A few weeks ago, a few of us headed to South Carolina to represent Chicago Metal Rolled at NOMMA’s Annual METALfab event. NOMMA, the National Ornamental and Miscellaneous Metals Association, is the trade association for the ornamental and miscellaneous metalworking industry. Each year, ornamental metalworking leaders and gurus gather to discuss the latest in the industry from intricately-designed railings and gates and complex structural jobs.
This year, circular staircases proved to be a trending topic and many attendees were interested in learning about how to curve stair stringers. Stair stringers are the main structural support for staircases and can be tricky if you’re looking for a specific curvature and rise.
When designing a stair stringer, keep these three tips in mind:
- Analyze designed radius vs. section modulus of the specified member to minimize distortion or rippling.
- Single rolled plate is the most cost effective for contemporary applications.
- Tube stringers will always be curved using stuffing – a steel member stuffed inside the tube – in order to maintain congruency. This makes the stringer heavier and should be taken into account when engineering load calculations.
When complete, stair stringers are a magnificent, structural focal point. Here is a great example of a stair stringer with a rustic, unique application in a state park. However, the original designed proved difficult for bending because it specified the use of hollow structural steel. Due to the extreme radius, we instead used a four-piece construction of ½” A588 steel plate rolled to a 12’9” inside stringer radius at 36.82 degrees and an 18’4” outside stringer radius at 28.16 degrees. After welding and grinding the plate, the final product resembled stringers made with an 18×6 tube.