What is Merge FE Column / Beam results with Example
How to merge the results from sub-frame analysis and results from the 3D building analysis?
After a model is completed, a building analysis is mandatory which will generate results for G and Q (including the pattern cases of G and Q) as well as lateral load cases. This will be followed by FE Chasedown analysis and only then the results can be merged.
Note that these options will only be available when FE chasedown analysis has performed for all storeys. (Select All Storeys > Check "Include Upper Storey Column Loads" > "Floor Mesh and Analysis").
Are they added up together simply by superposition?
When FE Analysis results are merged, ProtaStructure completely replaces unfactored load case results for G and Q (including the pattern cases of G and Q) of Building Analysis with the corresponding loadcase results of G and Q from the FE Chasedown analysis. This means that the final merged result will consist of gravity load cases (G & Q) derived from FE chasedown analysis while the results of lateral load cases will be from 3D building analysis.
Hence, the merging of results is not superimposition as we understand it, i.e. we are not discarding the smaller values of say G loadcase of Building Analysis and replacing it by a larger value of FE Analysis.
However, ProtaStructure always uses superposition to generate the results for design combinations. As such, if a conservative design is desirable, such as for design a transfer beam, it is possible to consider both Building Analysis and FE Chasedown analysis in the design of the members by :
- Run Building Analysis which will generate both gravity and lateral results
- Perform beam and/or column design.
- Run FE Chasedown which will generate different set of gravity loadcase results
- Merge FE Chasedown results with Building Analysis results
- Perform beam and/or column design using the design option to increase steel only when the previous steel is insufficient. Previous steel if sufficient would not be changed at all.
- For example, if the mid-span moment of the beam for FE Chasedown is found to be larger than that obtained from Building Analysis, the steel will be increased.
We will use a simple 2 storey structure similar to model used in the axial load comparison model as illustration.
"Merge Column/Beam Result with Building Analysis Results" should be unchecked before performing new round of building analysis. Else, the analysis result is wrong.
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