Form: Assign Automatic Area Mesh
SAP2000 allows area objects to be divided into smaller objects in the object-based model, and meshed into elements in the analysis model. Dividing the object is accomplished using the Edit menu > Divide Areas command. Meshing an area object is accomplished using the Assign menu > Area > Automatic Area Mesh command.
This topic addresses meshing an area object into elements in the analysis model.
Select the area objects to be meshed.
Click the Assign menu > Area > Automatic Area Mesh command to activate the Assign Automatic Area Mesh form.
Choose the option to specify how the object is to be meshed. The Area Object Dividing or Meshing topic explains how the program works and uses illustrations to show the effects of the various options.
Note: Meshing is performed on one area object at a time.
No Auto Meshing option. When this option is selected, the program will not mesh the selected area object into the analysis model, thereby treating the object as a structural element.
Mesh Area Into This Number of Objects (Quads and Triangles Only) option and Along Edge from Point 1 to 2 and Along Edge from Point 1 to 3 edit boxes. Use this option to specify that the selected object(s) be meshed into the number of objects specified using the edit box for each edge. The program adds points to the adjacent edges, at equally spaced intervals, and then automatically adds the same number of points along the opposite edges so that meshing lines can be drawn between the opposing points on the edges to create the specified number of objects/elements.
Mesh Area Into Objects of This Maximum Size (Quads and Triangles Only) option and Along Edge from Point 1 to 2 and Along Edge from Point 1 to 3 edit boxes. Use this option to specify that the selected object(s) be meshed into n number of objects of the maximum length specified in the edit box for each of the adjacent edges. The program adds points along each edge at equally spaced intervals such that the length of any of the resulting divided objects does not exceed the length specified in the edit boxes. The length specified determines the number of objects to be created and thus the number of points added to each edge.
Meshing Group drop-down list. This drop-down list near the upper right corner of the form can be used with the following options to make meshing of a complex model a little easier. Choose the previously defined group that contains both the selected area object and the line or point objects upon which meshing will be based. The ALL group is selected by default.
Mesh Area Based on Points On Area Edges (Quads and Triangles Only), Points Determined From option. Use this option to specify that the selected object be meshed based on specified lines and points. The specified lines and points must lie in the plane of the area object. These options may be used in combination. As appropriate, use the Meshing Group drop-down list near the top right corner of the form to select the previously defined group that includes the selected area object and the straight line or point object.
Intersection of Straight Line Objects In Meshing Group With Area Edges check box. Check this check box to specify that points be added, and thus the object meshed, at the intersection of the edge of the selected area object with a selected straight line object that has been drawn or defined to cross the selected object's edge. The program will not extend the selected line to make it intersect an edge; the selected line must already intersect an edge of the selected object. Note that the selected straight line object and selected area object must lie in the same plane and must both belong to the same previously defined Group (see Meshing Group above).
Point Objects In Meshing Group That Are On Area Edges check box. Check this check box to specify that the object be meshed based on a point drawn or defined on the object's edge. Note that the point object and the area object must both be selected and lie in the same plane. Also for this option, the point must lie on the edge of the selected object. The Draw menu > Snap To > Lines and Edges command may be helpful in placing the point accurately on the object's edge. Note that the selected point object and selected area object must lie in the same plane and must both belong to the same previously defined Group (see Meshing Group above).
Mesh Area Using Cookie Cut Based On Straight Line Objects In Meshing Group option. Use this option to specify that the selected object be meshed based on a selected straight line object. For this option, the selected line object does not need to intersect with the edge of the selected area object. If the selected line object does not intersect with the selected object's edge or fully transect the selected area object, the program places a point on the object's edge along the projected path of the selected line object. Note that the selected line object and selected area object must lie in the same plane and must both belong to the same previously defined Group (see Meshing Group above).
Mesh Area Using Cookie Cut Based on Point Objects In Meshing Group option and Rotation of Cut Lines From Area Local Axes (Deg) edit box. Use this option to specify that the selected object be meshed based on a selected point object. For this option, the selected point object does not need to lie on the edge of the selected area object. The program "draws meshing lines" that pass through the selected point to proportionately placed points on the area object's opposing edge or edges. Use the edit box to specify the rotation in degrees of the "meshing lines" from the original local 1 and 2 axes of the selected area object. Positive rotations appear counterclockwise when the local 3 axis is pointing toward you. Note that the selected point object and selected area object must both belong to the same previously defined Group (see Meshing Group above).
Mesh Area Using General Divide Tool Based On Points and Lines In Meshing Group option and Maximum Size of Meshed Object edit box. Use this option to specify that the selected object be meshed based on selected point or line objects and the maximum length for the resulting meshed object, as entered in the edit box. For this option, the selected point or line object must lie within the same plane as the selected area object and lie within the selected object (i.e., the point can not lie on the edge of the object and the line can not cross the edge of the area object or have its end points on the edge of the area object). The program divides the selected object into n number of objects based on the maximum size specified in the edit box and the locations of the selected points and lines within the area object. See the Area Object Dividing or Meshing topic for more clarification. Note that the selected point and line object and the selected area object must all belong to the same previously defined Group (see Meshing Group above).
Choose an option to specify the Local Axes For Added Points:
Make same on Edge if adjacent corners have same local axes definition check box. Use this check box to specify that the local axes definitions for new points added along the edges of an area object are the same as an adjacent area object corner point if the local axes definition for the adjacent corners are identical.
Make same on Face if all corners have same local axes definition check box. Use this check box to specify that the local axes definition for the new points on the face of the area object are set the same as a corner point of the area object if the local axes definitions for all of the corner points of the area object are identical.
Choose an option to specify the Restraints and Constraints For Added Points
Add on Edge when restraints/constraints exist at adjacent corner points (Applies if added edge point and adjacent corner points have same local axes definition) check box. Use this check box to specify that a restraint degree of freedom (or constraint) is added to new points on the edges of the area object if both adjacent corners have that degree of freedom restrained (constrained) and the local axes definitions for the adjacent corners and the new point are identical.
Add on Faces when restraints/constraints exist at all corner points (Applies if added face point and all corner points have same local axes definition) check box. Use this check box to specify that a restraint degree of freedom (or constraint) is added to new points on the face of the area object if all area object corners have that degree of freedom restrained (constrained) and the local axes definitions of all corners and the new points are identical.
Note: Unlike the Edit menu > Divide Areas command, the Assign menu > Area > Automatic Area Mesh command does not change the size or number of the objects; the meshing performed is internal and is handled similar to any other assignment. This allows for the meshing to be changed or removed without any effect on the area object geometry. Use the Display menu > Show Miscellaneous Assigns > Area command to display the Automatic Area Object Meshing and the Automatic Area Edge Constraints.
Example: Assignment of automatic area mesh is demonstrated in Problem A and Problem C.
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