Midas Civil dynamic and seismic analysis is the set of modal, damping, response-spectrum, and time-history procedures described in the Midas-Civil-Analysis-Reference.
How It Works
Free vibration is treated through eigenvector analysis and Ritz vector analysis. Ritz vectors are generated from initial load vectors and repeated static analyses that include inertia effects, so fewer load-relevant vectors can capture response than a broad eigenmode extraction.
Damping options include proportional and nonproportional forms: mass/stiffness/Rayleigh damping, strain-energy proportional damping, mode damping, element Rayleigh damping, and General Link damping. Response spectrum analysis decomposes an MDOF structure into modal SDOF responses and combines modal contributions using rules such as SRSS and CQC. Time-history analysis supports mode superposition and direct integration, with direct integration needed when stiffness or damping is nonlinear.
Solver Development Notes
Modal analysis requires consistent mass, stiffness, eigen extraction, normalization, and modal participation output.
Ritz vectors add a load-dependent reduced basis, so the initial load-vector contract is part of the input schema.
Rayleigh damping needs mode-frequency selection and safeguards against excessive damping after yielding.
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