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Beam Bridges - Design Technology Department

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In its most basic form, a beam bridge consists of a horizontal beam that is supported at each end by piers. The weight of the beam pushes straight down on the ... BeamBridges -DesignTechnology Beambridges Abeamor"girder"bridgeisthesimplestkindofbridge. Inthepasttheymayhavetakentheformofalogacrossastream buttodaytheyaremorefamiliartouslargeboxsteelgirderbridges. Therearelotsofdifferenttypesofbeambridges. Abeambridgeneedstobestiff.Itneedstoresisttwistingandbending underload. Initsmostbasicform,abeambridgeconsistsofahorizontalbeam thatissupportedateachendbypiers.Theweightofthebeampushes straightdownonthepiers. Underload,thebeam'stopsurfaceispusheddownorcompressed whilethebottomedgeisstretchedorplacedundertension. Ifweimaginethatthereisanimaginarylinerunningdownthecentre ofthebeamthislineremainsatitsoriginallengthwhilethematerial aboveiscompressedandthematerialbelowisstretched.Thisline isreferredtoastheneutralaxis. Thefartherapartitssupports,theweakerabeambridgegets.As aresult,beambridgesrarelyspanmorethan250feet.Thisdoesn't meanbeambridgesaren'tusedtocrossgreatdistancesitonlymeans thattheremaybeaseriesofbeambridgesjoinedtogether,creating what'sknownasa"continuousspan." TypesofBeamBridges   ALargeBoxGirderBridge ImageofaBeamBridge Beams Beamsusedinbuildingsmayvaryincrosssectionalshape.Some maybesolidorhollow.Belowarethreedifferentshapedbeams.The firstbeamisaboxsection,thesecondanIsectionbeam andthethirdanLsectionbeam.Solidbeamsareheavierthan hollowbeams.Beamsliketheone'sbelowaregivenaspecialcross sectionforstrengthandrigidity.Theymaybeasstrongasthe solidbeamsbutarealotlighter.Wemaydescribethemashavinga goodstrengthtoweightratio. ReinforcedConcreteBeams Concretebeamsthatareusedinbuildingsashorizontalsupporting piecesabovedoorsandwindows.Thesearecalledlintels.These lintelsarereinforcedwithsteelrodscastintheconcrete.Thesteel rodsarenormallyplacedbelowtheneutralaxis.Thecombinationof morethanonematerialmakesthereinforcedconcreteacomposite material.Thesteelenhancesthestrengthoftheconcretewhen stretchedundertension. Concreteisverystrongincompressionbutweakintension.Wedescribe thisasoneofthepropertiesofconcrete. Task 1.Usingcardandgluemakethethreebeamsabove.Testthebeams individuallyforstructuralstrengthandresistancetoloads(stress) incompressionandtension.Wecanachievethisbyplacingthebeams betweeneitherdesksorchairs.Ifweightsarehungorplacedontop ofthebeamsweshouldeventuallybeabletowitnesstheshapeof thebeamsaltering.Itwillindicatethepointsofweakness.They mayfoldorbenddependinguponhowmuchweightishungfromthem. 2.Testeachbeamwithincreasinglyheavierweights.Whilsthanging theweightsfromthebeamsrecordboththesizeoftheweightandthe structuraldamageifanyithasuponthebeam.Placetheseresultsinto aspreadsheetorrecordyourresultsinachartwithnotesdescribing thechanges. Youmayconsiderusinganewtongaugeorclockgaugetotestthebeams. 3.Onceyouhavecompletedyourexperimentexplainwhichbeamheldthe heaviestweightsforthelongestlengthoftimewithoutfoldingorcrumpling inanyway. 4.Explainwhythistypeofbeamappearedtobethestructurallystronger thantheothertwo? 5.Suggestwherethistypeofbeamisusedinarchitecturalstructures? 6.Usingadditionalcardattempttoincreasethestrengthofthebeam? Remembertoomuchadditionalcardwillmakethebeamtooheavy.Itwill endupwithalowstrengthtoweightratio.   Home  

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