Subject: Spheres on Power Lines
From: rwwaitt@aol.com (RWWaitt)
Date: 23 Oct 1996 22:40:50 -0400
As an engineer who has spent most of the past 22 years designing overhead
transmission lines, some of which have included some sort of marking, I
have read the recent string of posts with interest. A few notes:
1 - Material & Size
These markers are usually fiberglass balls, but I have seen some that were
of different shapes or materials (not aluminum, as one posting indicated).
Diameters range from 20 to 54 inches, with the 30 inch size most commonly
used in our area (Eastern Washington and Northern Idaho, in the USA).
They are available from several manufacturers, including Tana Wire Markers
and PR Industries.
Most are opaque and are available in red, white, and international orange.
One company (Aussie Flash-Light) supplies a marker which has an internal
flashing mechanism to make them visible at night. We haven't used this
type, and I can't comment about what happens if the power goes off.
2 - Reason
Markers are usually used to identify lines for aerial navigation, but not
only around airports. The state of Washington (and the FAA, as I remember)
requires their use anytime a line is over 150 feet above the ground. In
our area this usually means river or canyon crossings where aircraft may
be crossing or near the line.
The smaller balls may also be used in areas where FAA or local codes do
not require lines to be marked, but where experience may have shown that
some sort of marking is in the public interest.
These balls may or may not be used in conjunction with red-and-white bands
painted on the adjacent supporting towers.
They are **not** used to control vibration, although vibration damping
devices are sometimes attached to the line wire at locations close to the
marker balls.
3 - Location
Balls may be attached directly to the line, either to the conductors
themselves or to steel cables located above the line conductors ("static",
"shield", or "overhead ground" wires). Alternately, they may be located on
a separate, single steel cable offset a couple of hundred feet laterally
and parallel to the line conductors.
4 - Attachment method
If possible, these balls are installed at the time the wires are pulled
into place. Alternate methods include a couple of those already mentioned;
a lineman sitting on a board attached to a helicopter's landing struts, or
working on the ground from what the linemen call a "bucket truck", or
"cherry picker".
Considering the alternatives, helicopter application is a safe and
economical method for an existing crossing. Our company (Washington Water
Power) used the services of an aerial applicator to install balls on a
crossing of the Columbia River near Chelan, Washington.
These balls are usually attached to the conductor or overhead cable with
clamps or preformed wires which wrap around the conductor. One half of the
ball is attached to the conductor, then the second half is bolted to the
first.
5 - Lifetime
Unless they are damaged by some external action (the line falling down,
trees falling across the wire, or gunshot damage), fiberglass balls are
permanent. Some of ours have been in service for 25 years or longer.
One exception to this is an occasional, unpredictable experience of
spontaneous burning of fiberglass balls which have been attached directly
to the line conductors. The fiberglass itself burns and falls to the
ground, and all that remains on the wire is some soot and the metal
attachment hardware. (I would be very interested in discussing this with
anyone who has had a similar experience.)
6 - Personal
I may be contacted by e-mail, at work:
dwaitt@wwpco.com
or at home:
rwwaitt@aol.com
Subject: Re: WARNING to all NON-LICENSED ENGINEERS
From: Bob Falkiner
Date: Thu, 24 Oct 1996 00:09:27 -0400
In Canada, accredited universities offer engineering courses that
qualify for acceptance against P.Eng. qualifications. Don't take them,
then don't get the P.Eng.. IE it is self regulating, as no engineering
school can afford to become non accredited, so there is 100% compliance.
John Bower wrote:
>
> On the one hand, I can agree with the concept of licensing of
> engineers. In fact before the turn of the century there were mmany
> individuals portraying themselves as engineers who clearly were not.
> (there was a similar problem in the medical profession).
>
> On the other hand, why don't I, or many other graduates of accredited
> colleges, such as but not limited to Stanford, MIT, Cal Tech, Leghigh,
> Cornell, Princeton, Georgia Tech, RIT, Texas Tech. Drexel, etc. etc.
> and graudate with BSEE, BSME, BSChemE, etc. qualify as engineers?
