After analysis , I get the following warning in the output file :
**ERROR** PLATE NO. 2448(JOINTS 2017 - 2088 - 2160 - 2089)
IS BADLY SHAPED, WARPED, NOT CONVEX, OR NOT NUMBERED COUNTER-CLOCKWISE.
Plate element should be modeled using some rules. 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 1:4 should be avoided. 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. Kindly find the link to the document which explains the rules for proper modeling of plate elements.
http://communities.bentley.com/products/structural/structural_analysis___design/m/structural_analysis_and_design_gallery/257477.aspx