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Falgoust, Monica Kaeline (2005) ON THE VALIDITY OF THE WAGNER HYPOTHESIS IN THIN-WALLED OPEN-PROFILE MEMBERS. Master's Thesis, University of Pittsburgh. (Unpublished)

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The Wagner Hypothesis states that when a thin-walled open-profile member is subjected to an axial loading leading to global instability, the longitudinal stresses developing within the fibers composing the cross-section become inclined to the normal plane; thus taking on a helical shape with respect to the longitudinal axis of the member. It is assumed that the longitudinal fiber stresses act as "follower-forces" and thus assume the same inclination as the cross-sectional fibers and thus produce a torsional moment about the longitudinal axis of the member. Classical second-order theories for calculating critical buckling loads based on the line of shear centers for thin-walled open-profile members have been developed by Timoshenko and Vlasov, which include the use of the Wagner effect. However, a competing theory has been developed by Ojalvo that utilizes the line of cross-sectional centroids (rather than cross-sectional shear centers) as a reference axis while at the same time rejecting the use of the Wagner Hypothesis. Ojalvo proposes that the Wagner Hypothesis violates common statical principles as well as is deficient for not identifying the free body with which torsional equilibrium is expressed. The current study explored the validity of the second-order theories using nonlinear finite element techniques to produce critical buckling loads for various thin-walled open-profile members. Critical buckling loads obtained from this analysis were compared with numerical results provided by each theory as well as experimental results. Not only did the present research evaluate the behavior of various torsional members at their critical buckling loads, but it also explored the notion that the principal stresses take on a helical shape once torsion has occurred (i.e. the stresses do indeed behave as "follower-forces") using graphical representations of the members created within the finite element software. Conclusions were made based on the comparison of finite element results compared with theoretical results and experimental tests. The current study found that the Wagner Hypothesis is valid due to positive agreement between finite element results, numerical solutions, and experimental tests. Recommendations were made concerning the possibility of further research regarding this topic.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Falgoust, Monica
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairEarls,
Committee MemberLin, Jeen-Shangjslin@engr.pitt.eduJSLIN
Committee MemberOyler, Johnoyler@civ.pitt.eduOYLER1
Committee MemberHarries, Kentkharries@engr.pitt.eduKHARRIES
Date: 28 January 2005
Date Type: Completion
Defense Date: 3 December 2004
Approval Date: 28 January 2005
Submission Date: 21 November 2004
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Civil and Environmental Engineering
Degree: MSCE - Master of Science in Civil Engineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Mono-symmetric Cross-Sections; Structural Stability; Torsion
Other ID:, etd-11212004-131545
Date Deposited: 10 Nov 2011 20:05
Last Modified: 15 Nov 2016 13:51


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