.Velocity and Displacement Response SpectraHow velocity and displacement response spectra complement acceleration spectra — and why displacement spectra matter for long-period structures and isolation systems.Damping in Response Spectrum AnalysisHow damping ratio modifies spectral acceleration — and why selecting the correct damping value is critical for seismic response prediction.Effect of Damping Ratio on Seismic ResponseHow varying the damping ratio changes spectral acceleration — quantifying the sensitivity of seismic response to damping assumptions.Interpreting Multiple Damping CurvesHow response spectra with multiple damping curves are used — selecting the appropriate curve for structural and equipment damping.Frequency-Domain Interpretation of Seismic SpectraHow response spectra encode frequency-domain information — and how to read spectral shape to understand which frequencies drive structural response.Interpolation of Response Spectrum DataHow response spectrum data is interpolated for analysis — log-space interpolation, frequency points and the implications for modal response accuracy.Spectrum Scaling and ModificationHow response spectra are scaled for different hazard levels, damping ratios or site conditions — and the engineering implications of scaling.Conservative Use of Response SpectraHow conservatism enters response spectrum analysis — enveloped spectra, broadened spectra, and the trade-off between conservatism and realistic response prediction.Horizontal and Vertical Seismic SpectraHow horizontal and vertical seismic spectra differ — frequency content, amplitude and the implications for directional response analysis.Location-Dependent Floor Response SpectraHow floor response spectra vary with structural location — elevation, plan position and proximity to structural walls all change the spectral shape.
Modal Response Spectrum Analysis
Modal Response Spectrum AnalysisThe complete modal response spectrum method — from modal extraction through spectral acceleration lookup to modal combination — the workhorse of seismic structural assessment.Modal Analysis for Seismic AssessmentHow modal analysis is set up for seismic assessment — mass normalisation, base excitation formulation and the extraction of modes relevant to seismic response.Natural Frequencies and Mode Shapes — Seismic ContextHow natural frequencies and mode shapes govern seismic response — which modes contribute, which modes can be truncated and how mode shapes reveal load paths.Modal Participation FactorsHow modal participation factors quantify the contribution of each mode to base excitation response — and why they are essential for understanding modal truncation.Effective Modal MassHow effective modal mass determines the seismic force contribution of each mode — and how it is used to judge whether enough modes have been retained.Cumulative Modal Mass ParticipationHow cumulative modal mass participation is used as a practical criterion for modal truncation — typical thresholds and their limitations.Selecting the Required Number of ModesHow to determine how many modes are needed for a seismic analysis — mass participation, frequency range and the influence of local modes.Modal TruncationWhat modal truncation means — which modes are discarded, what response is lost and how truncation error is assessed.Missing Mass CorrectionHow missing mass correction accounts for the seismic contribution of truncated high-frequency modes — the residual rigid response of modes beyond the cut-off.Residual Rigid ResponseHow the residual rigid response from high-frequency modes is calculated and combined with modal response — and why it matters for equipment with high-frequency content.Mode Acceleration MethodHow the mode acceleration method improves on mode displacement by separating pseudo-static and dynamic contributions — relevant for high-frequency residual response.High-Frequency Residual ResponseHow high-frequency modes beyond the extracted range contribute to seismic response as rigid-body acceleration — and how this is accounted for in practice.Closely Spaced ModesHow closely spaced modes interact — and why SRSS can be unconservative when modal frequencies are within approximately 10 percent of each other.SRSS Modal CombinationHow the Square Root of Sum of Squares method combines modal peak responses — its assumptions, limitations and when it is appropriate.CQC Modal CombinationHow the Complete Quadratic Combination method accounts for modal correlation — and why it is preferred for structures with closely spaced modes.SRSS vs CQCWhen to use SRSS and when to use CQC — the engineering basis for choosing between modal combination methods.Choosing a Modal Combination MethodPractical guidance for selecting between SRSS, CQC and other modal combination methods — based on modal frequency spacing, damping and structural configuration.
