slotted holes connection question

[delagina]

i have an existing column.
i am a connecting new beam.
i need to slot the beam connecting to existing column for erection purposes.
other side of the beam is not slotted, connecting to new column.

if i am to use regular snug tightened condition for slotted holes.
can i ignore the fact that it's slotted and design the bolt and plate against bearing, shear, etc.. as if it were a regular hole.

simply put one end of the beam is slotted, other is not. can i design the bolt and shear plate as if there is no slot. or should i assume 2x shear for the non-slot.

thanks,

 

[connectegr]

If the connection is for shear only, then the slot (long or short) perpendicular to the load can be designed as a bearing connection. Note that the AISC 13th Edition tables for shear tabs use short-slots and a maximum eccentricity of 3 1/2". Remember to consider the maximum eccentricity that is allowed by the use of a long-slot when determining the shear capacity of the bolts and bending of the plate.

Also, long-slots in an outer ply will require a plate washer.

http://www.FerrellEngineering.com

 

[SteelPE]

I believe the standard practice is to allow for slots in the direction normal to the load on the beam. If this is a simple shear connection then slots parallel to the length of the beam would be acceptable. However, if you are trying to drive axial force through the beam then the holes should be standard size (if you are designing a bearing connection and not a sc connection).

I wouldn't think it would matter what end of the beam the slots were on... or even if both ends were slotted.

 

[delagina]

i have big axial loads because i will be transferring the horizontal loads to existing.

should i use slip critical connection?

or snug tight is ok?

the thing is this has been there practice for sometime and no one seems to check on this.

thanks,

 

[connectegr]

With axial loads and slots you should use slip critical connections. I would also recommend an knife plate connection (plate on both sides of the beam web), instead of a single plate. You can put the slots in the beam web with standard holes in the plates, eliminating the need for plate washers. Two plates provides and concentric connection for the axial load and puts the bolts in double shear. Check the beam web for tearout.

http://www.FerrellEngineering.com

 

[connectegr]

Another note. If you use knife plates the the first plate can be field welded using double fillets and the second plate should be partial penetration welded. A single fillet should not be used in an axial loaded connection.

http://www.FerrellEngineering.com

 

[delagina]

question:

if i have 6 kip beam axial for W14 say 3 bolt rows, going to existing column.

can DTI washer be enough even if i use slotted holes?

are there any DTI slip capacity?


thanks,

 

[connectegr]

DTI "direct tension indicator", is a load indicator to verify that the bolt has adequate pretension. Slip critical is a combination of faying surface condition and bolt pretension. The slip critical shear resistance of the bolt is the same whether the slot is short, long, or oversized. The surfaces must be prepared to provide a Class A slip coefficient.

6 kips is a relatively small axial load for structural steel. What is your material?

Your last post creates a little concern regarding your understanding of slip critical bolted connections.

http://www.FerrellEngineering.com

 

[delagina]

I am adding some new steel platform connecting to existing. I thought I will have big axial due to wind but it's only 6 kips maybe because many beams will connect to existing. So roughly 6 kips per beam.

I know slip critical is not the bolt but the friction between sufaces.
What I'm saying is for 6 kip for slotted is it necessary to specify slip critical or DTI is OK?

Thanks,

 

[connectegr]

Unless you have a preference from DTI washers to verify pretension, you should only specify the slip-critical requirement. Per RCSC there are several approved methods of pretensioning the bolts. DTI washers are only one of the choices.

http://www.FerrellEngineering.com

 

[nutte]

Connectegr,

The slip critical shear resistance of the bolt is the same whether the slot is short, long, or oversized.

I believe you mean:

"The slip critical shear resistance of the bolt is NOT the same whether the slot is short, long, or oversized."

 

[delagina]

ConnectEngr,

It is is our Steel Notes Drawing to use DTI for main field connectors. I have also confirmed this with the construction guy.

I still didnt get if this is ok or not for 6 kips?

Thanks,

 

[connectegr]

delagina,
I would still specify that the connections are to be slip critical. I understand your intent, but someone else may not. Especially when there is additional costs applied to the surface requirements. The simple understanding or DTI is that pretension of the bolts is required, only. Bolts can be pretensioned and still be considered bearing connections, such as in the use of tension control bolts. But, your condition requires slip-critical, so be clear.

If your final question is regarding the adequacy of a connection with 3 bolts for 6 kips axial. My simple answer is MAYBE. I would need to see the complete connection detail. What is the shear load? Plate thickness? 1 or 2 plates? Weld sizes? Bolt size and grade?

http://www.FerrellEngineering.com

 

[delagina]

no problem with clip angle thickness, bolts, etc.. i know how to design that.

the only concern i had was the slotted holes without using slip critical but dti.

i would just use round holes and not slotted. the problem though is construction group guy said if it doesnt fit during erection, they'll slot it in the field. ahahahah

i work inside a refinery plant doing small new structures connecting to existing.

anyway thanks.