Software Information

Curved girder analysis | Integral abutment bridges | Staged construction analysis

With IMD an eigen solution is computed using either Subspace, Lanczos or Guyan reduction eigenvalue extraction procedures. The resulting eigenvectors are then read into the LUSAS Modeller where the loading function is defined and the dynamic response calculated. Since the solution is only computed either for a given part of the structure across a specified time or frequency range, or for the whole structure at a specified sampling time or frequency a solution is obtained very rapidly.

Results can be displayed using the extensive graph plotting facilities or using the standard contour, vector or peak value features. Since both the damping (structural or viscous) and ‘time-step’ are specified within IMD there is no need to carry out a series of computationally expensive transient dynamics analyses to assess the effect of these parameters on the structural response. IMD thus offers large savings in design and analysis time and greatly reduces the computational resources required for linear transient dynamic analysis.

Typical uses of IMD include forced response when a dynamic analysis is being used to investigate the effects of structural resonance and spectral response where a dynamic analysis is being carried out to investigate the effects of ground motion on the structural behaviour. For spectral response problems the support excitation is defined using a spectral curve and the modal results may be combined using either the SRSS or CQC combination.

Using IMD the response to random vibration problems is computed using power spectral density (PSD) techniques which compute the response of a structure from the PSD input. Typically this may be used to compute the behaviour of a structure due to wind loading or the behaviour of a component mounted on an randomly vibrating platform such as an engine.

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