1. www.oasys-software.com Analysis Stages in GSA and Construction stage analysis using GSA Thomas Li, Thomas Ward & Chris Kaethner 30 June 2010

2. www.oasys-software.com GoToWebinar Attendee Interface 1. Viewer Window 2. Control Panel

3. www.oasys-software.com Analysis Stages in GSA

4. www.oasys-software.com Definition An Analysis Stage: A subset of elements from the whole model This may be ‘all’ or a smaller subset. Subset defined with standard GSA list syntax ( Check result by viewing only the stage in model ) May use different element properties for each stage ‘Analysis Stage Properties’ Remap element property numbers for each stage May use different model constraints for each stage Generalised Constraints Rigid Constraints Joints Constraint Equations Tied Interfaces

5. www.oasys-software.com Analysis An Analysis Stage is tied to an Analysis Task Available in GSS and GsRelax Results Viewing results is as normal Display of results is independent of current stage in view

6. www.oasys-software.com Considerations Enable in preferences Analysis stage column hidden in tables when not enabled in preferences Nodal restraints & Spring supports will both be applied to all stages (in which the nodes are active) To bring restraints into stage: Nodal restraints -- use Generalised Restraints Spring supports -- use Grounded springs Using selection lists List syntax always relates to original property definition Display View stage in viewport: Display options Highlight edges command will relate to the specific stage in view Display Labels Table colour by stage Local axes Remapping element properties must use the same local axes

7. www.oasys-software.com Construction Stage Analysis using GSA

8. www.oasys-software.com What is construction stage analysis To simulate crucial stages of a structure under construction and if necessary to obtain deformations and forces at each of the stages To consider the cumulative effects of the member forces and deformations from one stage to another

9. www.oasys-software.com Why need construction stage analysis In the real world, all structures are built in stages. To get more real or more accurate analysis results, construction stage analysis is needed To make sure the structures are safe at all stages of construction To get more accurate analysis results at the final stage When temporary supports etc are used in certain stages of construction

10. www.oasys-software.com Why need construction stage analysis Comparing final moment diagrams in multi-story frame from staged and non-staged analyses Without construction stageWith construction stage

11. www.oasys-software.com How information is transferred Understanding internal and external loads Internal loads – loads that will not produce overall resultant reactions in the structure, e.g. pre-stress, pre-strain, distortion and thermal loads External loads – loads that are externally applied to the structure, e.g. Node loads, element loads, gravity loads and grid loads. The process for carrying internal and external loads from one stage to the next is different Internal loads are carried over to the next stage by the deformation and a new automatically generated load case, so internal loads should not be included in the analysis of following stages External loads are not carried over to the next stage automatically. External loads should be included in the analysis of following stages

12. www.oasys-software.com How information is transferred Understanding form-finding analysis Form-finding analysis is a type of analysis. At the end of a form-finding analysis, there are no analysis results produced, but the nodal coordinates are modified and a new load case representing the element forces/moments is generated. Both normal and artificial ‘form-finding’ properties can be used in form-finding analysis There are three different types of form-finding analyses in GSA Form-finding analysis using normal element properties Soap-film form-finding analysis Force-density finding analysis

13. www.oasys-software.com How information is transferred An alternative way to represent analysis results (using form-finding analysis and the form-found model) In normal analysis, at the end of analysis (e.g. using 1.4L1+1.6L2), GSA gives analysis results include: Nodal displacements and rotations Element displacements and forces etc The alternative way – using form-finding analysis, at the end of form- finding analysis (also using 1.4L1+1.6L2), GSA does not give analysis results, but gives: A new model with modified nodal coordinates based on nodal displacements and original coordinates A new load case includes (say L3): [1] pre-stress force load representing element axial forces & [2] distortion load (out-of-fit rotation at element ends) representing element moments and shear forces If the new (form-found) model is analysed using loads 1.4L1+1.6L2+L3, the structure will not deform any more, but the element forces and moments will be the same as that from normal analysis using loads1.4L1+1.6L2

14. www.oasys-software.com How information is transferred GSA sample - comparing normal & form-finding analysis vv hh vv hh   Axial pre-stress force load Distortion load Original model Form-found model

15. www.oasys-software.com How to do construction stage analysis in GSA Stage 1 – do form-finding analysis (e.g. using 1.4L1+1.6L2). After this, the nodal geometry is modified and a new load case (say L3) is generated. If analysis results are required at the end of stage 1, they can be obtained from a normal analysis using the modified model and load combination of 1.4L1+1.6L2+L3. Stage 2 - do form-finding analysis using 1.4L1+1.6L2+L3 and the form-found model from stage 1. After this, the nodal geometry is further modified and a new load case (say L4) is generated. Analysis results for this stage can be obtained using the modified model and load combination of 1.4L1+1.6L2+L4.

16. www.oasys-software.com How to do stage analysis in GSA Stage 3 - do form-finding analysis using 1.4L1+1.6L2+L4 and the form-found model from stage 2. After this, the nodal geometry is further modified and a new load case (say L5) is generated. Further stages can be analysed in the same way if required, but remember to ignore the internal loads used in previous stages Between each stage, the structure can be modified manually, e.g. by removing temporary supports or adding new elements etc.

17. www.oasys-software.com Summary Use form-finding analysis to enable the locked-in stress etc to be transferred from the previous stage to the next stage, this produces a modified model and a new load case To obtain the analysis results at the end of a stage, analyse the form-found model by adding the newly generated load case to the existing load combination Internal loads should only be used once, then they will be embedded in the newly generated load case from the form-finding analysis, they should not be included in the subsequence form-finding or normal analyses Use ‘Analysis stages | Stage definition’ to build multiple models corresponding to each of the stages, so the GSA model does not need to be modified from one stage to the next during the construction stage analysis

18. www.oasys-software.com GSA examples of stage analysis Multi-story frame Without construction stageWith construction stage

19. www.oasys-software.com GSA examples of stage analysis Continuous beam

20. www.oasys-software.com GSA examples of stage analysis Removing element when using ‘Analysis stage’ method

21. www.oasys-software.com Questions? www.oasys-software.com