GGU-LATPILE: Step 10: Analyse system
- Matthias Jusko
Go to the "System" menu and select "Analyse".
The pile length and pile width were adopted from the "Editor 1/System input" dialog box. If you would prefer to use a different section, click the "Section: …" button and select the required section from the list of sections displayed. Confirm the input by pressing "OK".
EC 7 requires that a verification be performed to demonstrate that the soil stress (ks · w)d is smaller than the characteristic passive earth pressure eph,k (not reduced by a partial safety factor!). However, once analysis is complete it must be verified that the sum of the soil stress is smaller than the design passive earth pressure:
Using the preferences given so far you will see the following dialog box:
The program has determined that the passive earth pressure is smaller than the resulting soil pressure from the elastic analysis, which is not permitted. Therefore, confirm the question about iteration with "Yes". In the dialog box shown above, you can enter the iteration conditions. The default values have proved themselves in practice and will generally not need to be altered.
"Damping" prevents strong fluctuations around the actual solution during the iteration process. A value of 0.0 produces no damping, while a value of 0.99 produces very strong damping. Using "Allowable excess > passive" you specify the percentage by which the elastic stress may exceed the passive earth pressure before the iteration is ended. The "Max. number of iteration steps" can also be specified. If, after the specified number of steps, compression due to embedding is still greater than the passive earth pressure, iteration is terminated.
During iteration, the modulus of subgrade reaction is reduced. If the analysis requires a reduction over the whole length of the pile to a value below "Max. ks", iteration is aborted. This usually happens when the pile is not long enough to take the load.
When the iteration is complete info boxes appear; use "OK" to close them. You will then see a prompt for subsequent design; use "Yes" to close it. Then, select the "Find optimum section" option in the dialog box and confirm by pressing "OK".
You will then move directly to the design preferences dialog box (see menu item "System/Design defaults").
Adopt the data and confirm by pressing "OK". An appropriate message box then opens. The settings given in the box for the optimum section can be adopted:
The analysis and design of the pile are complete. The input and results are first displayed in message boxes, which you move through by clicking "OK". Because a different section to the originally selected HEB 300 was designed, the analysis should be repeated using the new HEB 140 section. Adopt the pile width of the newly selected pile by pressing the "Adopt" button and repeat the analysis and subsequent design of the HEB 140.
When the program starts the Sum V analyses are activated by default (see menu item "Partial factors + Sum V"). Immediately after analyses and design you will therefore see the following dialog box on analysis of the mobilised passive earth pressure:
Adopt the data and perform the analysis. The results are displayed in a message box. If you exit the message box by pressing "OK", the editor box analysis of the vertical capacity opens:
After accepting the settings by pressing "OK" the data are again displayed in a message box. By pressing the "Analyse again" button the above dialog box opens again and you can perform the analysis using the modified data.