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.

 

[Guest090822]

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

 

[bridgebuster]

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.

 

[BridgeSmith]

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

 

[STrctPono]

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...

 

[BridgeSmith]

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

 

[Guest090822]

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!

 

[SwinnyGG]

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.

 

[crossframe]

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.

 

[BridgeSmith]

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