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.

 

[JAE]

3/4" diameter ASTM A325 N bolts - usually bearing only (i.e. not pre-tensioned or slip critical unless needed)

 

[DrZoidberWoop]

My company prefers 7/8" diameter A325 bolts and 1-1/8" A490s. But we do mostly heavy industrial construction. When mixing bolt diameters, it's good to keep a minimum 1/4" difference between the sizes so that the erector can't make the mistake of installing the larger bolt in a reamed or oversized hole intended for the smaller diameter.

 

[spieng89]

I'll go down to 5/8" diameter for light loaded bearing only applications, but typically 3/4" is the starting point and increase in size for brace and uplift conditions.

 

[271828]

Just like JAE said: 3/4 in. diameter A325-N bolts.

 

[dik]

Nearly always 3/4" dia (not M20) conforming to ASTM F3125, Grade A325. Threads can be included in the shear plane and installation shall be snug tight. If I have lots of connections that are lightly loaded, I've used 1/2" dia and 5/8" dia A325 fasteners.

Dik

 

[JoshPlumSE]

When mixing bolt diameters, it's good to keep a minimum 1/4" difference between the sizes so that the erector can't make the mistake of installing the larger bolt in a reamed or oversized hole intended for the smaller diameter.

I totally agree with this sentiment. So, while I'll use 1/2" and 3/4", I'll never use 5/8"

 

[bridgebuster]

In the bridge world, we use 7/8" dia A325 most of the time. Occasionally 1" if 7/8" isn't practical. We generally avoid A490.

 

[jittles]

Same mentality as others here.

3/4" A325 by default.
Maybe 5/8" diameter in minor non-structural components.

Never a 3/4" A490 if they are needed, they would always be a unique, larger diameter to prevent mixups.

 

[STrctPono]

3/4" is most common for buildings
7/8" is most common for bridges

 

[dik]

Josh:
"I totally agree with this sentiment. So, while I'll use 1/2" and 3/4", I'll never use 5/8""

I never use both 1/2" and 5/8" on a project... one or the other.

Dik

 

[BridgeSmith]

For bridge structural bolting, we use exclusively 7/8".

FYI, we recently discovered that we should be including Grade F1852, since that is correct designation for the twist-off style, 120ksi bolts, in addition to Grade A325. The twist-off style are almost always what we get.

Also, A325, F1852, A490 and F2280 (150ksi twist-off style), are now "grades" under a single ASTM spec. - F3125.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[STrctPono]

Rod,

Utah allows TC bolts for bridges? You don't have corrosion issues with those? This is the one bolt type I won't touch. I know ironworkers love them though.

 

[BridgeSmith]

I don't know about Utah for sure, but here in Wyoming we use the TC bolts. For unpainted structures, we spec weathering steel for both the structural steel (ASTM A588) and the bolts (Type 3, per ASTM F3125)

Rod Smith, P.E., The artist formerly known as HotRod10

 

[BAretired]

3/4" diameter ASTM A325 N bolts - usually bearing only (i.e. not pre-tensioned or slip critical unless needed)

Why specify N bolts? I don't remember ever specifying that, in fact I would prefer if the threaded portion was excluded from the shear plane.

BA

 

[phamENG]

Simplifies procurement, I should think. With N bolts, you just need to make sure they're long enough. If you spec X bolts, then the required grip has to be more carefully considered for each condition. And, if you spec X and they miss it and the bolts show up fully threaded, you have a big headache (or the contractor does, which means there's one on its way to the engineer in a day or two...)

 

[dauwerda]

To add to what phamENG stated, you can also run into situations where the two ply's of steel being bolted together are different thickness, so to get X bolts, the erector needs to install the bolt in the correct direction...just one more thing that can easily be done incorrectly.

 

[BAretired]

So that means that you never design bolts assuming threads are excluded from the shear plane.

BA

 

[dik]

BART... not me... don't think I've ever done that.

Dik

 

[phamENG]

Essentially. It's one of those "only use as a last resort" sort of things. If the only way to get an economical connection or a connection that will fit within a set of confining conditions, it's a good tool to have. But if you don't have to use it, it's best not to leave the chance for error open.