Structural Steel Moment connection using slotted bolt holes 1

[Sebast73]

I am the E.O.R. of a 3-story ordinary moment frame building and am in the process of reviewing shop dwgs.
The designer whom is no longer with the company designed the moment connections using shop & field welded top & bot. plate with an oversized round hole for 3/4" A325 bolts, the fabricator proposing to use 13/16" X 1-1/8" slotted holes for field connections, I am comfortable with the 13/16" over size slot, but the 1-1/8" in the direction longitudinal with the beam seems excessive. Any input on this will be greatly appreciated.

I have attached a sample shop dwg for visual. My question is, without reanalyzing the connection which was previously designed, most likely, over designed with a safety factor, is the 1-1/8" slot too much of a net area loss for a 3/4" bolted connection. In the attachment, the example is a 6 bolt linear connection, top &bottom shop welded plates to form the connection.

 

[CANPRO]

Slots in the shear tabs should be ok as long as they maintain edge distances. Slots in the flange plates would be unacceptable.

 

[Sebast73]

Great thank you for input.

 

[PROYECTOR]

Hi Sebast73,

My question is, without reanalyzing the connection which was previously designed, most likely, over designed with a safety factor, is the 1-1/8" slot too much of a net area loss for a 3/4" bolted connection. In the attachment, the example is a 6 bolt linear connection, top &bottom shop welded plates to form the connection.

For a 3/4" diameter bolt, a 13/16" diameter hole is considered a 'Standard' hole, not an 'Oversized' hole. If you decided to change a 13/16" hole for a slotted hole with the slots parallel to the direction of the load (as shown for the flange plates), then the connection must be considered as slip-critical, which typically requires more bolts and special requirements for the faying surfaces. Also, for a 3/4 "diameter bolt, a 13/16" x 1-1 / 8" slotted hole is between a short slotted hole (13/16" x 1") and a long slotted hole (13/16 "x 1 7/8"). Therefore, 13/16 "x 1-1 / 8" holes should be considered long slots for design purposes.

For a bolted flange plate connection, I think it is more rational/typical to use oversized holes (5/16") in the flange plates and short-slotted holes (13/16" x 1") with the slot perpendicular to the direction of force in the web shear tab. This typically allows for mill and erection tolerances to be accommodated.

 

[Sebast73]

Thank you for the information, I will respond with the direction of recommend no slots in the flange plates, if so desired, more design required, therefore, leave it up to the detailer & owner to make the decision.

Thank you gentlemen for the input.

Sebast

 

[human909]

I've had a foot in both camps in my employment history. For obvious reasons fabricators and erectors love slotted holes. And I've seen all sorts of non approved slotting on site by contractors putting up steel. For simple connections this is largely tolerable. For moment connections (as commented above) it really isn't. In my experience when you have moment connections in your structure then extra supervision of the steel erection is beneficial. Cowboys not torquing bolts correctly or slotting holes when things don't line up can potentially drastically change the performance of a connection.

 

[Sebast73]

Absolutely agree, thank you, I will recommend additional Quality control when steel erection commences.