Slip Critical Bolts for Long Slotted Holes 2

[KootK]

I've read a number of papers which seem to imply that, whenever long slotted holes are used for single plate shear tab connections, the bolts must be slip critical. The attached paper mentions it at the top of page 10.

Why do long slotted holes necessitate slip critical bolting?

Thanks,

KK

 

[slickdeals]

I was not able to open the file, but I am not aware of any provisions specifically requiring SC bolts in LSL holes.

See Section 4.3 (3) of the RCSC (2004) specifications. It states that Slip critical connections are required for slotted holes, except when the direction of loading is approximately normal (80 to 100 degrees) with the loading perpendicular to the direction of the slot.

 

[slickdeals]

I stand corrected:
AISC Section J3.8 states that connections with slots transverse to the direction of the load shall be designed for slip as a serviceability limit state.

See also commentary for this section on Page 16.1-348 (AISC)

I am going to venture a guess. If the beam deflects under loads and goes into bearing because slip is not prevented, then it may induce some axial forces? Obviously, that would be a large deflection condition.

I am sure old timers here might be able to shed more light into the requirement.

 

[connectegr]

The reasoning behind the slip critical requirement is resistance to the horizontal component. As an eccentric connection, the bolt has a horizontal and vertical force. As a snug-tight (or bearing) connection the horizontal component must be resisted by the surface friction of the bolt against the hole, frictional force between the faying surfaces, and "bolt plowing".

Research was done at the University of Oklahoma, by Ben Wallace, concerning the use of snug-tight connections with slots in single plates.

However, this was only applied to short-slots for the current design examples.

http://www.FerrellEngineering.com

 

[nutte]

Slickdeals, generally speaking, bolts in LSL holes, slot transverse to the load, do not have to be slip critical. They can be bearing bolts. The section you reference says that if they are slip critical, it needs to be slip at service. It does not say that all bolts in LSL holes have to be slip critical.

Now, this is not to say that bolts in LSL holes for shear tabs can be bearing.

 

[KootK]

@Slick: I think that you were right the first time. J3.8 specifies the design requirments when using SC with slotted holes. However, it doesn't specify that you HAVE to use SC with slotted holes.

@Connect: why would one want to resist the horizontal bolt component? In a simple shear connection, wouldn't the horizontal movement help to permit the desired end rotation of simply supported beams?

Curiously, it seems that you can use LSL with the AISC extended end plate connection now (no SC required).

 

[connectegr]

Typically we only see long-slots in single plate connections to embeds. Provided the loading is shear only, with a single column of bolts, we design the connection for eccentricity and use bearing (snug-tight) bolts. Based on research by Dr. Wallace and Dr. Sherman, the combination of friction resistance and bolt plowing is adequate for the resistance of the horizontal component of the load. "Flexibility" of the connection is due to ductility of the plate, not slip of the bolts.

If standard holes or short-slots are used the rules for "standard" shear plates would apply.

http://www.FerrellEngineering.com

 

[ToadJones]

I guess for infill beams not part of a LFRS I see no problem with using LS holes

 

[KootK]

Ahh... I think that I get it now. It makes me wonder though:

Sometimes people use LSL holes to accomodate thermal movement. Would that same friction and plowing have to be overcome before any joint slip would occur?

 

[connectegr]

"a poor man's expansion joint"

I don't like using all caps, but...
DO NOT USE LONG SLOT SHEAR CONNECTIONS FOR EXPANSION JOINTS IN HEAVILY LOADED STRUCTURES

http://www.pittsburghlive.com/x/pittsburghtrib/news/s_494416.html

I have reviewed the expert reports of the connection which resulted in the collapse at the David Lawrence Convention Center. The connections were long-slotted single plate and knife angles connections, of large girders. In the cold Pittsburg winter the contraction of the member was restricted by the bolt plowing and friction. The connection welds were torn from the supporting member. An expensive retrofit was required. The expansion connections were replaced with slide-bearing stiffened seat connections. And the bolts were removed from the web connections.

http://www.FerrellEngineering.com

 

[KootK]

Yikes. Is there some kind of standard by which one can determine if a particular slotted connection is "heavily loaded"?

In my opinion, very few of the slip connections proposed by structural engineers are actually capable of doing any serious slipping. Particularly if they get rusty.

 

[connectegr]

I agree that these connections rarely slip as expected. And it is difficult to predict the performance. For structural connections, the bolts must be installed per RCSC. Long slots in structural connections are intended to account for erection tolerances, not free slipage. For "no load" attachments, bolts do not have a structural intent and can be finger tight to minimize the resistance.

http://www.FerrellEngineering.com

 

[ToadJones]

Connect-
I only live an hr or so from the center and I remember obtaining some details of the connections in a local newspaper or somewhere but have since lost them. Do you have any of those sketches?

 

[slickdeals]

See attached from ENR on the same topic

 

[ToadJones]

thats the one i had slick...thanks