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Re: Beam Analysis

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Tom,
Rather than trying to figure out the method of Enercalc - which I doubt that
Mike Brooks would care to share, I would make the following guess as to how
I would set it up:

1. Using the standard load formulas for multiple concentrated load,
trapezoidal and uniform loads, develop the formulas where the loads ARE NOT
continuous along the full length of the beam.
2. You will need conditional statements to handle the conditions based on
the location of the start and finish point of the load so that the
conditions that trigger various conditions in the beam calculations based on
the load location is tested. This does not have to be an iterative process
and can simply be done by establishing a simple flow chart and using the
path as the conditional.
3. Treat each load condition as a separate beam. The shear, moment and
deflection are additive at each point along the beam.
4. Break the beam into say 100 points along it's length so as to calculate
the shear, moment and deflection at each of the points and apply
conditionals to pull out the maximum values. This table is easily used to
graph the results as well.

The trick is insuring that you have sufficient size spreadsheet to
accommodate a decent number of load conditions.

I have been teaching this process to my students at College of the Desert.
Their problem was that they could resolve a problem with multiple
concentrated loads and another with multiple uniform loads, but were lost
when the conditions were combined. I ran through the problems at various
points along the beam and showed them how to developed the formulas using
a,b, and c (etc) for the individual distance between loads and start and
finish points of other loads. In uniform loads, I used a prime condition
(ie. a') to represent the changeable dimension. This allowed them to
understand that while within a uniform load, you treat the moment arm
slightly different than if you were outside the uniform load. This seemed to
work and they are having less problems. The point is that it was obvious
that the build up of the formulas allowed the students and me to see the
logic and relationship as we moved further to the right of the beam. The
resulting formulas would simplify the programming steps and logic.

It does get cumbersome, but when you consider the additive nature at each
point on the beam, you are not trying to solve for the exact moment or
deflection, but you are increasing the accuracy as you increase the number
of points on the beam.

If this does not help, go to the spreadsheet forum on the Structuralist
professional page (http://www.structuralist.net) and take the link on the
left side of the page to the spreadsheet forum. Graphics can be use as can
links to sample spreadsheets where we can work through the problem.

Hope this helps you.

Regards,
Dennis S. Wish, PE
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From: "Tom VanDorpe" <tvandorpe(--nospam--at)vcaengineers.net>
To: <seaint(--nospam--at)seaint.org>, <bpolhem(--nospam--at)swbell.net>
Subject: Re: Beam Analysis

Bill, thanks for your responce, but I need to develop a beam program to work
with our other in-house software.

So my question is, how do beam programs like Woodworks and Enercalc
calculate stress and deflection for general loads? Is it a numerical
integration?

Tom VanDorpe
VanDorpe Chou Associates, Inc.
(714) 978-9780