Single Angle Support

[fholicky]

Hello All,

I'm new here, but I have searched through posts in the past. This has been a great source of information!

We support our equipment from single angle supports that are continuously welded on the top and bottom of the vertical leg of the angle. When the support is place on the customer's beam, there are shear and bending stresses applied to the angle. All of the literature I have found addresses the problem by accounting for biaxial bending, but I do not think that is relevant in my case.

Is the only way analyze this to take the shear and bending stresses produced on the horizontal leg and finding the resultant stress (square root of the squares of the shear and bending stresses)? Is there another way to analyze this?

Thanks for whatever help you can give!
Francis

 

[ishvaaag]

If you weld an angle this way for significant length to a beam web it must take part on any variation of the load status that happens after weldment. Your load pass to the beam and any other load applied or retired from the beam will force the welds and through them your angle seat.

Now, if you were a bit more precise maybe we could be of more help. For small loads the affection of the web must not be critical nor the impact on the overall beam but this can't be said with generality, torsion may appear, excessive rotation, even -who knows- some bad status at the connection, that normally your design practice must be generally preventing.

Respect the design of weld seats there are examples standing, so I would look at the AISC manual or some book of structural steel design, I for sure have these examples at some but may not comply with your code or ways.

 

[fholicky]

This is a quick sketch of what I am referring to. Let me know if this is helpful. I am hoping to be able to calculate and allowable load per inch based on thickness and material.

 

[BAretired]

I think you are showing the fillet weld at the bottom of the angle wrong.

For long spans, the combined section is likely critical in lateral buckling at the top of the angle.

BA

 

[DaveAtkins]

It appears to me you are designing a haunch or bracket, not a bending member. Is this true?

DaveAtkins

 

[fholicky]

I'm not showing the weld incorrectly. Our equipment resembles a cube and we weld support angles on two sides of the cube. We weld the support angles on the top and bottom of the vertical leg for the entire length of the angle. There should be no bending or deflection over the length of the support angle.

The support angle is then placed on parallel beams to support the equipment. What I am trying to ascertain is the allowable load per inch of support angle before I would need to reinforce the angle with gusset plates.

Thank you for all of the responses!

 

[InDepth]

If I am reading this correctly its just taking the leg of the angle and treating it as a plate in bending (???)

 

[BAretired]

Francis,

Sorry, I misread your drawing. I don't know which code you are governed by, but in Canada we use Limit States Design (LSD).

The factored moment for the horizontal leg of the angle is phi*Z*Fy where phi is a resistance factor of 0.9, Z is the plastic modulus and Fy is the yield strength of the steel.

Per inch of angle leg, Z = bt²/4 but b = 1", so Z = t²/4 in³ per inch.

So Mf = 0.9 * t²/4 * Fy

Mf is the factored moment per inch and includes a load factor of 1.5 for Live Load, so the allowable moment Mall = 2*Mf/3.

Hope I interpreted it right this time.




BA

 

[fholicky]

BA,

No problem about the drawing; I realize that this design case is not what single angles are normally used for.

What is the resistance factor accounting for?

Do I need to account for the shear in the angle as well (perhaps using a unity check such as Shear/ShearAll + Moment/MomentAll <= 1)?


InDepth,

Yes, the horizontal leg would be in bending like a plate, but I believe it is in shear as well.

I think, and please correct me if I'm wrong, that the only help the vertical leg of the angle gives me is when looking at the stress in the welds/base metal.


Thanks again for the help!

 

[KBVT]

You do not combine shear and bending stresses into a composite stress. The two are analyzed separately and capacity equations are provided in your respective code.

 

[BAretired]

The resistance factor accounts for uncertainty in the strength specified and varies for different materials. It is 0.9 for structural steel, 0.85 for reinforcing bars, 0.80 for bolts, 0.67 for weld metal and 0.6 for concrete.

Shear in structural steel does not have to be considered in a unity check, although that is true for high strength bolts. Shear is a very minor factor in your application and will not govern. Deflection might govern and should be checked.

The vertical leg of the angle is also in bending. If there is a point load at the tip of the horizontal leg, the moment varies from 0 to a maximum at the weld. The moment in the vertical leg varies from maximum at the bottom to 0 at the top. The welds share the vertical load, but the top weld also carries a horizontal load of M/b where M is the moment and b is the height of the vertical leg.

BA

 

[fholicky]

Thanks for the information.

If the vertical leg is also in bending, is the horizontal force acting on the top equal to the vertical load acting on the horizontal leg?

 

[BAretired]

If the force is at the tip of the horizontal leg and the legs are of equal length, then yes. If the force is at the middle of the horizontal leg, then the horizontal force on the top of the vertical leg is only half the force on the horizontal leg.

The moment in each leg is deemed to be equal where the two legs meet. That is not strictly correct, because the lower weld is not a pin, but it is close enough.

BA

 

[fholicky]

BA,

I understand what you are doing, but I am not sure that you can treat that connection as pinned. Isn't it closer to a fixed support? If so, do I need to analyze it differently?

I was thinking that I could check the angle for bending stress at the edge of the radius using the I section for the horizontal leg. I also thought that I could check the shear stress in the welds and call it a day???

Thanks again for the comments!
Francis

 

[ishvaaag]

Here you have a printout of one Mathcad worksheet for one of these angles supporting a beam. Goes along more or less with what you say not because of what BAretired refers to doesn't exist but because less relevant to the checks. Pay then also attention to that.

If you don't place support at opposed faces the angles will also see unequal loading by the weight and this would be better determined from some 3D FEM model.

 

[BAretired]

It is best to draw a free body diagram of the angle with all of the loads acting on it. In the attached sketch, H is the horizontal force acting on each weld according to my previous assumption.

It is not clear where the HSS reaction occurs, so I have assumed positions as shown. The moment and shear of the horizontal leg can be easily determined from the diagram.

The moment in the vertical leg varies from M at the lower weld to 0 at the top weld assuming each weld acts as a pin.

BA