Combined Shear and Tension Stress 3

[RFreund]

This is probably a lay-up for someone. However I'm having a brain-shart. If you want to check a plate for combined shear and tension how should the stresses be combined?
For example a pair of plates connecting a beam to a column for a fixed for torsion and moment end condition. Is the combined stress check for the plate fv/Fv + ft/Ft ? or should they be squared? Also is the required force on the weld at the column and plate interface equal to F=sqrt(T^2+V^2) or should it just be the sum of the magnitudes?
Is this referenced in AISC or Salmon and Johnson...I feel like I have read more on this than I am recalling.

Thanks again

EIT

 

[jrw501]

Fy^2 = k^2(ft^2+fv^2)
k-->5/3 (safety factor)

1 = k^2(ft^2+fv^2)/Fy^2
Ft = 0.6Fy
Fv = 0.4Fy

(5/3)^2*[(3ft/5Ft)^2+3*(2fv/5Fv)^2]=1
(ft/Ft)^2+(4/3)(fv/Fv)^2 = 1

 

[jrw501]

First and second equations should say Fy^2=k^2(ft^2+3fv^3) and 1 = k^2(ft^2+3fv^2)/Fy^2 respectively.

 

[rb1957]

Ft = 0.6Fy
Fv = 0.4Fy


is this standard ? to say that the allowable tension is 60% of Fty ?

 

[jrw501]

It was for ASD as far as I know. I'm a young'n though, so I'm a bit more familiar with LRFD.

 

[RFreund]

The power is finally back on at work so I will post a sketch tomorrow.

jrw , rb1957 - Are you guys assuming that the stress in the perpendicular direction is zero with these equations?

Also does any one have an example or a reference that shows the von mises being utilized in design. I mean I think I understand the it but I would like to see an example. Basically determine the principle stresses in 3-directions and put them in the von mises equation?


EIT

 

[rb1957]

yes, for simplification

my last post was questioning limiting tension stresses to 60%fty (ie Ft = 0.6fty) ... looks very conservative. a thought is maybe your codes say when you have combined stresses, apply 60%Fty as your allowable ... if so, to me that's saying in lieu of a complicated combined stress equation, using 60%Fty is an acceptable alternative, else "fll your boots" and do to complicated combination (but then i'd use Ft = fty).

 

[jrw501]

Ft = 0.6Fy is the ASD equation for allowable stress for the tensile yield limit state.

Fv = 0.4Fy is the ASD equation for allowable stress for the shear limit state.

So it's not already accounting for combined stresses, but like I said, I'm not 'that' familiar with ASD, particularly with respect to how those equations were developed.

 

[RFreund]

Attached is the sketch of the connection I had in mind. I Suppose you could just weld the beam to the column all around however if you did use the plates - would the stresses be as rb and jrw have noted above?

rb and jrw - In the equations you have posted what "happens" the stress perpendicular to the normal stress ft?

Also any advice on a reference to an example problem involving von mises?

Thanks.

EIT

 

[RFreund]

My bad.

EIT

 

[rb1957]

we were "just" looking at a simplified von Mises stress with s1 and v. if your "perpendicular" stress is in-plane then it'd be s2. you can still calc von mises stress, as per the original formula. i can't comment on what your allowable would be, i'd've assumed fty (but i don't know your codes).

FWIW (which ain't much) i'd've assumed your gusset was effective in carrying in-plane shear only. if you want other loads to be reacted here, i'd provide other gussets (on the upper and lower caps, to provide a loadpath for torque and bending)

 

[BAretired]

Forget about von Mises. Take the shear in the vertical weld and the moment and torque in the horizontal plates.

BA