When does ASCE 7 require dynamic analysis instead of equivalent lateral force?

Per ASCE 7-22 Table 12.6-1, MRSA or linear time-history is required when the structure has horizontal or vertical irregularities, T ≥ 3.5 Ts, or when assigned to SDC D, E, or F with structural irregularities. Non-building structures per §15 and base-isolated structures per §17 also require dynamic methods.

How do you validate FEA results?

Every model includes a mesh convergence study (typ. 3 mesh densities), hand-calculation cross-checks for global statics (sum of reactions = applied load), modal mass-participation ≥ 90%, and where shake-table data exists, correlation of measured vs. predicted accelerations. Results outside ±10% of independent checks are investigated before sign-off.

Which solver do you use for nonlinear time-history?

Implicit Newmark-β (γ = 0.5, β = 0.25) with HHT-α numerical damping (α = -0.05) is the default in ANSYS and SAP2000. For severe contact, material softening, or impact we switch to explicit central-difference solvers in LS-DYNA or Abaqus/Explicit.

Do you provide reactions for anchor and weld design?

Yes. Per ASCE 7-22 §12.4.3 and ACI 318-19 Ch. 17, anchorage forces are extracted at each support node — including Ω0 amplification when required — and delivered in a format ready for SET-XP / HIT-HY / KB-TZ post-installed anchor or cast-in-place anchor design.

Can you couple FEA with shake-table testing?

Yes. We use FEA to design the test fixture, predict mode shapes for instrumentation placement, and correlate post-test data per ICC-ES AC156 §6.4. Combined analytical-experimental qualification is often the most economical path for heavy or geometrically complex equipment.

Computational Mechanics

Advanced Structural Finite Element Analysis

Linear and nonlinear, static and dynamic FEA for seismic and wind applications — modal, response spectrum, and time-history analysis of equipment, enclosures, non-building structures, and buildings. ANSYS, RISA-3D, STAAD.Pro, SAP2000, ETABS, Abaqus, and LS-DYNA with PE/SE stamped reports per ASCE 7-22, AISC 360, ACI 318, and IEEE-693.

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ASCE 7-22
AISC 360-22
ACI 318-19
IEEE-693
ICC-ES AC156
ASCE 41-17

Photorealistic FEA von Mises stress contour on a steel electrical enclosure with mesh overlay and stress concentrations at anchor bolts

Analysis methods we deliver

Method selection follows ASCE 7-22 Table 12.6-1, §15 (non-building structures), §16 (nonlinear response history), and ICC-ES AC156 §6.2 (rigid vs. flexible classification).

Linear Static

Small-deformation, linear-elastic stress and deflection checks under code-prescribed equivalent lateral loads (ASCE 7-22 §12.8 ELF, wind §27/30, snow §7). Used for sizing, code compliance, and serviceability of equipment frames, skids, supports, and braced structures.

ASCE 7-22 ELF and wind pressure checks
AISC 360 / AISI / ACI 318 member capacity
Stress concentration screening at welds, bolts, and re-entrant corners

Nonlinear Static (Pushover)

Geometric (P-Δ, large displacement), material (von Mises plasticity, concrete cracking), and contact (gap, friction) nonlinearities. Required for buckling-controlled members, anchorage with ductile failure, and ASCE 41 performance-based assessment of existing structures.

P-Δ and large-deformation effects
Material plasticity and concrete cracking
Bolt slip, gap closure, and contact nonlinearity

Modal (Eigenvalue)

Natural frequencies, mode shapes, and mass participation factors. Required input for ASCE 7-22 §12.9 Modal Response Spectrum Analysis (MRSA) and for confirming the rigid/flexible classification (T < 0.06s) in ICC-ES AC156 §6.2 and ASCE 7 §13.2.6.

First 30+ modes with ≥ 90% mass participation per ASCE 7-22 §12.9.1.1
Rigid vs. flexible classification (fn ≥ 16.7 Hz)
Lanczos / Block-Lanczos eigensolver for large models

Response Spectrum (MRSA)

ASCE 7-22 §12.9 modal response spectrum analysis using the site design spectrum (Sds, Sd1, TL). Modal responses combined by CQC, with directional combination per §12.9.1.4 and scaled to 100% of the ELF base shear.

ASCE 7-22 §11.4 site spectrum (Sds, Sd1, TL)
CQC modal combination, 100% × 30% directional combination
Base shear scaling to ELF and accidental torsion

Linear & Nonlinear Time-History

Direct integration (Newmark-β, HHT-α) with site-specific spectrum-matched ground motions per ASCE 7-22 §16. Used for non-building structures, base-isolated systems, post-installed anchors with ductile failure, and IEEE-693 high seismic qualification of substation equipment.

