Veneer relieving/shelf angles

[anchorengineer]

Hello,
I'm designing a shelf angle for brick veneer. I'm going to anchor this angle with post installed anchors at specific intervals along the span. The bending capacity is not a concern to me (Although I will check bending along the angle and shear at the anchor points). It is the length of the horizontal leg that I'm worried. After reading through BIA 31B it seems I just need to make sure that the deflection of the horizontal leg is less than 1/16". I'm still going to check the horizontal leg as a cantilevered beam fixed at the wall and check for bending and sehar as well. Does this make sense? Any suggestions?
Thanks!

 

[RHTPE]

What kind of structure are you anchoring the relieving angle to? I would strongly recommend the use of cast-in-place anchors if the structure is concrete. I have little faith in post-installed anchors for applications such as this.

Just my NTBH opinion.


Ralph
Structures Consulting
Northeast USA

 

[BAretired]

What do you mean by NTBH? And why do you use such silly acronyms, knowing full well that nobody understands what they stand for?

BA

 

[BAretired]

Why is it important that the deflection not exceed 1/16"? Why is this a necessary requirement? If it is, what is the problem in calculating the deflection? What is B1A 31B?

BA

 

[RHTPE]

Sorry BA - I despise acronyms also, but every now & then I like to make people scratch their heads. NTBH = never to be humble. I'll have to consider adding a definition to my signature.

Ralph
Structures Consulting
Northeast USA

 

[BAretired]

I never would have guessed "Never to be humble" in a million years, but thanks for the clarification.

BA

 

[DaveAtkins]

Yes, check for bending as well as deflection (I doubt shear will control).

DaveAtkins

 

[NateB]

Looks like BIA 31B addresses two issues:
1) Deflection is limited to L/600 or 0.3"
2) Torsional rotation is limited to 1/16" (not sure how that is measured)
Since you are anchoring back to a structure it would seem that the angle will be supported at regular intervals, making the deflection and torsional movement minuscule. Unless your steel thickness is thin, bending in the angle leg should not be an issue, but can be checked.

Nate

 

[anchorengineer]

I'm assuming that if your deflection is less than the 1/16" that means rotation/torsion is ok. Is this correct?

 

[BAretired]

A shelf angle will deflect and rotate. The rotation, expressed in radians, multiplied by the length of the outstanding leg will give the displacement due to rotation. That, added to the deflection will give the maximum displacement.

BA

 

[steellion]

Design the angle leg for local bending and deflection. If it is flush against the wall as I'm picturing it, torsion will not be a concern.

You also have to design the angle globally as a beam spanning between anchors.

 

[southard2]

I've always found the single angle design portion of the steel code confusing with respect to definitions. So in my practice I usually will size the brick ledger angle per the load tables published by BIA. Then to eliminate the possibility of torsion I'll use post installed anchor bolts at 2 to 3 ft on center. This way I have a bit or redundancy also.

I didn't know this until recently but if this is a constant horizontal support such as around the perimeter of the building you also need to specify a bit of a gap between steel ledger angle pieces since they too will expand and contract horizontally with temperature change. Not such a big deal in Florida but I imagine farther North it becomes a pretty important detailing consideration.

John Southard, M.S., P.E.

http://www.pdhlibrary.com

 

[VTPE]

AISC publishes a guide for single steel angles. In that it talks about bending of angles abotu axes other than the primary axes (which is what you are describing). Basically, you take the elastic deflection and multiply it by 1.86. This accounts for lateral torsional deflections of the angle caused by loads applied to secondary axes. If you limit that deflection to L/600 or 0.3", you will be OK.

One thing I often do is use a small W4 or a channel bolted to the wall every 6' or so then bolt an L4x3x3/8 angle to that. This accomplishes things:
1.) It reduces the amount of cold bridge through the envelope and thus the amount of potential serviceability problems.
2.) It reduces the outstanding leg and potential for deflections and rotations, and
3.) You can put horizontal slotted holes in the W4 and vertical slotted holes in the angle with class A finishes that can be tightened down slip critical. The combination of hoizontal and vertical slots allows for field adjustment. Bolting preserves any galvanizing. Slip critical design precludes failure in the direciton of load.