Directional Response
Seismic Directional ComponentsHow earthquake ground motion is decomposed into horizontal and vertical components — and how each component drives different structural response.East–West and North–South Seismic InputHow horizontal seismic input is applied along two orthogonal directions — and the implications for structures with non-axisymmetric stiffness.Vertical Seismic ResponseHow vertical seismic input differs from horizontal — higher frequency content, different spectral shape and different structural response mechanisms.Horizontal vs Vertical ResponseThe engineering differences between horizontal and vertical seismic response — frequency content, modal contribution and load path implications.Directional Combination of Seismic ResponseHow responses from orthogonal seismic directions are combined — 100-40-40, SRSS directional and the engineering basis for each rule.100-40-40 Seismic CombinationHow the 100-40-40 directional combination rule works — applying 100 percent of one direction with 40 percent of the orthogonal directions.SRSS Directional CombinationHow SRSS directional combination differs from 100-40-40 — taking the square root of the sum of squared responses from each direction.Simultaneous vs Non-Simultaneous Directional PeaksWhy directional combination is needed — peak responses in orthogonal directions do not occur simultaneously, and combining them requires a statistical approach.Directional Combination of Stress ResultsHow directional combination is applied to stress results — combining modal responses first, then combining directional responses, and the order of operations.Orientation of Equipment Relative to Seismic AxesHow the orientation of equipment relative to the seismic input axes affects response — and why orientation must be considered in qualification.
Stress & Force Recovery
Recovering Forces from Response Spectrum AnalysisHow forces are recovered from modal response spectrum analysis — modal force combination and the interpretation of peak forces.Recovering Displacements from Response Spectrum AnalysisHow displacements are recovered from response spectrum analysis — and why recovered displacements represent peak modal values, not a simultaneous deflected shape.Recovering Accelerations from Response Spectrum AnalysisHow accelerations are recovered from response spectrum analysis — absolute vs relative acceleration and the implications for equipment loading.Recovering Stresses from Response Spectrum AnalysisHow stresses are recovered from response spectrum analysis — modal stress combination and the critical interpretation of combined stress values.Modal Stress CombinationHow stress components from individual modes are combined — SRSS or CQC of each stress component separately, and why this matters for equivalent stress calculation.Von Mises Stress in Response Spectrum AnalysisThe problem of calculating von Mises stress from response spectrum results — why taking von Mises of combined modal stresses is not the same as combining von Mises of each mode.SRSS of Stress Components vs Von Mises of Combined ComponentsThe critical distinction between SRSS-combining individual stress components and computing von Mises from already-combined components — and which is correct.Peak Response vs Simultaneous Stress StateWhy response spectrum results represent statistical peak combinations, not a physically simultaneous stress state — and what this means for margin assessment.Element Force RecoveryHow element-level forces are recovered from seismic analysis — beam forces, shell resultants and solid stresses from modal response spectrum results.Interface Load RecoveryHow interface loads between structural components are recovered from seismic analysis — bolt loads, connection forces and equipment interface reactions.Support Reaction RecoveryHow support reactions are recovered from seismic analysis — and why reactions from modal combination differ from a static equilibrium check.Seismic Load EnvelopesHow seismic load envelopes are constructed — combining directional responses, load combinations and operating loads with seismic demand.Seismic Margin of Safety AssessmentHow margins of safety are calculated for seismic loading — comparing seismically recovered stresses and forces with allowables under relevant load combinations.
