Table Of ContentSource: Standard Handbook for Civil Engineers
1
Jonathan T. Ricketts*
ConsultingEngineer
PalmBeachGardens,Florida
S D
YSTEMS ESIGN
C ivil engineering is that field of engi- 5. Performservicesonlyinareasofcompetence;in
neering concerned with planning, other areas, engineers may engage or collabo-
design and construction of natural rate with qualified associates, consultants, or
resource development, regional and employeesforperformingassignments.
localwatersupplyandstormwaterfacilities,waste
managementfacilities,transportationfacilities,tun-
Accordingly,civilengineeringprojectsshouldbe
nels, buildings, bridges, and other structures for
planned, designed, and constructed to satisfy the
theneedsofpeople.Personswhoarequalifiedby
followingcriteria:
education and experience and who meet state
requirements for practicing the profession of civil
1. Theyshouldservethepurposesspecifiedbythe
engineeringarecalledcivilengineers.
ownerorclient.
2. They should be constructable by known tech-
niquesand withavailable labor andequipment
1.1 Performance Criteria for
withinatimeacceptabletotheownerorclient.
Civil Engineers 3. They should be capable of withstanding the
elements and normal usage for a reasonable
Asprofessionals,civilengineersshouldconformto
periodoftime.
thefollowingcanonsastheyperformtheirduties:
4. Projectswhencompletedshouldbeoptimum—
1. Holdparamountthesafety,health,andwelfare lowestcostforthepurposesintendedorthebest
of the public. (Welfare of the public implies a forthemoneyspent—asrequiredbytheowner
commitmenttosustainabledevelopmentwhich or client. Construction cost should not exceed
is meeting the current needs and goals of the theclient’sconstructionbudget,andoperation,
project while protecting the natural resource maintenance, and repair, when properly exe-
baseforfuturegenerations.) cuted,shouldnotbeexcessivelycostly.
2. Act for every employer or client as faithful 5. Projectsshouldbedesignedandconstructedto
agentsortrusteesandavoidconflictofinterest. meet pertinent legal requirements, conform
3. Applytothefullestextenttheirknowledgeand withgenerallyacceptedengineeringstandards,
andavoidendangeringthehealthandsafetyof
skilltoeveryclient’sproject.
constructionworkers,operatorsoftheprojects,
4. Maintain life-long learning, always willing to andthegeneralpublic.
participateintheprofessionalexchangeofideas
6. Projectsshouldbedesignedtomeetthegoalsof
andtechnicalinformation.
sustainable development which are meeting
project needs while conserving and protecting
environmentalqualityandthenaturalresource
*Revised and updated from “System Design” by Frederick
S.Merritt. baseforfuturegenerations.
1.1
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SYSTEMS DESIGN
1.2 n Section One
7. Projects, when properly operated, should be Foraprojecttobetreatedasasystem,asrequired
energyefficient. in systems design, it is necessary to know what a
8. To the extent possible, projects should display systemisandwhatitsbasiccharacteristicsare:
Asystemisanassemblageformedtosatisfyspecific
aestheticqualities.
objectivesandsubjecttoconstraintsorrestrictionsand
consisting of two or more components that are inter-
Theultimateobjectiveofdesignistoprovide,in
relatedandcompatible,eachcomponentbeingessential
precise, concise, easy-to-comprehend form, all the
totherequiredperformanceofthesystem.
information necessary for construction of the
Because the components are required to be
project.Traditionally,designersprovidethisinfor-
interrelated, the operation, or even the mere
mation indrawings or plansthat show what isto
existence, of one component affects in some way
be constructed and in specifications that describe
the performance of other components. Also, the
materials and equipment to be incorporated into
requiredperformanceofthesystemasawholeand
the project. Designers usually also prepare, with
theconstraintsonthesystemimposerestrictionson
legal assistance, a construction contract between
eachcomponent.
theclientandageneralcontractorortwoormore
Examples of civil engineering systems include
primecontractors.Inaddition,designersgenerally
buildings, highways, bridges, airports, railroads,
observeorinspectconstructionoftheproject.This
tunnels, water supply to meet human needs, and
should be done not only to help the client ensure
wastewatercollection,treatment,anddisposal.
that the project is constructed in accordance with
A building is a system because it is an as-
plans andspecifications but to obtain information
semblage constructed to serve specific purposes,
thatwillbeusefulfordesigningfutureprojects.
suchasshelterforhumanactivitiesorenclosureof
storedmaterials.Itissubjecttosuchrestrictionsas
buildingcodelimitationsonheightandfloorarea.
