Weight of Structural Steel
When calculating the weight of a steel structure, I usually calculate the weight of all of the various members and plates first. I then add an additional percentage to account for the weight of nuts and bolts. This percentage is usually between 2% and 5% of the total weight.
It makes sense that bolts will add additional weight beyond just the weight of the members. It is also complicated and time consuming to do it the "proper" way, e.g. deduct the weight of the hole and add the weight of the correct length and size of bolt. This is done with a spreadsheet or by hand and without the aid of specialized steel detailing software. Another complication is that furnished bolt lengths are partially determined by the fabricator.
My company has always done this. The one time that a third party reviewer asked why the steel weight was ~5% higher, we were unable to cite a code reference where this was called for.
How is the weight of fasteners typically included in steel weight calculations? This can either be for a bid weight or a design dead load weight.
As additional information, in all welded construction, the weight of bolts might be so minor that it is negligible. Some of my projects use completely bolted connections including built-up members.