Introduction to Engineering Design. Modelling, Synthesis and Problem Solving Strategies

406 Pages·2000·16.972 MB·English

by  Andrew Samuel and John Weir (Auth.)

laicepS tnemgdelwonkcA
We make consistent reference throughout this text to engineering judgement and wisdom. Some of this
wisdom si acquired through years of practice in the design profession, but much of it is gained through
close association with inspired and creative colleagues. Engineering design si an emerging discipline. Most
learning institutions offering courses in engineering struggle with the nature of engineering design experience
to be offered to students. It si a labour intensive activity. Our experience and wisdom in this emerging field
has been nurtured and developed by our continued, close association with William (Bill) Lewis. It si now
recognised that major technical change can occur through a series of paradigm shifts. In engineering
education at Melbourne, a paradigm shift took place when engineering design became a core part of the
engineering curriculum. This change can be, almost entirely, attributed to the inspired course management
and planning of Bill Lewis. Bill gained his Ph.D. in 1974 in a then almost unheard of field of research in
engineering courses, engineering creativity. Bill was the first to obtain a doctorate at Melbourne in engineering
design, and may well have been the first in the world to do so. Even before that achievement, in 1967, Bill
was the first to identify and publish a reasoned evaluation of formal educational objectives in engineering
design courses. These days engineering courses around the world offer problem-based and project based
learning experiences to undergraduates. With Bill's guidance and inspiration we have been offering such
learning experiences for more than 25 years. This book is a distillation of these experiences and Bill's
contribution si gratefully acknowledged.
tnemgdelwonkcA
Writing a text on engineering design, based on an on-going course programme, makes wide use of ideas
gleaned from both students and colleagues. Since its serious introduction to the undergraduate programme
at Melbourne in the early 60s, the design programme has been an organic component of the engineering
course. It has grown and has been honed and nurtured by ideas and contributions from many sources.
Some of these ideas were developed in formal planning sessions, but many are the result of informal
coffee-table discussions. For all of these, and the many opportunities to work with insightful colleagues
and inspiring students, we are grateful. Special thanks are due to Colin Burvill, Bill Charters, Bruce Field,
Jamil Gholel, Errol Hoffmann, Barnaby Hume, Janusz Krodkiewski, Wayne Lee, Stuart Lucas, Jonathan
McKinlay, Peter McGowan, Peter Milner, Alan Smith, Craig Tischler, and the many hundreds of
undergraduates who continue to keep us on our mettle.
Andrew Samuel
John Weir
Melbourne, 1999
laicepS tnemgdelwonkcA
We make consistent reference throughout this text to engineering judgement and wisdom. Some of this
wisdom si acquired through years of practice in the design profession, but much of it is gained through
close association with inspired and creative colleagues. Engineering design si an emerging discipline. Most
learning institutions offering courses in engineering struggle with the nature of engineering design experience
to be offered to students. It si a labour intensive activity. Our experience and wisdom in this emerging field
has been nurtured and developed by our continued, close association with William (Bill) Lewis. It si now
recognised that major technical change can occur through a series of paradigm shifts. In engineering
education at Melbourne, a paradigm shift took place when engineering design became a core part of the
engineering curriculum. This change can be, almost entirely, attributed to the inspired course management
and planning of Bill Lewis. Bill gained his Ph.D. in 1974 in a then almost unheard of field of research in
engineering courses, engineering creativity. Bill was the first to obtain a doctorate at Melbourne in engineering
design, and may well have been the first in the world to do so. Even before that achievement, in 1967, Bill
was the first to identify and publish a reasoned evaluation of formal educational objectives in engineering
design courses. These days engineering courses around the world offer problem-based and project based
learning experiences to undergraduates. With Bill's guidance and inspiration we have been offering such
learning experiences for more than 25 years. This book is a distillation of these experiences and Bill's
contribution si gratefully acknowledged.
tnemgdelwonkcA
Writing a text on engineering design, based on an on-going course programme, makes wide use of ideas
gleaned from both students and colleagues. Since its serious introduction to the undergraduate programme
at Melbourne in the early 60s, the design programme has been an organic component of the engineering
course. It has grown and has been honed and nurtured by ideas and contributions from many sources.
