column eccentricity

[nrguades]

In a wide-flange beam framed into TS column where the column is cut or slot for the shear plate connection, is it right that the beam reaction will be assumed to extend into the column centerline and the effect of connection eccentricity can be neglected supposing the connection is designed for combined shear and moments? thanks...

 

[ChipB]

I've always neglected this eccentricity on TS columns & most wide flange columns. If I have a column that is near 100% allowable stress, I bump it up to a size that isn't. (When in Doubt, Make it Stout, school of design). If I have a heavy reaction on the flange of a deep column (like crane railways), then I design for the moments due to the connection. The biggest TS I've called out is 8x8, and typically these are used in commercial areas not heavy industrial, so reactions are "light". If you use software for design, you can specify beam setbacks, and the software should account for the eccentricities.

 

[DaveAtkins]

The single plate connection tables in AISC were developed assuming the reaction occurs at the weld line (that is, the bolts are designed for 3" eccentricity). Therefore, to be technically correct, a tube colun or wide flange column with a shear plate connection on just one side should be designed for the eccentricity to the face of the column (this is what I do). However, in the November 2002 issue of Modern Steel Construction, Charles Carter of AISC notes that exterior columns have been traditionally designed neglecting eccentricity, with no problems, due to the restraining effect of the connection.

DaveAtkins

 

[CSEllc]

Regardless wether is is a WF or TS column, I always include the eccentries in my column design. I generally use the distance from column center line to the centerline of the bolts...bolts are usually about 2 to 3" away from the face of the column. In the weak-direction of WF columns, I generally use 3" as my eccentricity since the thickness of the web is rather small.

On interior colums, I check my columns two ways, the first with full LL on both sides, second is with full LL on one side and only DL on the other. (I generally just proportion the LL out....I don't run a full second set of calculations....I'm not that anal about it.) You would be surprised the number of times the "unbalanced" load condition increases the column size.

On the exterior or perimeter columns, I use the full LL in both directions, with the appropriate eccentricity.

 

[nrguades]

Is there any beam - column connection detail that will avoid load eccentricity? How about beams that bear directly on top of TS column? Is there such thing as minimum eccentricity required by AISC specs? thanks...

 

[jheidt2543]

OSHA requires a minimum eccentric load to be considered for erection purposes, I believe it is 300 lbs at 10", but check it for yourself. It's not a lot, but does make a difference in some situations.

 

[CSEllc]

The OSHA req't is 300# with an 18" eccentricity. That is to be the weight of an iron worker with "full" gear hanging off the side of the column as a beam is being lifted. I believe it only applies to columns but not posts. you need to check OSHA's definition of what consitutes a column vs. a post. In my opinion, it is really meant to be used for the design of the base plate anchor bolts. It's part of the requirteing a minimum of (4) anchor bolts on all columns but not on posts.

Idon't know off any conection that does not casue some sort of eccentric load, unless you are bearing directly over the top of a column.