Suite of 11 spectrum-matched 3-component records (ASCE 7-22 §16.2)
Rayleigh damping calibrated to first two modes (typ. 5%)
IEEE-693 sine-beat / time-history for substation equipment

Wind — Static & Dynamic

ASCE 7-22 directional and envelope procedures for MWFRS and C&C. Gust effect factor for rigid (Gf = 0.85) and flexible (T > 1s) structures. Across-wind vortex shedding screening for slender stacks and ducts using NBCC / ASCE 7 §31 procedures and CFD when geometry is governed by separated flow.

ASCE 7-22 Ch. 27/30 directional and C&C pressures
Vortex shedding lock-in and aeroelastic checks
Wind tunnel / CFD coupling for non-standard geometries

Dynamic analysis in practice

Modal extraction feeds every dynamic procedure — from response spectrum to nonlinear time-history. Mass participation, mode shape, and frequency content drive both the analysis method and the selection of input ground motions.

Modal analysis FEA result of a tall vertical pressure vessel on skirt support showing the first lateral bending mode shape with deformation contour — **Modal analysis** — first lateral bending mode of a skirt-supported vertical pressure vessel. Block-Lanczos eigensolver, 30+ modes extracted, ≥ 90% cumulative mass participation per ASCE 7-22 §12.9.1.1.

Response spectrum analysis FEA result of an elevated steel water storage tank on a braced tower showing lateral seismic displacement contours — **Response spectrum (MRSA)** — elevated water storage tank on a braced steel tower analyzed per ASCE 7-22 §12.9 and §15.7. Site-specific Sds and Sd1, CQC modal combination, 100% × 30% directional combination, and impulsive/convective mass treatment for the contained fluid.

Software stack

We pick the solver to match the problem — implicit, explicit, or code-driven design — not the other way around.

ANSYS Mechanical / Workbench

Solid, shell, and beam FEA with full nonlinear capability — material plasticity, contact, large deformation. Used for equipment enclosures, weldments, and IEEE-693 qualification analyses.

RISA-3D

Code-compliant frame analysis and design (AISC 360, ACI 318, NDS, AISI). Used for braced and moment frames, equipment skids, pipe racks, and mezzanines.

STAAD.Pro

3D structural analysis with integrated AISC, IS, BS, and Eurocode design. Used for industrial structures, non-building structures per ASCE 7-22 §15, and response spectrum analysis.

SAP2000 / ETABS / SAFE

Static, modal, response spectrum, time-history, and pushover (FEMA 356 / ASCE 41) for buildings, base-isolated structures, and seismic retrofit studies.

Abaqus / LS-DYNA

Explicit and implicit nonlinear FEA for impact, blast, post-buckling, and fragility studies. Used when ANSYS implicit solvers stall on severe contact or material softening.

RAM, Tekla Structural Designer, IDEA StatiCa

Building gravity and lateral systems, connection design (CBFEM), and integrated steel/concrete checks per AISC 360-22 and ACI 318-19.

Deliverables

Every engagement produces a stamped, code-traceable report ready for AHJ, HCAI/OSHPD, or owner review.

PE / SE stamped FEA report with assumptions, model, and code references
Mesh convergence study and sensitivity analysis on key parameters
Stress, deformation, and reaction summaries with allowable / capacity ratios
Modal frequency and mass-participation tables (ASCE 7-22 §12.9 compliant)
Response spectrum and time-history results with combination cases
Anchorage reactions for downstream concrete anchor design (ACI 318-19 Ch. 17)

Typical use cases

FEA pays back fastest where code procedures are conservative or the geometry is outside the scope of standard formulas.

Equipment & enclosure qualification

Solid/shell FEA of cabinets, skids, and weldments for IBC, ICC-ES AC156, IEEE-693, and HCAI/OSHPD OSP/OPM submittals.

Non-building structures (ASCE 7-22 §15)

Pipe racks, vessels, stacks, cooling towers, and tanks. Modal + response spectrum or time-history with §15 R, Ω0, Cd values.

Seismic retrofit & ASCE 41 evaluation

Tier-3 nonlinear pushover and time-history of existing buildings for BSE-1E / BSE-2E performance objectives.

Wind-sensitive & dynamic structures

Slender stacks, antennas, and outdoor enclosures with vortex shedding, gust resonance, and along/across-wind response.

Related work

Shake Table Testing

Pair FEA with ICC-ES AC156 shake-table programs for fixture design, instrumentation planning, and post-test correlation.

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Anchor & Bracing Design

Reactions extracted from FEA feed ACI 318-19 Ch. 17 anchor design and ASCE 7-22 §13 bracing per our anchor and bracing specialty pages.

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FEMA E-74 Assessments

Quantitative FEA backs up E-74 mitigation recommendations for vulnerable equipment and distribution systems.

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Frequently asked questions

Scope an FEA package for your project

Talk to a board-certified engineer about model fidelity, solver choice, and code path for your seismic or wind application.

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