How to reduce .DAT file size

We have an ongoing project with a larger number of nodes and history. 

 When we want to work a small section we copy  the model and delete the segments away form the area of interest.  

The problem is the DAT file size remains very large even though there are only small number of  nodes left.

How can we reduce the file size?
We can copy the area interest  into a new model, but want to keep all the load combinations etc from the original model.