Title page for ETD etd-05182005-135746


Type of Document Master's Thesis
Author Patel, Hardik D
Author's Email Address hdpatel@vt.edu
URN etd-05182005-135746
Title Use of Permanent Magnets to Improve the Seismic Behavior of Light-Framed Structures
Degree Master of Science
Department Civil Engineering
Advisory Committee
Advisor Name Title
Charney, Finley A. Committee Chair
Plaut, Raymond H. Committee Member
Roberts-Wollmann, Carin L. Committee Member
Keywords
  • Friction dampers
  • Permanent magnets
  • Passive energy dissipation devices
  • Light
Date of Defense 2005-05-12
Availability restricted
Abstract
Light-framed wood structures generally have satisfied the life safety objective of

the current seismic design approach. The main source of energy dissipation in such

structures is the inelastic behavior of the connectors connecting framing and sheathing

elements. Wood framed structures when subjected to strong ground excitations experience

structural and non-structural damage which may incur large repair/replacement costs or

may even render the structure out of service. Thus, it is very important to apply

techniques to mitigate the seismic response of the light-framed structures and avoid large

monetary losses.

It is proposed to use commercially available permanent magnets, incorporated in

the form of passive friction dampers, to dissipate a part of input energy induced due to

strong ground motions, thereby reducing the inelastic energy dissipation demand of the

lateral load resisting system. The force of attraction between the permanent magnet and

ferromagnetic material like steel was utilized to produce the required friction resistance. A

sliding wall configuration consisting of flexible permanent magnets and steel plates

sandwiched between the plywood sheets was analyzed for its effectiveness in mitigating

the response of a two story wood shear wall structure. The structural analysis program

SAP2000 was used to perform nonlinear dynamic analysis of the finite element models

generated using the meshing algorithms incorporated into ‘WoodFrameMesh’. Nonlinear

link elements available in SAP2000 were used to model the friction between the flexible

magnet sheet and the steel plate. The effects of various modeling parameters on the

solution of the nonlinear analysis were studied so as to arrive at appropriate values to

represent the friction problem. Also the friction damped structure was analyzed to study

its forced and free vibration characteristics. Further, the responses of the friction damped

structure and the undamped structure were compared when subjected to different ground

accelerations. The response of the friction damped structure was also compared to that of

the structure in which the proposed friction dampers were replaced by normal shear walls.

A huge reduction in the response of the friction damped structure was observed when

compared to the response of the undamped structure. The friction damped structure was

also analyzed for different values of modal damping ratios. Over all about 60-80% of the

input energy was dissipated by friction damping in all the cases. The slip resistance of a

flexible permanent magnet sheet was also verified in the laboratory. Above all the

magnetic properties of commercially available permanent magnets and the effects of

strong permanent magnets on human health were also studied.

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