Download Application Note - Footing Analysis

Application Note - Footing Analysis
The values of the multipliers on the soil/wall interface properties specified in the Wizard are not relevant
to this example since a different approach for their creation is used. See box below for more information.
Material Name
Footing
cu
(kN/m2 )
5000
γ
(kN/m2 )
24
Multiplier on tan φ
Multiplier on c0 , cu
1
1
Table 2: Footing and soil-footing interface properties
Key modelling concept: Soil/structure interface properties in LimitState:GEO
Often when dealing with soil/structure interaction problems, it is desirable to define
a soil/structure interface property that is a function of the adjacent soil. A typical
example is a retaining wall where the interface adhesion and friction will be some
multiplier (≤ 1) of the adjacent soil strengths. This may be set using Derived Mohr
Coulomb Material type and entering multipliers for cohesion (c0 , cu ) and shear
resistance (tan φ0 ) in the Property Editor. If the Wizard is used, this material is
automatically applied to all the soil-structure interfaces using the specified multipliers.
Note that:
• If the interface friction property is to be a function of φ0 rather than tan φ0 , a
standard material type (e.g. Mohr Coulomb) instead of a derived material type
should be used.
• If the interface friction property is to be a function of φcrit but the actual value
used for the adjacent soil in LimitState:GEO is not a critical state angle of shearing resistance but e.g. a peak value, then it will be necessary either to make a
modification to the multiplier or to use a standard material as above.
5. In the Loads tab, set the Variable vertical load to 200 kN/m and click Next>.
6. In the Scenarios tab, application of partial factor sets and long/short term analysis modes can be specified.
In this example Eurocode 7 Design Approach 1 Combinations 1 and 2 (EC7 DA1/1 and DA1/2) for long
term analyses are to be checked. Select Multiple scenarios and create the two Scenarios as defined in
the first two columns of Table 3. Click Finish. (NB For simplicity, the pore pressures in the clay are
conservatively assumed to be zero in the drained analyses, assuming the water table lies a short distance
beneath the problem geometry.)
Scenario
1
2
Scenario details
EC7 DA1/1, long term analysis
EC7 DA1/2, long term analysis
Adequacy Factor
1.50
1.19
Table 3: Scenarios and analysis results
7. The Wizard automatically sets the Loading Type of the applied load and the self weight of the footing to
Unfavourable. Check these settings in the Property Editor by selecting the relevant Solids or Boundary.
The wizard does not automatically set the weight of the soil above the footing as Unfavourable. However
in this example this will be done. Click on the relevant Solids and set the Loading Type to Unfavourable.
8. Switch on the Grid using the View/Show Grid function or
3
.