Forms: Lateral Displacement Targets, Add Auto Calculated Lateral Displacement Targets
For displacement optimization, ETABS 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.
Assuming that appropriate steel frame, concrete frame, composite beam, composite column, or steel joist auto select list assignments have been made, the displacement targets will be considered in steel frame design, concrete frame design, composite beam design, composite column design, or steel joist design.
Specify a displacement optimization specification as follows:
Assign auto select sections to selected frames before running the analysis. Auto select lists must be assigned to the frame elements for the displacement optimization to work. When ETABS 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 displacement target may never be reached no matter how many times the analysis and design are run.
Click the Design menu > Set Lateral Displacement Targets command to access the Lateral Displacement Targets form. Use the form to specify displacement targets for various load cases. Our intent is that the user picks a point, typically at the roof level of the building, and specifies a maximum displacement target (in any direction) for one or more load cases.
Click the Add button to begin specifying the displacement data.
Load Case drop-down list. Select the Load Case for which displacements are to be optimized.
{Tower and} Story and Joint Label drop-down lists. Specify the location of the displacement by selecting the {tower and} story level and a joint ID.
Max Displacement edit box. Specify the target displacement (in any direction) in the current length units for the specified load case.
Delete button. If necessary, highlight the displacement optimization specification to be deleted. Click the Delete button.
Sort button. Click this button to arrange the rows of data alphabetically by Load Case.
Repeat Steps 1, 2 and 3 as needed.
Rerun the analysis using the new section sizes to review the displacements. Displacement optimization is an iterative process that typically requires the analysis and design to be rerun multiple times. Note that it is not guaranteed that the displacement target will be reached using this option.
Ignore Specified Target Displacements check box. Check this check box to exclude the displacements from a design iteration(s) without deleting them. Uncheck the check box to include displacements in design.
Drift Ratio edit box, Base Story for Drift drop-down list, and Apply Auto Targets button. These options and button are enabled if a joint(s) is selected before the Design menu > Set Lateral Displacement Targets command is used.
Drift Ratio edit box. The value for the drift ratio specified here is applied at the selected joint(s).
Base Story for Drift drop-down list. Select the level of the structure where the displacement begins.
Click the Apply Auto Targets button to have ETABS automatically calculate the maximum displacement for selected points based on the value specified in the Drift Ratio edit box and the story level selected in the Base Story for Drift drop-down list.
See also