Understanding Arches - Lintels Carrying Masonry

[Hunter90]

Hi everyone,

I was asked by the architect to design a 13.5 ft steel angle lintel to carry brick loading with an arch height of 1.5 ft above horizontal (see picture above). I took 37psf brick loading and calculated the centroidal point load of the distributed brick loading and placed it at the center of the span.

When analyzing this condition with both ends fixed (enabling to act as a true arch with thrust on each end binding the arch), the horizontal forces appeared too large to transfer down. The arch sits at 12 feet high with brick veneer columns on each end of arch) situated at the entrance of a home. I tried designing a concrete column within the brick veneer encasement, but the moment due to lateral thrust is quite large. I was able to design a cantilevered concrete column with enough rebars on the tension face to resist the thrust, but the column sits on slab on grade. The slab will not be able to take that moment, and a large subgrade footing would be required in my opinion (keep in mind I am an E.I.T w/ 2 years experience and our office is lacking a senior structural engineer).

Reconsidering my options, and reading up on some books, I realize if we can create a roller condition (as shown in the image above), then we can design the angle to take all the bending (removing the arch resisting mechanism). This I believe is a much more economical solution as we can design a curved angle to take the loading. [highlight #EF2929]The question is, how do you create a roller condition on one end of the angle which will rest inside veneer bricking?[/highlight] Do you just have it embedded the minimum distance and have it grouted? And when it comes to the ultimate loading, the grout would crack and "roll" out laterally?

Any input would be much appreciated.

Thank you.

 

[JAE]

For an arch like that, and not having adequate wall (buttresses) on each side to take the thrust, I'd hang the angle from structure above (hangers behind the brick veneer).

Curved angles spanning 13.5 ft. look like trouble to me - and you'd need to keep the deflection down to avoid excess cracking.
Angles, with top extended legs in compression at the tip are prone to buckle as well.

 

[Hunter90]

thank you Jae, your input is much appreciated. I will consider how to hang the angle as well and yes, lateral torsional buckling is the other factor needing to be considered.

 

[SlideRuleEra]

Hunter90 - An arch 13.5' long with a rise of 1.5' is not too deep. Perhaps you can have a beam-that-looks-like-an-arch fabricated from steel plate. Use brick veneer on both sides. Just a thought for a work-around solution.

 

[Hunter90]

Thank you SlideRuleEra, that is a good idea, so you would load the top plate to hold the brick above, and do an in-fill from bot arch plate to top plate.

I will see if this can be done, but the $$ is always the driving factor for these light residential construction jobs. Possibly I could run a top horizontal angle and a curved angle running parallel below to pick up the infill (basically taking your flanges and replacing with an angle each).

 

[mfrad]

Try a tied arch. Use an angle at the bottom.