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.

The Problem

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.

  • $\begingroup$ If you don't get an answer here try asking a quantity surveyor $\endgroup$
    – Fred
    May 6, 2015 at 13:39
  • $\begingroup$ We do what you do - add a percentage, which is generally between 2% and 5% (depending upon the type, configuration, etc). But I don't have a cite or reference, so am not advancing this as an answer. $\endgroup$
    – achrn
    May 7, 2015 at 13:16
  • 2
    $\begingroup$ Like @achrn, where I work also simply adds a percentage of the total weight. We don't, however, have any references for this. This is where you arrogantly tell your client "this is industry standard and also covers any possible losses in the yard". Also, the fact that the reviewer complained about this means one of two things: they're fresh in the business or your project simply didn't have much else for them to complain about and, well, they need to show something "wrong" for what the client's paying them, right? $\endgroup$
    – Wasabi
    Jun 2, 2015 at 19:24

1 Answer 1


Caltrans Bridge Design Aids, Section 11 adds 3% for welds and bolts:

Furnish Structural Steel (Bridge) and Erect Structural Steel (Bridge)

  1. Segregate by type of steel and estimate in kilograms.
  2. Include bearings (except PTFE Spherical Bearings), anchor bolts, shear connectors, and expansion dams (except where expansion dams are galvanized or embedded in concrete).
  3. Ignore small, non-repetitive cuts, copes, and bolt holes.
  4. Add 3% for welds and bolts.

This is applicable to new bridges -- retrofits may have a much higher percentage of bolt weight.

  • 3
    $\begingroup$ CableStay - Great reference, but please clarify that your reference is for cost estimation and not design dead load estimation. $\endgroup$
    – AndyT
    Jul 29, 2015 at 8:09

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