X-bolt Responsibility in the field

[gregroberson]

I am an EIT trying to determnine the responsibilty of X-bolt direction during erection in the field. Does the direction of the X-bolt fall under means and methods or is it the responsabitlity of a steel detailer to indicate direction in addition to indicated the type.

Acting as a connection engineer and steel detailer hired by a fabricator, If I design a connection that required X-bolts, I obviously have to clearly indicate X-Bolts required on steel erection and shop drawings.

However, should the steel erector (AISC cert. or not)be aware to install the X-bolt with the bolt threads excluded from the shear plane? If not, would the steel detailer be required to "show" the bolt direction for each and every connection instance I have X-bolts in?

Any thoughts would be appreciated.

Greg

 

[hokie66]

Good question, and that is why I have always avoided designing and specifying X-bolts.

 

[dhengr]

Tke a look at this...

http://www.modernsteel.com/steelinterchange_details.php?id=492

 

[gregroberson]

I have also been discouraged from using the X-bolts. . . when possible. I have some situations that are just too close for comfort. They will be brought to the engineers attention and should have a different section size anyway.

The article was great and was exaclty what I was looking for. Thnaks for the rapid responses guys. We will be providing a detail showing the thickness indicated in the document and how to arrange washers if necessary.

 

[connectegr]

I would advise against the use of X bolts, as a standard in light construction with beam web thicknesses less than 5/16. For several reasons:

1. Field inspection is minimal for bearing (snug tight) connections. You may be lucky if proper attention is given to the pretensioned bolts.

2. In many cases bearing or block shear will govern over the increased capacity of the bolts.

3. For thin web member or thin connection material, the additional strength is rarely needed.

4. The iron workers rarely work with the shop drawings and primarily refer to the erection drawings. Showing direction of installation and the potential errors can offset the savings of a handful of bolts.

For heavy construction the use of X bolts can be standardized with minimal specific erection instruction. As the engineer the use of X bolts can be foolproof with a little consideration of the applications.

http://www.FerrellEngineering.com

 

[gtaw]

As an Ironworker with 40 years of experience, I can say that the difference between snug tight, slip critical, and X-type bolts are subjects covered in Ironworker apprenticeship training.

A good bolting foreman will typically list the required bolt lengths and type of bolts by marking the requirements on the connection. When X-type connections are required, that too is communicated to the ironworkers. As a force of habit, most ironworkers install HS bolts as if they were X-type, even if not a requirement.

The inspector should be aware of the differences as well. High strength bolting is just one of several endorsements available to AWS CWI's. The inspector with the appropriate endorsement should verify the proper bolts are used and installed in the proper manner.

It is all a matter of knowing which erectors provide skilled management and skilled workers and those that do not know the difference and make no distinction. The same holds true with inspectors.

I tell people that 10% of the doctors, engineers, tradesman, and inspectors excell at their chosen professions. 80% don't really enjoy their work, but make a living doing what they do, and the 10% that cause 90% of the problems are the few we remember.

Best regards - Al

 

[connectegr]

gtaw
I respect your professionalism, but I think you represent the 10% that excel. I have worked with and met some exceptional iron workers, that certainly work hard and take pride in their work. And they are the majority of iron workers. But on 100 jobsites, I bet less than 30 will have an inspector with the RCSC endorsement, and none of the actual tradesmen will have any specific bolt installation training. Other than you and I, I can count on my fingers the number of iron workers/inspectors that I have met with the endorsement. As a member of the RCSC Spec Committee, I believe this is an area where more guidance can be provided. As you mentioned the only inspector qualifications for structural bolting are provided by other organizations, AWS or ICC. RCSC does not have the staff or infrastructure for such a program. The RCSC Education Committee is working on videos for the training of iron workers. But even these concentrate on the preverification and installation of pretensioned bolts. And these will require some enforcement to make the iron workers watch and retain the information. I believe some understanding of the expected performance of these connections would be beneficial. And the consequences of improper installation.

In most cases of bearing connections, even loose bolts will not impact the connection performance. But when X bolts are the design intent, consideration for the "what-ifs" should be shared by the designer. As I mentioned, thin web members don't benefit much from the use of X-bolts, but they are an option. Clear erection instructions should be provided. Bolting is generally completed after the piece is temporarily supported in place. In a predominantly snug-tight job, the handful of connections with thin outer plies need to be extremely well identified. Although this is simple to you and I, more general instruction and supervision is given to pretensioned bolts, and snug tight connections are often given a passing glance by the inspector. Design using X-bolts has practical and economical advantages and I use them frequently. But for many designs they eliminate a single row of bolts or less. And if installed incorrectly, can result in a grossly inadequate connection.

A colleague of mine keeps 3 TC bolts on his desk. Frequently a fabricator, detailer, or engineer will visit his office and ask about the three identical bolts. He will tell them the first is a SC bolt, the second and N bolt, and the third is an X bolt. He will move the bolts around like a shell game and of course magically identify the bolts again with confidence. About half the guests ask, how does he know. And these are people working within our industry.

http://www.FerrellEngineering.com