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RE: Stair stringer design for continuous kinked stringer
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- Subject: RE: Stair stringer design for continuous kinked stringer
- From: "Bill Allen" <t.w.allen(--nospam--at)cox.net>
- Date: Tue, 11 Dec 2007 08:11:34 -0800
Conrad –
You just provided the perfect definition of an engineer: One who takes something simple and makes it complicated. I hope your not billing for all those hours when your designing stair stringers.
:o)
T. William (Bill) Allen, S.E. Consulting Structural
Engineers -----Original Message-----
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(--nospam--at)bigpond.com Adelaide South Australia From: Jim Wilson
[mailto:wilsonengineers(--nospam--at)yahoo.com]
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 |
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