1.2 Systems Constraintsincludeabilitytowithstandloadsfrom
humanactivitiesandfromnaturalforceslikewind
Systems design of a project comprises a rational, and earthquakes. The assemblage generally con-
orderlyseriesofstepsthatleadstothebestdecision sists of a roof, floors, walls, doors, windows,
for a given set of conditions (Art. 1.9). The pro- structural framing for supporting the other com-
cedurerequires: ponents, and means for heating, ventilating, and
coolingtheinterior.
Analysisofaprojectasasystem Ahighwayorarailroadisasystemconstructed
Synthesis, or selection of components to form a for the specific purpose of providing a suitable
systemthatmeetsspecificobjectives surface, or road, for movement of vehicles.
The restrictions are imposed by the terrain to be
Appraisal of system performance, including com-
traversed by the highway or railroad, vehicle
parisonswithalternativesystems
characteristics,andvolumeoftraffic.Ahighwayis
Feedbacktoanalysisandsynthesisofinformation used primarily by rubber-tired vehicles whose
obtained in system evaluation, to improve the velocity and direction of travel are controlled by
design human drivers. A railroad is used by vehicles
equipped with steel wheels designed to ride on
The prime advantage of the procedure is that, railsthatcontroldirectionoftravel,whilevelocityis
through comparisons of alternatives and data controlleddirectlybyahumandriverorindirectly
feedback to the design process, system design by remote controls. Both highway and railroad
converges on an optimum, or best, system for the assemblages consist of a right-of-way and road
given conditions. Another advantage is that the betweenpointstobeserved,entrancesandexitsfor
procedureenablesdesignerstoclarifytherequire- vehicles, traffic-control devices, safety devices,
mentsfortheprojectbeingdesigned.Stillanother bridges, tunnels, stations for refueling and
advantage is that the procedure provides a servicing vehicles, stations for embarking or
common basis of understanding and promotes disembarking passengers or loading or unloading
cooperation between the specialists in various freight, and convenience stations for drivers and
aspectsofprojectdesign. passengers.
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SYSTEMS DESIGN
Systems Design n 1.3
A tunnel is an underground system and a essential to the required performance of the
bridge is an aboveground system constructed for system. Also, every component affects the per-
the specific purpose of providing passage for formanceofatleastoneothercomponent,andthe
pedestrians, vehicles, pipes, cables, or conveyors requiredperformanceofthewholesystemimposes
past obstructions. A tunnel is subject to such restrictionsoneverycomponent.
restrictions as exclusion of earth, rock, and
unwanted water from the passageway, whereas a
bridge must carry the passageway at required
distancesaboveobstructions.Atunnelassemblage Subsystems n A group of components of a
consistsprimarilyofthepassagewayandsupports
systemmayalsobeasystemcalledasubsystem.It
or lining for housing the passageway. The
toomaybedesignedasasystem,butitsgoalmust
assemblagemayalsoincludedrainage,ventilation,
betoassistthesystemofwhichitisacomponentto
and lighting provisions. A bridge assemblage
meet the system objectives. Similarly, a group of
consists primarily of the passageway, structural
components of a subsystem may also be a system
framingforsupportingit,andpiersandabutments
calledasubsubsystem.
for holding the other components at suitable
For brevity, a project’s major subsystems often
heightsabovetheobstructions.
are referred to as systems. For example, in a
Water supply is a system with the specific
building, such major subsystems as structural
purposeofprovidingwatertomeethumanneeds.
framing, walls, or plumbing are called systems.
