Title page for ETD etd-02142005-120040


Type of Document Dissertation
Author Ibrahim, Yasser El-Husseini
Author's Email Address yibrahim@vt.edu
URN etd-02142005-120040
Title A New Visco-Plastic Device for Seismic Protection of Structures
Degree PhD
Department Civil Engineering
Advisory Committee
Advisor Name Title
Charney, Finley A. Committee Chair
Murray, Thomas M. Committee Member
Plaut, Raymond H. Committee Member
Roberts-Wollmann, Carin L. Committee Member
Singh, Mahendra P. Committee Member
Keywords
  • Earthquakes
  • Seismic
  • Passive control
  • Dampers
  • Viscoelastic
  • Visco-plastic
Date of Defense 2005-02-07
Availability unrestricted
Abstract
A new visco-plastic damper for seismic protection is introduced. This device combines and enhances many of the proven characteristics of both displacement-dependent and velocity-dependent devices.

The device consists of a block of a high-damping viscoelastic material sandwiched between two steel shapes (plates or channels) bent in a certain configuration to amplify the deformations in the device in order to obtain large tensile and compressive strains in the viscoelastic material. Under low levels of vibrations, the device dissipates energy through amplified strains in the viscoelastic material only; however, under moderate to strong levels of vibrations, a new source of energy dissipation is added through the yielding of the steel elements. The inelastic behavior of the steel elements is controlled by the rigidity of the viscoelastic material. In addition to the energy dissipation, the device provides stiffness through the steel elements as well as the viscoelastic material. Moreover, one of the main advantages of the device is that its behavior is fully controlled through different parameters.

First, a nonlinear time history analysis was conducted on structures with a preliminary model of the device using SAP2000 program to check the effectiveness of the device on the response of different structures under ground excitations. The device resulted in better improvement in the structural response compared to the existing viscoelastic dampers.

A three-dimensional finite element model was developed for the device using the finite element package, ABAQUS. The hyperelastic and viscoelastic behavior of the block of the viscoelastic material were considered. The inelastic behavior of the steel elements was considered as well using the Von Mises yielding criterion. The device was analyzed under different dynamic loadings with different frequencies.

Three simplified models were developed using SAP2000 program in order to facilitate the modeling of the device for structural engineers. These models were compared to the detailed finite element model to check their accuracy. The best model was used in the analysis of a multi-story steel frame with the visco-plastic devices under different ground excitations. Two different arrangements of the device were considered. The devices caused significant reduction in the story displacements, base shear and bending moment at column bases.

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