transverse intermediate stiffener and shear resistance 5

[keyen]

Does the transverse intermediate stiffener shown in this pic increase the shear resistance? If so, how? This seems counter-intuitive to me (blame my mechanical background if you wish).

 

[KootK]

There are a couple of options at least, and they are related:

1) One of the shear failure modes is shear buckling of the beam web. The stiffeners can be made to effectively brace the web against that kind of buckling.

2) With properly proportioned and spaced stiffeners, one can utilize tension field theory for the beam shear design. Basically, you treat the beam as a truss with the stiffeners being the compression struts and diagonal strips of beam web being the tension webs. Most steel codes have a section describing this shear model. Certainly AISC and CISC do.

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.

 

[keyen]

KootK, thanks for the clear and prompt response. The shear buckling makes sense to me. The field theory is over my head.

 

[jayrod12]

Don't feel bad... Koot flies over many people's heads.. Him and a few others on this board are on different levels from the rest of us Laymen.

 

[271828]

There are several theories.

Basler's theory from the early 1960s is the basis of the AISC and AASHTO strength equations. Like KootK typed, after buckling, the web is idealized as a truss, and the stiffeners are in compression. This is explained in Salmon and Johnson.

Hoglund's Swedish research is from the early 1970s, and is the basis of some European code strength equations. By his theory, stiffeners increase the plate buckling coefficient, so increase the web buckling strength. They also allow frame action in the flanges.

Lee, Yoo, and colleagues have shown that the transverse stiffeners do not resist much axial load, so Basler's model is a bit inaccurate in assuming truss behavior. The stiffeners mostly hold the web in line while web stresses redistribute, including increased web compression stresses near the stiffeners. They provide strength equations in their 1998 paper and talk about behavior in their 2006 paper, among others.

 

[271828]

"The field theory is over my head."

Surely not, as it's pretty easy. Check out the explanation in the plate girder chapter of

http://www.amazon.com/Steel-Structures-Design-Behavior-Edition/dp/0131885561

 

[KootK]

@Jayrod: welcome to the KootK Christmas card recipient list.

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.

 

[hokie66]

Welcome back, 271828. Haven't seen you around lately.