GGU-SLAB: Procedure for the subgrade reaction modulus method
Design the system to be analysed.
Start the GGU-SLAB program and go to the "File/New" menu item. Select the type of system (here: subgrade reaction modulus method) and the safety concept.
If necessary, adapt the page coordinates to your system. To do this, go to the "Page size + margins/Manual resize (editor)" menu item.
Then select the "FEM mesh/Define nodes" menu item.
Click the governing nodes (points) in your system using the mouse. The points are numbered. Alternatively, you can enter the system nodes in a table using the menu item "FEM mesh/Edit". When defining new nodes, the new node is assigned the default subgrade reaction modulus. This can be edited in the "Subgrade/Default subgrade" menu item.
If the nodes are outside of the page coordinates, go to the menu item "Page size + margins/Auto-resize" or use the [F9] function key.
Then go to the "FEM mesh/Manual mesh" menu item and join groups of three nodes to form triangle elements. You create the coarse structure for your system in this manner. Alternatively, you can utilise the "FEM mesh/Automatic" menu item to have the program do this job for you.
If you want to alter the locations of mesh nodes, go to the menu item "FEM mesh/Edit", "FEM mesh/Change" or "FEM mesh/Move".
If you need to analyse a simple rectangular slab with a varying model point array, you can use the menu item "FEM mesh/Array" ("irregular" button) to perform the mesh generation in just a few seconds.
If you need to alter the subgrade reaction moduli, use the menu items "Subgrade/Individual subgrade", "Subgrade/Modify" or "Subgrade/In section". Using "Subgrade/Subgrade contours" it is possible to view the selected subgrade reaction moduli distributions.
If you need to delete a triangle element, select the menu item "FEM mesh/Manual mesh" once again and click the three corner nodes of the appropriate element. In this menu item, try double-clicking in a triangle element.
If you need to assign different material properties to triangle elements (e.g. a different slab thickness), use the menu item "Boundary/Individual materials" or "Boundary/(Materials) In section" and assign different material numbers for one or more elements. An input line appears for each material number in the "System/Slab material" menu item.
The screen contents can be refreshed at any time using the [ESC] or [F2] keys.
You can create a finer structure for your system from the coarse structure, by selecting the menu items "FEM mesh/Refine individually", "FEM mesh/Section" or "FEM mesh/All".
You can edit the system as required even after refining your mesh by using "FEM mesh/Define nodes", "FEM mesh/Manual mesh", etc.
Whatever you do, to acquire a numerically favourable FEM mesh the menu item "FEM mesh/Optimise", and here the "Diagonals" button, should be used.
You can create acute angled, and thus numerically unfavourable, triangle elements for demonstration purposes using the menu item "FEM mesh/Move". Then select the "FEM mesh/Optimise" menu item ("Topology" button) and follow the effects on the screen.
Define the governing boundary conditions for your system, e.g. via the menu items "Boundary/Single displacement" or "Boundary/(Displacement) In section".
Define the governing action boundary conditions for your system, e.g. via the menu items "Boundary/Point loads" or "Boundary/Line loads".
If needed, edit the material numbers using the "Boundary/Individual materials" menu item.
If needed, edit the material properties using the "System/Slab material" menu item.
If beam elements are used in the system (e.g. joists), define the location of beam elements using the menu item "Boundary/Beams" by placing a section along the required node. After pressing the [Return] key you can assign the defined beams a material number. The beam stiffnesses (EJ and GJ) can then be edited in "System/Beam materials".
If you need to simulate the influence of single springs perpendicular to the slab (e.g. piles or slightly yielding supports), go to the menu item "Boundary/Single springs" and click the system nodes to be assigned single springs. Then enter the spring constant.
A simple check of the defined boundary conditions is possible by going to the "Boundary/Check" menu item.
Once mesh generation is complete, go to the "System/Analyse" menu item and start the analysis. If necessary, the program performs a bandwidth optimisation before carrying on with the analysis, to acquire a numerically favourably configured equation system. After bandwidth optimisation the program asks which equation solver you want to use. If you are not sure which of the two to use, click "Equation solver info". If you want to rule out a disallowed tension bedding for certain soils, activate the appropriate check box in the start dialog box. Once the analysis is complete the program then checks whether bedded slab areas are lifted. The subgrade reaction modulus is set to "0" in these areas and the analysis performed once again. This process is carried on iteratively until no more bedded slab areas are subject to tension.
Once analysis is complete you can output the results as a log to the printer or save them to a file, as preferred. In general, this type of result presentation is less than satisfactory.
Instead, go immediately to the "Evaluation" menu. A variety of evaluation options are provided here. The menu items "Evaluation/Coloured" or "Evaluation/3D" are particularly impressive. The dialog boxes which then appear can almost always be closed using "OK", without further changes having to be made. The program will generally suggest sensible input data. The "Determine extreme values" button should be clicked once, however, otherwise an error message containing a correction suggestion will appear.
If you have a WINDOWS colour printer installed, you can create colour output by going to "File/Print and export" and then pressing the "Printer" button in the subsequent dialog box. Grey scale is used for mono printers.
Experiment a little with the examples provided.