Some of these ideas were developed in formal planning sessions, but many are the result of informal
coffee-table discussions. For all of these, and the many opportunities to work with insightful colleagues
and inspiring students, we are grateful. Special thanks are due to Colin Burvill, Bill Charters, Bruce Field,
Jamil Gholel, Errol Hoffmann, Barnaby Hume, Janusz Krodkiewski, Wayne Lee, Stuart Lucas, Jonathan
McKinlay, Peter McGowan, Peter Milner, Alan Smith, Craig Tischler, and the many hundreds of
undergraduates who continue to keep us on our mettle.
Andrew Samuel
John Weir
Melbourne, 1999
PREFACE: THE NEED FOR THIS BOOK
"... Engineers are proud of their ,noisseforp anxious to sing its praises. But they cannot seem to get beyond perfunctory and
non personal expressions of the satisfactions they denve from their work. Many of them are 'turned on' by what they .od
But they are unwilling or unable to reveal their inner emotions to na audience" Samuel .C Florman - ehT existential
pleasures of engineering
Theodore von Karman, that polymath of the early challenge of estimating and, occasionally, making
20th century, defined the difference between arbitrary design choices, tempered by insight into
scientists and engineers thus: the problem. teY another challenge si to find the
"Scientists look at things that era and ask 'why'; engineers right modelling method for analysing our chosen
dream of things that never were and ask 'why not ~''' design. Here too we offer guidance, but the
Engineering design si lla around us every day of ultimate decision is left up to the designer. We do
our lives. Almost every artefact we touch, chairs, not prescribe how to solve problems. On the
doors, cutlery, light-globes, the list si endless, and contrary, we only ask that the design challenges
every system we use, transport, mail, supermarket, offered are solved by rational argument.
banking, health care, power distribution and so on, Occasionally we ask that the rationale include
has an engineering design component. Engineers sufficient information to allow a certificating
were involved in the design of these artefacts and authority to evaluate the solution. In these cases
systems. How did this happen? What si involved cogent argument will be needed to support the
in designing something? Even more importantly, soundness of design choices. Apart from these
how does one become a designer? minor limitations the field si there to be explored.
This book si addressed to young engineers on It is not intended that anyone memorise any
the threshold of entering the profession. The formulae or codified information offered in the
objective is to give experience in successfully text. We sincerely hope to engage the interest of
designing simple engineering artefacts. These young engineers and to develop their
artefacts are the essential building blocks of larger understanding of the material presented.
more complex systems yet to be experienced. teY Moreover, we hope to stimulate further enquiry
the design elements introduced here encapsulate or even challenges to our approaches, where it si
the richness of the full design experience of much felt we have skimmed over important issues. We
larger and more complex engineering systems. The act only sa guides in the journey through this book,
design steps involved here mimic the experiences pointing out the significant features of the design
to be had in the design of much more complex .yrenecs However, the journey si there for the reader
systems, but the examples offered provide easily to enjoy!
evaluated success with the much simpler systems The book si subdivided into two major parts.
addressed in this book. Part :1 Modelling and synthesis, including Chapters 1
The activity of designing artefacts offers many to ,5 deals with some focused issues of designing
challenges. The process si essentially synthetic engineering components for structural integrity.
rather than analytic in substance. Identifying the Part 2: Problem-solving :seigetarts An engineering ,erutluc
real substance of the design problem si probably including Chapters 6 and 7, introduces some
the greatest challenge encountered by designers. broader issues in design.
