Semi-Circular Steel Veneer Lintel

[marinaman]

How many of you guys have designed semi-circular steel angle lintels?

I’ve got a building with several semi-circular openings in a row along a wall length. The openings are 11 feet wide....making the brick veneer arch 5’-6” tall above the spring line. There’s only 4’ Or so of brick wall between arches.

Being a curved member like this, I do not know of a good design guide by which to select the angle size.

I am also concerned about thrust. I’m concerned, not only about thrust of one lintel....but since these openings are multiple along a wall length, I’m worried there will be a cumulative effect of thrust.

The wall is TALL too. The wall is 24’ tall, veneered in brick, and backed in metal studs. Its a steel framed building...with the metal studs acting as cladding that backs the veneer. Windows in the wall are 11’ Wide with a circular top. The top of window is at 18’ and the spring line is at 12’-6”. I’ve got 8 of these windows in a row.

I’m thinking a 7” x 4” x 3/8” angle.....with the end at the spring lines horizontal to fit in the brick joint......but really, I’m working off the hip....and I’m concerned about thrust.

What do you guys think? Any good design guides out there that you know of. I’ve already looked at 31A of the BIA....they don’t really address this.

 

[jayrod12]

The thrust from each window cancel each other out at the intermediate brick piers, it's only at the ends of the walls that you need to ensure you've got enough capacity for the thrust load. Have you talked to any local masons or done some research into the old masonry arch type framing. It may be easier to just have them build a wood form and construct a masonry arch like the old days.

 

[WARose]

It's just like thrust from regular arching action (in the wall, over a opening): it has to be accounted for.

If you've got 31A....you've got one of the best resources out there. Most of the rest (for masonry) are built around the resultant never getting outside of the middle third/kern (i.e. "minor" arches). The design of supporting (curved) angles is another one where there aren't many resources. When I did commercial work I did this a few times. You just have to model it, check the stresses developed (keeping in mind that this is a curved beam: the normal flexural formula isn't applicable), checking buckling, and support reactions (including thrust). I'm not aware of any start to finish reference that does that.....it's knowledge from several different areas.

 

[dhengr]

Marinaman:
The roll formed stl. angle lintels provide a nice clean finished surface for the underside of the arches. They provide a nice clean, well defined surface on which to start laying the brick arch, but they are probably not sufficient for the initial arch masonry work by themselves. They are just too flimsy without extra bracing. Then, when the full arch (half circle) is built, they are probably not really needed any longer, from the structural standpoint, as the arch is basically self-supporting if designed and built properly. Shallower arches may need the stl. lintel from the structural standpoint. The same basic thrusts will exist whether you use the stl. lintels or not, and as Jayrod12 suggests, the interior thrusts cancel each other, and only the two end thrusts need special attention. The exception to this is during the building or if a window opening arch ever needs repair, etc., then you will have interior unbalanced trusts which need attention. The 4’ intermediate piers and the stl. stud back-up need special attention since they take all the vert. and lateral loads from the 15’ sections of wall and window openings, and some extra horiz. framing is needed to get the lateral loads over to the piers from the 11’ window openings. Some additional ties are likely desirable around the arch, and btwn. the brick veneer and the back-up to keep things well tied together. Take a look for some Brick Industry Assoc. (BIA) Tech. Notes on veneer and arch design and construction. Also, take a look at your regular Structural Engineering textbooks for basic arch design considerations.

 

[WARose]

The same basic thrusts will exist whether you use the stl. lintels or not, and as Jayrod12 suggests, the interior thrusts cancel each other, and only the two end thrusts need special attention.

I would disagree that they "cancel" out. Maybe in terms of overturning or (net) shear......but in terms of anchorage and the compressive force in the bond beam: no. The last time I did this, I remember specifically reinforcing one of the bond beams for the compression (as a column). If it doesn't have out-of-plane support at that point.....it can get slender fast.

@marinaman: You may run across a book called 'The Masonry Arch' by Jacques Heyman (from 1982). It's a pretty good one, but it doesn't address this situation.

 

[dhengr]

WARose:
“cancel out” may have been a bad choice of words, ‘are essentially equal’ may have been a better phrase. Except that Jayrod12 and I were talking about the overall loads/forces in/on the wall and the fact that those arch trust forces must be reacted (counteracted, in the case of an adjacent arch) by sufficient wall structure around them. I (we?) never intended that internal wall forces/stresses caused by the arches should be ignored in the wall design. But, that the thrust from the last arch needs sufficient wall length beyond the arch (or some such structure) to react the thrust from that arch.