If we simply open a Version 16 or earlier project in Version 17, we are going to be presented with a very messy and haphazard set of Building Materials. In the example below I have opened a version 16 file in ArchiCAD 17 and as you can see, I have a number of duplicated materials with a 9 digit number after them.
In a new feature of ArchiCAD 17 we can merge similar attributes together.
Select all but one of the similar building Materials, hit Delete, then choose the single remaining Building Material to merge them into.
In the image above, I have selected the first 7 Structural Concrete materials, then pressed the Delete… button. In the dialog box that appears I have chosen the Delete and Replace with… option and chosen the last Structural Concrete from the popout menu.
Using this process will merge all of the selected Building Materials into 1.
Then simply go to the Name: field and remove the 9 digit code.