>
> Does some P.E. out there mean to tell me that their a more
> knowledgeable engineer with his/her license and an undergraduate degree
> from a state college than say a person with their Phd, Masters and
> Bachelor degree from MIT. I think the most appropriate answer is
> "probably not".
>
> I think this is more a case of the engineering societies trying to grab
> for more membership or presitige than concern for people "posing" as
> engineers and causing problems. If this were not the case, then I could
> see no reason why achieving a passing grade from an approved college
> does not qualify you as some level of "engineer". Certainly why I was
> in school (one of the top engineering schools in the U.S., there was
> little emphasis on taking the EIT's. What it sounds like to me is that
> these societies are trying to force me into unemployment, and guess
> what, that pisses me off! I hold 5 U.S patents, several foreign patents
> and can calculate as well as many of the P.E.'s that I have worked
> with. This is a selfish grab for more power as I see it. It would be
> different if the engineering schools pushed the idea of the tests like
> law schools stress the board exam, but they don't.
Subject: Re: WARNING to all NON-LICENSED ENGINEERS
From: "C. Wayne Parker"
Date: Tue, 22 Oct 1996 15:10:38 -0400
Peter Carmel wrote:
>
> You know, I've been following this thread from the beginning, and I can't
> help but smile at all this. You PE's fail to acknowledge that the term
> "engineer" is not used the same as "doctor" or "lawyer", and never has.
> History is against you. It is unfortunate that garbagepeople want to be
> called sanitary engineers, but that is what we have. My suggestion is that
> we simply ridicule people who choose such titles, that will shame them into
> using more accurate job titles.
I appreciate Peter's comments, however allowing free and frequent use of the title
"Engineer" before the public will make the term meaningless. It's like marking all
paperwork "Urgent": pretty soon, nothing is urgent and all is routine. I know you're
not suggesting that everyone be called some type of engineer, but it should mean
something when it is used.
> Fact is that most engineering work is done by non-registered engineers. All
> work that may endanger human life requires a PE to approve the plans, and
> rightly so. From my point of view, a PE simply serves the function of
> licensing and standarization. If your design is faulty, we can find you.
> What is the problem? The problem is ego. A PE doesn't make you a "better"
> engineer.
"Simply serves the function of licensing and standardization"? Ouch! Don't forget
about proof of some acceptable level of qualifications (beyond squeeking through
engineering school) and legal acceptance of responsibility. I doubt few non-P.E.s, if
any, have taken out liability insurance. People who have adopted the title "Engineer"
for themselves, with some preceeding descriptor, have probably done so because it makes
them and their job seem more important. Who's ego is really at work here? Kinda makes
you wonder doesn't it? You're right: a P.E. doesn't (in itself) make you a better
engineer; what it does do is legally make you an Engineer.
> I'm in the HVAC field, working as a sales rep. I have an ME degree from an
> accredited university, 13 years of experience, and am a full member of
> ASHRAE. I work with engineers all the time, in their offices, and on the
> phone. They call me because they know I have detailed knowledge of what I
> sell, and that I can often prevent costly mistakes. My job title is "sales
> engineer", and I will defend that title, even though some others who do
> similar things (without the degree/experince) also call themselves that. I
> think that those who have no degree/and/or/experience know that they are not
> engineers. There is no confusion. Just ego.
You have disproven your own case, Mr. Carmel! You say both you and others, who have no
degree/and/or/experience, call yourselves Engineers!? Yes, there IS confusion! Just
how does the public know "who" they are talking to when they call or meet with you or
others??? Do we have to ask each person we meet or call what their qualifications are?
Non-graduate? Graduate of non-accredited college? Graduate of accredited college?
EIT? or P.E.?...A person's qualifications, background, and experience make a
difference. As a P.E., I can't just take anyone's word over the phone, or even in
person, as absolute truth; I am legally responsible for what I do - not my company, me.
When people tell the public they are an Engineer, they ought to be one, legally. JMHO.
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C. Wayne Parker, P.E. c4p@ornl.gov
Lockheed Martin Energy Systems, Inc. ...but, I speak
Oak Ridge National Laboratory for myself...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Subject: THINKING PROCESS (was: Is Mechanics of Materials misleading ?)