In the examples offered in this text we have diluted Chapter 1 introduces structural integrity and the
this challenge by clearly identifying the building nature of failure, units and the notion of structural
block to which each specific design problem distillation. Chapter 2 offers a brief introduction to
belongs. Nevertheless we will still experience the engineering materials, failure modes and
XV
I A paraphrase was used by John E Kennedy ni a political speech
Contents, preface and common terminc'ogy j
introduces failure predictors (theories of failure), not prescribe how others should use the text. Both
based on engineering mechanics. Chapters 3 and 4 parts are self contained and may be taught or read
deal with the design synthesis of specific separately in any order. We hasten to point out,
engineering components, with extensively however, that even in Part 1 we offer design
explored case examples. Chapter 5 reviews the experiences with opportunities for creative
work of Part ,1 and offers case examples in the expression in design choices. We also conjecture
design of engineering systems. We conclude this that the particular design experiences offered in
part of the text with some explorations of Part 1 may be clearly described by the general
engineering misconceptions and some experiences design procedures introduced in Part .2 We leave
of engineering design judgement under severe the support or refutation of this conjecture to
time constraint. readers.
In Chapter 6 we introduce the operational model
of the design process and its various stages, through Andrew Samuel
the evolution of design problems. Chapter 6 John Weir
identifies and explores some broad, nontechnical Melbourne, 1999
issues that significantly influence the successful
delivery of design project objectives. Finally, in
Chapter 7 we briefly introduce economic, social,
and environmental influences on design.
Most introductory texts in design explore either
Part 1 or Part 2 of this text, but it si rare to find
them together in a single book. We suggest that
this separation is the direct result of Western
European, mainly German, influence on design
thinking. In the European school of thought,
design for structural integrity has been identified
with focused analytical objectives of deriving some
specific details of component geometry.
Additionally, in the European school, that type of
design took place after the gross structural or
embodiment decisions had been made by some
broader creative process. In that school of laires
,ngised allowing the design analyst to influence the
embodiment decisions would be seen sa opening
the setagdoolf to a whole range of iterative redesign
issues, that might severely impact on -ot-tpecnoc
launch times.
Current thinking in design has more-or-less
rejected these limitations on the total design
programme. We subscribe to the notion that
successful design must take place in a creative
environment, where lla influences are considered,
sa far sa possible, concurrently. So, why do we deal
with particular design experiences in structural
integrity, before considering the broader issues in
design? The answer to this question lies in
pedagogy. This book si addressed to both teachers
and students of design. Our experience with design
education has led us to the conclusion that some
early success with component design, sa offered
in Part ,1 si far more motivating and accessible for
students than the broader issues of design dealt
with in Part 2 of this book. Nevertheless, we do
xvi
COMMONLY USED SYMBOLS AND DESIGN TERMINOLOGY
A area, cross-section area a small change in quantity, extension/
c,C most commonly a parametric constant of compression
proportionality e strain
corrosion allowance /1 efficiency, welded joint efficiency
C
D,d diameter 0,0 angle, twist per unit length (torsion)
base of Naperian logarithm, eccentricity 2/ coefficient of friction, Poisson's ratio,
e
E modulus of elasticity s'gnuoY( )suludom dynamic viscosity
f stress intensity, function v kinematic viscosity )p/t.Q
F force rJ ratio of circumference of circle to diameter
F actual factor of safety P density
a design factor of safety rc direct-stress (general)
g acceleration due to gravity r shear-stress (general)
G shear modulus of elasticity q) diameter ratio
!,v / second moment of area about x-axis;polar elba,uollA :eulav bound or limit on some specified
second moment of area output variable (e.g. r< 96 MPa)
k,K spring constant , stiffness, kinetic energy Compromise" arbitration between conflicting
K c fracture toughness coefficient objectives (e.g. accepting an increase in mass for a
reduction in stress level" this si also called a tmde-
K,/(.i. modifying factors for endurance limit
,1 L length measure
Cot~icting sevitcejbo (also, occasionally, gnitepmoc
mass, end-fixity ratio
m objectives): design objectives that negatively
P pressure influence each other (e.g. low mass coupled with
q load/unit length high strength, large volume coupled with small
R,r radius surface area; high reliability coupled with low cost)
r laer interest rate (lending rate - :tniartsnoC mandatory requirement to be fulfilled
inflation rate) by the design (e.g. must be manufactured in
,~S S material endurance limit(material Australia; must meet Federal Drug Administration
property); component endurance limit Authority requirements)
ultimate tensile stress (material property) "airetirC scales on which we measure the relative
S U
S yield stress (material property) level of achievement of design objectives (e.g. the
t,T y material thickness, time, temperature criterion for a "low "ssam objective si mass in kg).
