How come there is no category for weldments??

Anyway... I have a weldment that there is a total of 15 tubes or plates. There are 2 plates that are identical and 2 separate sets of tubes that are identical. SolidWorks is only recognizing 1 set of tubes as such. All other quantities are listed as 1 each. Even the properties for each item are identical. Is there anyway to make the software see the parts are the same? Why would these be viewed as different?