Forms: Load Cases, Load Case Data, Design Load Type
Use the Define menu > Load Cases command to define how loads are to be applied to the model, and how the structural response is to be calculated. An unlimited number of named static or modal load cases can be defined. Load patterns by themselves do not create any response (forces, deflections, etc.). A load case must be defined to generate results.
Before defining any static load cases, define the load patterns that will be needed using the Define menu > Load Patterns command. If a modal load case is to be defined, specify the mass source first using the Define menu > Mass Source command.
TIP: Every time a new load pattern is defined, the program automatically creates a corresponding load case of the same name.
Note: Load cases also can be accessed by expanding the tree under Load Definitions > Load Cases on the Model tab in the Model Explorer window.
Use the Define menu > Load Cases command to access the Load Cases form:
Add New Case button. Click this button to access the Load Case Data form and define a new static or modal load case. Each load case must have a unique name. The options displayed on that form depend on the load case type that is selected from the Load Case Type drop-down list. Click the Modify/Show Notes button to add notes about the load case to the model file.
Static option. The default setting of Static is the most common choice. For a static type, the analysis options are linear or nonlinear (uplift, cracked, or long term cracked). If nonlinear (long term cracked) has been selected, creep coefficient and shrinkage strain should be specified to effectively compute long-term deflections. The load case may start with zero initial conditions, or with a stiffness determined from a nonlinear load case allowing for the use of cracked section stiffnesses in linear analyses. The loads applied will be selected from a drop-down list of previously defined load patterns multiplied by a scale factor. If multiple load patterns are to be applied of differing load types (e.g., DEAD and LIVE), click the button to access the Design Load Type form to specify how SAFE should identify the load case results for use in design.
Modal option. The Modal load case type allows for the extraction of either eigen or ritz vectors, or the import of external modal information from ETABS. The load case may start with zero initial conditions, or with a stiffness determined from a nonlinear load case allowing for the use of cracked section stiffnesses in the modal calculations. If SAFE is calculating the modes, specify the maximum and minimum number of vectors the program should attempt to find. If modal data is imported from ETABS using the File menu > Import command, all modal parameters should be set in ETABS before exporting a SAFE floor file. For additional information on Eigen- and Ritz-Vectors, see the Modal Analysis chapter in the CSI Analysis Reference manual.
Three other load case types are used by the program depending on the type of load pattern specified. These load case types are not directly editable by the user, and information regarding these load cases is available only in the modify/review mode when using the button discussed below.
Multi-Step Static: The Multi-Step Static load case type is used by SAFE to create live-load pattern or “skip” loading. A load case of this type is automatically created for each PATTERN LIVE type load pattern. Results will be computed using a Range scheme (the Range combination calculates minimum and maximum force quantities for each element, and any response from a load pattern will be assumed to be zero in addition to its calculated value in order that the absolute magnitude of the combined value is not reduced). The load case may start with zero initial conditions, or with a stiffness determined from a nonlinear load case allowing for the use of cracked section stiffnesses in the analysis.
Response Spectrum: The Response Spectrum load case type is used only with the import of ETABS response spectrum results using the File menu > Import command. All of the response spectrum parameters, such as the number of modes and the excitation function and the modal combination method should be set in ETABS before exporting a SAFE floor file.
Hyperstatic: The Hyperstatic load case type is a type of analysis required by certain codes when performing design with post-tensioning. A load case of this type is automatically created any time tendons exist in the model. Reactions from the specified Base Load Case linear load case are applied to a modified model where the supports have been removed.
Add Copy of Case button. Highlight a load case in the list shown under Load Cases and click this button to access the Load Case Data form. All edit boxes, drop-down lists, and option selections (except for the Load Case Name) on that form will be populated with values identical to those of the highlighted load case. Values may be revised as necessary and then saved to create a new load case. This option is available only for static and modal load cases.
Modify/Show Case button. Highlight a load case in the list shown under Load Cases and click this button to access the Load Case Data form. On that form, data in the edit boxes and drop-down lists, and option selections may be reviewed, and revised if necessary. This option is available for all load cases, including program generated Multi-Step Static, Response Spectrum, and Hyperstatic load cases, but is limited primarily to review for these load case types.
Delete Case button. Highlight a load case in the list shown under Load Cases and click this button to immediately delete the highlighted load case from the model. This option is available only for static and modal load cases.
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