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Title: Effects of seismic loading on slender steel structures with semi-rigid joints
Author: Kwarteng, Kenneth Owusu
Awarding Body: Oxford Brookes University
Current Institution: Oxford Brookes University
Date of Award: 2011
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Abstract:
A literature review of existing research on rack structures shows that connection models that are often adopted for the study of frame behaviour are usually based on the pre - yield stiffness. Record of experiments carried out and connection models developed from such experiments show that there is no reported study on the post - yielding behaviour of these connections under seismic loads. Seismic excitations often cause connections to rotate well beyond yielding and therefore requiring consideration of the post - yielding stiffnesses which developed in the connections to allow all the excessive stresses developed from the seismic effects to be re - distributed to other parts of the structure in prevention of premature collapse. The current study is an investigation into the semi - rigid and post - yielding behaviour of a beam end connector used in the UK storage rack industry. The pre and post - yielding behaviours of the connection under seismic condition undergo "pinching" which is the degradation of stiffness in the connection as a result of persistent loading and unloading of the beam, causing; significant wear and tear in the connection. The deterioration in the connection is manifested through material yielding, permanent geometric change and fatigue failure. The pinching behaviour in the connection was determined through experiments, which were conducted as part of this research. The experiments showed a steady rise in moment resistance within the elastic range of the connector. In this range every stiffness curve generated from the connection showed a slight deviation from the preceding curve but similar in shape. As the applied loads increased the connection behaved plastically with non recoverable looseness developing around the neutral or zero position as a result of the permanent deformation. There was then a sudden drop in strength followed again by a gradual increase in moment capacity which led to a shape similar to a butterfly wing, a "butterfly -shaped" moment rotation curve. The pinching was associated with significant looseness in the connection and this was shown in the moment rotation curve to get bigger with increases in the number of load cycles and magnitude of the applied load. A connection model to describe the "butterfly shaped" stiffness curve was then developed through regression analysis and this was used for the study of rack frame behaviour under seismic loading. A procedure for non linear dynamic analysis, based on Newton - Raphson and Newmark's methods was developed using stability functions to derive the structural stiffness and the pinching properties of the connections were then incorporated for the study. The research finally gives a revised design methodology, incorporating the pinching behaviour of the connections in comparison with existing design codes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.579170  DOI: Not available
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