Dear Karol,

I see different way to work on your request.

1°) Since the version 2016 or 2016, there is a possibility to add special attribut any bars.

So by using this bars type, you should be able to make filtering on your report for example.

So you could create a special attribut field which use to name your element and than assign it per group of element.

2°)The second possibility should be to use the "Assembly group" tool. This is a special tool from the Engineering module which allow you to group bars and also fixture Under one name that you can set.
It's easy to use and you can create a legend/report which display this Assembly group name.
I will attached an FAQ about this tool.

3°) You can use a precast module name "iParts or DET" to place bars Inside element. Without doing any grouping. When you place any bars on a element, the bars are belong to the element and you can output a report/legend only for this element.
Inside a precast element, you can set few bars as subgroup (this was what i did on the FAQ with assembly group too).

I prefer the last one

Bye & Good Use!