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The Determination of Lithospheric Rheology and Long-Term Interplate Coupling in Japan: Finite Element Modeling
Type of Document Dissertation
Author Huang, Shaosong
URN etd-14101210109603140
Title The Determination of Lithospheric Rheology and Long-Term Interplate Coupling in Japan: Finite Element Modeling
Degree PhD
Department Geophysics
Advisory Committee Advisor Name Title
I. Selwyn Sacks Committee Co-Chair
J. Arthur Snoke Committee Co-Chair
Edwin S. Robinson none
Kenneth A. Eriksson none
Richard D. Law none

Keywords lithosphere rheology
subduction-zone interplate coupling
finite-element modeling

Date of Defense 1996-09-26
Availability unrestricted
Abstract

Northeast Japan experienced an

approximately constant,

compressional deformation during

the last 5 million years resulting from

the steady subduction of the Pacific

plate. Because the direction of the

maximum compression axis is

approximately perpendicular to the

strike of the island arc, 2-D

finite-element modeling can be used

to examine the deformation over

time of the island-arc lithosphere.

The model geometry is based on

geophysical and geological data, and

each model run requires an assumed

rheology and interplate coupling.

Novel to our modeling is the ability

to include erosion/deposition loading

and the creation of strike-slip faults,

based on a dynamically-applied

fracture criterion. The criterion for

acceptability is how well a model

matches observed present-day

topography, gravity, and seismicity

patterns. Results given below are for

models that satisfy this criterion.

The long-term effective elastic

thickness is 10 km in the inner arc,

increasing to about 50 km near the

trench. The effective elastic

thickness in the inner arc is therefore

much smaller than the about 30 km

short-term elastic thickness

estimated from seismological data.

The viscosity of the lower crust is on

the order of 1022 Pa s or less.

The strength of interplate coupling

off Sanriku is about two to four

times greater than off Miyagi, and

there is about twice as strong a

coupling at greater depths. The

relative strength of coupling

correlates well with the observed

interplate seismicity. Hence the

inferred weaker coupling off Miyagi

indicates a lack of seismogenic

potential -- a low probability for

large earthquakes in that region, not

just a long return cycle.

The same modeling procedure was

also applied to southwest Japan.

The viscosity of the lower crust is

not more than 1021 Pa s, and the

elas tic thickness is about 10 km.

The calculated strength of interplate

coupling for southwest Japan is

about 1.5 times greater than for the

off-Sanriku region in northeast

Japan, which correlates well with the

fact that there have been great

(M> Cool

earthquakes in the Nankai

Trough region, but none that large in

the off-Sanriku region.

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http://scholar.lib.vt.edu/theses/available/etd-14101210109603140/unrestricted/etd.pdf

http://scholar.lib.vt.edu/theses/available/etd-14101210109603140/unrestricted/etd.pdf

Seismic Performance of Rail-Counterweight System of Elevator in Buildings

Type of Document Dissertation
Author Rildova, --
Author's Email Address rildova@vt.edu
URN etd-10052004-201201
Title Seismic Performance of Rail-Counterweight System of Elevator in Buildings
Degree PhD
Department Engineering Science and Mechanics
Advisory Committee Advisor Name Title
Mahendra P. Singh Committee Chair
David Y. Gao Committee Member
Romesh C. Batra Committee Member
Saad A. Ragab Committee Member
Scott L. Hendricks Committee Member

Keywords elevator
seismic response
counterweight

Date of Defense 2004-09-16
Availability unrestricted
Abstract
Elevators serve a critical function in essential facilities such as hospitals and need to remain operational during and after earthquakes. However, they are still known to malfunction during earthquakes even after several design and sensing improvements required by the current code have been incorporated. Most of the damages were experienced or caused by the rail-counterweight system. Being the heaviest component of an elevator, the counterweight induced strong dynamic effects to the guiding system sometimes even collided and damaged the passenger car.
A realistic analytical model of rail-counterweight system of an elevator that includes details of the supporting system is developed in this study. The nonlinearities caused by closing of the code specified clearances play an important role in determining the dynamic behavior of the system, and are thus included in this study. Also included are the acceleration inputs from different floor of building and the effect of different location of the counterweight along the guide rail. Parametric study is carried out to investigate the effect of different parameters on the seismic responses of the rail-counterweight system.

In order to improve the seismic performance of the rail-counterweight system, several protective schemes are investigated. One simple approach is to increase the damping of the system using additional discrete viscous dampers. However, there is not much space available for installing the devices, and placement parallel to the spring at the roller guide assemblies is not quite effective due to contact between the restraining plate at the roller guide assemblies and the rail that makes the roller guides ineffective.

