From: Conrad Harrison
Sent: Monday, December 10, 2007
Subject: RE: Stair stringer design
for continuous kinked stringer
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
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
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!
From: Jim Wilson
Sent: Tuesday, 11 December 2007
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?