Finite Elements Raft Foundation Analysis
FE Raft Foundation Analysis is only available at the foundation storey (ST-00). It can be accessed by clicking “
FE Raft Foundation Analysis” from the “
Analysis” tab.
Prior to FE Raft Foundation Analysis, it is necessary to complete Building Analysis to determine the loads to be used in the raft foundation analysis.
Finite Element Raft Foundation Analysis Form
- Soil Subgrade Coefficient: This coefficient will be used for determining the rigidity of the springs used for modelling of the soil behaviour. Basically, it is a spring stiffness (kN/m) per m2 of ground, hence the units kN/m3.
- Use the Subgrade Reaction Values Assigned to Slabs for Soil Stress Checks: If this option is checked, slabs with user defined soil subgrade coefficient in the "Slab Properties" will be taken into calculation.
- Include Column Sections in FE Model: This option is checked to allows rigid perimeter of the column to be considered in analysis. The slab/foundation will be meshed to the perimeter of the column rather than the centreline
- Ignore Soil Bearing Capacity: Where piles are introduced to carry the load, the soil bearing capacity can be totally excluded either by setting the coefficient of subgrade reaction to zero, or more conveniently by checking the option “Ignore the Bearing capacity of the soil”.
- If this option is unchecked, then raft will also sit on the soil. It is expected the resultant piles forces to be decreased as load is shared with the "non-suspended" raft.
- Note that if you have mixed piled mats and pads then you have to introduce a ground bearing pressure in order to avoid infinite displacements.
- Apply Live Load Reduction (All Combinations): If live load reductions have been defined and this option is checked, the reductions will be applied in all combinations. If no live load reductions have been defined, checking this option has no effect.
- Display Analytical Model Before Analysis: If this option is checked, it will allow you to examine/check the meshing generated in layout before analysis
- Use ‘Sparse Solver’ for FE Analysis: The purpose of the sparse solver is to reduce the time required for analysis. For certain model types a dramatic reduction in the analysis time can be achieved, for other models it may be less significant.
- Shell Element Size: Adjust the mesh size and click “Floor Mesh and Analysis” to mesh the floor and perform FE Raft Foundation Analysis
This option will only appear if piles have been defined in the foundation
Although when designing to Eurocodes, live load reductions need only be applied to combinations in which Q is a leading action, it is not currently possible to make this distinction in ProtaStructure’s FE foundation model. Reductions can only be applied to all combinations or none at all.
Post-Analysis Processes and Report
Once the analysis has completed the “Post-Analysis Processes and Reports” page is automatically displayed.
- Allowable Stress of Soil: This allowable soil stress will then multiply by factor and checks will be based on this pressure.
- Positive and Negative Moment Factors: These factors should be defined before clicking the “Analysis Post-processing” button to review the results. Output results that are viewed in the Post-processor and Analysis Results Reports are factored using the values entered in these fields
- Display Analytical Model: After FE Floor Analysis is done, clicking "Display Analytical Model" will open "FE Storey and Foundation Model" to view the visualized result for selected storey. See: FE Storey and Foundation Model
- Analysis Results Report: Other than the visualized result, FE Floor Analysis result can be viewed and generated in text form after completion of the analysis without any errors. The analysis result reports can be prepared for selected nodes, and slabs. In all tab pages, you select items to be included using the visible lists and then press the “Create Report” button to generate the report
- Transfer Foundation Beam Results: When this button is pressed, Foundation Beam FE analysis result will be transferred and used for foundation beam design (by selecting “Foundation Beams” option in “Design” tab)
- Pile Results Report: Clicking the button will generate a formatted report comparing the maximum pile compression and tension results against their capacities. The report can optionally include results for all load cases and for all load combinations.
This option will only appear if piles have been defined in the foundation
For more understanding, please refer to example in:
Raft Foundation and Piled Raft Foundation Analysis & Design Example
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