From: Kandachar
Date: Thu, 24 Oct 1996 09:56:56 +0100
Browsing through this newsgroup recently, I stumbled acrooss a post from
Bob Carpenter, who wrote under the subject: Is Mechanics of Materials
misleading ?, the following:
"I have to come to Tony's defense. I didn't think it was babble,
in fact I found it enlightening. The original poster was struggling
with the problem of trying to resolve a conflict with a colleague.
Tony's logic-based method offers a structured approach that allows
you to fully understand why you have certain opinions on a subject;
and if you understand why you hold a certain position or belief it's
easier to persuade others to your side - or to see the flaws in your
thinking, making it easier to accept an alternate position.
So, Tony - what's a good book to learn more about this method?"
I got curious, but I could not get hold of Tony’s original message on my
server. So I requested Tony Rizzo (who has actively contributed to
recent discussions on FEA) to provide information about: 1. His logic
based method and 2. The good book Bob was referring to.
Tony wrote back:
I've attached an article to this message. The article
describes the Thinking Processes, which are the logic-based
methods that Bob mentions. I don't know if Bob has had
training in the Thinking Processes. But I do know that
approximately 85 people at Boeing have had it.
Other than the course materials, the only reference of which I
am aware is this, "Goldratt's Theory of Constraint - A Systems
Approach to Continuous Improvement"; H. William Dettmer; ASQC Press;
ISBN 0-87389-370-0.6x9.
Dettmer does a good job of presenting the Thinking Processes
for which Goldratt is credited.
Unfortunately, I missed the discussion on sci.engr.mech that
caused Bob Carpenter to come to my rescue. Had I seen it,
I would have responded to his original request for a reference.
If you would be so kind as to forward this message to him,
or to post it to the group, I'd appreciate it.
Tony Rizzo
So, here it goes:
--------------------------------------------------------------------
THE THEORY OF CONSTRAINTS (TOC) AND THE THINKING PROCESSES
The Theory of Constraints (TOC) is a management philosophy that looks
at an organization as a complete and complex system. It presumes that
the system consists of any number of components that interact with each
other, and it strives to improve the performance of the entire system.
Observations of complex systems, by Eli Goldratt and others, have
led to the conclusion that the performance of a complex system is
usually constrained to any given level not by many aspects of the
system but by only one aspect. For example, the flow of data through
a circuit board is limited by one aspect of the circuit, such as the
parasitic capacitance of adjacent circuit paths. The flow of traffic
on Route 24 W, in the vicinity of Short Hills, NJ, is limited by one
incorrectly designed section of the highway. These comprise bottlenecks
that act as physical constraints; this leads to the definition of a
constraint, below.
A constraint is anything that prevents the system from doing more of
what it was designed to to. For the circuit board, it's whatever
keeps the board from transmitting more data. For the highway, it's
whatever keeps the highway from transmitting more vehicles. For a
business, it's whatever keeps the business from generating more profits.
However, for organizations, there also exist constraints that are not
physical. These are called policy constraints. Some that come to
mind quickly are policies such as "We're a long-distance company. We
don't do local calls," or, "We don't pay overtime to engineers," or,
"We don't make and sell products for which we can't achieve a profit
margin of at least 5%." But there are many other policies, at work
within all organizations, that limit their performance. These are
always difficult to identify. Hence, there exists the need for the
Thinking Processes.
The Thinking Processes (TP) are tools with which we can identify policy
constraints, eliminate them, and replace them with more effective
and more desirable solutions. The TP also give us the means with
which to construct those more effective solutions, communicate them
to others whose collaboration is necessary (these include customers),
and with which to create thorough implementation plans.
One good way to look at the TP is this. They are tools with which
we can identify what needs to be changed, to what it needs to be
changed, and how we can make the change happen effectively.
The TP consist of five tools. They are called the Current Reality
Tree, the Evaporating Cloud, the Future Reality Tree, the Prerequisite
Tree, and the Transition Tree. These are described below.