See also ecnamroCoep elbairav
strain energy/unit volume
31
v,V velocity, potential energy, shear force ngiseD :laog the primary functional objective of a
design (usually expressed in terms of a ngised )deen
W transverse load
ngiseD :deen expression of a means for solving a
P axial load
problem, withot reference to embodiment (e.g. a"
x,X axis direction snaem of gnivomer dirt from ,"gnihtolc instead of a"
y,Y axis direction gnihsaw )"enihcam
z,Z axis direction Design :elbairav variables in the control of the
,IC thermal coefficient, angle designer (e.g. material choice; length; diameter;
31 hollowness ratio number of spokes)
XVII ,,m
Contents, preface and common terminology
Design parameter: combination of performance :sevitcejbO the desired features, or characteristics
variables (or )airetirc whose improvement usually of the design, that determine its ultimate
contributes to success in achieving the design effectiveness or suitability for a given task (e.g. the
objectives (e.g. strength to weight ratio for mass driver's seat must be comfortable; the can opener
limited design; strength to stiffness ratio for must be safe, cheap and portable)
deflection limited design)
Objective function: single unit mathematical
Design Audit (sometimes Design Reviezv): combination of design objectives (e.g. total cost =
identification of the design goal of a given some function of component costs; or, total energy
embodiment and the ,sevitcejbo ,airetirc stnemeriuqer use = some function of the energy used by the
and stniartsnoc (the ngised )seiradnuob that lead to the several design components)
current embodiment of a design. While the Design
ecnamrofreP :elbairav output variables (not directly
Audit does not seek to modify the design, it seeks
under the control of the designer, but indirectly
to evcaluate how well the design embodiment
determined by the values of the design variables)
meets its design goal within the identified design
that describe the performance of a system in
seiradnuob
fulfilling design objectives (e.g. strength, cost,
:ssenevitceffE capacity of component or system to pump flowrate, engine power, mass). See also
perform as required (e.g. an automobile si an airetirC
effective personal transport device, but it si an
Optimisation: maximising or minimising an
inefficient high-volume people mover)
objective function so as to achieve the best
Ejficienff: ratio of output to input (e.g. transmission combination of design objectives (e.g. minimising
efficiency of a gear box si the ratio output power/ a cost function, or maximising a benefit function)
input power)
Requirement: non-mandatory, flexible, design limit
Endurance limit: limiting stress level for ferrous (e.g. "the tsoc must eb ssel than some deificeps value")
materials: the material will withstand infinite
Rule-of-thumb :)citsirueh( informal decision making
numbers of cyclic load applications if stresses are
procedure based on experience and wisdom (e.g.
kept below the endurance limit (S')
the fundamental frequency of vibration for most
eruliaF :rotciderp combinations of multi-axial stresses mechanical systems si less than 1 kHz)
that predict component failure (e.g. maximum
:ssertS force per unit area
shear stress failure predictor, MSFP,
elbawollf~ < ,iaf'~ ( = S/2) Trade-off: arbitration procedure that allows
devaluing one objective in favour of improving the
Goal: the ultimate purpose of the design (e.g. to
value of some other objective (e.g. accepting a loss
reduce accidents at level crossings; to provide safe
in efficiency for an improvement in reliability)
and effective storage for liquid fuel under pressure;
to provide a simple mechanical cleaning system tsroW elbiderc :tnedicca limiting design condition that
for clothes) assigns the maximum loads to be sustained by a
component (e.g. for selecting the loads on standard
Governing requirement: the most demanding
office chair, we consider the heaviest person-
constraint or requirement on a system facing
97.5th percentile male - balancing the chair on two
multiple requirements or modes of failure; the
of its legs; considering wind loading on electric
design requirement that imposes the most severe
power distribution cables, we work with winds of
value on a particular design variable (e.g. for a shaft
the highest velocity observed in any 50 year period.