Therestrictionsonthesystemaregenerallycriteria
Their components that meet the definition of a
for quantity and quality of water. The assemblage
systemarereferredtoassubsystems.Forinstance,
usually consists of a water source; means for
plumbing consists of water-supply, wastewater,
extracting water in desired quantities from the
and gas-supply subsystems. The wastewater sub-
sourceandconveyingittopointswhereitisneeded;
system in turn includes various fixtures for col-
aplantfortreatingthewatertomeetqualitycriteria;
lectinganddischargingwastewater;soilandwaste
pipes with diameters adequate for passing the
pipes; pipe supports; traps; drains; sewers; and
desired quantities without excessive loss of pres-
vents. In a complex system, such as a building,
sure;valves;reservoirs;dams;andfixturesandother
subsystems and other components may be com-
devicesforflowcontrolatpointsofuse.
binedinvariouswaystoformdifferentsystems.
Sewage collection, treatment, and disposal is a
system with the specific purpose of removing
wastewater from points where it is created and
discharging the wastes in such condition and in 1.3 Systems Analysis
such locations that human health and welfare are
In systems analysis, a system is resolved into its
not endangered and there is little or no adverse
basic components. Subsystems are determined,
effect on the environment. The restrictions on
and then the system is investigated to determine
the system generally are quantity and character-
the nature, interaction, and performance of the
istics of the wastes, quantity of water needed for
system as a whole. The investigation should
conveyance of the wastes, and criteria for the
answersuchquestionsas:
products to be discharged from the system. The
assemblageconsists offixturesorother meansfor
Whatdoeseachcomponent(orsubsystem)do?
collectingwastesatthesourceandremovingthem
withwater;meansforconveyingthewastewaterto Whatdoesthecomponentdoitto?
atreatmentplantandthentransportingthetreated
Howdoesthecomponentserveitsfunction?
products to points of disposal or reuse; the
treatment plant where the wastes are removed or Whatelsedoesthecomponentdo?
rendered innocuous; means for safe disposal or Whydoesthecomponentdothethingsitdoes?
reuse of the treated wastes and water; pipes;
Whatmustthecomponentreallydo?
valves;andvariousdevicesforflowcontrol.
Note that in all the preceding examples the Canthecomponentbeeliminatedbecauseitisnot
system consists of two or more interrelated, essential or because another component can
compatible components. Every component is assumeitstasks?
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SYSTEMS DESIGN
1.4 n Section One
1.4 Goals, Objectives, and range of values within which the performance of
Criteria thesystemmustliefortheobjectivetobemet.The
criterionshouldbecapableofservingasaguidein
Before design of a system can commence, the evaluationofalternativesystems.Forexample,for
designershouldestablishtheowner’sgoalsforthe fire resistance of a building wall, the criterion
system. These goals state what the system is to mightbe2-hfirerating.
accomplish,howitwillaffecttheenvironmentand
other systems, and how other systems and the Weights n In addition to establishing criteria,
environment will affect the project. Goals should the designers should weight the objectives in
be generalized but brief statements, encompas- accordance with the relative importance of the
sing all the design objectives. They should be objectives to the client (see also Art. 1.10). These
sufficiently specific, however, to guide generation weightsalsoshouldserveasguidesincomparisons
of initial and alternative designs and control ofalternatives.
selectionofthebestalternative.
Asimpleexampleofagoalis:Designabranch
post-office building with 100 employees that is to 1.5 Constraints and
be constructed on a site owned by the client. The Standards
building should harmonize with neighboring
structures. Design must be completed within 120 Besides establishing goals and objectives for a
daysandconstructionwithin1year.Construction systematthestartofdesign,thedesignersshould
costisnottoexceed$1,250,000. also define constraints on the system. Constraints
The goals for a systems design applied to a are restrictions on the values of design variables
subsystemservethesamepurposeasforasystem. thatrepresentpropertiesofthesystemandthatare
Theyindicatetherequiredfunctionofthesubsystem controllablebythedesigners.
andhowitaffectsandisaffectedbyothersystems. Designersareseldomcompletelyfreetochoose
any values desired for properties of a system
component.Onereasonisthatacomponentwitha
Objectives n With the goals known, the desired property may not be readily available, for
designers can define the system objectives. These
instance, a 9-in-long brick. Another reason is that
objectivesaresimilartogoalsbutsupplyindetail
thereusuallyarevariousrestrictions,whichmaybe
the requirements that the system must satisfy to
legal,suchasbuildingorzoningcoderequirements,
attainthegoals.
