Splice Connection 1

[GTrinh97]

I am working on designing a bolted beam splice connection for a W-Beam, with the splice located at one-third of the beam's length. However, after reviewing the AISC Steel Construction Manual (15th Edition, Volume 1), I was unable to find an example that specifically addresses this type of connection. Could anyone provide resources or examples that I could use as a reference?

 

[SethGuthrie]

Are you thinking of a flange-plated connection for (minimal) moments along with a shear plate or are you thinking of a combined moment end plate?

 

[GTrinh97]

Yes ! It will be a flange-plate connection for moments along with shear plate.

 

[SethGuthrie]

Most of the examples are written for columns, but the principles are all the same. In the 16th edition see section 11, e.g. Flange-Plated FR Moment Splices on 11-12. I could send you some output from RAM Connection that shows all of the various code checks we perform, if that's helpful.

 

[BridgeSmith]

Sounds like a fairly typical beam splice for bridge girders. You might look up examples for those, or one of the splice design programs. AISC has a free splice design Excel spreadsheet design available. It's kind of clunky compared to some others (BRASS-Splice, etc.).

 

[GTrinh97]

@SethGuthrie Yes, please! Thank you so much for that.

 

[SethGuthrie]

Sample output for a beam splice (the moment part and the shear part are done independently). I ran this for AISC 360-16, but we have -22 now also. This one is for a single load combination.
Link good for a week:

https://bentley.sharefile.com/d-s8ca9a2984bda4be5bcd308e46c5d6f62

 

[human909]

Sky Civ:

https://skyciv.com/quick-calculators/bolted-splice-connection-calculator/

 

[Tomfh]

What is American practice regarding slip critical bolts for these type of connections? When do you use slip critical as opposed to regular fully tensioned bearing style bolts?

 

[BridgeSmith]

What is American practice regarding slip critical bolts for these type of connections? When do you use slip critical as opposed to regular fully tensioned bearing style bolts?

Not sure I understand the difference between fully tensioned and slip critical, but at least in bridge construction, all the superstructure bolts are slip critical, including the splice bolts. The geometric control tolerances are very tight, and even the slippage allowed when the bolts go into bearing would produce unacceptable adverse changes in the finished grade and excessive stresses in other parts of the superstructure.

 

[Tomfh]

Not sure I understand the difference between fully tensioned and slip critical,

By slip critical I was referring to fully tensioned bolted joints that work via friction, i.e. they're not intended to slip into bearing. In Australia we categorise tensioned bolts into TB (Tensioned, Bearing), and TF (Tensioned, Friction).

 

[CANPRO]

Not sure I understand the difference between fully tensioned and slip critical...

The difference is in the surface prep. You can have fully tensioned bolts and still not have a true slip critical connection if you don't have proper surface finish. For bridge construction (in my area anyway) we'd use a class B primer, but if for a building, a beam as described by OP would only have a "slip critical" surface prep if specified. It is not often you see a true slip critical connection in building construction where I practice.

 

[BridgeSmith]

Ok, there's connections specified as slip critical, where the friction coefficient and bolt tension have to provide enough friction force to prevent slip. I get that.

What I don't understand is why you'd specify fully tensioned bolts in an application that's not slip critical? What does fully tensioning the bolts do that a snug tight condition would not accomplish for a bearing type connection, if prevention of slip is not required?

 

[CANPRO]

One instance I can think of is for seismic bracing per the requirements of CSA S16-19 clause 27.1.6. Haven't read that in depth in a while, and reading it again now the requirements aren't completely clear. Pre-tensioned high strength bolts are required, but the connection doesn't have to be design specifically as slip-critical. The clause states "when designed as bearing-type connections, have surfaces of Class A or better, or provide the equivalent slip resistance by increasing the number of bolts, bolt size, bolt strength, or any combination thereof". I'm not sure how you provide equivalent slip resistance if you haven't provided at least a Class A surface, unless you're using some tested surface finish what a quantifiable slip resistance that isn't Class A or B. The commentary for that clause states "The requirements for bolted connections ensure that friction plays a role in load transfer and that too rapid a slip into bearing is avoided".

In this case I believe you're providing slip critical conditions without necessary designing a slip critical connection. Not the exact scenario you were questioning, but a bit of a gray area.

My point in the my first reply was that pre-tensioned bolts doesn't necessarily equate to a slip-critical connection. Clearly that was already understood, mis-interpretation on my end.

 

[BridgeSmith]

CANPRO, it sounds like the seismic bracing you referenced requires a specified slip resistance. By my way of thinking, that's a slip critical connection, even though the friction coefficient doesn't have to meet the one of the pre-defined classes for the faying surfaces. The AASHTO bridge design specs allow the use of a lower coefficient of friction in slip-critical connections than the 0.30 for a class A surface condition:

Subject to the approval of the Engineer, coatings providing a surface condition factor less than 0.30 may be used, provided that the mean surface condition factor is established by test.

It also includes this commentary on slip-critical connections subjected to seismic loads:

During earthquake motion, there is the potential for full reversal of design load and inelastic deformations of members or connections, or both. Therefore, slip of bolted joints located within a seismic load path cannot and need not be prevented during a seismic event.

 

[Tomfh]

What I don't understand is why you'd specify fully tensioned bolts in an application that's not slip critical? What does fully tensioning the bolts do that a snug tight condition would not accomplish for a bearing type connection, if prevention of slip is not required?

In Australia, fully tensioned bolts are common for structural connections in buildings (including bracing, splices; etc), while the bridge code requires the use of friction bolts, which seems to align with your experience working with bridges.

As for why you’d bother with tensioned bearing bolts, theyre an intermediate option between Snug Tight (S) and Tensioned Friction (TF) bolts. Although they don’t fully meet slip-critical requirements, they do in practice reduce movement more effectively than Snug Tight bolts - often functioning as defacto slip critical bolts - as well as providing much higher clamping force in situations like axially loaded end plates.

The assumption with tensioned bolting (without friction) is that the amount of slip is generally small or not critical in practice, although this can be a very unreliable assumption at times.

That’s why I’m interested in understanding the practices in the United States and Europe—specifically, what is the standard practice regarding when to switch to TF bolts for connections and splices in building design?

 

[DanKile]

The "Research Council On Structural Connections" has additional requirements on when to use pretensioned vs snug-tight.

4.2. Pretensioned Joints
Pretensioned joints are required in the following applications:
(1) Joints in which fastener pretension is required in the specification or code that invokes this Specification;

(2) Joints that are subject to significant load reversal;

(3) Joints that are subject to fatigue load with no reversal of the loading direction;

(4) Joints with ASTM A325 or F1852 bolts that are subject to tensile fatigue;

and,

(5) Joints with ASTM A490 or F2280 bolts that are subject to tension or combined shear and tension, with or without fatigue.

4.3. Slip-Critical Joints
Slip-critical joints are required in the following applications involving shear or combined shear and tension:
(1) Joints that are subject to fatigue load with reversal of the loading direction;

(2) Joints that utilize oversized holes;

(3) Joints that utilize slotted holes, except those with applied load approximately normal (within 80 to 100 degrees) to the direction of the long dimension of the slot;

and,

(4) Joints in which slip at the faying surfaces would be detrimental to the performance of the structure