LOGIC STRUCTURES --
The Current Reality Tree, the Future Reality Tree, and the Transition
Tree are sufficiency-based logic diagrams. They consist of a collection
of simple declarative statements that are linked with cause-and-effect
relationships. The Evaporating Cloud (a conflict resolution diagram)
and the Prerequisite Tree are necessity-based logic diagrams. The
difference between the two types of logic diagrams is explained below.
A necessity-based logic diagram is one that identifies conditions
that are merely necessary for a particular effect to exist. However,
these conditions need not be sufficient to cause the effect. For
example, it is necessary that I ingest food, if I am to survive.
Clearly, the effect in which I'm interested is my continued survival.
But, while ingesting food is a necessary conditions, it is obviously
not sufficient for my survival. Other conditions must exist. These
include the conditions that I breathe clean air and that I drink clean
water, among others.
A sufficiency-based logic diagram is one that identifies all the
conditions that are necessary and SUFFICIENT to cause a particular
effect.
For example, consider the statement "An electric light shines inside the
room." This effect does not exist without cause. Three things must
exist
before the effect "An electric light shines inside the room" can exist.
One is that there must be a working electric light inside the room.
Another is that the light be plugged into a working outlet. A third is
that the light's switch be in the "on" position. Each of the three
causes
is necessary for the effect to exist, but it is insufficient. Together,
the three necessary conditions are sufficient to CAUSE the effect.
The cause-and-effect relationships between these statements are read
as follows: IF (there is a working electric light inside the room),
AND IF (the light is plugged into a working outlet), AND IF (the
light's switch is in the "on" position), THEN (an electric light
shines side the room.)
If we consider the following example, then we may see why sufficiency-
based logic constructs are such powerful tools. Let's say that we
want to improve the quality of the output of our organization.
We want to have the effect "The defect rate of our manufacturing
operation is less than five percent." Let's say, too, that currently
the defect rate is nine percent, and that a run-chart shows that
our manufacturing system is in a state of statistical control. At
this point, many would resort to exhortations, in the form of posters
that proclaim "Work Smarter Not Harder," or "Do Quality Work." But
rather than accept this widely used quality improvement method, let's
see if in fact such tactics are sufficient to cause our desired effect.
Let's embed the conditions in a sufficiency-based logic construct:
IF
employees see posters with the words "Work Smarter Not Harder,"
AND IF
employees see posters with the words "Do Quality Work",
THEN
the defect rate of our manufacturing operation decreases from nine
percent to five percent.
Obviously, the two conditions that we hope will cause the desired effect
are not sufficient. They aren't even necessary. So why do so many
companies have such posters on their walls? Maybe it's best that we
discuss the individual tools at this time.
THE CURRENT REALITY TREE --
The Current Reality Tree is a sufficiency-based logic diagram that
captures the experience and subject-matter-expertise of the involved
individuals. The Current Reality Tree is constructed with the strict
application of a handful of rules of logic. It's construction is
perhaps the most time-consuming part of the strategic planning process.
But every second of effort is worthwhile, because the Current Reality
Tree lets us identify the root causes and, at times, the core problem
for our organization, i.e., one condition that, when eliminated,
takes with it most of the unwanted effects.
Identifying the root causes and the core problem is a vital part of
any improvement process. By identifying and attacking these, we
avoid wasting resources and time in fighting mere symptoms. We are
able to treat the disease, so that the symptoms don't return. The
Current Reality Tree is the tool that shows us that disease.
THE EVAPORATING CLOUD --
Once we have identified the core problem, it is necessary for us
to identify a solution to the core problem. Frequently, a valid
solution is the condition that is the opposite of the core problem.
For example, if an organization's core problem is an ineffective
advertising policy, then the solution of choice might be "We have an
effective advertising policy." But is it always this simple? Not a
chance!
Think of it. The core problem is probably one that has existed for
a long time. Most likely, everyone in the organization knows that it
is a problem, but they probably don't know that it is the source of
most of the organization's headaches. If the core problem has existed
for such a long time, perhaps years, why hasn't it been solved earlier?
The answer is conflict. Within the organization there are interests
that would be jeopardized by the solution to the core problem.
Therefore,
the problem persists. The organization simply learns to live with it.
