Bolt heads up or down?

[MIKE_311]

Here is a question: on a steel girder, with a field splice, the bottom flange splice plate bolts. I have always detailed splices with the heads on the underside and the stickthough and nut on the top side of the bottom flange. This could apply to bottom lateral bracing as well.

I realize I never knew the exact reason I do this, it's just something I learned and never asked why. My argument is that you can verify the underclearance to the head of nut. A co-worker thinks that placing the bolt head-up is better since if the nuts works loose, you wont lose the bolt.

 

[SwinnyGG]

underclearance to the head of nut

I don't know what that means - but my point of view would be bolts should be 'captive' by gravity whenever possible.

Maybe it doesn't matter; if your splice is slip critical, and things come loose, maybe the building falls down whether the bolts fall out or not. If it's not slip critical, maybe tension on the splice keeps the bolts in even if the nuts work themselves loose.

Either way I'd still want the bolt heads on top of the joint, if for no other reason than the fact that your erection subcontractor will have a much easier time installing things. You'll also have the benefit of not having an angle shim (assuming they're needed on the beam flange side of the connection) trying to turn itself along with the nut as the joint is brought up to tension.

 

[STrctPono]

From FHWA Steel Bridge Design Handbook - Splice Design

 

[BridgeSmith]

With the bolt heads on the outside, 1) it's a mirror of the top, 2) it doesn't infringe on the clearance or free board underneath, and 3) since twist-off fasteners are used almost exclusively, tensioning of all the bolts can be done from a position beside the girder.

Bolted bridge girder splices are slip-critcal connections, and therefore require fully tensioned bolts. The nuts coming loose is not something you really have to worry about.

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

 

[dik]

Agree... and for mechanical equipment suspended from the roof, where there could be vibration, I rely on Locktite Red...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BridgeSmith]

I don't know what that means

Agree... and for mechanical equipment suspended from the roof, where there could be vibration, I rely on Locktite Red...

Since this was posted in the "bridge Engineering" forum, I assumed the OP was talking about bolted field splices for bridge girders...

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

 

[dik]

Just to make a point that if the connection is critical... vibration from traffic, whatever... I rely on glue...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[MIKE_311]

STrctPono illustrated my question. Is there a practical reason why bottom flange bolts are orientated this way?

 

[STrctPono]

I think BridgeSmith answered it. Biggest reason that I've always understood is tightening of the bolt which is always done by turning the nut. Easier access to the nut for the iron workers when it is on top of the flange.

 

[BridgeSmith]

Just to make a point that if the connection is critical... vibration from traffic, whatever... I rely on glue...

For bridge girders we rely on the 39 kips (min) tension in the bolts; no problems so far.

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

 

[BridgeSmith]

Biggest reason that I've always understood is tightening of the bolt which is always done by turning the nut.

Actually, with twist-off bolts, it holds the nut and turns the bolt until the splined end shears off, but it is accomplished completely from the nut side of the plate.

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

 

[dik]

slip critical works for me, too... usually use snug tight, but if there's a chance of something falling down with vibration... glue...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BridgeSmith]

On bridges, anything subject to vibration requires a slip-critical connection, so very rarely would there be a need for threadlocking compound.


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

 

[bridgebuster]

This is from the NYSDOT Steel Construction Manual

"For horizontal installations, the bolt shall be installed with the nut shielded from the weather whenever feasible. For vertical installations, the bolt heads shall be up."

 

[BridgeSmith]

This is from the NYSDOT Steel Construction Manual

"For horizontal installations, the bolt shall be installed with the nut shielded from the weather whenever feasible. For vertical installations, the bolt heads shall be up."

Interesting...at first, I assumed that wouldn't be applicable to girder splices, but according to the splice details in their standard details, they do put the bolt heads up on the bottom flange splices.

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

 

[SwinnyGG]

Bolt heads up does make sense from the standpoint of eliminating crevice corrosion which I hadn't considered before.

 

[dik]

SGG... how would the orientation affect crevice corrosion? just more exposure?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[MIKE_311]

Ha! see this is why asked this question!

Great discussion!

 

[Guest090822]

New York DOT puts the heads “up” so if for some reason the nut ever comes loose the connection can still function in shear/bearing. However, as Bridgesmith pointed out, the bolts are torqued so unlikely to come undone. Only way it could happen is if an ironworker and inspctor miss one when torquing the bolts.

 

[MIKE_311]

From Penndot: