Editing a Model Editing a Model

In the MEDIT Menu, one can define and delete elements, nodes, load groups, and element load attributes in much the same way as when defining a model. One can also redefine mapping of panel loads to nodes. In fact, all commands used during INMODEL can be used in MEDIT.

To delete objects already in the database, the following commands are provided:


     ED_CLASS,  ~CLASS_NAME, SEGNO,   ......

     CL_DELETE,  :CLS_SEL(1), :CLS_SEL(2), .......

     ELA_DELETE,  :ELE_LOAD_SEL(1), :ELE_LOAD_SEL(2), .......

     LG_DELETE,  :LG_SEL(1), :LG_SEL(2), .......

     EL_DELETE,  :ELE_SEL(1), :ELE_SEL(2), .......

These commands edit elements and classed and delete classes, element load attributes, load groups, and elements respectively, and the selectors are selectors defining the quantities to be deleted. In using the commands which delete quantities, care must be taken, since if a class is deleted, then all elements which use that class will also be deleted. Also, when using the ELA_DELETE command, notice that the selectors operate only on the element name. In other words, while one can define element load attributes by either class, nodes defining the element, or name, one can only delete them by element name. A word of caution is in order here. Once something has been deleted from the database, all data associated with this quantity is lost. Thus, if one has already performed a structural analysis and he deletes an element or class, then the structural results for the elements deleted will be lost. It is better to "deactivate" elements, as described later, than delete them.

Notice that there is no command for deleting a node. Since nodes are simply points that are connected with structural elements, there is no need for such a command. In order to relocate a node, simply redefine its associated point. This will move the end of a beam or the corner of a plate that references the relocated node.

Often, elements exist for some stages of an analysis and are absent for other stages. This notion can be modeled by deactivating elements when they are not present with the command:


Here, OBJECT(i) is as described above and the available options are -ACTIVE and -INACTIVE. All elements selected with OBJECT(i) will have the activity defined by the option immediately preceding the object.

The command:


It serves the same purpose as the -OFFSET option on the INMODEL command. Thus, if a model is defined entirely in the MEDIT menu, member end offsets can still be generated by issuing this command after the model has been defined. As with all things in MEDIT, GEN_OFFS only generates offsets on elements which have been defined before the command is issued.

The command:


will change the diameter and thickness of tubular members with classes which match the selector :C_SELECT. It will take the original area and compute a new diameter and thickness which produces d D/T ratio between the two limits and which has the same area as the original sizes. The new dimension will be changed to the nearest D_INCREMENT. By default, all classes will be checked, D/T_MIN is 30, D/T_MAX is a huge number, and D_INCREMENT is 1/8 inch or 2 mm depending on the units being used. With the defaults, the new dimensions will be multiples of either 1/8 inch or 2 mm.

A simple way to define element dependent buckling lengths is provided with either of the two commands:

     XBRACE, ELE_NAME(1), ELE_NAME(2), ......, ELE_NAME(n)

     XBRACE, *CEN_NODE, *NODE(1),  ......, *NODE(n)

With either of these commands, one is defining the buckling length of an element to be based on the tension-compression behavior of another element. With the first form of this command, the buckling length of ELE_NAME(1) is based on ELE_NAME(2), ELE_NAME(2) on ELE_NAME(3), ..., and ELE_NAME(n) on ELE_NAME(1). The second form accomplishes the same thing, but here *CEN_NODE is the common node between a set of elements, and *NODE(i) are the other ends. In other words, the two forms are identical provided ELE_NAME(1) is an element between *NODE(1) and *CEN_NODE, ELE_NAME(2) is between *NODE(2) and *CEN_NODE, etc. An illustration of the use of the XBRACE command is shown in Figure 22. For a complete discussion on how the buckling length depends on the brace element, see the section on defining elements. Notice that with either of these forms, one should define either the nodes *NODE(i) or the elements ELE_NAME(i) in order around the center node.