This is where the Evaporating Cloud comes in.
With the Evaporating Cloud we verbalize the conflict. We also uncover
the assumptions or the real conditions that cause the conflict.
Frequently, when the assumptions that feed the conflict are verbalized,
the involved parties realize immediately that they've been laboring
under
false assumptions. In such instances, the conflict evaporates rapidly,
just like a cloud of steam.
At other times, the assumptions are quite valid. They are real
conditions
that exist in the organization's environment, and they pose a real
threat to the people whose interests fuel the conflict. Under these
circumstances, we can still resolve the conflict. Often, we can
identify some action that we can take, to make at least one such
condition no longer valid. Thus, again, we evaporate the conflict
and unshackle the organization. This is how we identify what to change
and, partially, what to change it into. We say partially, because
the solution isn't yet complete. To flesh out our solution, we
need the next tool.
THE FUTURE REALITY TREE --
The Future Reality Tree is another sufficiency-based logic diagram.
However, it differs from the Current Reality Tree in one important way.
While the Current Reality Tree links undesirable effects, the Future
Reality Tree begins with our solution of choice and links desirable
effects.
The Future Reality Tree is a what-if exercise. With it we get the
chance
to evaluate and improve our solution, before we begin implementing it.
With the Future Reality Tree we are able to identify what is missing
from our solution. After all, it is a sufficiency-based construct. So,
if we've failed to identify all the necessary and sufficient conditions
with which to cause our desirable effects, then the Future Reality Tree
makes the deficiencies apparent.
But there is another, equally important reason for using the future
reality tree. With some careful thinking, we can also use it to
identify what negative effects our solution is likely to cause. Why
is this important? Because it gives us the opportunity to improve
our solution, by modifying it so as to avoid those negative effects
entirely. Why should we cause problems that we can avoid?
THE PREREQUISITE TREE --
The Prerequisite Tree is a necessity based logic structure. It's
purpose is to help us identify all the intermediate steps that we need,
to reach an ambitious goal like our chosen solution.
To build the Prerequisite Tree, we begin by listing all the obstacles
that stand between the organization and its stated objective. Then, for
each obstacle, we identify a condition that overcomes the obstacle.
This
is usually a mutually exclusive condition. For example, if one obstacle
were, "We don't have an advertising plan in effect," then a condition
that
would overcome it might be, "Many customers are calling and requesting
our product." In other words, the condition that many customers are
requesting our product becomes an intermediate objective, among many
others. This is how, by focusing on individual obstacles, we identify
the smaller objectives that lead us to our more ambitious goal.
THE TRANSITION TREE --
The Transition Tree is the fifth and last of the Thinking Process
tools. The Transition Tree is our step-by-step implementation plan.
With it, we literally transition the organization, from its current
state to its desired future state.
The Transition Tree is a slightly different kind of sufficiency-based
logic structure. To build the Transition Tree we identify those actions
that we need to take, given our current environment, to achieve the
intermediate objectives that we identified earlier with the Prerequisite
Tree.
The parenthetical statement, "given our current environment," is
crucial.
Our actions must make sense, in light of the organization's current
state
and environment. For this reason, with every logic construct of the
Transition Tree we identify what action to take, why the action is
needed,
and why it is sufficient to meet the need.
The effort that we put into building a Transition Tree brings us more
than
the obvious benefit of having a thoroughly thought-out plan. Since the
Transition Tree causes us to identify the reason for each planned
action,
it also helps us tremendously when the time comes for us to delegate
sections of our plan to subordinates. When we do delegate sections of
our Transition Tree, our subordinates' need for explanation and
justification is satisfied automatically. This powerful feature
of the Transition Tree helps us overcome some of the resistance to
change that is an integral part of human behavior.
SUMMARY --
The Theory of Constraints and the Thinking Process tools are already
being used to great effect in many companies throughout the world.
These companies manage change, rather than letting change manage them.
Many of them already have reported astounding results.
(C) Tony Rizzo, 1996. rizzo@hogpb.att.com
This article may be reproduced only in its entirety. Any
reproduction must include the author's name. This article may
be published in formal publications, either in print or in
electronic form, without written permission from the author.
