Form: Lateral Displacement Targets
For displacement optimization, SAP2000 predicts which members should be increased in size to control the displacements based on the energy per unit volume in the members. The members with more energy per unit volume are increased in size a larger percentage than those with smaller energies per unit volume. Some members with small energy per unit volume may be decreased in size if they are still acceptable for strength considerations.
Note: Auto select lists must be assigned to the frame members for the displacement optimization to work. When SAP2000 increases or decreases a section size, it uses the available sizes in the auto select list. If the appropriate sections are not included in the auto select lists, the desired displacement target may never be reached no matter how many times the analysis and design are rerun.
Specify a displacement optimization specification as follows:
Click the Design menu > Steel Frame Design > Set Displacement Targets command to open the Lateral Displacement Targets form, which can be used to specify displacement targets for various load cases. The intent is that a point is picked, typically at the roof level of the model, and a maximum displacement target (in any direction) is specified for one or more load cases on that point.
From the Static Linear Case drop-down list in the Loads area of the form, select the load pattern for which the displacement is to be optimized.
Specify the location for the displacement by specifying a Point.
Specify the target displacement in the Max Displacement edit box.
Click the Add button.
Repeat Steps 1 through 5 as needed.
Run the design (Design menu > Steel Frame Design > Start Design/Check of Structure) and then rerun the analysis (Analyze menu > Run Analysis) using the new section sizes to view the displacements by right clicking on selected points. Displacement optimization is an iterative process that typically requires that the analysis and design be run multiple times. There is no guarantee that the desired displacement target will be reached using this option.
Tip: To rerun the analysis, it will be necessary to delete the design results (i.e., unlock the model, or use the Delete Results button on the Set Analysis Cases to Run form). This will not adversely affect the specification of displacement targets.
Modify a displacement optimization specification as follows:
Click the Design menu > Steel Frame Design > Set Displacement Targets command to access the Lateral Displacement Targets form.
Highlight the displacement optimization specification to be modified in the Loads area of the Lateral Displacement Targets form. Note that the data for the specification appears in the boxes at the top of the Loads area. Modify the data in the boxes as desired.
Click the Modify button.
Rerun the analysis using the new section sizes to review the displacements.
Delete a displacement optimization specification as follows:
Click the Design menu > Steel Frame Design > Set Displacement Targets command to access the Lateral Displacement Targets form.
Highlight the displacement optimization specification to be deleted in the Loads area of the Lateral Displacement Targets form.
Click the Delete button.
Deactivate Targets check box. Check the Deactivate Targets check box to exclude the displacements from a design iteration(s) without deleting it. Uncheck the check box to include displacements in the design.
See Also