oreconomic,physical,chemical,temporal,psycho-
Whenlistingobjectives,thedesignersmaystart
logical, sociological, or esthetic. Such restrictions
with broad generalizations that they will later
mayfixthe values ofthe componentpropertiesor
developatmoredetailedlevelstoguidedesignof
establisharangeinwhichtheymustlie.
the system. Certain objectives, such as minimi-
zation of initial costs, life-cycle costs, or construc-
Standards n At least one standard must be
tion time, should be listed. Other objectives that
associated with each constraint. A standard is a
applytothedesignofalmosteverysimilarproject,
value or range of values governing a property of
suchasthehealth,safety,andwelfareobjectivesof
the system. The standard specifying a fixed value
building codes, zoning, and Occupational Safety
maybeaminimumormaximumvalue.
and Health Administration regulations, are too
For example, a designer may be seeking to
numeroustolistandmaybeadoptedbyreference.
determine the thickness of a load-bearing concrete
Objectives that are listed should be sufficiently
masonry wall. The governing building code may
specific to guide planning of the project and
statethatthewall,basedonwindloadrequirements
selection of components with specific charac-
andtheheightofthewall,shallbenolessthan8in
teristics. Also, some objectives should specify the
thick.Thisrequirementisaminimumstandard.The
degreeofcontrolneeded foroperation ofsystems
designermaythenselectawallthicknessof8inor
providedtomeettheotherobjectives.
more.Therequirementsofotheradjoiningsystems,
however,indicatethatforthewalltobecompatible,
Criteria n At least one criterion must be wall thickness may not exceed 16in. This is a
associated with each objective. The criterion is a maximum standard. Bricks, however, may be
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SYSTEMS DESIGN
Systems Design n 1.5
availableonlyinnominalwidthsof4in.Hence,the designs, designers may represent the system by a
constraints limit the values of the controllable modelthatenablesthemtoanalyzethesystemand
variable,inthiscasewallthickness,to8,12,or16in. evaluate its performance. The model should be
simple, consistent with the role for which it is
selected, for practical reasons. The cost of for-
1.6 Construction Costs mulatingandusingthemodelshouldbenegligible
comparedwith the cost ofassembling andtesting
Constructioncostofaprojectusuallyisadominant
theactualsystem.
design concern. One reason is that if construction
For every input to a system, there must be a
cost exceeds the owner’s or client’s construction
known,correspondinginputtothemodelsuchthat
budget, the project may be canceled. Another
the model’s responses (output) to that input are
reason is that some costs, such as interest on the
determinable and correspond to the system’s
investment, which occur after completion of the
responses to its input. The correlation may be
project often are proportional to the initial cost.
approximate but nevertheless should be close
Hence, owners usually try to keep that cost
enoughtoservethepurposesforwhichthemodel
low. Designing a project to minimize construction
istobeused.Forexample,forcostestimatesduring
cost, however, may not be in the owner’s best
theconceptual phaseofdesign,acostmodelmay
interests. There are many other costs the owner
be used that yields only reasonable guesses of
incursduringtheanticipatedlifeoftheprojectthat
construction costs. The cost model used in the
shouldbetakenintoaccount.
contract documents phase, however, should be
Forexample,afteraprojecthasbeencompleted,
accurate.
theownerincursoperationandmaintenancecosts.
Modelsmaybeclassifiedasiconic,symbolic,or
Such costs are a consequence of decisions made
analog.Theiconictypemaybetheactualsystemor
during project design. Often, postconstruction
apartofitormerelybearaphysicalresemblanceto
costs are permitted to be high so that initial costs
the actual system. The iconic model is often used
can be kept within the owner’s construction
for physical tests of a system’s performance, such
budget;otherwise,theprojectwillnotbebuilt.
