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RE: Golf Course Bridge

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Well-spoken Mr. Turk,

The myth was most certainly perpetuated in my college by the very same
vicious and misinformed rumor within the Undergrads of our school of
engineering.  I have to admit that the coverage for Influence Lines in our
Structural Analysis class was limited to about a 1/2 hour of class during
the last week of school with no assignment to reinforce it.  I think this is
just a small symptom of the larger problem that 4 years is just not enough
time for a degree in Structural Engineering, but that is just my opinion.  I
am convinced that I gained more during that additional year of class work in
Graduate school relative to understanding Structural Engineering as a whole,
than the previous 4 years of being an undergrad combined.  But then again,
NOTHING compares to actual work experience!



Scott C. Bernard
Structural Engineer
Universal Building Specialties, Inc.
210 Neptune Rd.
Auburndale, FL 33823
Phone: 800-282-9583
Fax: 863-967-1082
E-mail: scott(--nospam--at)ubsdesign.com
World Wide Web: http://www.ubsdesign.com/

-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Tuesday, June 05, 2001 2:53 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Golf Course Bridge

Bill Cain wrote:

. > Of course, since the EIT after your signature on a prior posts indicates
. > that you have probably been educated since advent of the frequent use of
. > the computer for structural analysis, you may not have learned influence
. > lines. Refer to most any text on indeterminate analysis such as Norris
. > and Wilbur or Kinney for a discussion of this technique. It will give
you
. > a much better feel for the structure than reams of computer printouts.

Amen!!!

When I last taught structural analysis, I decided not to use the term
"influence lines," because horror stories about how hard influence lines
were
had frightened the students.  (Probably the difficulty of influence lines
was due to the teachers' lack of experience in creating them.)  Instead,
after we had finished shear and moment diagrams, I gave (amid groans) the
students an assignment to calculate the shear and moment at each 1/10th
point
for a 1 kip load as the load moved across the beam from 1/10th point to
1/10th point and to put the results in a table.  Before the next class
period, one of the students stopped by my office and asked if we were going
to study influence lines; that she had heard that they were "really hard."
I
told her that she just did.

The derivation for maximum moment due to a series of concentrated moving
loads is/should be derived in any elementary strength of materials or
elementary structural analysis text book and it is, essentially, as Bill
describes, i.e., for a simply supported beam, the centerline of the span is
placed half way between the resultant of the concentrated loads and the
concentrated load below which maximum moment will occur.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

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