Reinforcing a beam for shear - is it possible?

[cessna98j]

We are trying to determine whether or not it is possible to reinforce a W24x250 beam for shear near a support. Since the shear is only in one small portion of the beam, it seems uneconomical to increase the size of the already enormous beam when it is just one small portion that needs more shear capacity and the flexural capacity is ok. We had thought about welding a doubler plate to the web to increase the web cross section area in the high shear area, but we have not been able to find much info on whether or not this is a very effective solution.

Has anybody had success with a doubler plate or something similar to increase shear capacity in a beam?

A diagram for clarity...

720k
|
V
==============================================
XXXXX <--- doubler plate?
W24x250 (spanning over top of W24x250)
XXXXX
==============================================
-----
|
| W24x250
|
-----

 

[msquared48]

Sure - treat it as designing a built-up plate girder, putting in bearing and web stiffeners as required between the load and the support to change the aspect ratio of the web steel to something acceptible. Doublers may not be needed.

Mike McCann
MMC Engineering

 

[jike]

I was going to suggest a web doubler another idea might be to have a pair of stiffeners and a diagonal stiffener similar to a truss. Another possibility might be to add a member on top of the existing beam to help distribute load and to increase shear capacity.

 

[JAE]

The new AISC steel specification includes provisions for doubler plates - specifically at points of concentrated loads like what you have.

The W24x250 (Fy = 50) provides 738.5 kips of shear capacity ([&phi;]V_n per AISC 360-05, Section G2.

Section G3 offers a tension field option to look at - not sure what capacity this would offer.

Section J10 discusses the doubler plate usage.

 

[nutte]

Doubler plates are very expensive for the shop. Keep this in mind when deciding to change the member size or not.

 

[civeng80]

Just do a little estimate to make sure that getting a larger beam is not cheaper, sometimes you may be surprised to find out a larger cleaner beam may be cheaper. Maybe a 10 minute talk to a steel fabricator may answer your question.

 

[Lion06]

what do the other support conditions look like? Are all of the supports beams or are some columns? How many spans is the beam and which support number is this?

 

[cessna98j]

It's quite a complicated little piece to explain, not sure how to post a picture but that would probably help clear things up.

The top W24 is bearing on the bottom W24 at a 22.5 degree angle, and has the same conditions at the opposite end with the same shear and bearing on a W24 at a 22.5 degree angle. The bottom support steel is in the shape of an octagon attached to 8 columns. The upper steel is in the shape of an octagon as well, but is rotated 22.5 degrees relative to the lower steel. This upper octagon of steel is to provide continuous support to a cement silo with some pretty massive loads. The upper octagon of steel bearing on the lower octagon of steel is necessary because the lower octagon of steel is at too large of a radius to provide continuous support to the silo.

Thanks all for your input, it is very helpful to get some other ideas on how to tackle this.

 

[trainguy]

You should check out seismic design requirements for eccentrically braced frames. It's a very similar animal to what you need...

A small region of an I-beam shear web with all the stress and stability concerns neatly spelled out.

I'm not sure if AISC has a section on this, but I bet the Canadian CISC hdbk has this.

tg