Seismic FEA Model Checklist

Purpose

This checklist is used before running a seismic analysis to confirm that the finite element model is fit for dynamic purposes. A model that produces acceptable static results can still be dynamically wrong through incorrect mass lumping, inconsistent units, or supports that are too stiff or too flexible. Each item below should be confirmed or explicitly justified before the modal extraction or response-spectrum run is treated as valid.

Model definition and units

• Consistent unit system confirmed (mass, length, force, time, density all compatible) — Mixed units are the most common source of erroneous natural frequencies
• Gravity acceleration value matches the unit system (9.81 m/s^2 or 386 in/s^2)
• Material densities assigned to all elements with mass, not substituted as equivalent nodal forces
• Material properties are elastic and temperature-appropriate for the seismic load case
• Element formulations are consistent — no mixing of thin and thick shell elements without justification

Mass distribution

• All significant mass sources included: structural self-weight, equipment, contents, attached piping, cable trays, ballast
• Non-structural mass (cladding, insulation, grout) included or explicitly excluded with justification
• Mass lumped at nodes or distributed consistently — choice documented and appropriate for the frequency range of interest
• Rotary inertia included for beam elements where rotational modes matter
• Centre of gravity of lumped masses verified against physical layout drawings
• No massless nodes that should carry mass (e.g. equipment centres of gravity offset from mounting nodes)

Boundary conditions and supports

• Support stiffness values reflect the actual mounting, not idealised rigid constraints unless justified
• Anchor bolt flexibility included where anchors are in tension or shear and the structure is flexible
• Base plate flexibility modelled or its effect on anchor loads assessed separately
• Contact or interface conditions at the base reflect the actual detail (welded, bolted, grouted)
• No spurious constraints that suppress real modes (e.g. over-constrained panel edges)

Dynamic formulation

• Lanczos or subspace eigensolver used with sufficient mode extraction (at least 2x the highest frequency of interest)
• Frequency shift specified if low-frequency rigid body modes are expected
• Mass matrix type (lumped vs consistent) selected appropriately for the element types used
• Damping ratio assigned per mode or globally — value justified for the construction type
• Response spectrum input matched to the damping ratio used in the analysis

Pre-run sanity checks

• Static analysis under self-weight produces reactions that match hand calculation of total weight
• Fundamental frequency estimated by hand (Rayleigh or Dunkerley) and compared to FE result
• Total model mass reported by the solver equals the expected total mass
• No warning messages about near-singular mass matrix or excessive pivot ratios
• Model check for duplicate nodes, free nodes, or unconnected elements completed