required to resist both fracture and excessive
Such winds are identified by the bureau of
deflection, the governing requirement is that
meteorology sa 50 year return winds)
which necessitates the larger shaft diameter)
:gnidleiY condition of failure observed in metals,
:noitaretI systematic, goal-directed, trial and error
generally taken to be the limit of linear elastic
solution to a problem
behaviour (e.g. in CS 1040 steel yielding occurs at
Mode of failure: technically precise description of approximately 210 MPa)
the failure (e.g. yielding, rupture, fatigue, buckling,
excessive deflection)
XVlII
Chapter l
1
INTRODUCING MODELLING AND
SYNTHESIS FOR STRUCTURAL INTEGRITY
With them the sdees of Wisdom did I ,wos
And with mine nwo hands wrought to make it grow; Edward Fitzgerald, ehT Rubaiyat of Omar Khayydm, 1889
This is a book about the basic elements of exceeding either the specified maximum
engineering design. We begin with an emphasis stress, specified maximum deflection, or both
on structural integrity, and later broaden our of these specifications. Examples are:
concern to various philosophical and practical 140 MP a maximum shear stress allowed in
issues. The book is addressed to engineering certain qualified welding materials, or
undergraduates who are being exposed to maximum deflection of 1/300 the span in
engineering design thinking and reasoning for the architectural beams;
first time in their courses. Many texts on
Service loads are those loads, specified or
engineering design of machine elements treat
unspecified, that the designer considers as
structural integrity from a purely analytical point
credible to be imposed on the component
of view. Readers of such texts are rarely offered
during its service life. In the context of
opportunities to apply the process of design
structural integrity, a service load will usually
synthesis to real-life engineering problems.
be specified sa a force (N), a moment (Nm), or
Engineering texts present encapsulated experiences
a pressure (Pa). More generally, design loads can
with design problems pared down to a manageable
be thought of as thermal (kW/m2), electrical
scale. Real-life engineering si full of uncertainties
(A/m2; kW), information-processing
and risks, impossible to replicate effectively in the
(decisions/hr; bits), or even in terms of such
formalised medium of a textbook. Nevertheless,
concepts sa trafic intensity (e.g. passengers/hr).
first-time students of engineering need to be
introduced to the myriad choices and decisions that The mature description of service loads is
designers must face. probably the aspect of component design requiring
Our focus in this first part of the text si on design the greatest creative input by the designer, in terms
for structural integrity. For the purposes of our of engineering wisdom and judgement. Often the
study; we define structural integrity sa the capacity service loads are unknown and need to be
of engineering components to withstand service estimated before design can begin. In the case of
loads, effectively and efficiently, during their critical design, such sa airframes, considerable in-
service life. This definition involves several service test data si used to enable suitable service
concepts that need further elucidation. load estimates. For critical components, and those
subject to fatigue failure, (e.g. airframes and motor
Engineering component in this context means any
vehicle components) these estimates are almost
engineering structure, which may be
invariably followed up by field testing of
constructed from several interconnected
prototypes. We explore service loads a little further
elements into a single entity. Examples are
in section 1.3, Structural distillation.