Structural Modelling
Seismic FEA Modelling StrategyHow to build an FEA model suitable for seismic analysis — mass distribution, stiffness representation, boundary conditions and the modelling decisions that govern response prediction.Mass Modelling for Seismic AnalysisHow mass is represented in seismic FEA models — lumped vs consistent mass, non-structural mass and the effect of mass distribution on modal response.Lumped Masses and Non-Structural MassHow non-structural mass — equipment, contents, cladding — is represented as lumped mass in seismic models and why it can dominate response.Equipment Mass RepresentationHow equipment mass is represented in seismic FEA models — point mass, distributed mass and the effect of equipment mass location on response.Support StiffnessHow support stiffness affects seismic response — rigid vs flexible supports and the implications for modal frequencies and floor response spectra.Boundary Conditions for Seismic ModelsHow boundary conditions are specified for seismic analysis — base fixity, floor flexibility and the representation of structural interfaces.Floor and Foundation FlexibilityHow floor and foundation flexibility modify seismic input — and why assuming rigid supports can be non-conservative for equipment qualification.Joint Stiffness in Seismic ModelsHow joint stiffness affects seismic response — bolted and welded joint representation and the effect of joint flexibility on modal frequencies.Bolted Joint Representation in Seismic ModelsHow bolted joints are represented in seismic FEA — rigid links, spring elements, contact and the trade-offs of each approach for dynamic response.Welded Joint Representation in Seismic ModelsHow welded joints are represented in seismic FEA — typically rigid or shared nodes, and when weld flexibility matters for dynamic response.Contact and Gap Behaviour Under Seismic LoadingHow contact and gap elements behave under seismic loading — opening, closing and sliding at interfaces and the implications for linear response spectrum analysis.Cabinet and Frame ModellingHow electrical and control cabinets are modelled for seismic analysis — frame elements, panel elements, mass distribution and the representation of internal equipment.Panel ModellingHow cabinet panels and structural panels are modelled for seismic analysis — shell elements, stiffness representation and the effect of panel modes on response.Local Panel ModesHow local panel modes can appear in seismic analysis — and why they may or may not contribute to equipment qualification depending on frequency and coupling.Avoiding Non-Physical Local ModesHow to identify and eliminate non-physical local modes in seismic models — mesh sensitivity, artificial constraints and mode shape inspection.Mesh Strategy for Seismic AnalysisHow mesh density affects seismic analysis results — mass distribution, stiffness representation and the trade-off between mesh refinement and model size for modal analysis.Model Reduction for Seismic AssessmentHow model reduction techniques are used to make seismic analysis tractable — static condensation, component mode synthesis and the trade-offs of each method.Substructuring and SuperelementsHow substructuring and superelement methods are applied to seismic analysis — reducing large structural models while preserving dynamic characteristics.Component Mode SynthesisHow Component Mode Synthesis (CMS) combines substructure modes into a reduced system — and its application to seismic analysis of large structural assemblies.
Equipment & Cabinet Qualification
Seismic Qualification of EquipmentWhat seismic qualification of equipment means — demonstrating that equipment will perform its safety function during and after an earthquake — and the analysis and test routes to qualification.Seismic Qualification of CabinetsHow electrical and control cabinets are seismically qualified — structural integrity and functional integrity requirements and the analysis and test approaches used.Seismic Analysis of Electrical CabinetsHow seismic analysis of electrical cabinets is performed — modelling, floor response spectra input, stress recovery and qualification checks.Seismic Analysis of Control CabinetsHow seismic analysis of control cabinets differs from electrical cabinets — instrument density, internal mass distribution and functional integrity requirements.19-Inch Rack-Mounted EquipmentHow 19-inch rack-mounted equipment is assessed for seismic loading — rack dynamic behaviour, slide rail interaction and equipment-to-cabinet interface.Rack-Mounted Equipment Dynamic BehaviourHow rack-mounted equipment behaves dynamically — the rack as a flexible frame, equipment as distributed mass and the interaction between them.Equipment-to-Cabinet InteractionHow equipment inside a cabinet interacts with the cabinet structure — mass coupling, resonance and the load path from equipment to cabinet to floor.Internal Equipment Mass RepresentationHow the mass of internal equipment is represented in cabinet seismic models — point mass, distributed mass and the effect on modal response.Shelf and Rail BehaviourHow shelves and slide rails behave under seismic loading — load transfer, lateral stiffness and the potential for resonance or disengagement.Door and Panel BehaviourHow cabinet doors and panels behave under seismic loading — rattle, deformation, latch loading and the implications for functional qualification.Cabinet Frame Load PathsHow seismic loads travel through a cabinet frame — from internal equipment mass through shelves and rails to the frame and base connections.Cabinet Base ConnectionsHow cabinet base connections transfer seismic loads to the floor — anchor bolts, baseplate stiffness and the load path from cabinet to structure.Equipment Functional Integrity Under Seismic LoadingWhy seismic qualification requires functional integrity, not just structural survival — relays chatter, connector engagement, instrument accuracy and post-event operability.Structural Integrity vs Functional QualificationThe distinction between structural integrity — the cabinet survives — and functional qualification — the equipment performs its safety function — and why both are required.Seismic Qualification of Mounted ComponentsHow individual mounted components — relays, breakers, instruments — are seismically qualified, and the relationship between component qualification and cabinet-level qualification.Cabinet-Level vs Component-Level QualificationWhen cabinet-level qualification is sufficient, when component-level qualification is required, and how the two approaches relate and combine.
