Transverse Stiffener Design for Steel Beam Strengthening for Shear

[Sanira]

Hi,

I have an existing beam that needs to be reinforced for additional loads. For flexure, I have added top and bottom plates. However, for shear strengthening, I need to add transverse stiffeners. When I look into AISC 15th Ed. Manual section G2.1(a) for rolled I shaped members, it doesn't have anything regarding transverse stiffeners. Can I use section G2.1(b) which has provisions for transverse stiffeners? I think section G2.1(b) is for built-up plate girder, not rolled I shaped members. Furthermore, if I use section G2.1(b), the criteria h/tw< 1.1 sqrt (kE/Fy) doesn't match with the one for rolled shaped members which is h/tw<2.24 sqrt (E/Fy). Can anybody help me with this one?


Thanks,

 

[r13]

I'll try add plates to the web in lieu of stiffeners. Shear behavior is quite different in deep builtup girder than rolled shapes. I don't think the provisions there would provide much help for your problem.

 

[Agent666]

Transverse stiffeners only increase the shear capacity by virtue of decreasing the web slenderness in deeper beams with thinner webs, effectively dealing with preventing shear buckling of the web.

So if you didn't have a slenderness issue then they do nothing.

Doubler plates like retired noted are the most practical if not the only way to increase the shear capacity unless you can increase the depth of the beam by welding another I beam or Tee underneath.

 

[KootK]

I believe that you can use stiffeners to improve shear capacity in this situation but you need to use a different AISC clause than G2.1(b).

Consider that G2.1(a) already gives you [Cv1 = 1.0] and that [Cv1=1.0] is the most favorable outcome of G2.1(b) possible. So, if your section already satisfies the limits of G2.1(a), there's no additional capacity to be had by using G2.1(b).

The place to go, I think, is G2.2 which can be applied to all cross sections and utilizes tension field action methodology to capitalize on available, post-shear buckling capacity.

 

[271828]

If h/tw <= 1.1*sqrt(kv*E/Fy), with kv = 5.34 for unstiffened, then it's controlled by yielding, so adding shear stiffeners won't help. In this case, you would need doublers instead.

Do not use G2.2 to try and get more strength by tension field action for a web with h/tw<=1.1*sqrt(kv*E/Fy for kv=5.34). TFA only develops after buckling, so it isn't a thing for a web that's not controlled by buckling.