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Analysis Types

The most common analysis in GSA is a linear static analysis. If a model is set up and loading defined a linear static analysis can be initiated using the 'analyse' (sigma) button.

Other analysis types need to be set up using the analysis wizard to specify the particular parameters to control that analysis.

Analysis Options​

The main analysis options in GSA are:

  • Static analysis – linear static, static P-delta or nonlinear static
  • Dynamic analysis – modal dynamic, Ritz analysis, explicit time-history analysis and response analysis. Both modal and Ritz option can be linear or can include P-delta effects (modal P-delta and Ritz P-delta). The response analyses require a modal or Ritz analysis on which to base the response analysis which can be response spectrum analysis, linear time history analysis, harmonic analysis, footfall induced vibration analysis or periodic excitation analysis.
  • Buckling analysis – modal buckling and component buckling.
  • Raft analysis – soil-structure interaction, in Raft and piled-raft analysis steps. (Using PDisp).
  • Bridge analysis
  • Envelope analysis – a method of calculating results for combination cases with many permutations, Envelope analysis records the permutation number for the maximum and minimum requested values rather than relying on the result calculation each time they are requested.
  • Mass analysis – to determines the mass of the structure and the breakdown of mass.
  • Form finding analysis – for use with fabric and cable element models to determine the structural form. Analogous to hanging chain model.
  • Model stability analysis – an analysis of the stiffness matrix to identify potential ill-conditioning problems.

Features & Limitations​

Static – A direct solution of the linear analysis problem (except where nonlinear elements such as tie, strut, cable and some spring elements are used). Result cases can be combined post-analysis. Ignores nonlinear effects except for strut and ties.

Modal dynamic – Calculates the dynamic characteristics of the structure (natural frequencies and mode shapes) using eigenanalysis, based on required number of eigenpairs. This is an iterative solution considering linear behaviour only – struts, ties and cables are modelled as bars.

Ritz – Calculates approximate natural frequencies and mode shapes using force-dependent Ritz vectors. This considers only linear behaviour – struts, ties and cables are treated as bars.

Buckling – Calculates the buckling characteristics (load factors and mode shapes) using eigenanalysis. This is an iterative solution considering only linear behaviour – struts, ties and cable are treated as bars. Does not consider buckling modes involving warping.

Static P-delta – similar to static analysis but the stiffness matrix is modified using geometric stiffness (from the same or another analysis case).

Modal dynamic P-delta – similar to modal dynamic but stiffness is modified using geometric stiffness (from a defined load case).

Ritz P-delta – similar to Ritz, but stiffness is modified using geometric stiffness (from a defined load case).

Explicit time history – a nonlinear time history analysis using explicit time integration.

Nonlinear static – applies load and uses dynamic relaxation to iterates until nodal forces are in an equilibrium state. It won’t find all possible results (e.g. snap through buckling may lead to more than one valid solution). Generally this will be slower than a direct solution and may not always converge. Currently does not handle brick elements.

Component buckling – allows determination of the effective length of a component (/member), taking into consideration the restraint afforded by the rest of the structure.

Response spectrum – earthquake response based on statistical characterisation of seismic event. Based on modal dynamic or Ritz analysis results.

Harmonic – response to a steady state sinusoidal excitation. Based on modal dynamic or Ritz analysis results.

Linear time history – responses of structures subjected to dynamic loads or base acceleration. Linear response only, i.e. large deformation and material plasticity are ignored. Based on modal dynamic or Ritz analysis results.

Footfall – dynamic response analysis of structures subjected to the actions of human footfall. Based on modal dynamic or Ritz analysis results.

Periodic excitation – similar to footfall but requires the user to define the periodic excitation functions.

Raft – soil-structure analysis of raft and piled-raft analysis. Superseded by modelling using brick elements.

Bridge – bridge load optimisation with automatic path generation and influence analysis. Lane by lane, and carriageway optimisation. As the number of analysis cases in the bridge analysis task depends on the bridge specification and influence effects etc. all bridge analysis related data are locked once there is a bridge analysis task.

Envelope – batch envelope generation and storage of envelope results. An alternative to the traditional 'on-the-fly' envelopes.