I have a project where the contractor is using ASTM F1852 Tension Control (twist-off) bolts. The project is outdoors and uses weathering steel and weathering fasteners. The main members are hollow steel sections that are utilizing bolted splices.

As the contractor is tensioning the splice bolts, he is letting the twisted off portion of the bolt (spline) fall into the the hollow sections. You can hear the metal pieces ping all the way down the tower legs. There are no access holes to be able to retrieve these pieces. They are permanently in the hollow steel members.

We have used these types of bolts in other structures, but this is the first time that I have run into the situation where the splines are left in place. I have not seen an part of a specification that specifically speaks to this situation.

Will this cause any future issues for the structure?

The only possible issue that I can see is that in the future, the collection of splines will rust together and clog the weep holes in the base of the members.

  • 2
    $\begingroup$ Uhg, I hate contractors who are sloppy and careless. I'd fire him if you can and he won't change his ways. ... Anywho, are there any utilities in this space? Random bits of metal can be a problem for electrical, plumbing, and mechanical systems. ... Anywhere you have 2 dissimilar metals is also a candidate for galvanic corrosion. Plain dirt and humidity can be a sufficient electrolyte. And, if you are near the ocean, it's a matter of how much rather than "if". $\endgroup$ – Brock Adams Oct 13 '15 at 6:05
  • $\begingroup$ There's a good chamnce that all will be well. But, Murphy will look for a location that accumulates splines, water and organic matter and try to build a galvanic cell. If there are several choices Murphy will choose a location where the resultant corrosion jhas most chance of causing problems. You MAY bne able to check the likely electrochemical potentials between the spline and tower materials. Odds are the tower will corrode preferentially. $\endgroup$ – Russell McMahon Oct 13 '15 at 8:41
  • $\begingroup$ I'm not worried about galvanic corrosion between the splines and the tower metal. These are the same materials are touching throughout the entire structure. The bolts are holding it all together. $\endgroup$ – hazzey Oct 13 '15 at 11:49

One aspect I would be concerned with is if any utilities have been run yet.

  • Galvanized parts sitting on soon-to-be pressurized copper tubing could be a recipe for disaster in the making.

  • Galvanized parts striking electrical components likely won't be an issue as the electrical connections should be strong enough to not be affected. However, this seems to be an invitation for Murphy's Law to rear its head.

As mentioned in the comments, debris accumulating at the base of the main members could cause a host of issues from preferential corroding to blocking the weep holes.

Another consideration is with future construction. If future work requires drilling up through the base of those main members, additional debris could fall down during the drilling process. Likewise, that debris could present additional scraping hazards when pulling new utilities through that hole.

| improve this answer | |

If they were coated bolts, I would worry that you are adding more uncoated material inside to corrode (the shear plane becomes exposed metal with reduced cathodic protection) but since they are weathering steel, there isn't a big difference. One potential issue would be that they prevent water from evaporating at the bottom of the tube, even if the weep hole is still functioning. Liquid water will escape through the weep hole, but the inside of the tube and especially the top of the base plate will be damp. As I understand it, weathering steel needs wet and dry cycles to build and maintain its corrosion resistant layer, so enough airflow for the inside to dry out will be important. Depending on your climate, I don't know if a pile of the splines will limit airflow and prevent the dry half of the cycle from every happening. This could plausibly lead to accelerated corrosion at a pretty critical part of the column.

As far as I know, I don't believe that the RCSC addresses the issue, but you might be able to stretch the AISC Code of Standard Practice to require it as part of final cleaning in 7.18. More realistically, cleaning of any materials not required for the construction is probably in a specific contract. I'm a little unclear how the splines are getting stuck on the inside, since the shear wrench has to touch the spline, so there should be plenty of access to control them. Also, if there is not access to the spline side, how is the inspector verifying that the end is properly sheared? Maybe your situation is in a tapered column or something, but I'm having trouble visualizing.

Overall, I don't think I'd worry much about it, but if you are worried it might be easier to add a few extra weep holes that to try to get them to remove the splines.

| improve this answer | |
  • $\begingroup$ The section is large enough that the iron workers are actually sticking their head and arms into the section to work the gun. The nuts are on the inside to that the button-head of the bolt is on the outside (aesthetics). It is still purely laziness. $\endgroup$ – hazzey Oct 14 '15 at 0:46
  • $\begingroup$ Oh, so they can reach the connection from the open (top) end of the tube? $\endgroup$ – Ethan48 Oct 14 '15 at 1:22
  • 1
    $\begingroup$ There are large holes cut on either side of the splice so that they can reach inside. Plates get welded over the holes when they are done. $\endgroup$ – hazzey Oct 14 '15 at 11:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.