Another method is to convert the top part of the weights into a tuned mass damper. This method can reduce the maximum stress in the rail if designed properly. The effectiveness of the passive tuned mass damper can be improved further by using it in an active mode by installing an actuator between the mass damper and the counterweight frame. The numerical results that confirm the effectiveness of such an active tuned mass damper are presented. As an alternative to the fully active control scheme, a semi-active control scheme using a magnetorheological damper device between the mass damper and the frame is also studied. This control approach is found to be as effective in reducing the seismic response as a fully active scheme. Since this MR damper can be operated using a simple battery, the external power requirements for implementation of this approach are quite minimal.

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http://scholar.lib.vt.edu/theses/available/etd-10052004-201201/

The Effects of Bolt Spacing on the Performance of Single-Shear Timber Connections Under Reverse-Cyclic Loading

Type of Document Master's Thesis
Author Albright, Dustin Graham
URN etd-08032006-173242
Title The Effects of Bolt Spacing on the Performance of Single-Shear Timber Connections Under Reverse-Cyclic Loading
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Dr. Joe Loferski Committee Co-Chair
Dr. Thomas E. Cousins Committee Co-Chair
Dr. Raymond H. Plaut Committee Member

Keywords reverse-cyclic loading
timber connections
single-shear
bolt spacing

Date of Defense 2006-04-24
Availability unrestricted
Abstract
Much previous experimentation related to wood structures has employed monotonic loading to replicate static situations. However, instances of natural hazards have raised interest in the response of structural connections to dynamic loads. This increased interest led the Consortium of Universities for Research in Earthquake Engineering (CUREE) to develop a testing protocol for reverse-cyclic loading, which involves cycling loads through zero in order to test specimens in both tension and compression. With the CUREE testing protocol in place, recent research has been devoted to understanding the effects of reverse-cyclic loading on multiple-fastener connections.

Experimentation by Heine (2001), Anderson (2002), Billings (2004) and others contributed to a better understanding of bolted connection behavior under reverse-cyclic loading. However, some questions remained. Billings was unable to consistently produce yield modes III and IV, meaning that her suggested bolt spacing of seven times the bolt diameter (7D) could not be applied to connections subject to these yield modes without further testing. In addition, the work of Anderson and Billings raised questions regarding the proper measurement of bending yield strength in bolts and the relationship between the bending yield strength and the tensile yield strength. These topics are each addressed by this project and thesis report.

Results of the connection testing presented in this report can be used in conjunction with the work of Anderson and Billings to critically evaluate the 4D between-bolt spacing recommended by the National Design Specification (NDS) for Wood Construction (AF&PA, 2001). Results of the bolt testing provide a supplement to the search for a reliable method for the measurement of bending yield strength in bolts.

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http://scholar.lib.vt.edu/theses/available/etd-08032006-173242/

Finite Element Analysis of the Application of Synthetic Fiber Ropes to Reduce Seismic Response of Simply Supported Single Span Bridges

Type of Document Master's Thesis
Author Taylor, Robert Paul
URN etd-07182005-141918
Title Finite Element Analysis of the Application of Synthetic Fiber Ropes to Reduce Seismic Response of Simply Supported Single Span Bridges
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Raymond H. Plaut Committee Chair
Carin L. Roberts-Wollmann Committee Member
Thomas E. Cousins Committee Member

Keywords Cable Restrainer
Bridge
Springs
Synthetic Fiber Ropes
Seismic

Date of Defense 2005-07-07
Availability unrestricted
Abstract
Movement of a bridge superstructure during a seismic event can result in damage to the bridge or even collapse of the span. An incapacitated bridge is a life-safety issue due directly to the damaged bridge and the possible loss of a life-line. A lost bridge can be expensive to repair at a time when a region?s resources are most strained and a compromised commercial route could result in losses to the regional economy. This thesis investigates the use of Snapping-Cable Energy Dissipators (SCEDs) to restrain a simply supported single span bridge subjected to three-dimensional seismic loads. SCEDs are synthetic fiber ropes that undergo a slack to taut transition when loaded.

Finite element models of six simply supported spans were developed in the commercial finite element program ABAQUS. Two seismic records of the 1940 Imperial Valley and 1994 Northridge earthquakes were scaled to 0.7g PGA and applied at the boundaries of the structure. The SCEDs were modeled as nonlinear springs with an initial slackness of 12.7mm. Comparisons of analyses without SCEDs were made to determine how one-dimensional, axial ground motion and three-dimensional ground motion affect bridge response. Analysis were then run to determine the effectiveness of the SCEDs at restraining bridge motion during strong ground motion. The SCEDs were found to be effective at restraining the spans during strong three-dimensional ground motion.

