| Matrix or Vector | Midside Nodes [1] | Shape Functions | Integration Points |
|---|---|---|---|
| All | With midside nodes | w = C1 + C2x + C3x2 | 3 |
| All | Without midside nodes | w = C1 + C2x | 2 |
| Load Type | Distribution |
|---|---|
| All Loads | Same as shape functions |
The logic is very similar to that given for SURF154 in SURF154 - 3-D Structural Surface Effect with the differences noted below:
For surface tension (input as SURT on R command)) on axisymmetric models (KEYOPT(3) = 1), an average force is used on both end nodes.
For surface tension with midside nodes, no load is applied at the middle node, and only the component directed towards the other end node is used.
When using large deflections, the area on which pressure is applied changes. The updated distance between the two end nodes is used. For plain strain problems, the thickness (distance normal to the X-Y plane) remains at 1.0, by definition. For plane stress problems, the thickness is adjusted:
(13–250)
where:
tu = final thickness used. 
ti = thickness for user input option (input as TKPS on R command) εz = strain in thickness direction (normal to X-Y plane) Using the assumption of constant volume:
(13–251)
where:
εx = strain along the length of the element εy = strain normal to the underlying solid. Assuming further that:
(13–252)
yields:
(13–253)