Lintel Angle

[McEngr]

If I am designing a lintel angle for a masonry opening that does not have enough arching action to support its own weight, how do I design the lintel for torsion? I've looked at my textbooks and Salmon & Johnson don't go into this - especially for ASD design. Also, is there a source for this type of practical problem? Thanks,

McEngr

 

[McEngr]

Also, I have a few masonry books that define the limitations of when a lintel beam needs to be designed, so please don't go on tangents. I just want a solution.

Thanks.

 

[scottiesei]

I've done this quite a few times. HOWEVER, I usually use 2 angles, one on each side. Typically for the spans and loads that I designed for, the angle was much stronger than what was required. If you have a relative small opening with a moderate amount of loading, you may be able to sell the fact that the angle you are using is much stronger than what is required and neglect the torsion. What is the application? There may be other alternatives.

 

[scottiesei]

Also, we typically bolted the angle through the masonry at 24" intervals. That helps resist the angle twisting out.

 

[kevo_55]

Also, we typically bolted the angle through the masonry at 24" intervals. That helps resist the angle twisting out.

scottie is right. By bolting directly to the masonry every so often you'll effectively eliminate your torsion on the single angle.

As for the no bolting option, the masonry will act at it's centroid on one of the legs of the angle. The distance between this point and the angle's shear center will be your moment arm for the torsion.

I believe that you can get the rest..... just do a little Tc/J and take a look at page 5-310 of the ASD and you're done.

 

[lavadave]

If you're using a single angle be very careful about the lateral bracing of the angle or it will deflect sideways. The deflections for single angles can easily be more than you'd anticipate.

 

[McEngr]

I've done this quite a few times. HOWEVER, I usually use 2 angles, one on each side. Typically for the spans and loads that I designed for, the angle was much stronger than what was required. If you have a relative small opening with a moderate amount of loading, you may be able to sell the fact that the angle you are using is much stronger than what is required and neglect the torsion. What is the application? There may be other alternatives.

I'm surprised you're allowed to get away with this. It seems that Architects don't want the angle to be shown. If you put it on both sides, wouldn't someone complain?

 

[McEngr]

Also, we typically bolted the angle through the masonry at 24" intervals.  That helps resist the angle twisting out.

scottie is right. By bolting directly to the masonry every so often you'll effectively eliminate your torsion on the single angle.

As for the no bolting option, the masonry will act at it's centroid on one of the legs of the angle. The distance between this point and the angle's shear center will be your moment arm for the torsion.

I believe that you can get the rest..... just do a little Tc/J and take a look at page 5-310 of the ASD and you're done.

Well, conventionally, don't you need to design the angle for bending then? If so, then it seems that only small openings would suffice. That brings up another question, even if I'm designing for bending about the shear center, is it as easy as using the section modulus for stress? What do I use in chapter F for the allowable bending stress? Thanks.

I'm in metal buildings... I plan to go into consulting if you've noticed my posts lately. I've got an unusual situation here where we are providing the lintel angles on a project in our metal building package.

 

[kevo_55]

McEngr,

You're right you also must design for bending. I thought that you were just worried about torsion.

For bending you'll be designing for bending about the geometric axis. (Use the section which starts on 5-309 of the green book) Be careful about your units with EQ 5-4 and be sure to also check your local effects in 5.1.

Of course, if you bolt to the masonry you'll really cut down on your Lb which helps with your length effects. :beerchug

As for moving to a consulting firm, I highly recommend it. It doesn't matter what you do, but you'll be out of the "sales mentality" situations. I was in this type of company for my first 3 years of employment and have since moved to consulting. It isn't for everyone, but I seem to like consulting better.

 

[scottiesei]

For the aesthetics, well it depends on your finishes. You can easily cover an angle by gyp or stucco. If you are supplying large amounts of headers, you may want to look into something called powers steel lintels. I typically use angles for a fix.

 

[McEngr]

McEngr,
You're right you also must design for bending. I thought that you were just worried about torsion.

For bending you'll be designing for bending about the geometric axis. (Use the section which starts on 5-309 of the green book) Be careful about your units with EQ 5-4 and be sure to also check your local effects in 5.1.

Of course, if you bolt to the masonry you'll really cut down on your Lb which helps with your length effects.  :beerchug

As for moving to a consulting firm, I highly recommend it. It doesn't matter what you do, but you'll be out of the "sales mentality" situations. I was in this type of company for my first 3 years of employment and have since moved to consulting. It isn't for everyone, but I seem to like consulting better.

Thanks kevo and scottie, you guys have been very helpful. Seeing as how I'm in metal buildings, I feel like I couldn't offer much help to you except for what the exam reference material provides. Oh yeah... and I suppose that I'm pretty proficient in wind/seismic for low-rise. I know that there's a lot out there that I don't know yet.

Still waiting on results... :wait

 

[kevo_55]

McEngr,

Don't worry man about the metal buildings gig. Each engineer will have their own strengths and weaknesses.

Ha! I have no strengths test-wise. I work in an engineering consulting firm doing curtain wall (cladding). I had to learn everything for the exams because I work with aluminum, stone, and glass all day. :tone:

Good luck on the job hunting by the way! rayers:

 

[lavadave]

McEngr

Maybe you could be a little more specific about the problem your trying to solve. Is this a loose lintel? Is it supporting brick or CMU and how thick? I really don't think a single angle is a good idea unless there's no other choice.

 

[McEngr]

McEngrMaybe you could be a little more specific about the problem your trying to solve. Is this a loose lintel? Is it supporting brick or CMU and how thick? I really don't think a single angle is a good idea unless there's no other choice.

It's a metal building with multiple openings for 6040 windows and 3070 walkdoors. The gabled endwalls are bearing shearwalls that will support the metal building purlins by means of a ledger angle. This is pretty common, but I guess I'm not sure about how to design for the leg of the angle by means of thickness. This is the way I've done it before:

Reaction x distance from half the leg = Moment.

S = (1ft increment) x t^2/6

Fb = 0.6 x Fy

Check to make sure fb is less by using M/S and making sure it has a decent, safe margin.

I was unaware of page 5-312 leading up to 5-319 of the ASD book. This is invaluable information! I hope that my designs in the past haven't been largely underdesigned by my afforementioned method (this is for ledger angles for purlins only).