Anchorage & Supports
Seismic Anchorage FundamentalsHow seismic anchorage works — transferring inertial loads from equipment to structure through anchor bolts, baseplates and welded connections, and the failure modes that govern design.Anchor Bolt Analysis Under Seismic LoadingHow anchor bolts are analysed for seismic loading — combined tension and shear, concrete capacity, edge distance and group effects.Baseplate Behaviour Under Seismic LoadingHow baseplates behave under seismic loading — prying, bending, stiffness and the interaction between baseplate flexibility and anchor load distribution.Anchor Tension and Shear InteractionHow tension and shear are combined in anchor bolt design under seismic loading — interaction equations, code requirements and the physics of combined loading.Anchor Group Load DistributionHow seismic loads are distributed among multiple anchor bolts in a group — eccentricity, baseplate flexibility and the calculation of individual anchor loads.Concrete Anchorage ConsiderationsHow concrete capacity governs anchorage design under seismic loading — concrete breakout, pull-out, side-face blowout and the effect of cracking and edge distance.Welded Base ConnectionsHow welded base connections are designed for seismic loading — weld capacity, baseplate stiffness and the load path from equipment to structure.Bolted Base ConnectionsHow bolted base connections are designed for seismic loading — anchor bolt type, preload, baseplate stiffness and the trade-offs between welded and bolted connections.Seismic Support StructuresHow equipment support structures are designed for seismic loading — frames, brackets, platforms and the load path from equipment to building structure.Equipment Skid Seismic AnalysisHow skid-mounted equipment is analysed for seismic loading — skid stiffness, equipment mass distribution, anchorage and the interaction between skid and supporting structure.Bracing for Seismic LoadsHow bracing is designed for seismic loads — cross-bracing, eccentric bracing and the effect of bracing stiffness on seismic response of supported equipment.Support Flexibility and Load RedistributionHow support flexibility redistributes seismic loads — and why assuming rigid supports can produce incorrect anchor loads and modal frequencies.Uplift and SeparationHow seismic overturning moments produce uplift and separation at base connections — and the implications for anchor bolt design and linear analysis assumptions.Sliding and Friction Under Seismic LoadingHow sliding and friction affect seismic response of unanchored or flexible equipment — and why linear analysis cannot capture sliding behaviour.Anchorage Failure ModesHow anchorage connections fail under seismic loading — bolt fracture, concrete breakout, baseplate yielding, weld fracture and the sequence of failure in overload conditions.