_______________________________________________________________
I enjoyed reading this thanks to Bob Carpenter and Tony Rizzo. I hope
all the folks interested in performance improvement and involved in
change management would enjoy reading too.
- Prabhu Kandachar
Faculty of Industrial Design Engineering
Delft University Of Technology
The Netherlands
Subject: Re: sheet piles ==> beams? (Repost, long)
From: ajmosk@engin.umich.edu (Andrew Moskalik)
Date: Thu, 24 Oct 96 14:43:46 GMT
In Article ,
enrique.juaristi@crpht.lu (Enrique Juaristi) wrote:
>There was an excellent response to this posting by Mr. Andrew Moskalik
>which has mysteriously disappeared. I think it might add some good ideas
>to this discussion if it was put up again.
Why, thanks for the compliment. I've actually made two posts, so I'll
repost both (which makes this quite long, I'm afraid). I've added a couple
comments at the end of this article. Here they are again:
______________________________________________________________________________
POST I:
In Article ,
enrique.juaristi@crpht.lu (Enrique Juaristi) wrote:
>In article <53tg8v$6v5@newsb.netnews.att.com>, rizzo@hogpb.ho.att.com
>(-A.RIZZO) wrote:
>
>> In article ,
>> Enrique Juaristi wrote:
>> >
>> >It seems to be reasonable to consider a steel sheet pile as a beam, and
>> >therefore calculate its deflections by means of the classical beam theory.
>> >But does this analogy still hold when two sheet piles are locked together?
>> >and three?
>> >
>> >Enrique Juaristi
>>
>> Would you care to clarify what you mean by "sheet pile?"
>
>A steel sheet pile is a special kind of element used in civil engineering.
>It is basically a long and slender bent steel sheet whose profile looks
>like a "U" and has "interlocks" on both edges to allow the interconnection
>of several sheet piles into what is called a "steel sheet pile wall".
>These sheet pile walls are used basically for retaining landfills and
>water.
>
>Let me draw it for you (one image=1000 words!)
>
> ______ This is the profile. For the rest, it's just like a normal
> / ! beam: long and thin.
><__/ !__> The > and < signs represent the interlocks.
>
>
> How are
>> the sheets oriented with respect to the plane of bending?
>
>I see these sheet piles as beams with a rather special profile. Besides, I
>think 3D effects will not fail to appear as soon as deformations become
>large. But within the small deformation domain, I'd like to know if, in
>practice,the normal beam theory is applied.
>
> What do
>> you mean by "locked together?" What do you mean by "and three?"
>
>In fact you can lock together as many of these as you want. But then, the
>resulting structure is not really a beam anymore, but a strange sort of
>shell. But clearly, you cannot apply the beam theory anymore. But what is
>the limit number of beams?
I believe that you can treat any number of piles locked together as a beam,
as long as, 1) the length of the beam is greater (by some reasonable factor)
than the height, and 2) the applied load is *evenly applied* on all piles
(and not concentrated on only the center one, say).
However, the "classical" beam theory you use will not necessarily be a
"simple" classical beam theory where stress = My/I. Two additional factors
must be considered:
1. UNSYMMETRICAL BENDING (TWISTING)
In which orientation are the sheet piles locked together? Are they like so:
______ ______
/ \ / \
<__/ \__*__/ \__>
or like so:
______
/ \
<__/ \__*__ __>
\ /
\ /
------
In the first case, if the load is applied vertically, the beam will move
only vertically. An applied load at an angle, however, will cause an
additional twisting. In the second case, since the section is
unsymmetrical, even an applied vertical load will cause the beam to twist.
2. SHEAR STRESSES
Since the cross-sectional area is small, shear stresses in the beam will be
much more important, particularly if the beam is relatively short. You may
be able to ignore this effect even so, but I think you still need to
calculate it.
For information on calculating shear stresses and bending/twisting coupling,
refer to an advanced mechanics of materials book. I would recommend
"Advanced Mechanics of Materials" by Boresi, Schmidt, and Sidebottom (pub:
John Wiley & Sons). Not only do I like it personally, but the first two
authors are Civil Engineers. These are topics, however, that you are likely
to find in many similar books.
