Let us look at a simply supported WF beam. Let us say that the bm. is an
existing floor beam and under gravity load it is functioning well without
any signs of overstressing, and as we know the bot. flg. of this beam would
be in tension. Now for one reason or another we add to the bot. flg. by
welding identical pieces of steel to each side of it, starting from the
beam center line all the way to the left support, creating width
differential at the mid span . Would this beam become overstressed under
the same loading condition, develop cracks and eventually fail? If it does
then "LESS IS MORE". Remember in this case we ADDED to the bottom flange.
Karim Hosseinzadeh, SE
> From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
> To: SEAOC Newsletter <seaint(--nospam--at)seaint.org>
> Subject: Re: Welding Code AWS D1.1
> Date: Friday, April 16, 1999 3:51 PM
> >Thanks for your comment. I do agree with you with regards to stress
> >concentration around a round hole. I consider this case a lessening of
> >material due to hole cut outs,
> Not true. The stress concentration at a round hole is 3 even where the
> hole diameter is negligible with respect to the flange width.
> >where is the logic in this that the 8" x1/2 flange can safely withstand
> >load but the 14 5/8 x 15/16 flange may become overstressed and develop
> >cracks. Unless it is shown by tests that the smooth transition is needed
> >prevent the overstressing of the smaller flange.
> The concentrated stress develops in the smaller flange right next to the
> discontinuity, and it develops because of the mismatch in stiffness
> across the interface width. The stress concentration doesn't apply to the
> entire flange width, and will be a consideration for fatigue only. The
> whole flange won't be overstressed but the small area at the
> discontinuity sure will. Typically what happens is crack formation and
> gradual extension under cyclic service loading, and fracture the first
> time it takes a big hit.
> Christopher Wright P.E. |"They couldn't hit an elephant from
> chrisw(--nospam--at)skypoint.com | this distance" (last words of Gen.
> ___________________________| John Sedgwick, Spotsylvania 1864)