By default, SAP2000 saves only the final state for a nonlinear static analysis. Use the Results Saved for Nonlinear Static Load Cases form to select intermediate results to monitor how the structure responds during loading. This is particularly important for static pushover analysis, when the capacity curve needs to be developed. The items on the form depend on the Analysis Type selected (Nonlinear or Nonlinear Staged Construction).
Results Saved - Nonlinear Analysis
Final State Only option. This is the default. When this option is chosen, SAP2000 will save only the final state for a nonlinear static analysis.
Multiple States option. When this option is chosen, SAP2000 will save multiple states. The state at the beginning of the analysis (Step 0) will be saved as well as a number of intermediate states determined on the basis of the options selected in the other areas of the form:
Minimum and Maximum Saved Steps options. The Minimum Number of Saved Steps and Maximum Number of Saved Steps provide control over the number of points actually saved in the analysis. If the minimum number of steps saved is too small, you may not have enough points to adequately represent a pushover curve. If the minimum and maximum number of saved steps is too large, the analysis may consume a considerable amount of disk space, and it may take an excessive amount of time to display results.
The program automatically determines the spacing of steps to be saved as follows. The maximum step length is equal to total force goal or total displacement goal divided by the specified Minimum Number of Saved Steps. The program starts by saving steps at this increment. If a significant event occurs at a step length less than this increment, the program will save that step too and pick up with the maximum increment from there. For example, suppose the Minimum Number of Saved Steps and Maximum Number of Saved Steps are set at 20 and 30 respectively, and the target is to be to a displacement of 10 inches. The maximum increment of saved steps will be 10 / 20 = 0.5 inch. Thus, data is saved at 0.5, 1, 1.5, 2, 2.5 inches. Suppose that a significant event occurs at 2.7 inches. Then data is also saved at 2.7 inches, and continues on from there being saved at 3.2, 3.7, 4.2, 4.7, 5.2, 5.7, 6.2, 6.7, 7.2, 7.7, 8.2, 8.7, 9.2, 9.7 and 10.0 inches.
The Maximum Number of Saved Steps controls the number of significant events for which data will be saved. The program will always reach the force or displacement goal within the specified number of maximum saved steps; however, in doing so, it could have to skip saving steps at later events. For example, suppose the Minimum Number of Saved Steps is set to 20, the Maximum Number of Saved Steps is set to 21, and the pushover is to be to a displacement of 10 inches. The maximum increment of saved steps will be 10 / 20 = 0.5 inch. Thus, data is saved at 0.5, 1, 1.5, 2, 2.5 inches. Suppose that a significant event occurs at 2.7 inches. Then data is also saved at 2.7 inches, and continues on from there, being saved at 3.2 and 3.7 inches. Suppose another significant event occurs at 3.9 inches. The program will not save the data at 3.9 inches because if it did, it would not be able to limit the maximum increment to 0.5 inch and still get through the full pushover in no more than 21 steps. Note that if a second significant event occurred at 4.1 inches rather than 3.9 inches, the program would be able to save the step and still meet the specified criteria for maximum increment and maximum number of steps.
Save Positive Increments Only check box. When this check box is checked, the program will save the steps having positive increments only. This option is primarily of interest for static nonlinear (pushover) analysis under displacement control (i.e., the Displacement Control option is selected on the Load Application Control for Nonlinear Static Analysis form). In the case of extreme nonlinearity, particularly when a frame hinge sheds load, the pushover curve may show negative increments in the monitored displacement while the structure is trying to redistribute the force from a failing component.
When this check box is unchecked, the program will display negative increments. The negative increments of ten may make the pushover curve confusing. However, displaying them can provide insight into the performance of the analysis and the structure.
It is recommended that the Save Positive Increments Only check box be checked in most cases, except when the analysis is having trouble converging.
Results Saved - Staged Construction
End of Final Stage option. When this option is chosen, SAP2000 will provide results for only the final stage of the construction sequence.
End of Each Stage option. When this options is chosen, SAP2000 will provide results for each stage in the construction sequence.
Start and End of Each Stage option. When this options is chosen, SAP2000 will provide results for the start and end of each stage in the construction sequence.
Two or More Times in Each Stage option. When this options is chosen, SAP2000 will provide output for two or more steps for each stage in the construction sequence.
Minimum Number of Steps for Application if Instantaneous Load edit box. Enter a value for the minimum number of steps used in the application of an instantaneous load.
Minimum Number of Steps for Analysis of Time Dependent Items edit box. Enter a value for the minimum number of steps for a time-dependent item, such as creep.
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Access the Results Saved for Nonlinear Static Load Cases form as follows:
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