pressure vessels, bicycle frames, flywheels,
Eflkiently, in this context, means either at least cost
springs, shafts of electric motors, airframes
or at least mass. Cost-limited designs, the most
and the frames of motor vehicles or buildings;
common case, must consider all aspects of
Effectively withstanding loads is defined as the cost, including material, manufacture,
capacity to accept service loads without maintenance, and most importantly, design
Introducing modelling and sisehtnys I
costs. In general, for relatively simple 1950s. Although controversial at the time, it si now
components, the cost of manufacture si of generally agreed that the aircraft failures were due
the same order of magnitude sa the material to stress concentrations near the sharp comers of
cost. In contrast to this, design time is some rectangular windows in the fuselage. It seems
expensive and needs to be spent wisely. clear that the Comet designers were unaware of
Hence, the wise, or experienced designer will the significant variability of fatigue data, and failed
not spend expensive design time to eliminate to take this into account in their design (Hewat
a few extra grams of material from a relatively and Waterton, 1956).
simple and cheap component. Quite often, On a grand scale, we accepted Sir Isaac Newton's
for simple components, one that does eht job si models of the physics of motion universally for
likely to be most efficient. Mass-limited nearly 400 years. In fact, they were, and still are,
designs require considerable analysis. With referred to sa Newton's Laws. Einstein's hypotheses
complex shapes, finite element analysis a( on relativity forced a paradigm shift in physics
computer-based stress analysis procedure) thinking. We no lolager regard the laws of physics
offers opportunities for mass optimisation .~-~ sa absolute truths, .but merely sa conjectures, or
working hypotheses, to be used until refuted by
For the purposes of design, once the service loads
physical experiment (Popper, 1972).
have been established, the mechanical analysis of
In Section 1.1 we identify some characteristic
a component requires mathematical modelling of
features of engineering failures. We start by offering
the component structure. The model allows us to
four propositions about failures, and we describe
translate loads into stresses or deflections.
some simple engineering tools to be used in design
Naturally, the more closely the mathematical
for structural integrity failure avoidance). We also
model represents reali~, the more accurately we
offer some spectacular examples of failures,
can identify stresses or deflections. As a precursor
characterised by their social, economic or
to analysis, we must make absolutely clear that the
environmental impact.
results of our analyses reflect only the behaviour
The key elements of design for structural
of our model, and not the behaviour of the laer
integrity are:
component. Even experienced designers
sometimes overlook this consideration. The (cid:12)9 service load estimation; and
spectacular failure of the Tacoma Narrows (cid:12)9 structural modelling.
suspension bridge is an example of the
Both of these elements require sound
complacency of structural engineers with models.
engineering judgement. We need to establish a base
As Professor Henry Petroski notes (Petroski, 1994):
reference frame for our capability in making such
"In the half-century following the accomplishment of judgements. In Section 2.1 we explore the notion
the Brooklyn Bridge, suspension bridge design evolved in of engineering estimation. We also set the reference
a climate of sseccus and selective historical amnesia.., ot frame for what we expect first-time users of this
eht Tacoma Narrows Bridge. Now, a half-century after text to know, in order to make effective use of the
that s'egdirb lassoloc ,espalloc there si nosaer ot eb denrecnoc remaining chapters.
that the design of newer bridge types will eb carried out Material properties and material selection are
without drager ot apparent selcyc of sseccus and failure." closely interwoven with design for structural
The Tacoma Narrows Bridge was of lighter integrity. Chapter 2 introduces material properties,
design than previously built bridges, since it was formal definitions of failure and failure predictors
designed to carry vehicular, rather than rail traffic. to be used in design for structural integri~.
Wind loads on previously designed suspension In Chapters 3 and 4 we offer simple
bridges were modelled sa causing static lateral mathematical models for several generic
deflections only. The lighter deck structure of the engineering components: columns, shafts, pressure
Tacoma bridge was susceptible to severe torsional vessels, springs , as well as bolted joints, pinned
vibrations, a loading clearly overlooked in the snoitcennoc and welded joints. These components, and
design, and this eventually caused its failure their respective mathematical models, represent
(Farquharson, .2.1)9491 the basic building blocks of our approach to
Another famous case of improper modelling si modelling the failure-behaviour of more complex
the recorded tragic disasters suffered by the Comet engineering structures.
