Release 11.0 Documentation for ANSYS
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SHELL28 is used to carry shear load in a frame structure. The element has three degrees of freedom at each node: translations in the nodal x, y, and z directions, or rotations about the nodal x, y, and z axes. See SHELL28 in the Theory Reference for ANSYS and ANSYS Workbench for more details about this element.
The geometry, node locations, and the coordinate system for this element are shown in Figure 28.1: "SHELL28 Geometry". The element is defined by four nodes, a thickness, and material properties. The only material properties actually used are GXY and DENS. GXY may be entered directly or calculated from EX and either NUXY or PRXY. Also, EX must be input, whether or not GXY is entered. The element coordinate system orientation is as described in Coordinate Systems. Real constant SULT is the ultimate shear stress used for the margin of safety calculation. ADMSUA is the added mass per unit area. KEYOPT(1) is used to select whether the element should be used as a shear panel or as a twist panel. Only the lumped mass matrix is available.
Element loads are described in Node and Element Loads. Temperatures may be input as element body loads at the nodes. The node I temperature T(I) defaults to TUNIF. If all other temperatures are unspecified, they default to T(I). For any other input pattern, unspecified temperatures default to TUNIF. Temperatures are used only for material property evaluation.
A summary of the element input is given in "SHELL28 Input Summary". Element Input gives a general description of element input.
I, J, K, L
| UX, UY, UZ if KEYOPT(1) = 0 |
| ROTX, ROTY, ROTZ if KEYOPT(1) = 1 |
| THCK - Panel thickness |
| SULT - Ultimate shear stress |
| ADMSUA - Added mass/unit area |
EX, PRXY (or NUXY), GXY, DENS, DAMP
None
T(I), T(J), T(K), T(L)
Stress stiffening
Element behavior:
Shear panel
Twist panel
The solution output associated with the element is in two forms:
Nodal displacements included in the overall nodal solution
Additional element output as shown in Table 28.1: "SHELL28 Element Output Definitions"
Several items are illustrated in Figure 28.2: "SHELL28 Stress Output". Solution Output gives a general description of solution output. See the Basic Analysis Guide for ways to view results.
The Element Output Definitions table uses the following notation:
A colon (:) in the Name column indicates the item can be accessed by the Component Name method [ETABLE, ESOL]. The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.
In either the O or R columns, Y indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and a - indicates that the item is not available.
Table 28.1 SHELL28 Element Output Definitions
| Name | Definition | O | R |
|---|---|---|---|
| EL | Element Number | Y | Y |
| NODES | Nodes - I, J, K, L | Y | Y |
| MAT | Material number | Y | Y |
| VOLU: | Volume | Y | Y |
| SXY | Average of four corner shear stresses | Y | Y |
| XC, YC, ZC | Location where results are reported | Y | 3 |
| TEMP | Temperatures T(I), T(J), T(K), T(L) | Y | Y |
| SXY(I,J,K,L) | Shear stresses at corner nodes | Y | Y |
| SXY(MAX) | Maximum of four corner shear stresses | Y | Y |
| SMARGN | Margin of safety on shear | Y | Y |
| FDIK, FDJL | Forces along diagonals I-K and J-L | 1 | 1 |
| FLI, FJI | Forces at node I from node L and node J | 1 | 1 |
| FIJ, FKJ | Forces at node J from node I and node K | 1 | 1 |
| FJK, FLK | Forces at node K from node J and node L | 1 | 1 |
| FKL, FIL | Forces at node L from node K and node I | 1 | 1 |
| SFLIJ | Shear flow on edge I - J | 1 | 1 |
| SFLJK | Shear flow on edge J - K | 1 | 1 |
| SFLKL | Shear flow on edge K - L | 1 | 1 |
| SFLLI | Shear flow on edge L - I | 1 | 1 |
| FZI | Z - Force at node I | 1 | 1 |
| FZJ | Z - Force at node J | 1 | 1 |
| FZK | Z - Force at node K | 1 | 1 |
| FZL | Z - Force at node L | 1 | 1 |
| MDIK, MDJL | Moments about diagonals I-K and J-L | 2 | 2 |
The values are output in place of FDIK and FDJL only if KEYOPT(1) = 1
Available only at centroid as a *GET item.
Table 28.2: "SHELL28 Item and Sequence Numbers" lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table of this manual for more information. The following notation is used in Table 28.2: "SHELL28 Item and Sequence Numbers":
output quantity as defined in the Table 28.1: "SHELL28 Element Output Definitions"
predetermined Item label for ETABLE command
sequence number for single-valued or constant element data
Table 28.2 SHELL28 Item and Sequence Numbers
| Output Quantity Name | ETABLE and ESOL Command Input | |
|---|---|---|
| Item | E | |
| FDIK (MDIK) | SMISC | 1 |
| FDJL (MDJL) | SMISC | 2 |
| FLI | SMISC | 3 |
| FJI | SMISC | 4 |
| FIJ | SMISC | 5 |
| FKJ | SMISC | 6 |
| FJK | SMISC | 7 |
| FLK | SMISC | 8 |
| FKL | SMISC | 9 |
| FIL | SMISC | 10 |
| FZI | SMISC | 11 |
| FZJ | SMISC | 12 |
| FZK | SMISC | 13 |
| FZL | SMISC | 14 |
| SXY | SMISC | 15 |
| SXYI | SMISC | 16 |
| SXYJ | SMISC | 17 |
| SXYK | SMISC | 18 |
| SXYL | SMISC | 19 |
| SXYMAX | SMISC | 20 |
| SMARGN | SMISC | 21 |
| SFLIJ | SMISC | 22 |
| SFLJK | SMISC | 23 |
| SFLKL | SMISC | 24 |
| SFLLI | SMISC | 25 |
Zero area elements are not allowed. This condition occurs most often when the elements are numbered improperly.
This element is most often used with a latticework of beam or spar elements. If this element is used alone it is almost always unstable, because it carries only shear (and not tension or compression) loading.
This element is not recommended for general use. Its use should be restricted to applications which have historically used such an element. For all other applications, you should use other shell elements such as SHELL41, SHELL43, SHELL63, SHELL181, and SHELL281, which automatically combine tension, compression, bending, shear, and twisting effects.
This element is based on the premise of having only shear, but no normal stress along the edges. Since this is possible only for rectangles, you can expect the accuracy of the element to degrade if nonrectangular shapes are used.
