Base Plates at Columns with Brace Gussett Plates

[Galambos]

Just curious what everyone elses does when it come to a brace at the base of a column. Do you weld the gusset to the col and bp or just the column? do you center the bolt pattern in both directions on the column? do you shift the anchor rods and account for the eccentricity?

just looking for some ideas to retool what we've been doing.

ted

 

[dik]

I usually use a thicker base plate without the gussets. Base plate thickness has to be in excess of 2" before I start looking at alternative methods of designing it.

Dik

 

[Tomfh]

ditto

 

[JAE]

Where a diagonal brace (for and X or chevron) comes into the bottom of a column, we usually select a work point at the centerline of the column at the bottom of the baseplate and then set a control line (centerline of the brace) from that point. This usually creates a need to connect the gusset plate to both the column and the baseplate.

If you are designing/detailing for seismic, be sure to set your brace back far enough from the ends of the gusset plate welds to allow inelastic out-of-plane buckling in the gusset without tearing at the column/plate welds. See the AISC Seismic Commentary for a good detail of this.

 

[WillisV]

Agree with JAE - for bases of braced frames we typically select the workpoint at CL of column and weld the gusset to the column and to the baseplate (extended if necessary).

 

[DaveAtkins]

I agree with JAE and WillisV--just be cautious that the vertical component of the reaction may induce some bending into the column, due to the stiffening effect of the gusset plate on the base plate. The stiffened base plate may cause a uniform resisting pressure under the base plate, eccentric to the vertical load from the column/diagonal.

DaveAtkins

 

[JLNJ]

If the forces are small maybe you can allow the detailer some flexibility in the workpoint in order to keep the goemetry simple.

As JAE said, when you make the workpoint the bottom of the base plate you will usually need to connect to the plate and the column. Often you'll see inexperienced detailers keep the workpoint in the correct location but then try to get approval on a connection arrangement which eccentrically loads into the column only. Stay away from those!