"Pete Keillor" wrote in message
...
On Thu, 3 Jan 2013 07:27:37 -0500, "Jim Wilkins"
wrote:

"Jonathan Banquer" wrote in message
news:fc6ef649-61d0-4b27-b953-
...It's why most engineers can't machine their way out of a
paper bag. Like you, they think they're smarter than real
machinists
and that their smarts can make up for the experience of cutting
lots
and lots of different parts made out of different materials. Here
is
a
news flash for you bubba... it can't.

That certainly wasn't the case at Segway where the engineers
monopolized the CNC machines and forced me to use the manual ones.

The flip side is machinists with no clue about Statics or Dynamics
who
take shortcuts like this one that caused the Kansas City Skyway
collapse. In case the explanation isn't clear, the threads bore the
load meant to be carried by the core of the rod. Unless the coupler
has been carefully dimensioned to stretch at the same rate as the
rod,
the threads will fail progressively inwards from the ends at a load
far below the rod's tensile strength. Nonintuitively a thicker
coupler
makes a weaker connection by concentrating the load on the first few
threads instead of distributing it over all of them. I learned this
from a lecture by the accident investigator.
http://www.churcharchitect.net/1142004.htm

jsw


See the Wikipedia article.
http://en.wikipedia.org/wiki/Hyatt_R...lkway_collapse

It's interesting to note that yes, the contractor suggested a
modified
design to enable actual construction of the walkways in the field
which finally led to the collapse, but the engineering firm made the
original dumbass design that created the need for some type of
modification, the original being hanger rods threaded all the way
from
the second floor walkway to the fourth floor walkway, and
secondarily,
support beams welded from two channels to make a box beam, with the
hanger rods passing right through the welded seam, the weakest point
on the beam.

Plenty of blame to go around on that one.

Pete Keillor

IIRC the fabricator didn't have enough clearance around his lathe to
turn the rods in one piece, and didn't want to sub the job out. The
full-length rods were also expensive/difficult to transport.