BehaviorandStrengtheningofHollowSection TubularK-joints

Abstract

Thischapterpresentsabrief summaryfor the currentresearch.Itincludes the mainconclusionsas wellas recommendationsfor future work.

A comprehensiveliteraturereviewisinvestigatedinordertocover different aspectsofresearch thatdealswith the hollow sectionK-joints.Itis foundthattheusageofhollowsectionsisexpandingevery day andbeing includedinsuperstructuresallovertheworld.Oneof theproblemsthatface the usageofK-stiffenedhollowsectionsisthatnotmany studiedthestiffeningon K-hollowsections.Themainaim ofthisresearchistostudy thebehaviorof stiffenedandunstiffenedcircularhollowsectionK-jointunder axialloadingand theeffectofdifferentgeometricparametersonthemaximum capacityofthe hollowsectionjoints.

A finite element model is developed using ANSYS finite element package. Differentfactorsaretakenintoconsiderationwhenmodelingthe circular hollow sectionK-jointsuchasmaterialandgeometric nonlinearitiesin additiontothe geometric imperfections.

The proposedfinite elementmodelsare validatedagainstpreviously publishedexperimentalandanalyticalresultsby differentresearchers.The comparisonshowedagoodagreementintermsofultimatecapacity,failure mode andload todisplacementrelationship. Therefore,the modelisconsidered reliable enoughtosimulate the specimenscarriedinthe lab.

Samefactorsthatwereconsideredinthevalidatedmodelareconsidered inthe modelsusedfor the parametric studyinidealconditions.

Acomprehensiveparametricstudy iscarriedinordertoinvestigatethe effectofgeometricparametersonthemaximum capacity ofunstiffenedhollow sectionK-joints.Inadditionto,increasethemaximumcapacity ofjointsby usingdifferenttechniquesfor strengthening.

Theresultsobtainedfrom finiteelementmodelsforunstiffenedCHSK- joints are compared to their corresponding obtained fromAISC equations. However, the AISC isfoundtobe conservative insome cases.

The main studied geometric parameters are diameter ratio between branchandchord(β),Theratio ofbranchto chordwallthickness (τ),radiusto thicknessratioof thechord(),Theratioof chordpreload toyieldnormal capacityofthechord(R)andThe unequalbranchloading(Ra).Itisfoundthatt diameterratiobetweenbranchandchord(β), radiustothicknessratioofthe chord()havethemajoreffectonthecapacityoftheCHSK-joints,andby usingrightcombinationsthe maximumcapacitycanbe rapidlyincreased.

Anotherparametricstudy iscarriedusingthesameunstiffenedjointsand introduceddifferentmethodsofstiffeningtoincreasethemaximum capacity of thejoints. Different geometric parametersare investigatedinadditionto stiffenerssizes.

Themainstudiedparametersinthestiffenedstudy arestiffeningusing innerringstiffeners, addingacollar platetothechordandusingagussetplate. Ineachcaseofstiffening theeffectofdiameter ratiobetweenbranchandchord (β) andradius to thicknessratio of the chord() and different stiffener size and thicknessare investigated. The stiffeningusinggussetplateisfoundtogive the maximumincrease injointcapacity.

6-2 Conclusions

Basedon the numericalanalysisresultsofaxial loadedunstiffenedand unstiffenedCHS K-jointwithdifferentgeometricconfigurations, thefollowing conclusionscanbe made:

6-2-1Conclusionsofgeometric configurationsof unstiffenedCHSK-joint

- β,andchordpreloadappeartobethemosteffectiveparametersonthe strengthof the joint.

- Chordplastificationisconsideredtobethedominantmodeoffailurefor alljointsexceptwhenbranchlocalfailure takesplacewhichhappenson valuesof >25andτ <0.4.

- Astheβvalueincreasesthejoint’sultimatecapacityincreaseforsame andviceversa withvalue forsame β.

- Asthe(R)valueincreasestheultimatecapacityofthejointdramatically decreases.

- Theτvaluehasaneffectonthecapacityofthejointastheτvalue increasestheultimatecapacityofthejointincreasesforconstante,and βvalues.

- Theunequalloadingonthebrancheshasaneffectonthecapacityofthe joint;asthe(Ra)value decreasesthe ultimatecapacity ofthejoint decreasesfor constantτ, andβvalues.

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