effect of web plate 1

[KenStructural]

Assuming i have steel beam,and a stiffener plate along the length spaced @ 300mm on centers. Can i use the 300mm spacing of stiffener plate as the un supported length of the compression flange?

 

[ishvaaag]

No. The intent of bracing at the compression flange is the prevention of LTB (Lateral Torsional Buckling) in which the beam rotates laterally. Adding stiffeners does little to prevent such rotation and hence assuming the distance between stiffeners as unsupported length of the compression flange would be in error (except the tensile flange itself has such rotational stiffness that can perfectly sustain the lateral fixity of the compression flange through competent stiffeners, that almost never uses to be the case).

 

[slickdeals]

It helps with local buckling.

 

[frv]

slick- shear buckling, right?

 

[FishTheStructure]

Yes frv,

Stiffener plates (or transverse stiffeners) are used to increase shear capacity by allowing development of a "web tension field" in thin webbed sections. They resist local shear buckling which is buckling out of the plane of the web.

The unsupported length of the compression flange is a failure type related to bending known as lateral torsional buckling. If you Google some pictures of LTB failures you will see that the web is not buckled; the local cross section is intact. The failure is an overall buckling type so the web stiffeners will do nothing against this.

Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein

 

[frv]

Fish.. I'm aware of tension field action, but in the context of the thread, I thought perhaps slick was referring to LFB, as shear buckling is rarely a problem in normal WF applications. If so, that's the first time I had ever heard of stiffener plates being used to mitigate LFB (or CFB, as noted in the spec).

 

[SAIL3]

No, you can not.....