Life-cyclecostisthesumofinitial,operating,and as load or wind-tunnel tests or adjustment of
controlsforairorwaterflowintheactualsystem.
maintenancecosts.Ideally,life-cyclecostshouldbe
Symbolic models represent by symbols a
minimized, rather than initial or construction cost,
system’s input and output and are usually
becausethisenablestheownertoreceivethegreatest
amenable to mathematical analysis of a system.
returnontheinvestmentintheproject.
They enable relationships to be generally, yet
Nevertheless,aclientusuallyestablishesacon-
compactly, expressed, are less costly to develop
struction budget independent of life-cycle cost.
andusethanothertypesofmodels,andareeasyto
Thisoftenisnecessarybecausetheclientdoesnot
manipulate.
haveadequatecapitalforanoptimumprojectand
Analog models are real systems but with
places too low a limit on construction cost. The
physical properties different from those of the
client hopes to have sufficient capital later to pay
actual system. Examples include dial watches for
forthehigheroperatingandmaintenancecostsor
measuring time, thermometers for measuring
for replacement of undesirable, inefficient com-
temperature (heat changes), dial gauges for
ponents. Sometimes, the client establishes a low
measuring small movements, flow of electric
construction budget because the goal is a quick
current for measuring heat flow through a metal
profitonearlysaleoftheproject,inwhichcasethe
plate, andsoap membranes for measuring torsion
client has little or no concern with the project’s
inanelasticshaft.
future high operating and maintenance costs. For
Variables representing a system’s input and
these reasons, construction cost frequently is a
properties may be considered independent vari-
dominantconcernindesign.
ables,oftwotypes:
1.7 Models 1. Variables that the designers can control:
x ,x ,x ,...
Forconvenience in evaluating the performance of 1 2 3
a system and for comparison with alternative 2. Variablesthatareuncontrollable:y ,y ,y ,...
1 2 3
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SYSTEMS DESIGN
1.6 n Section One
Variables representing system output, or per- costs of all the subsystems, to which should be
formance,maybeconsidereddependentvariables: addedcontractor’soverheadandprofit.
z ,z ,z ,... These variables are functions of the For more information on cost estimating, see
1 2 3
independent variables. The functions also contain Art.4.7.
parameters, whose values can be adjusted to
calibrate the model to the behavior of the actual
system.
1.8 Optimization
Cost Models n As an example of the use of Theobjectiveofsystemsdesignistoselectthebest
models in systems design, consider the following systemforagivensetofconditions;thisprocessis
costmodels: known as optimization. When more than one
C¼Ap (1:1) propertyofthesystemistobeoptimizedorwhen
thereisasinglecharacteristictobeoptimizedbutit
whereC¼constructioncostofproject is nonquantifiable, an optimum solution may or
A¼convenientparameterforaproject,such may not exist. If it does exist, it may have to be
found by trial and error with a model or by
asfloorarea(squarefeet)inabuilding,
methodssuchasthosedescribedinArt.1.10.
length(miles)ofahighway,population
When one characteristic, such as construction
(persons) served by a water-supply or
cost, of a system is to be optimized, the criterion
sewagesystem
maybeexpressedas
p¼unit construction cost, dollars per unit
(squarefeet,miles,persons) Optimize zr¼fr(x1,x2,x3,...,y1,y2,y3,...)
This is a symbolic model applicable only in the (1:4)
early stages of design when systems and sub- wherez ¼dependentvariabletobemaximizedor
systemsarespecifiedonlyingeneralform.BothA r
minimized
and p are estimated, usually on the basis of past
experiencewithsimilarsystems. x¼controllablevariable,identifiedbysub-
X script
C¼ Aipi (1:2) y¼uncontrollable variable, identified by
whereA ¼convenientunitofmeasurementforith subscript
i
system f ¼objectivefunction
r
p ¼costperunitforithsystem
i
Generally, however, there are restrictions on the
This symbolic model is suitable for estimating
valuesoftheindependentvariables.Theserestric-
project construction cost in preliminary design
tionsmaybeexpressedas
stages after types of major systems have been
selected.Equation(1.2)givesthecostasthesumof f (x ,x ,x ,...,y ,y ,y ,...)(cid:1)0
1 1 2 3 1 2 3
the cost of the major systems, to which should be f (x ,x ,x ,...,y ,y ,y ,...)(cid:1)0 (1:5)
2 1 2 3 1 2 3
added the estimated costs of other systems and
f (x ,x ,x ,...,y ,y ,y ,...)(cid:1)0
contractor’soverheadandprofit. n 1 2 3 1 2 3
X
C¼ Ap (1:3) SimultaneoussolutionofEqs.(1.4)and(1.5)yields
j j the optimumvalues ofthevariables. The solution
whereA ¼convenientunitofmeasurementforjth may be obtained by use of such techniques as
j
subsystem calculus, linear programming, or dynamic pro-
gramming, depending on the nature of the vari-
p ¼costperunitforjthsubsystem
j ablesandthecharacteristicsoftheequations.
