Tension Members (Bolted vs Pin-Connected vs Eyebar) 2

[Struct-007]

Is there a guideline or rule of thumb about when to consider [Bolted Connection] vs [Pin Connection] vs [Eyebar] to connect tension members?

Pin Connection is in Section D5 of AISC360-10.
Eyebar is in Section D6 of AISC360-10.

Thanks!

 

[BAretired]

Bolts are standard in most situations. Pins are used when rotation is required. Eyebars are used when rotation and translation is required.

BA

 

[Struct-007]

Makes perfect sense.. Thank you!

 

[KootK]

Eyebars are used when rotation and translation is required.

How do eye bars accommodate translation? I may not actually understand the technology.

Is there a guideline or rule of thumb about when to consider [Bolted Connection] vs [Pin Connection] vs [Eyebar] to connect tension members?

Bolting certainly is the most common method but, to answer your question well, we'd need to know what kind of situation and structure you're considering. For example, rod members are frequently used as building lateral bracing elements and will usually be connected using a pin and clevis system which is, in many respects, similar to an eye bar.

In the space that is buildings and bridges, I struggle to think of a modern application in which eye bars would be used. It's a big old world though so, if there are such modern applications, I'm sure that somebody here will clue me in.

 

[BAretired]

The sketch below indicates an eyebar as I understand it. I have used them a few times, mainly to avoid temperature stress in a long, narrow corridor where it was inconvenient to provide a roller bearing.

EDIT: After reading the remainder of this thread, I believe that the member shown in the sketch above would more correctly be called a "hanger" than an "eyebar".

BA

 

[r13]

If you are attaching/pulling cable, use eyebar. For structural shape, use bolted connection. Pin is quite often seen in lifting devices.

 

[r13]

After seeing BA's sketch, I realize I misunderstood eyebar for eyebolt. BA is correct, it is usually used in connection requires flexibility, that allows the connected member to move longitudinally through joint rotation.

 

[KootK]

Ahh... got it. Thanks for the explanation BA.

 

[Agent666]

One other distinction between pins and bolts is that pins typically do not have a means of pulling the plies together. As such pins can also be subject to bending.

Bolts have nuts and are typically at a minimum tightened to a snug condition pulling the plies together. Which may not entirely prevent rotation, but it will prevent the need to consider bending in the bolt, as loads are transferred in shear through the bolts.

I had a similar question from an old colleague a few weeks back, for a single bolt in a connection he was insisting initially it was treated as a pin, I was arguing with him that it was still a bolt based on the above reasoning,

 

[hokie66]

BA's solution is a type of hinge or rocker. You wouldn't use that to join tension members.

Pins are most commonly used in architecturally exposed structural steel.

See the attachment for my understanding of what an eyebar looks like as a tension member.

https://www.researchgate.net/figure...-truss-bridges-until-the-early_fig1_275635269

The Clifton Suspension Bridge in Bristol, designed by the noted English engineer Brunel, is a good example of eyebars used in tension structures.

https://en.wikipedia.org/wiki/Clifton_Suspension_Bridge

 

[BAretired]

I didn't know the term "eyebar" when I used them. I likely called them "hangers", but the eyebar or hanger is strictly a tension member.

Wikipedia defines them this way:
In structural engineering and construction, an eyebar is a straight bar, usually of metal, with a hole ("eye") at each end for fixing to other components. Eyebars are used in structures such as bridges, in settings in which only tension, and never compression, is applied. Also referred to as "pin - and eyebar construction" in instances where pins are being used.[1]

BA

 

[r13]

My definition is a little different than the mighty Wikipedia - an eyebar is a tension member with one, or both ends connected to the other element by a "pin". Simply speaking, eyebar and pin are two different elements, although often used together in structural connections, that is referred to as pinned connection.

 

[Ingenuity]

From AISC 360-16 specification perspective, an eye-bar has only one limit state - tensile yielding - BUT you have to meet the dimensional requirements (§ D5). If you don't then it is a pin connected member and you have to check all the limit states, and other dimensional requirements (§ D6).

 

[r13]

You have to do both checks for this type (eyebar with pin) of connection due to their distinct structural function and behavior.

 

[Lomarandil]

I couldn't get Hokie's link to load, but here is what I think of when I hear eyebar:

https://www.enr.com/articles/19053-caltrans-begins-long-term-repairs-to-bay-bridge-eyebar

In that case, fracture toughness became an issue.

They're very efficient uses of material, but hard to justify in most new builds now that we have improved types of high-strength fasteners.


Separately, part of my understanding of the bolt and pin dichotomy is that when pins are desired (to allow rotation), the contact stresses need to be limited to ensure you don't have local plastic deformation which would limit that rotation. Bolts (and rivets) are allowed to deform locally, because we don't care.

----
just call me Lo.

 

[hokie66]

Yes, Lo's post is concerning eyebars. Here is another eyebar bridge. This one collapsed.

https://en.wikipedia.org/wiki/Silver_Bridge

 

[BAretired]

The following is a link to a very interesting video about the Silver Bridge collapse giving some history of its inauguration and some explanation of the reason for the collapse:

https://www.youtube.com/watch?v=8w5Fjouvma8

BA

 

[r13]

BA,

Thanks. A great video with excellent closing remarks, especially on "redundancy". Also worth to note is the "fading" of safety factor due to change in time and uses.