Use the Property/Stiffness Modification Factors form to specify modification factors for the analysis of section stiffnesses of the shells and frames in the model.
Modification factors can be defined as part of shell section properties (i.e., Deck, Slab, Wall) or frame section properties and assigned directly to shell and frame objects. Note that when modification factors are assigned directly to an object that also has modification factors defined as part of its section properties, the two factors are multiplied. Therefore, it is intended that modification factors be specified using the section property definition or object assignment, not both.
The definition of modification factors as part of section properties allows application of modification factors on the basis of section type.
The object assignment allows application of modification factors on an "object-by-object" basis (although multiple objects can be selected) regardless of section type.
Note that the modification factors affect only the analysis properties. They do not affect the design properties. The default for all modification factors is 1.
Note: Modification factors cannot be assigned to Auto Select lists, which usually consist of multiple sections. If an Auto Select list is selected from the list of names in the Select Property Type area of the form, the Auto Select form appears. Close that form by clicking the Cancel button to return to the Frame Property Type form and choose an individual section before continuing.
For Shells
The f11, f22 and f12 modifiers are essentially equivalent to modification factors on the thickness of the shell element.
The m11, m22 and m12 modifiers are essentially equivalent to modification factors on the thickness3 of the shell element.
Specify modification factors as part of the definition as follows:
Access the Property/Stiffness Modification Factors form for slabs, decks, and walls as follows:
Click the Define menu > Section Properties > {Slab, Deck, Wall} Section command to display the {Slab, Deck, Wall} Properties form.
Click the Add New Property button or highlight a previously defined {slab, deck, wall} section and click the Add Copy of Property or the Modify/Show Property button to display the {Slab, Deck, Wall} Property Data form.
Click the Modifiers (Currently Default) Modify/Show button.
Access the Property/Stiffness Modification Factors form for frame sections as follows:
Click the Define menu > Section Properties > Frame Sections command to display the Frame Properties form. Then do one of the following to access the Frame Section Property Data form:
Click the Add New Property button to display the Frame Property Shape Type form; select a Section Shape and click the OK button, or click a shortcut Frequently Used Shape Types button.
Highlight a previously defined frame section definition and click the Add Copy of Property or the Modify/Show Property button
Click the Property Modifiers Modify/Show Modifiers button.
Assign modification factors to deck, wall, slab, and frame objects on an object-by-object basis as follows:
Select the object(s) to be assigned modification factors.
Click the Assign menu > Frame > Property Modifiers or the Assign menu > Shell > Stiffness Modifiers command, depending on the type of object selected.