aircraft of the DeHavilland company in the early
I. I Minimum mass with imposed stress or deflection constraints.
1.2 Quoted in Petroski (I 994)
I Chapter l
t 5
We propose that most engineering structures measured by the economic, environmental or
may be treated as a combination of several social impact caused by the failure.
cooperating, much simpler, engineering structural Proposition :4 Failure si essentially related to risk:
elements. Moreover, if we understand how these
given extreme conditions, lla structures or systems
simpler elements behave under loads, and we can
can fail. The engineer's task si to:
recognise the underlying, simpler engineering
elements which constitute a given practical (cid:12)9 generate design specifications that best meet
structure, we are exercising structural distillation and the required operating conditions of the
design thinking. structure or system within acceptable levels
of risk;
This simplistic approach to structural integrity
si clearly applicable to practical design situations (cid:12)9 identify the limits ofkn0w-h0w associated
where a relatively conservative or safe design si with the structure or system and assign factors
required. For designs of complex structures, of ecnarongi (commonly referred to sa factors of
exposed to limit loads (or beyond in some cases, safety) to cope with these limits, also within
such sa racing cars, or racing yachts), we advocate acceptable levels of risk ~ this brings with it
the application of more sophisticated techniques the notion of worst elbiderc .tnedicca
of structural analysis. Nevertheless, even the more
subtle problems become easier to understand and
to explore, once we have a good basis for 1.1.1 Some spectacular structural failures
understanding how simpler structures behave. In
Section 3.1 we introduce structural distillation, and In what follows we present some spectacular
we investigate its application to a wide range of structural failures, and examine the causes and
common engineering components. outcomes associated with them.
(a) Oil tank collapse in the field
1.1 Structural integrity and the
Figure 1.1 shows two of six collapsed oil tanks at a
nature of failure
West African installation. The tanks were 15.5m
diameter and 16.5m in height. At the time of
Proposition/:Engineers are inherently concerned erection, the tops were being assembled when a
with failure and our vision of success si to develop severe storm struck. The wind blowing over the
modelling tools to avoid it. Moreover, by studying tops exerted both direct pressure on the outside of
failures we develop clear ideas about causal the tanks sa well sa causing negative pressure inside
relationships in complex real-life engineering the tank on the walls facing into the wind. The
situations, often too difficult to model completely loss incurred was more than $US 1 million.
realistically for structural analysis. According to the investigators, there were several
Proposition 2: Engineering failures may be contributing factors to this loss. All six tanks had
categorised as technical, operational or been erected to their full height before
unpredictable: construction of the top covers commenced, and
the tanks had not been reinforced internally to
(cid:12)9 technical failures are most commonly due to
support them in a storm. Furthermore, the
insufficient information about the nature of
construction took place at a time known to be the
the structure, its material, its loading, or its
worst storm season in that part of the world.
operating conditions;
While no lives were lost nor any human injuries
operational failures are most commonly due incurred, the financial loss was substantial.
to improper operating practices or conditions;
unpredictable failures are most commonly (b) Collapsed hoarding in Dubai
the result of special circumstance or acts of
Figure 2.1 shows a collapsed hoarding around a
God.
clock-tower being built in Dubai. The hoarding
Proposition 3: Incentives to avoid engineering was erected to shield the site from view during
failures are related to failure intensity- the degree construction. In a storm, resulting in maximum
of seriousness of the failure. Failure intensity si wind speeds of 62 km/h, the hoarding collapsed
Introducing modelling and synthesis
6
erugI-~ I. I Collapsed lio tanks ni West Africa (2 of 6 similarly damaged tanks shown) After Schaden legeipS 2/94 3J
Figure 2.1 Collapsed hoarding ni Dubai: After Schaden legeipS 2/94
3.1 Schaden legeipS snoitcelfer'( of )'eruliaf si publication a of hcJnulP ecnarusnieR Company, Munich, Germany