Qualification by Analysis & Test
Seismic Qualification by AnalysisHow seismic qualification by analysis is performed — response spectrum analysis, stress recovery, margin assessment and the documentation required for qualification by analysis.Seismic Qualification by TestHow seismic qualification by test is performed — shake table testing, required response spectrum, test response spectrum and acceptance criteria.Analysis vs Test QualificationWhen to qualify by analysis, when to qualify by test, and when both are needed — the engineering basis for selecting the qualification route.Shake Table Testing FundamentalsHow shake table testing works — table specifications, input motion, control systems and the practical considerations for seismic qualification testing.Required Response Spectrum for TestingHow the Required Response Spectrum (RRS) is developed for seismic qualification testing — and how it relates to the floor response spectrum at the equipment location.Test Response SpectrumHow the Test Response Spectrum (TRS) is generated and compared with the RRS — and why the TRS must envelop the RRS for qualification to be valid.Test Input Motion DevelopmentHow the input motion for shake table testing is developed — spectrum-compatible time histories, multi-axis inputs and the practical constraints of table capability.Multi-Axis Shake Table TestingHow multi-axis shake table testing is performed — simultaneous horizontal and vertical input, table control and the advantages over single-axis testing.Test Fixture EffectsHow test fixtures affect seismic qualification test results — fixture stiffness, resonances and the representation of in-service boundary conditions.Test Boundary ConditionsHow test boundary conditions are specified and verified for seismic qualification — and why boundary condition mismatch between test and service can invalidate results.Test Instrumentation for Seismic TestingHow seismic qualification tests are instrumented — accelerometer placement, control sensors, response measurement and the data needed for qualification evidence.Accelerometers for Seismic TestingHow accelerometers are used in seismic qualification testing — type, sensitivity, mounting, calibration and the selection of measurement locations.Analysis-to-Test Correlation for Seismic QualificationHow seismic analysis results are correlated with shake table test data — modal correlation, response comparison and the resolution of discrepancies.Modal Survey Before Seismic TestWhy a modal survey before seismic testing is valuable — identifying natural frequencies, mode shapes and potential resonances before the qualification test.Resonance Search TestingHow resonance search testing is performed before seismic qualification — low-level sine sweep or random excitation to identify frequencies and damping.Post-Test Inspection for Seismic QualificationHow post-test inspection is performed after seismic qualification testing — visual inspection, functional checks, structural integrity verification and documentation.Qualification Evidence and AcceptanceHow seismic qualification evidence is compiled and assessed — test reports, analysis reports, inspection records and the acceptance criteria for qualification.
Nonlinear & Advanced Methods
Linear vs Nonlinear Seismic AnalysisWhen linear response spectrum analysis is adequate and when nonlinear methods are required — gap closure, sliding, yielding and contact behaviour under seismic loading.Nonlinear Time-History Analysis for Seismic AssessmentHow nonlinear time-history analysis is performed for seismic assessment — material nonlinearity, contact, large displacement and the direct integration of seismic input.Seismic Time-History AnalysisHow seismic time-history analysis is performed — ground motion selection, scaling, direct integration and the interpretation of time-domain results.Artificial Time HistoriesHow artificial ground motion time histories are generated — matching a target response spectrum while preserving realistic duration and phase characteristics.Spectrum-Compatible Time HistoriesHow spectrum-compatible time histories are developed — modifying recorded or artificial motions to match a target response spectrum within a specified tolerance.Contact Nonlinearity Under Seismic LoadingHow contact nonlinearity affects seismic response — gap opening and closing, sliding, impact and the implications for linear response spectrum analysis.Gap and Impact Behaviour Under Seismic LoadingHow gaps and impact between structural components during seismic loading affect response — and why these cannot be captured by linear analysis.Sliding and Friction Under Seismic Loading — Nonlinear ResponseHow sliding and friction change seismic response — nonlinear energy dissipation, load redistribution and the implications for unanchored equipment.Plasticity in Seismic AssessmentHow material plasticity is treated in seismic assessment — ductile energy dissipation, hinge formation and the trade-off between linear and nonlinear methods.Large Displacement Effects Under Seismic LoadingWhen large displacement effects matter in seismic analysis — geometric nonlinearity, P-delta and the implications for structural stability assessment.Seismic Fragility AnalysisHow seismic fragility analysis quantifies the probability of failure as a function of seismic input level — and its use in probabilistic safety assessment.Probability of Failure Under Seismic LoadingHow the probability of failure under seismic loading is calculated — combining seismic hazard, structural response and capacity distributions.Beyond-Design-Basis Seismic AssessmentWhat beyond-design-basis seismic assessment means — evaluating structural and equipment response at seismic input levels beyond the design basis earthquake.Seismic Margin AssessmentHow seismic margin assessment quantifies the margin between the design basis earthquake and the earthquake that would cause failure — and its use in safety evaluation.Sensitivity and Uncertainty in Seismic AnalysisHow sensitivity and uncertainty are assessed in seismic analysis — damping, mass, stiffness and input spectrum variability and their effect on response.Probabilistic Seismic AssessmentHow probabilistic seismic assessment combines hazard, response and capacity — and how it differs from deterministic response spectrum analysis.
