This menu is active only in the state of Analysis. In form finding or patterning, it makes no sense to talk about foundations.
To use this feature of WinTess, we need to:
- have calculated the structure. That is, loads have been applied and balance has been found.
- have defined the type of soil through the General Data submenu.
- have defined some nodes as Class 3-Foundation. Normally, WinTess3 automatically defines this way:
- the ends of a 0-Tube type bar without displacement (type “111” nodes)
- the corners of the membrane without displacement (type “111” nodes)
In the General data window, we set the characteristics of the soil and the foundation that will be used.
First we find the drop-down Reference values of a series of soil types. Selecting one of them modifies the soil properties. Then we can modify these values if real ones (obtained from a Geotechnical Soil Assessment) differ from the standard values given by the program . We can even change the name of the soil to adapt it to the reality of the location.
The values you need to set are:
- Density (relative or t/m3)
- Cohesion (t/m²) This value usually plays a favourable role (it gives smaller foundations), therefore it must be used with precaution. If the check box “Protects foundation from the rain” is not checked, the Cohesion value is doubtful and should be entered as zero or a very small value.
- Soil friction angle (in degrees)
- Soil-concrete friction angle (in degrees) This value can never exceed the previous value (soil friction angle) and it is recommended that you do not exceed 2/3 of that value.
- Compression soil bearing capacity (t/m²) This value is mainly used for vertical or inclined compression loads. Normally it’s a calculated value, which means that it has incorporated the safety factors, but we can decide it with the box that we’ll discuss later.
Then we need to know if a permanent pavement exists and if there is in it an internal concrete slab. This permanent pavement will be taken into account when analyzing foundations. If this pavement exists we must enter:
- Total weight of the pavement (concrete slab included if it exists)
- Check box if this pavement protects foundations from the rain. This value will affect friction between footings and soil.
- Check box if a reinforced concrete slab exists. If so, enter slab thickness.
- Finally we must indicate if this slab contributes only with self weight or with a shearing resistance.
In the following box Lateral soil resistance we must indicate if we are going to analyse horizontal forces with earth pressure at-rest soil (on the safe side), with passive earth pressure, limiting kp = 1 (on the safe side, but not so much) or with passive earth pressure with no limitation (in this case we must accept that foundations can move a little). If the third option is selected a warning is shown for the user:
In the box Soil-concrete friction we can define three values for the friction. Normally we will take average as standard, but if something protects foundations from the rain and the soil is not wet we can use good. If not, we will use bad. These values are not too important but can be decisive in some cases.
Finally we must enter the safety factor for foundations. If we want to change it, WinTess will address us to Safety Factors window. If we would like to have different safety factors for different subjects (displacements, stresses…) we should modify other soil properties since only a single safety factor is used for foundations.
If, at the end, we press OK button, all footings will be re-analysed according to the values we have established in this window. If we don’t want to do it, we should press Cancel button instead.
When you click this menu, if there are Class 3-Foundation nodes, the footings are calculated to withstand the forces produced by the reactions in them. These footings appear on screen graphic and can be activated and deactivated using the button at the top right .
If for some reason we want to delete any of the calculated foundations, this menu allows us to delete them numerically.
In this table, we find all the representative data of the concrete footings in a neat way:
- Footing Number of the footing (it is not the node number)
- Node Number of the node where the footing is.
- Fh Horizontal force applied to the footing
- Fv Vertical force applied to the footing
- Mom. Overturning moment applied to the footing
- A Footing dimension parallel to Fh
- B Footing dimension parallel to Fh
- H Height of the footing
- Vol. Volume of the footing
- Weight Weight of the footing
- Ratio Value that indicates if the footing supports the loads to which it is subjected. It is possible that on having redone the Analysis, we may forget to re-calculate the foundations. The program does not do it automatically.