Treść książki

Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
6
HansDeBacker,AmelieOuttier,PhilippeVanBogaert
1.THEORTHOTROPICSTEELBRIDGEDECKCONCEPT
1.1.Introduction
Duetotheircontributiontothegeneralresistanceofthestructure,by
significantlyreducingthetotalweightoftheconstruction,orthotropicsteeldeck
platesareoneofthemostcommonlyuseddecksystemsforlargerspanbridges.
Thiscontributionalsoallowsthedesignoftiedarchbridgesofamoremoderate
spanbutwithanextremelylowstructuraldepth,e.g.astructuraldepthofonly1
mforadoubletrackrailwaybridgewithalengthjustover110m.Therecent
designpracticeinBelgiumhasusedthisadvantageforabout10archbridges,
mostofthemapartofthedevelopmentoftheEuropeannetworkofHighSpeed
Lineswhereaconsiderablenumberofshorttomediumspanbridgesforthe
high-speedrailwaylineshavebeendesigned.However,orthotropicdeckplates
arealsohighlysensitivetofatiguedamage,requiringanin-depthfatigue
analysis,ensuringthefulfillmentofallfatiguecriterions.Thisproblemismainly
causedbymanystressconcentrationsandlargeamplitudesofstressvariations
causedbyroadtrafficinparticular.Recentinternationalresearchhasextensively
studiedthisphenomenon[1].
1.2.Stressfieldinanorthotropicdeck
Thecomplexstressfieldinanorthotropicroadbridgecanbeattributed
tothreedifferentactionsworkinginaunion.Thefirstoftheseactionsiscaused
bythemembranestressesoccurringbecauseofthebendingofthelateralmain
girdersofthebridge,withthebridgedeckitselfactingastheirupperflanges.
Thisaction,infact,representsthemainactionoftheoverallbridgeconcept.
Theorthogonalanisotropy(i.e.orthotropicbehavior)ofthedeckwiththe
distributionoftheloadworkingonthedeckcorrespondingtodifferentrigidities
oftheribsandthecrossbeamsisresponsibleforthesecondactionexistinginthe
deckplate.
Finally,thelocalbendingalonglongitudinalortransverseaxisofthedeck
plateelementsunderdirectwheelloadingcausesthethirdactionexistinginan
orthotropicroadbridge.Thelargeststressconcentrationsforthisdeckconcept
arefoundattheribswherelongitudinalstiffenersareconnectedtothedeckplate
andbothhoggingandsaggingbendingeffectsarefound,aswellasatthe
intersectionofbothlongitudinalandcrossstiffeners(seeFig.1).
1.3.Influenceofwearingcourses
Roadpavementsonthedeckplatemaycontributetothedispersalof
concentratedwheelloadsfromroadtraffic.Thishasalsobeenobservedfor
railwayloading,wheretheballastmaydispersethetrackloads.However,
wearingcoursesandpavementsarenotalwaysavailableorsufficienttoreduce
theheavytrafficloads,forinstanceinthecaseofmovablebridges.Anexample