From: Conrad Harrison <sch.tectonic@bigpond.com>
To: seaint@seaint.org
Sent: Monday, December 10, 2007 11:55:57 PM
Subject: RE: Stair stringer design for continuous kinked stringer
Jim
Sounds like a simple plane frame. I'm assuming it's a two element cranked beam with supports at either end, and no internal support at the crank.
If it has one pinned support and a roller support then it is determinate, and not much more complicated than a simple span beam: straighten it out for analysis if it makes it easier, adjusting the loads accordingly. If both supports pinned, then it is indeterminate then need to employ methods for indeterminate structures: slope-deflection or moment distribution etc. Alternatively may find a suitable rigid-frame formula in Kleinlogel or Roarkes, failing that see if can find a simple plane frame program.
As for the proper way: any method which produces a robust design-solution which has acceptable level of performance, minimum risk of failure, and when pushed to failure fails in an acceptable manner, is the proper way. So a simplified model can be used as long as there is compatibility of assumptions through out the design.
Therefore would treating the angle joint as a pinned joint result in collapse? Can the platform be considered as a cantilever propping the end of the stringer? Having sized members assuming pinned joints, what is the effect of inserting a redundant rigid joint? Having used a simplified model, what effect is using a more realistic behavioral model going to produce, given that the load inputs could be considered fictitious? Does the application warrant "accurate" calculation of deflection and natural frequency? Is a more accurate analytical method required for safety, or is it simply required to reduce material content and possibly robustness in the process?
Though the real solution struck me as maybe a need for getting a good rest!
Regards
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic@bigpond.com
Adelaide
South Australia
From: Jim Wilson [mailto:wilsonengineers@yahoo.com]
Sent: Tuesday, 11 December 2007 02:07
To: seaint@seaint.org
Subject: Stair stringer design for continuous kinked stringer
What is the proper way to analyze/design a steel channel stair stringer when the stringer is continuous from the angled riser through to the end of the level platform? There would be a laterally braced full pen weld at the angle point.
Is this just a simple span beam calc for the full length? Or is there another way to model the angled section with simple methods?
Jim Wilson, PE
Stroudsburg , PA