This symbolic model may be used in the design Direct application of Eqs. (1.4) and (1.5) to a
development phase and later after components of wholecivilengineeringproject,itssystemsandits
the major systems have been selected and greater largersubsystems,usuallyisimpracticalbecauseof
accuracy of the cost estimate is feasible. Equation thelargenumberofvariablesandthecomplexityof
(1.3) gives the construction cost as the sum of the their relationships. Hence, optimization generally
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SYSTEMS DESIGN
Systems Design n 1.7
has to be attained differently, usually by such system because of the effect of its weight on
methodsassuboptimizationorsimulation. columnsandfootings.Alow-costroofmaybevery
heavy,requiringcostlycolumnsandfootings.Cost
ofalightweightroof,however,maybesohighasto
Simulation n Systems with large numbers of
offsetanysavingsfromlessexpensivecolumnsand
variables may sometimes be optimized by a
footings.Analternativeroofmayprovideoptimum
process called simulation, which involves trial
results.)
and error with the actual system or a model. In
simulation, the properties of the system or model
areadjustedwithaspecificinputorrangeofinputs
to the system, and outputs or performance are 1.9 Systems Design
measureduntilanoptimumresultisobtained.
Procedure
Whenthevariablesarequantifiableandmodels
areused,thesolutionusuallycanbeexpeditedby
Article 1.2 defines systems and explains that
useofcomputers.Theactualsystemmaybeused
systemsdesigncomprisesarational,orderlyseries
whenitisavailableandaccessible,andchangesin
ofstepswhichleadstothebestdecisionforagiven
itwillhavelittleornoeffectonconstructioncosts.
set of conditions. Article 1.2 also lists the basic
For example, after installation of air ducts in a
components of the procedure as analysis, syn-
building, an air conditioning system may be
thesis,appraisal,andfeedback.Followingisamore
operated for a variety of conditions to determine
formaldefinition:
the optimum damper position for control of air
Systems design is the application of the scientific
flowforeachcondition.
methodtoselectionandassemblyofcomponentstoform
the optimum system to attain specified goals and
Suboptimization n This is a trial-and-error objectives while subject to given constraints or
processinwhichdesignerstrytooptimizeasystem restrictions.
byfirstoptimizingitssubsystems.Suboptimization The scientific method, which is incorporated
issuitable when components influence each other into the definitions of value engineering and
inseries. systemsdesign,consistsofthefollowingsteps:
Consider,forexample,astructuralsystemfora
building consisting only of roof, columns, and 1. Collecting data and observations of natural
footings. The roof has a known load (input),
phenomena
exclusive of its own weight. Design of the roof
2. Formulatingahypothesiscapableofpredicting
affectsthecolumnsandfootingsbecauseitsoutput
futureobservations
equals the loads on the columns. Design of the
columns affects only the footings because the 3. Testingthehypothesistoverifytheaccuracyof
column output equals the loads on the footings. its predictions and abandoning or improving
Design of the footings, however, has no effect on thehypothesisifitisinaccurate
anyoftheotherstructuralcomponents.Therefore,
the structural components are in series, and they
maybedesignedbysuboptimizationtoobtainthe Systems design should provide answers to the
minimum construction cost or least weight of the followingquestions:
system.