If your entire structure has only one applied load that is *not* evenly
spread among the piles, then I think you do have a strange sort of shell
effect as the stress gets distributed. I imagine beam theory will still
hold if you have a very long beam and the you can consider the effect of the
point loading an "end effect," but that's gonna be a judgement call.
_______________________________________________________________________________
POST II:
In Article <544kl4$l1c@sjx-ixn4.ix.netcom.com>, zagz@ix.netcom.com(Ken
Zagzebski ) asks:
>In ajmosk@engin.umich.edu
>(Andrew Moskalik) writes:
(snip)
>>1. UNSYMMETRICAL BENDING (TWISTING)
>>In which orientation are the sheet piles locked together? Are they
>like so:
>>
>> ______ ______
>> / \ / \
>><__/ \__*__/ \__>
>>
>>or like so:
>>
>> ______
>> / \
>><__/ \__*__ __>
>> \ /
>> \ /
>> ------
>>
>>In the first case, if the load is applied vertically, the beam will
>move
>>only vertically. An applied load at an angle, however, will cause an
>>additional twisting. In the second case, since the section is
>>unsymmetrical, even an applied vertical load will cause the beam to
>twist.
>>
>
> _____
> / \ _ _
>If <_/ \_> behaves like < \ / > for vertical loads
>with the appropriate sign change, \____/ , which I think it
>does, why wouldn't
> _____
> / \ ^
> <_/ \___ _ | is vertical direction
> \ / > |
> \____ /
>behave like
> _ _ _ _
> < \ / * \ / >
> \_____/ \_____/
>
>when subject to the same vertical loads ?
>
Assuming that the two plies are tied together solidly, then the asymmetry of
the second section causes the neutral axis location to change. For
instance, the section
_____
/ \ <-----
<_/ \_>
has a horizontal neutral axis approximately where the arrow is. The section
_____ _____
/ \ / \ <-----
<_/ \_*_/ \_>
has a neutral axis in the same place. On the other hand, the section
_____
/ \
<_/ \___ _
\ / >
\____/
is no longer symmetric left-to-right, so under a vertical load, the section
twists and the neutral axis is *not* horizontal (in fact, it runs from upper
left to lower right). An experiment to prove my point: hold a long thin
ruler at an angle like shown below and push down; the ruler twists to the left.
___ F
\ \ |
\ \ |
\ \*
\ \
\ \
\ \
\__\
Back to the original question: of course, if you assume that the two
sections are *not* tied together solidly, and slippage occurs at the section
joint, then the two piles bend *indepentantly*, and thus act precisely like
they did before joining.
_______________________________________________________________________________
Note, though, that Paul Ransom has a valid comment on this last paragraph,
which I agree with:
>In article <5475g6$ifb@james.freenet.hamilton.on.ca>,
>ad026@james.freenet.hamilton.on.ca (Paul Ransom) wrote:
>
>>> Back to the original question: of course, if you assume that the two
>>> sections are *not* tied together solidly, and slippage occurs at the section
>>> joint, then the two piles bend *indepentantly*, and thus act precisely like
>>> they did before joining.
>>
>> Not quite. If the two pile are similarly oriented, then they will
>> generally act as you describe since they will both deflect similarly and
>> there will be no longitudinal shear across the joint.
>>
>> However, if the piles are alternately reversed;
>> 1) each one independently may have different bending characteristics in
>> positive and negative flexure and,
>> 2) they will definitely not share a similar neutral axis with adjacent
>> piles.
>----------------------------------------------------------------------------
Additionally, Ken Zagzebski, in another article, commented that the
"twisting" effect would be much less pronounced (i. e., ignorable) if you're
talking about a sheet pile *wall* (many piles) rather than just two or three
piles. Again, a valid comment.
Note that I'm entering this discussion with a mechanical background, so I'm
not really familiar with the actual construction, use, or loading of these
sheet piles. I'm fairly certain, though, that you can use beam theory to
adequately evaluate these piles, as long as you correctly evaluate any
"non-standard" effects (such as the topics discussed above).
Andrew Moskalik