Software Implementation
Seismic Analysis in NastranHow seismic analysis is performed in Nastran — modal extraction, response spectrum processing and the distinction between SOL 103, SOL 103+ and dynamic solution sequences.Modal Response Spectrum Analysis in NastranHow modal response spectrum analysis is set up in Nastran — modal extraction, spectrum input, modal combination and post-processing for seismic assessment.Seismic Analysis in AnsysHow seismic analysis is performed in Ansys — modal analysis, response spectrum analysis and the post-processing of seismic results.Response Spectrum Analysis in AnsysHow response spectrum analysis is set up in Ansys — spectrum input, modal combination method selection, directional combination and stress recovery.Seismic Analysis in AbaqusHow seismic analysis is performed in Abaqus — modal extraction, response spectrum, direct integration and the choice between linear and nonlinear methods.Response Spectrum and Dynamic Methods in AbaqusHow response spectrum and dynamic analysis methods are configured in Abaqus — spectrum input, modal combination, damping and the post-processing of seismic results.Seismic Post-ProcessingHow seismic analysis results are post-processed across solvers — stress recovery, modal combination, directional combination and the interpretation of peak responses.Seismic Result Verification Across SolversHow seismic analysis results are verified across different solvers — cross-checking modal frequencies, mass participation and recovered stresses between Nastran, Ansys and Abaqus.
Verification, Review & Reporting
Seismic Model VerificationHow seismic FEA models are verified — mass check, modal frequency check, mass participation check and the verification of spectrum application.Seismic Analysis Sanity ChecksPractical sanity checks for seismic analysis — base shear, overturning moment, floor acceleration, modal frequency ranges and the quick checks that catch modelling errors.Checking Modal Mass ParticipationHow to check modal mass participation in a seismic analysis — cumulative participation, directional mass and the criteria for sufficient mode retention.Checking Response Spectrum ApplicationHow to verify that the response spectrum has been applied correctly — spectrum direction, damping curve, scaling and the spectral acceleration at key modal frequencies.Checking Boundary Conditions in Seismic ModelsHow to verify that boundary conditions in a seismic model are correct — base fixity, floor flexibility, interface stiffness and the effect on modal response.Checking Mass DistributionHow to verify mass distribution in a seismic model — total mass, mass by direction, centre of gravity location and the identification of mass modelling errors.Checking Support ReactionsHow to check support reactions from a seismic analysis — base shear, vertical reactions, overturning moment and the comparison with hand calculations.Checking Peak ResponsesHow to check peak responses from a seismic analysis — peak displacement, peak acceleration, peak stress and the comparison with order-of-magnitude estimates.Sensitivity to DampingHow to assess the sensitivity of seismic response to damping assumptions — varying the damping ratio and checking the effect on peak response and margin.Sensitivity to Support StiffnessHow to assess the sensitivity of seismic response to support stiffness — varying the support stiffness and checking the effect on modal frequency and response.Sensitivity to Mass DistributionHow to assess the sensitivity of seismic response to mass distribution — varying the mass and checking the effect on modal frequency, participation and response.Seismic Analysis Peer ReviewHow peer review is performed for seismic analysis — independent model check, assumption review, result verification and the documentation required for technical sign-off.Seismic Qualification ReportingHow seismic qualification is reported — analysis assumptions, input spectra, model description, modal results, stress recovery, margins and the evidence chain for qualification.Seismic Assumptions and TraceabilityHow seismic analysis assumptions are documented and traced — input spectra source, damping values, boundary conditions, mass modelling and the chain from requirement to result.Seismic Analysis LimitationsWhat seismic response spectrum analysis cannot capture — nonlinearity, contact, time-domain phasing, simultaneous stress states and the limitations that must be stated in reporting.Defensible Seismic Verification WorkflowThe complete seismic verification workflow — from requirements through input spectra, model definition, modal assessment, spectrum application, modal combination, directional combination, force and stress recovery, load combinations, qualification checks, verification and reporting.