Question:  Error message in output file: “Plate No. …is badly shaped, warped, not convex, or not numbered counter-clockwise.”

Explanation :  There are several rules that need to be observed when modeling a structure with plate elements.  These rules arise from the mathematical algorithms the program uses to model plates.  Failure to follow these rules will result in error and warning messages in the output file.

1. A plate element’s aspect ratio should be as near to 1:1 as possible.  Aspect ratio is defined as the ratio of the length of the shortest side to the longest side of the element.  Aspect ratios in excess of 4:1 should be avoided.  In other words, a triangular (3-noded) plate element should be shaped as near to an equilateral triangle as possible, and a quadrilateral (4-noded) element should be shaped as near to a square as possible.

Consider the plate element shown in the figure below:

The aspect ratio of this element is approximately 19:1.  Running the analysis of a model that includes a plate shaped like this will generate an error message indicating that the plate is “…badly shaped.”  To remedy this problem, this quadrilateral plate should be broken into two triangular plates.

1. The angles between adjacent sides of 4-noded plates should be as near to 90 degrees as possible.  You should try at all times to keep interior angles of a plate element between 60 and 120 degrees.   Concave sides of a plate element are not allowed, that is, interior angles must never exceed 180 degrees.

If you try to run the analysis on a model that includes a plate element shaped like the one shown in the figure above, the error message, “…not convex” will be printed in the output file.

1. When assigning nodes to an element in the input data, the nodes must be specified either in clockwise or counterclockwise order around the perimeter of the element.

If you try to run the analysis on a model that includes a plate element where the nodes are not specified in either clockwise or counterclockwise order, the error message, “…not numbered counter-clockwise” will be printed in the output file.

All nodes of a (4-noded) plate element must lie on the same plane.  If one of the nodes is not coplanar with the other three, the error message, “plate is…warped” will be printed in the output file.  You may use the Check For Warped Plates command in the Tools menu to locate plates whose nodes are not coplanar