fill the K-zone ?

Date 06-24-2007 00:40

This is typical LRFD doubler plate welding. What you have to watch out for is warp and tilt of the flanges in that area. With the extra work involved in LRFD Doubler plates, you would think that someone as intelligent as an engineer could figure out that it would be more cost effective to use a heavier column and get rid of the extra welding, and the additional heat bending necesssary to straighten out the flanges. Don't worry about the "K" area metallurgy.

By swnorris (****)

Date 06-25-2007 10:46

We see this a lot. The engineer is designing to meet specific loads, so, the possibility of substituting to heavier sections to eliminate web doublers is left up to the fabricator. This is usually discussed during a pre-detailing meeting and then presented to the EOR for approval.

By Joseph P. Kane (****)

Date 06-25-2007 11:18

So, the fabricator or the fabricator's detailer is responsible. Good! The morons will go out of business and the better run operations will survive! My apologies for doubting the engineering profession.

By eekpod

Date 06-25-2007 12:37

We have done this a number of times as well. It's especially difficult when the doubler plate is only on one side of the web. When there are two doubler's( one on each side of the web) it's a little easier to keep the flanges from "tilting" out of square because you can go from side to side with the heat from wedling, but only one side is harder.
We put alot of strongbacks on the ends of the flanges to keep them as straight and square as possible. Watch your heat in the "K" or the "K" section may totally collapse and warp/distort itself and the part will be junk. I took a few days of one time and came back to a part that had to be scrapped because the welder didn't care about his work and welded one entire side of a 1" thick doubler plate. The heat distorted the K section so bad it couldn't be used, what a waste.
Also what we do it put a few holes in a line down the center of the plate and plug weld it down, other wise depending on the thickness and weld size the plate might "bow" up from expansion because it has nowhere else to go. Chris

By swnorris (****)

Date 06-25-2007 13:25

It's not so much an issue with flange warpage as it is the potential for weld cracking near or in the K area. Welding highly restrained joints such as those associated with doubler plates induces residual stresses. All steel is not entirely homogenous, and variations in mechanical properties exist. In addition to the normal variations, the process of mill rotary straightening alters the mechanical properties by strain hardening the K area. Material variations in the K area may include a reduction in ductility and toughness resulting in reduction of CVN values, an increase in hardness, yield strength and ultimate strength, and an increase in the ratio of yield to ultimate strength.

By Bob Garner (***)

Date 06-25-2007 18:09

Just some info from AISC Seismic Design Manual, Seismic Design Provisions, ANSI/AISC 341-05:

Section 9.3c Panel Zone Doubler Plates: Doubler plates shall be welded to the column flanges using either a complete joint penetration groove welded or fillet welded joint that develops the ............etc.

Section 7.5: Corners of continuity plates and stiffeners placed in the webs of rolled shapes shall be clipped as described below. Along the web, the clip shall be detailed so that the clip extends a distance of at least 1 1/2" beyond the published k detail dimension for the rolled shape. etc.

Section 9.3c would seem to permit a full groove weld in this area. This isn't what I was expecting either. Only on Heavy Section columns (flanges thicker than 1 1/2") is there a requirement to avoid welding in the k area. See Commentary, C6.3
This has to do with reduced notch tougnness in this area of rotary straightened W shapes.

Bob

By mountainman (***)

Date 06-25-2007 18:19

thanks to all who replied, very helpful indeed.

thanks.
jj