Doubler Plate design for beam web
Doubler Plate design for beam web
(OP)
Hi,
I have a situation where I need to splice the existing beam. I cannot add flange plates due to construction restraints and need to transfer the splice forces through the beam web splice plate only. The tension force is 300k and the beam web is 0.5''. Beam web does not work for block shear strength. So I am planning to add doubler plate at the web to account for thicker web. Any inputs? Is there any resources out there which talks about the design?
Thanks
I have a situation where I need to splice the existing beam. I cannot add flange plates due to construction restraints and need to transfer the splice forces through the beam web splice plate only. The tension force is 300k and the beam web is 0.5''. Beam web does not work for block shear strength. So I am planning to add doubler plate at the web to account for thicker web. Any inputs? Is there any resources out there which talks about the design?
Thanks






RE: Doubler Plate design for beam web
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
another day in paradise, or is paradise one day closer ?
RE: Doubler Plate design for beam web
if you wanted to be "sexy" about the design you could make the splice plate as a "fish mouth", tapering towards the ends, as the load gradually shears from the caps to the splice.
another day in paradise, or is paradise one day closer ?
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
Adding doubler plate make the web thickness larger thus helping the block shear. Am I missing something here?
The force is around 500kips tension. Web alone is sufficient for 350kips. Adding doubler plate on both sides of the web, increases the web thickness thus block shear capacity. The weld around the double plate will be designed to resist all 500kips of force.
Yes, I can weld the doubler plate to the web. The doubler plate will be 20'' long.
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
If I've misunderstood something, perhaps a sketch of the situation is in order?
RE: Doubler Plate design for beam web
I suspect so but it's pretty hard to tell without a sketch. As I see it, the splice plate pulls on the doubler plates which, in turn, pull on the original beam web in block shear, as was originally the case. If that's the case, then the only improvement would come about if, somehow, the perimeter of your doubler plates were somehow substantially larger than the welded perimeter of your splice plates were. And if the doubler plates could be made that large, then I don't see why the splice plates themselves simply couldn't be made that large, obviating the need for the doubler plates altogether.
What I wanted to know was how far into the existing beam you could potentially take the splice plate. Like winelandv, I don't understand why you cant extend the splice plate until the welded or bolted perimeter is sufficient for block shear.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
Cannot achieve the block shear capacity by extending the splice plate with additional bolts. The plate becomes too large.
RE: Doubler Plate design for beam web
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
Be careful with how close your double plates get to the beam flanges - you'll restrict access and won't be able to weld all around as you're showing.
Is there any reason you can't add plates to the underside of top flange and to the bottom flange as well?
RE: Doubler Plate design for beam web
isn't the problem "merely" making a load transfer into the doubler good for 500,000 lbs ?
and accounting for shear lag (the load from the
capsflanges).however you do this, working within the inside of the beam flanges, and now also with a length limitation, there is a limit on how much load you can ship. If the load required is bigger than the capacity then ... redesign.
another day in paradise, or is paradise one day closer ?
RE: Doubler Plate design for beam web
Going back to what I had been doing, the doubler plate length is selected based on weld requirement. The block shear for the doubler plate itself is not a problem. To just give you an idea, web can handle 70% of the tension force in block shear.
Adding to this, doubler plate thickness was chosen so that the web thickness + doubler plate thickness works for the block shear. The doubler plate alone cannot carry the entire 500kips of the load.
RE: Doubler Plate design for beam web
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
Shear lag needs to be accounted for, but the block shear failure also needs to be accounted for in tension connections. It's a simultaneous failure of tension rupture at the part perpendicular to the load and shear yielding or rupture at the part parallel to the load. I'm not sure if it's in the AISC LRFD 1st or 2nd editions, but it is in the AISC 13th edition - Section J4.3. I've attached a snip of tension member showing the shear and tension areas.
So in BAGW's situation, it's checking for a 3-sided shape pulling out of the base material.
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
This was especially well articulated so I'm going to piggy back onto it by adding one critical piece. The part of the block shear that went into the beam web in the first check, is still in the beam web for the second check in my opinion. Hence the inefficiency of the concept.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
I completely agree. Have to check two block shears as CANPRO pointed out. Thanks
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
Really? So soon? That's an impressive degree of mental plasticity for a structural engineer. It takes most folks 100+ posts to get past their egos.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Doubler Plate design for beam web
RE: Doubler Plate design for beam web
LOL. I was missing the point for the doubler plate shear break out at the beam web. Thats what will control now. The Bolt region is fine with doubler plate.
RE: Doubler Plate design for beam web
we're welding the doubler to the web, either under the splice plate or on the opposite side, so we have to check "block shear" around the perimeter of the doubler (to verify that the beam is ok).
then we have to check block shear in the splice plate for some %age of the load (some load sheared into the doubler).
of course, we have to check net section (doubler + splice plate) where all to load has left the beam; presumbly the beam net section is already checked.
and we have to check the fasteners (shear and bearing) and the welds.
so it sounds as though the critical failure now (prompting this redesign) is block shear in the beam, (cause the doubler takes some of the beam load away) ... but we don't gain much;
secondary failures could be splice plate area (if beam block shear is ok, then thicker plates would work) or fasteners (bigger bolts could work ?).
another day in paradise, or is paradise one day closer ?