Difference between web-shear and flexure shear

[Yousef ZAA]

Hello,
Can some one give me a hint on the differnce between web-shear and flexure shear strength?

 

[BAretired]

Shear is shear. Where did you come across these terms? Are you talking specifically about steel, concrete, wood, or any material?

BA

 

[rb1957]

be careful, why add "strength" to "flexural shear" ?

a beam in bending is going to have web shear, in the web (who'd thunk it !?) for the shear load creating the bending.

the caps experience an increase in load (which is "just" the other side forces of the shear web, yes?) which could be flexural shear.

another day in paradise, or is paradise one day closer ?

 

[HTURKAK]

Consider the shear daigram of a RC beam.. The zones which diagonal tension cracks develop are called web shear zones.. and the cracks are called web-shear cracks or diagonal tension cracks.

The sketch below explains the terminology..

 

[Agent666]

I interpreted it as shear and flexural shear interaction in steel. Under a certain percentage of the shear capacity you can ignore the flexural interaction. Over this percentage, you will have to account for the reduction in shear capacity due to flexure, or alternatively you can can think of it as a flexural capacity reduction in the presence of higher shear forces in a web.

https://engineervsheep.com

 

[KootK]

It's probable that we're talking about shear in prestressed concrete. My understanding of the situation is this:

1) Flexure-Shear failure in prestressed concrete is quite alanagous to regular shear failure in non-prestressed concrete. The presence of axial prestress in prestressed members changes the character of it a bit but, fundamentally it's similar: a flexural crack that turns and becomes a shear crack. The dominant concern with this type of shear failure is the maintenance of transverse member shear capacity.

2) Prestressed members sometimes have a characteristic that CIP members rarely have: the webs are sometimes significantly thinner than both "flanges". As a result a web shear failure mode is possible which is not necessarily initialed by a flexural crack. The dominant concern with this type of shear failure is the maintenance of longitudinal member shear capacity.

That's the best that I can muster for theory. At the end of day, some clever folks tested stuff and shear failures presented themselves in two forms deemed mechanically different enough to warrant separate checking procedures.

 

[Yousef ZAA]

Thank you very much guys, yes I meant it in prestressed concrete.

 

[cooperDBM]

Those terms are specific to ACI's shear failure model for prestressed beams, using the more detailed method. HTURKAK's diagram illustrates where each may be critical, though you generally check both at each section.

Koot, both of your figures look like a web shear failure to me. Cracking above the prestressing and extending down to where it fails in splitting along the strands.

 

[KootK]

I disagree. There are flexure cracks there to serve as initiators. More pragmatically, I'm not sure that it's even possible to web shear a stocky solid member. But yeah, perhaps there's a better pic out there somewhere without the eventual horizontal crack over the prestress.

 

[KootK]

Something like this conceptually.

 

[rapt]

Normally when we design, flexure and shear are designed as 2 separate actions. So we have to look at 2 possibilities in calculating shear

- Flexure shear is the empirical calculation model used to determine shear capacity in a section that is cracked in flexure, so there is combined flexure and shear affecting the shear capacity.

- Web shear or Principal Tensile shear is the calculation model for a section that is uncracked in flexure. So there is really only shear stress at the section with a small amount of flexure. Normally around the point of contra-flexure in a continuous member or at a simply supported end support.

If you go to the Canadian MCFT, the effects of tensile strain due to flexure and shear are combined at a section to give a principal tensile strain/stress based on a Mohr's circle combination of the 2 strains/stresses. This model can therefore handle anything from pure shear to very high combined flexural and shear stress in the one model, so there is no longer a need to look at the 2 separately.