Form: Auto Construction Sequence Load Case
An auto sequential construction case provides an automated method of creating static nonlinear staged construction cases that are specifically tailored to model construction sequence loading. Note that only one auto sequential construction case can be defined per model file.
Before defining the automatic sequential construction cases, define the Load pattern(s) that will be used to define the Load Pattern (see below) for the active structure.
Click the Define menu > Auto Construction Sequence Cases command to display the Auto Construction Sequence Load Case form.
Select the type of construction sequence to be defined:
Case Is Active check box. If this check box is unchecked, the auto construction sequence is inactive. No construction sequence case is defined. Use this option to disable the existing construction sequence.
Auto Construction Sequence Load Case Name edit box. Use the name for the load case suggested in the associated edit box or type a new name in the box.
Geometric Nonlinearity Option drop-down list. Geometric nonlinearity effects are considered on all elements in the structure. Typically, the P-delta option is adequate. If reasonable, it is recommended that the analysis be performed first without P-delta (i.e., select None from the drop-down list), adding geometric nonlinearity effects later. The following options are available:
None option. All equilibrium equations are considered in the undeformed configuration of the structure.
P-Delta option. The equilibrium equations take into partial account the deformed configuration of the structure. Tensile forces tend to resist the rotation of elements and stiffen the structure, and compressive forces tend to enhance the rotation of elements and destabilize the structure. This may require a moderate amount of iteration.
P-Delta plus Large Displacements option. All equilibrium equations are written in the deformed configuration of the structure. This may require a large amount of iteration.
Construction Sequence
Combine this number of Stories in each Construction Sequence Group edit box. Enter the value for the number of stories in each sequence. This means the structure will start with n stories in the first stage, n more stories will be added in the second stage for a total of 2n stories, and so on.
Exclude this Group Until the Last Step check box and drop-down list. Check this check box to specify that a Group be excluded from the construction sequence until the last step. Use the drop-down list to select the Group.
Loads Applied area. Use the edit boxes, buttons, and display lists in this area to specify the Load Pattern. The distribution of load applied on the structure for a given construction sequence case is defined as a scaled combination of one or more of the following:
Any load pattern.
A uniform acceleration acting in any of the three global directions. The force at each joint is proportional to the mass tributary to that joint and acts in the specified direction.
A modal load for any eigen or Ritz mode. The force at each joint is proportional to the product of the modal displacement, the modal circular frequency squared (w2), and the mass tributary to that joint, and it acts in the direction of the modal displacement.
The load combination for each construction case is incremental, i.e., it acts in addition to the load already on the structure if starting from a previous static nonlinear case.
Add button.
Select a load from the Load drop-down list.
Enter the appropriate value in Scale Factor edit box.
Click the Add button.
Delete button.
Highlight the load to be deleted in the display list.
Click the Delete button.
Design Combinations - Replace Dead Type Cases with this Case in All Default Design Combinations check box. When this check box is checked, the Construction Sequence Case being defined will replace the default Dead case used in all default design combinations created by the program.
See also