What diameter bolts do you typically call off for steel construction? 3

[MJC6125]

I'm curious what diameter bolts people typically call off for steel construction (i.e. typical beam-to-beam & beam-to-column connections)? I assume calling off the same diameter everywhere on a project is best, that way the installer doesn't accidentally grab an undersized bolt for a connection.

 

[MotorCity]

We always design the bolts assuming that the threads are included in the shear plane. Then you're covered either way. As a practical matter, it is very difficult to enforce and nearly impossible to verify in the field. Ever tried to explain to an iron worker that the threads cannot be in the shear plane?

 

[AaronMcD]

Same, I always assume threads in shear plane. I can't recall ever designing a connection otherwise. I just don't want to have to think about every connection and whether it will work or not. Usually the nut is so close to the shear plane and the thicknesses vary. I wouldn't trust myself to install that correctly much less a random steel worker.

3/4" bolts seem to work for the lighter residential loads I deal with. Occasionally I'll have a high load in a shallow beam or something and wish I was using 7/8" but I can usually figure out how to make 3/4" work.

http://www.hellodwell.design

 

[bridgebuster]

On NYSDOT bridge projects, all threads are excluded.

 

[skeletron]

3/4" A325 on nearly everything except non-structural components (5/8") and heavier industrial which sometimes required 1" or 1-1/4" A325 or A490.

 

[Guest090822]

For buildings it’s normally A325-3/4” bolts. For bridges 7/8” diameter.

 

[Ron]

A325-3/4. For slip critical, same bolts with a turn-of-nut or calibrated wrench torque requirement.....yes, I still believe you can get good results with a proper torque value as determined through Skidmore-Wilhelm device in the field and a proper torque wrench. Also will consider tension control bolts and load indicating washers.

 

[dik]

Ron:
The calibrated wrench method is discouraged by the CISC (Canadian Steel Org) and I specifically exclude it in my Project Notes. From their publication:

The relationship between pretension and torque is a complicated one, however, and it reflects such factors as the thread pitch, thread angle and other geometrical features of the bolt and nut, and the friction conditions between the various components of the assembly. As a consequence, it is generally agreed that derived torque vs. pretension relationships are unreliable [6, 28]. The RCSC Specification [15] is explicit upon this point. It states that, "This Specification does not recognize standard torques determined from tables or from formulas that are assumed to relate torque to tension." A torque-based installation method is possible provided that the installation wrench is calibrated. This would have to be done using a representative sample of the bolts to be installed. At one time, the S16 Specification did allow this, but it has not been permitted for many years. The turn-of-nut method of installation is simpler, provides consistent levels of bolt preload, and leads to fewer disputes in the field.

Added:
I would think that with the scatter of results that the standard deviation would greatly reduce the A325 capacity.

Dik

 

[JLNJ]

If I have small members but I still want to connect them with two bolts, I will go to 1/2" diameter bolts. I like the redundancy of two smaller bolts versus one larger bolt.

Plus, you can have framing connections which are relatively "standard", just with smaller bolts closer together.

 

[dik]

JLNJ:

Great... do it lots of times... and use them with 3/4. I don't use 1/2" and 5/8" on the same project, one or the other.

Dik

 

[wannabeSE]

Don't ask me for a cogent reason, but our office typically specifies 7/8" for most building and 3/4" for light buildings. Also this might be a west-coast or California thing, but F1852 twist-offs are specified for all typical. Some (many) contractors prefer these because they are fast to install, can be tightened from one side, and it is obvious if they are not tightened.

 

[cliff234]

We typically delegate connection design to the steel fabricator’s licensed professional engineer. This is common and accepted practice in our part of the country and this practice is recognized per AISC 303-16 (AISC Code of Standard Practice). We leave it up to the fabricator to determine what bolt type and diameter to use. Some fabricators prefer ¾” bolts, and others prefer 7/8” bolts for typical shear connections. Sometimes larger bolts are used for connections with large reactions (Truss member connections, braced frame connections, transfer girder connections, etc). Unless we fully design and detail the connections on the contract documents, there is generally no need for us to specify a bolt diameter.

(Note: Delegating connection design to the fabricator’s engineer does not relieve the EOR from responsibility for ensuring that the connections are properly designed by the fabricator's engineer.)

 

[kingnero]

Under EU regulations, bolts for structural applications have to be at least M12 (1/2").