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Bolt heads up or down?

Bolt heads up or down?

Bolt heads up or down?

(OP)
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.

RE: Bolt heads up or down?

Quote (Mike_311)

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.

RE: Bolt heads up or down?

From FHWA Steel Bridge Design Handbook - Splice Design

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

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


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

RE: Bolt heads up or down?

Quote:

I don't know what that means

Quote:

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

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

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.

RE: Bolt heads up or down?

Quote:

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.smile

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

RE: Bolt heads up or down?

Quote:

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

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

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."

RE: Bolt heads up or down?

Quote:

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

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

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

RE: Bolt heads up or down?

(OP)
Ha! see this is why asked this question!

Great discussion!

RE: Bolt heads up or down?

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.

RE: Bolt heads up or down?

(OP)
From Penndot:

RE: Bolt heads up or down?

Welcome to the USA - I’m sure some states are doing things differently!

RE: Bolt heads up or down?


Quote (Only way it could happen is if an ironworker and inspctor miss one when torquing the bolts.)


A loose bolt could be overlooked. The NYSDOT spec requires checking 10% of the bolts in a connection, minimum of two, but if any bolt comes up short all bolts have to be checked. When I worked as an inspector, over tightened bolts were more common than loose bolts.

RE: Bolt heads up or down?

Quote:

Only way it could happen is if an ironworker and inspctor miss one when torquing the bolts.

Thus the popularity of the twist-off bolts. You can tell at a glance if they're not tensioned.

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

RE: Bolt heads up or down?

Quote (BridgeSmith)

Thus the popularity of the twist-off bolts. You can tell at a glance if they're not tensioned.

Yes, but TC bolts also still rely on proper lubrication beneath the head/nut to ensure correct friction and thus avoid premature twist-off. A bucket of TC bolts sitting in an open keg getting rained on and beaten on by the sun will have severely diminished lubrication. Also, TC bolts are the worst for corrosion. You shear off the spline of the bolt exposing an ungalvanized chink in its armor.

If I were to play Devil's Advocate, the DTI squirter washer has all the same benefits of the TC bolt seeing as it is immediately visually apparent that it has been tensioned with less downsides. Not that I am advocating for their use...

RE: Bolt heads up or down?

Yes, the TC bolts have to be properly stored before installation. However, they're not galvanized, anyway, so the sheared end is no more subject to corrosion than the rest of the bolt. where the girders will be painted, we use the standard bolts, and for weathering steel girders, we specify the weathering steel bolts, so in either case, the bolts have the same corrosion protection as the girders. Anyway, if the end of the bolt past the nut rusted away to nothing, it wouldn't compromise the connection.

The squirter type DTI's with standard bolts and nuts are possibly more accurate than the TC bolts, but not as easy to verify, more expensive, and more difficult and time consuming to install and tension correctly. When properly stored, TC bolts are accurate enough.

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

RE: Bolt heads up or down?

Bridgesmith and buster - agree 100%. When I was an inspector I never saw a bolt get missed. You can tell by looking after you’ve torqued about half a million bolts!

RE: Bolt heads up or down?

Quote (dik)

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

With the nut up, the first thread is exposed and will catch and hold water, so you've got potential crevice corrosion between the nut and bolt.

Probably a minor concern in the grand scheme.

RE: Bolt heads up or down?

I've always thought it was as much (or more) for aesthetics than any other reason. In the states 'round these parts, bolt heads are on bottom for both top and bottom flanges and on outside of exterior girders. Presents a cleaner look that way.

RE: Bolt heads up or down?

Quote:

In the states 'round these parts, bolt heads are on bottom for both top and bottom flanges

We put the heads on top of the top flange splices to minimize the protrusion into the deck, and thereby potential interference with other components (and tripping hazards). As I mentioned earlier, it also allows 'rattling' (tensioning) of all TC bolts from one position at the same height for each side of the girder.

It also allows for verification of bolt tensioning, even after the deck has been poured.

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

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