Shear vs Bending force

A rectangluar beam of 1.25" High x 1" Wide (Area = 1.25 sqin)

the beam is only 1" long

force is evenly distributed along 1" x 1" face

Beam is rigidly mounted to wall (Figure its a part of the steel wall machined out, so like a block sticking out)

is the block in shear or bending or both?

I thought there was some sort of ratio when figuring this stuff that if the Beam height is more the the beam length than the object is only in Shear.

 

If I understand you correctly, an axial load is being applied evenly to the 1x1 face. The "beam" is in both bending and shear, but since the beam is so short, shear will more than likely control your situation. Determine max shear and moment at the critical location (at the face of the wall), then determine bending and shear stress based on the section properties. Compare to allowable bending and shear stress to see if your "beam" is safe under the applied load.

 

[fishercd]

Be careful in how you compute the bending and shear stresses! The standard BendingStress = Mc/I equation won't be very accurate considering the low aspect ratio of the beam. The ShearStress = VQ/junk will also be not as accurate. This case isn't too far off from a bearing type stress either.

 

[vtl]

Mohr circle should be close enough.

 

[0321]

i think beam is both in shear & bending. but consedering its small ratio shearing would be more prominent

 

[rlflower]

The analytical approach might lead you to a different conclusion than the emperical approach. Just step back and look at it for a moment. If the applied load is located at a distance from the support equal to or less than the depth of the member, then what happens? The member will naturally tend to act as a truss in response to the load, transfering the load directly to the supports with little or no internal stresses resulting in bending. Mohr's circle should prove me right.

 

[boo1]

I dissagee with the Mohr's theory recommendation, which is ordinarly utilized for "brittle materials" design. I think the maximum-shear theory or the von Mises criterion would be better ductile materal selection.

Yes the member is in both shear and bending. I agree with strucengnr, 0321 and fishercd on the domianace of the shear and bearing. Due to the size of the section I would consider it as a machined part and not a structure. Enshure you include appropriate allowable stress reductions for welding, fillet radius, size, and stress concentrations.

Cheers

 

[jheidt2543]

This is an aside to boo1's answer.

Why is a "machined part" treated differently than a "structure"? In this case a one member structure. And, for the same steel material, are the allowable stresses different? If so, where do I find that information?

I've always wondered what those &quot;Mechanical Guys&quot; (as in ME's) do for a living <G>.

 

[boo1]

I consider structural design more globally, with established design guidance of the code AISC body. I used the &quot;machined part&quot; terminology to differentiate there are other design consideration. Other stresses should be considered. The size 1&quot;x1.25&quot; section is made me think in that direction.

Cheers

 

[jheidt2543]

boo1,

Thanks for clearing that up, we're back on the same wavelength!

 

[trainguy]

At times like this, do what is what is productive. What is the value of shear stress, versus the allowable stress? If it's less than 10-15% of allowable, call it a day, and move on!
People pay us the big bucks to be practical, and efficient.
I would call that part a shear lug, by the way. If you want to get into details about the nomenclature of structure type, maybe you could get yourself a PH D or something...

 

[kreative]

hi train guy when u say 10-15% of allowable stress u mean allowable shear stress?

 

[boo1]

A design of 10-15% allowable then the loading would be insignificant.

Area=1.25&quot;
Fy=36,000 (assumed)
Shear=0.4 x Fy
10% ~ 1,800 lbs

 

[trainguy]

Kreative, I think you miss the jist of my post. Point is, if your stresses are on the low end, it's probably not an issue. OK, for the record, I meant allowable shear, because it's pretty apparent that any Von-Mises approach would give you a value very close to the shear stress alone.

 

[peteswift]

I have done some work stressing out short circular projections a long time ago.


The block will be in shear and bending:-

The maximum stress from bending lies on the top and bottom surface of the block and will be tensile and compressive. This will go from max to 0 at the neutral axis.

The max stress from shear lies down each side of the block and is a parabola with the maximum at the centre. Therefore where the bending stresses are at their maximum the shear stresses are minimum and visa versa. The area in between you can combine vectorally using mohrs circle or any other method.

If the height to dept ratio is less than 5:1 then bending will dominate. Work out the bending stresses ignore the shear. Yours is 1.25:1. In the practical world work the both out and add the maximums you know it will be ok.