This option defines dilatation on a structure bar. Open the Dilation dialog by clicking 
on the Bar tab in the Load Definition dialog.
You can define the dilatation of a structure bar in this dialog. You can enter the dilatation value as an absolute (units of length) or a relative (in relation to a bar's length) value. Positive dilatation values indicate an elongation of a bar; negative values indicate shortening of a bar.