CHAPTER 19 Structural Idealization..................................................................
Sofarwehavebeenconcernedwithrelativelyuncomplicatedstructuralsectionswhichinpracticewould
beformedfromthinplateorbytheextrusionprocess.Whilethesesectionsexistasstructuralmembers
intheirownright,theyarefrequentlyused,aswesawinChapter11,tostiffenmorecomplexstructural
shapessuchasfuselages,wings,andtailsurfaces.Thus,atwo-sparwingsectioncouldtaketheform
showninFig.19.1,inwhichZ-sectionstringersareusedtostiffenthethinskinwhileanglesections
formthesparflanges.Clearly,theanalysisofasectionofthistypewouldbecomplicatedandtedious
unlesssomesimplifyingassumptionsaremade.Generally,thenumberandnatureofthesesimplifying
assumptionsdeterminetheaccuracyandthedegreeofcomplexityoftheanalysis;themorecomplex
theanalysis,thegreatertheaccuracyobtained.Thedegreeofsimplificationintroducedisgovernedby
theparticularsituationsurroundingtheproblem.Forapreliminaryinvestigation,speedandsimplicity
areoftenofgreaterimportancethanextremeaccuracy;ontheotherhand,afinalsolutionmustbeas
exactascircumstancesallow.
Complexstructuralsectionsmaybeidealizedintosimpler“mechanicalmodel”formswhichbehave,
undergivenloadingconditions,inthesame,orverynearlythesame,wayastheactualstructure.We
shallsee,however,thatdifferentmodelsofthesamestructurearerequiredtosimulateactualbehavior
underdifferentsystemsofloading.
19.1 Principle...............................................................................................
InthewingsectionofFig.19.1,thestringersandsparflangeshavesmallcross-sectionaldimensions
comparedwiththecompletesection.Therefore,thevariationinstressoverthecrosssectionofastringer
Fig.19.1
Typical wing section.
Copyright©2010,T.H.G.Megson. PublishedbyElsevierLtd. Allrightsreserved.
DOI:10.1016/B978-1-85617-932-4.00019-1 537