structure geogrid import command

Syntax

structure geogrid import keyword

Primary keywords:

from-file    from-geometry

Create geogrid elements from an outside source.

from-file s <format keyword> [geogridimportoptions]

Create elements from the geometry file s.

The optional format keyword can be used to specify the format of the file. The options are dxf, geom, or stl. [CS: work out what needs to happen here later; formats should have links] If not specified, the format is assumed from the file extension.

from-geometry s [geogridimportoptions] <range>

Create elements from the geometry set named s. The range applies to the list of edges in the geometry set.

Keyword Block

Any of the following keywords may be optionally supplied for use with the major keywords of structure geogrid import: from-file and from-geometry.

id i

Specify the ID that will be assigned to all new elements created by this command. If this value is not given, then the next available ID will be used. The ID controls potential joining of the element nodes to an existing element, as follows. At each potential new node location, a new node is created unless all of the following conditions are fulfilled: 1) the ID is given; 2) an existing node is found “near” the potential new node location; and 3) the found node is part of an element of the same type with ID equal to i.

group s1 <slot s2 >

Assign the created elements to group s1. The group is assigned to the slot named s2 if supplied; it is assigned to the slot named Default if not. Use of the group logic is described in Group.

cross-diagonal <b >

If specified, a cross-diagonal mesh of four triangles will be created with a node lying at the centroid of all quadrilaterals; otherwise, a cross-hatch mesh of two triangles will be created dividing the quadrilateral.

When connecting elements to the grid, it is best to locate nodes at gridpoints. If the finite-element type can resist bending (DKT, DKT-CST, or DKT-(CST Hybrid) elements), then incompatibilities can develop along element faces and zone faces, because the transverse (out-of-plane) displacement field varies cubically across element faces, but varies only linearly across zone faces. Thus, when connecting bending-resistant elements rigidly to zone faces, it is best to utilize a cross-hatch mesh, because the middle node of the cross-diagonal mesh will be constrained to translate according to the linear displacement field of the zone face. This over-constrains the elements and can produce near-zero moments at these mid-nodes when present in a nonzero moment field.

distinct

Eliminate sharing of nodes among created elements. Every element will create a new set of nodes, even if they are at the same location in space and elements share the same ID number. This option is most commonly used with a later structure node join command to create links connecting nodes at the same location in order to apply custom inter-element behavior.

element-type keyword

Specify the finite element formulation used by each structural element. If no element type is specified, then the element type will be DKT-CST. Note that the type of finite element is associated with each structural element as it is created and cannot subsequently be altered. The finite element type of existing structural elements is printed by the structure geogrid list element-type command. The value of the keyword supplied must be one of the following three-noded finite elements:

s

Attempt to match the string s to one of the available keywords below, and treats as that option

cst

CST (6 degrees-of-freedom) finite element. This is a membrane element; it resists membrane, but not bending, loading.

csth

CST Hybrid (9 degrees-of-freedom) finite element. This is a membrane element; it resists membrane, but not bending, loading.

dkt

DKT (9 degrees-of-freedom) finite element. This is a plate-bending element; it resists bending, but not membrane, loading.

dkt-cst

DKT-CST (15 degrees-of-freedom) finite element. This is a shell element that combines the DKT and CST elements to resist both bending and membrane loading.

dkt-csth

DKT-(CST Hybrid) (18 degrees-of-freedom) finite element. This is a shell element that combines the DKT and CST Hybrid elements to resist both bending and membrane loading.

internal

This keyword only applies if the from-faces option was used. Specifies that all internal and surface faces in the range will have elements created on them. Normally only surface faces are considered.

maximum-length f

Break the element into segments no greater than length f. The segments setting, if provided, is overridden as needed by this setting.

segments i

Break the element into i equal segments, creating new nodes as needed. The default value is 1, indicating that only one element will be created.