Suboptimizationofthesystemmaybeachieved 1. Whatdoestheclientorowneractuallywantthe
by first optimizing the footings, for example, project to accomplish (goals, objectives, and
designing the lowest-cost footings. Next, the associatedcriteria)?
designofboththecolumnsandthefootingsshould
2. What conditions exist, or will exist after
be optimized.(Optimization ofthe columnsalone
construction, that are beyond the designers’
will not yield an optimum structural system
control?
because of the effect of the column weight on the
footings.) Finally, roof, columns, and footings 3. Whatrequirementsfortheprojectorconditions
together should be optimized. (Optimization of affecting system performance does design
theroofalonewillnotyieldanoptimumstructural control(constraintsandassociatedstandards)?
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SYSTEMS DESIGN
1.8 n Section One
4. What performance requirements and time and 2. Designofapre-engineeredbuilding(iftheclient
costcriteriacan theclient anddesignersuseto needsseveralofthesametypeofstructure).
appraisesystemperformance? 3. Assembling a building with prefabricated
components or systems. This type of construc-
Collection of information necessary for design
tion is similar to that used for pre-engineered
oftheprojectstartsattheinception ofdesign and
buildings except that the components pre-
may continue through the contract documents
assembled are much smaller parts of the
phase. Data collection is an essential part of sys-
buildingsystem.
temsdesign,butbecauseitiscontinuousthrough-
outdesign,itisnotlistedinthefollowingasoneof 4. Specification of as many prefabricated and
thebasicsteps. standard components as feasible. Standard
To illustrate, the systems design procedure is components are off-the-shelf items, readily
resolved into nine basic steps in Fig. 1.1. Because availablefrombuildingsupplycompanies.
value analysis is applied in steps 5 and 6, steps 4 5. Repetition of the same component as many
through8coveringsynthesis,analysis,andapprai- times as possible. This may permit mass
sal may be repeated several times. Each iteration production of some nonstandard components.
shouldbringthedesignclosertotheoptimum. Also,repetitionmayspeedconstructionbecause
Toprepareforstep1,thedesignersshoulddraw fieldpersonnelwillworkfasterastheybecome
up a project program, or list of the client’s familiarwithcomponents.
requirements, and information on existing con-
6. Design of components for erection so that
ditionsthatwillaffectprojectdesign.Insteps1and
building trades will be employed continuously
2, the designers use the available information to
onthesite.Workthatcompelsonetradetowait
define goals, objectives, and constraints to be
forcompletionofworkbyanothertradedelays
satisfiedbythesystem(seeArts.1.4andl.5).
constructionandiscostly.
Modeling n In step 4, the designers should
Synthesis n In step 3, the designers must
represent the system by a simple model of
conceive at least one system that satisfies the
acceptable accuracy. In this step, the designers
objectives and constraints. To do so, they rely on
should determine or estimate the values of the
theirpastexperience,knowledge,imagination,and
independent variables representing properties of
creative skills and advice from consultants,
thesystemanditscomponents.Themodelshould
including value engineers, construction experts,
then be applied to determine optimum system
and experienced operators of the type of facilities
performance (dependent variables) and corre-
tobedesigned.
sponding values of controllable variables (see
In addition, the designers should develop
Arts. 1.7 and 1.8). For example, if desired system
alternativesystemsthatmaybemorecost-effective
performance is minimum construction cost, the
and can be built quicker. To save design time in
modelshould beusedtoestimate thiscostandto
obtaining an optimum system, the designers
select components and construction methods for
should investigate alternative systems in a logical
thesystemthatwillyieldthisoptimumresult.
sequence for potential for achieving optimum
results.Asanexample,thefollowingisapossible
sequenceforabuilding: Appraisal n In step 5 of systems design, the
designers should evaluate the results obtained in
1. Selectionofapre-engineeredbuilding,asystem step 4. The designers should verify that con-
struction and life-cycle costs will be acceptable to
thatisprefabricatedinafactory.Suchasystem
theclientandthattheproposedsystemsatisfiesall
is likely to be low cost because of the use of
objectivesandconstraints.
mass-productiontechniquesandfactorywages,
which usually are lower than those for field
personnel. Also, the quality of materials and ValueAnalysisandDecisionnDuringthe
constructionmaybebetterthanforcustom-built preceding steps, value analysis may have been
structuresbecauseofassemblyundercontrolled appliedtopartsoftheproject(seeArt.1.10).Instep
conditionsandclosesupervision. 6,however,valueanalysisshouldbeappliedtothe
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SYSTEMS DESIGN
Systems Design n 1.9
Fig. 1.1 Basicstepsinsystemsdesigninadditiontocollectionofnecessaryinformation.
