Transitions in thickness

By G. Livermore Date 07-31-2003 23:55

At a W shape column to beam connection where the column has flange/web stiffeners that weld to the flanges of the beam, is a transition between unequal thicknesses required?
D1.1 states that for static non-tubular butt joints a 2 1/2 to 1 transition is required in cases where the joint is subject to 1/3 of the allowable stresses.

It has been sugested to me that this joint is actually a T-joint and that the stiffener plates can be as thick as practable (easier to align) with no transition to the smaller beam flange as long as the thickness of the flange is maintained.

IMHO this is a butt joint and the stairstepping of the backing creates a sqaure notch on the underside functioning as a stress raiser

Any suggestions?

By jwright650 (*****)

Date 08-05-2003 15:07

G. Livermore,
It sounds like you are describing a Beam to Column field moment connection where the beam is framing to the web of the column. Texas "T" connections sometimes do have stiffeners in the web of the column that are thicker than the flanges of the beam(s) framing in. Most often it is because of 2 different depth beams framing opposite the web and the thicker stiffeners allow aligning the bottom flanges.

Is it a requirement per the specs to remove the backing strip or can it remain in place?

The AISC has a publication "Steel Design Guide Series #13" (copyright 1999) that addresses this issue and I'll quote so I won't mess it up,

" Appendix "D" (starts on page 95) Titled "Column Stiffening Considerations for Weak Axis Moment Connections" Note #3 at the top left of page 99 states"Connection plates that are made thicker or wider for control tolerances, tensile stress, and shear lag need not to be ground or cut to a transition thickness or width to match the beam flange to which they connect." Figure #1 is along side this paragraph and shows the thicker stiffeners with out any transition of the thicker stiffener plates.

Hope this answers your question about transitioning the plates,
John Wright

By jwright650 (*****)

Date 08-05-2003 15:32

BTW, the joint is a butt joint welded with a B-U4a joint configuration.
John Wright

By G.S.Crisi (****)

Date 08-07-2003 20:20

The American Institute of Steel Construction (AISC) has a Recommended Practice for Structural Steel Welding which you can (or at least could) dowload for free from their site.
www.aisc.org
Giovanni S. Crisi
Sao Paulo - Brazil