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SYSTEMS DESIGN
1.10 n Section One
wholesystem.Thisprocessmayresult inchanges principals and other senior professionals.
only to parts of the system, producing a new Checkers should seek to ensure that calculations,
system, or several alternatives to the original drawings, and specifications are free of errors,
designmaybeproposed. omissions, and conflicts between building
Insteps7and8,therefore,thenewsystems,or components.
at least those with good prospects for being the For projects that are complicated, unique, or
optimum, should be modeled and evaluated. likelytohaveseriouseffectsiffailureshouldoccur,
Duringandafterthisprocess,completelydifferent theclientorthedesignteammayfinditadvisable
alternativesmaybeconceived.Asaresult,steps4 to request a peer review of critical elements of
through8shouldberepeatedforthenewconcepts. theprojectorofthewholeproject.Insuchcases,the
Finally,instep9,thebestofthesystemsstudied reviewshouldbeconductedbyprofessionalswith
shouldbeselected. expertise equal to or greater than that of the
original designers; that is, by peers, and they
shouldbeindependentofthedesignteam,whether
DesignbyTeam(Partnering)nForefficient
part of the same firm or an outside organization.
execution of systems design of a civil engineering
Thereviewshouldbepaidforbytheorganization
project,adesignorganizationsuperiortothatused
that requests it. The scope may include investi-
for traditional design is highly desirable. For
gation of site conditions, applicable codes and
systems design, the various specialists required
governmental regulations, environmental impact,
should form a design team, to contribute their
designassumptions,calculations,drawings,speci-
knowledgeandskillsinconcert.
fications, alternative designs, constructability, and
One reason why the specialists should work
conformancewiththebuildingprogram.Thepeers
closelytogetheristhatinsystemsdesigntheeffects
should not be considered competitors or replace-
of each component on the performance of the
mentsoftheoriginaldesignersandthereshouldbe
whole project and the interaction of components
ahighlevelofrespectandcommunicationbetween
mustbetakenintoaccount.Anotherreasonisthat
both groups. A report of the results of the review
for cost-effectiveness, unnecessary components
shouldbesubmittedtotheauthorizingagencyand
should be eliminated and, where possible, two or
theleaderofthedesignteam.
more components should be combined. When the
(For additional information on peer review
components are the responsibility of different
contact the American Consulting Engineering
specialists, these tasks can be accomplished with
Council, 1015 15th Street, N.W., Washington, DC
ease only when the specialists are in direct and
20005, website www.acec.org or the American
immediatecommunication.
Society of Civil Engineers, 1801 Alexander Bell
In addition to the design consultants required
Drive,RestonVirginia20191-4400,www.asce.org).
for traditional design, the design team should be
staffed with value engineers, cost estimators,
construction experts, and building operators and
ApplicationofSystemsDesignnSystems
users experienced in operation of the type of
design may be used profitably in all phases
project to be constructed. Because of the diversity
of project design, but it is most advantageous in
of skills present on such a team, it is highly
the early design stages. One system may be
probablethatallramificationsofadecisionwillbe
substituted for another, and components may
consideredandchancesformistakesandomissions
be eliminated or combined in those stages with
willbesmall.
littleornocost.
In the contract documents phase, systems
Project Peer Review n The design team design preferably should be applied only to the
should make it standard practice to have the details being worked out then. Major changes are
outputofthevariousdisciplinescheckedattheend likely to be costly. Value analysis, though, should
of each design step and especially before incor- be applied to the specifications and construction
poration in the contract documents. Checking of contractbecausesuchstudiesmayachievesignifi-
theworkofeachdisciplineshouldbeperformedby cantcostsavings.
a competent practitioner of that discipline other Systems design should be applied in the
than the original designer and reviewed by construction stage only when design is required
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