لينک دانلود:
http://scholar.lib.vt.edu/theses/available/etd-07182005-141918/unrestricted/Thesis.pdf

Finite Element Analysis of the Seismic Behavior of Guyed Masts

Type of Document Master's Thesis
Author Hensley, Gregory Martin
URN etd-07062005-161028
Title Finite Element Analysis of the Seismic Behavior of Guyed Masts
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Raymond H. Plaut Committee Chair
Carin L. Roberts-Wollmann Committee Member
Elisa D. Sotelino Committee Member

Keywords Mast
Finite Element
Synthetic Fiber Ropes
Seismic Response
Guy Wires

Date of Defense 2005-06-16
Availability unrestricted
Abstract
Seismic design of guyed masts, commonly used in the broadcasting and telecommunications industries, has not been fully addressed in the United States. There is no specific design code, and only a limited amount of research has been reported on the subject. This research investigates the behavior of guyed masts incorporating synthetic ropes as guys, with a particular focus on the effect of snap loads on the mast behavior. This is the third phase of a multi-stage project aimed at analyzing the potential for Snapping-Cable Energy Dissipators (SCEDs) to minimize lateral response in structures.

A finite element model of a 120-m-tall guyed mast was developed with the commercial program ABAQUS. The three-dimensional behavior of the mast was observed when subjected to two ground motion records: Northridge and El Centro. Three orthogonal earthquake components were input, two horizontal and one vertical. A series of parametric studies was conducted to determine the sensitivity of the response to guy pretension, which is a measure of the potential slackness in the guys during response. Additionally, the studies examined the effects of guy stiffness, mast properties, and directionality of input motion.

Deflections, bending moments, guy tensions, and base shears were examined. The results were used to characterize the trends in the structural response of guyed masts. The level of slackness in the guys changed the behavior, and the lessons learned will be used to continue research on the application of SCEDs in structures.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-07062005-161028/unrestricted/Thesis-GMH.pdf

A New Visco-Plastic Device for Seismic Protection of Structures

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
Finley A. Charney Committee Chair
Carin L. Roberts-Wollmann Committee Member
Mahendra P. Singh Committee Member
Raymond H. Plaut Committee Member
Thomas M. Murray 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.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-02142005-120040/unrestricted/Yasser_Ibrahim_Dissertation.pdf

Investigation of the Effects of Spacing between Bolts in a Row in a Single-Shear Timber Connection Subjected to Reverse Cyclic Loading

Type of Document Master's Thesis
Author Billings, Mary Anna
URN etd-11192004-143258
Title Investigation of the Effects of Spacing between Bolts in a Row in a Single-Shear Timber Connection Subjected to Reverse Cyclic Loading
Degree Master of Science
Department Structural Engineering and Materials
Advisory Committee Advisor Name Title
W. Samuel Easterling Committee Chair
Joseph R. Loferski Committee Co-Chair
Thomas E. Cousins Committee Member

Keywords reverse cyclic loading
spacing between bolts
multiple bolts
bolted wood connections

Date of Defense 2004-09-16
Availability unrestricted
Abstract
This thesis presents the results of testing to determine if spacing between bolts in a multiple-bolt, single-shear connection subjected to natural hazard loading affects seven strength and serviceability parameters: maximum load, failure load, E.E.P. yield load, 5% offset load, elastic stiffness, E.E.P. energy, and ductility ratio. This research also determines if a statistical difference exists between previously published research for 4D spacing as compared to results produced by this research for five alternate spacings: 8D, 7D, 6D, 5D, and 3D. Finally, this research determines which of the spacings examined: 8D, 7D, 6D, 5D, 3D; produced the most optimal results for each examined strength and serviceability parameter where optimization is based on economy and performance.

Three connection configurations with five different spacings between bolts were subjected to reverse cyclic loading for a total of one hundred and fifty tests. The reverse cyclic protocol was based on recommendations by the Consortium of Universities for Research in Earthquake Engineering (CUREE) for testing woodframe structures. The same connection configurations were also subjected to monotonic loading for an additional forty-five tests.

Results of this research can be used to evaluate the current design recommendation presented in the National Design Specification (NDS) for Wood Construction (AF&PA, 2001) of spacing bolts at four times the bolt diameter (4D) to determine if a different spacing should be recommended for natural hazard loading conditions.

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Earthquake engineering is based on the fact that real structures yield when subjected to ...
... Earthquake engineering is based on the fact that real structures yield when subjected to ground ... 1 Introduction 1.1 Background Earthquake engineering is based on the fact that real structures yield when subjected to design ...
http://scholar.lib.vt.edu/theses/available/etd-02192004-232758/unrestricted/Thesis.pdf

Analysis of Buckled and Pre-bent Columns Used as Vibration Isolators

Type of Document Master's Thesis
Author Sidbury, Jenny Elizabeth
URN etd-12122003-123751
Title Analysis of Buckled and Pre-bent Columns Used as Vibration Isolators
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Raymond H. Plaut Committee Chair
Thomas M. Murray Committee Member
W. Samuel Easterling Committee Member

Keywords vibrations
Vibration isolator
dynamic response
buckled structures
passive vibration isolation

Date of Defense 2003-12-04
Availability unrestricted
Abstract
Analysis of Buckled and Pre-bent Columns Used as Vibration Isolators

By

Jenny E. Sidbury

Dr. Raymond H. Plaut, Chairman

Charles E. Via, Jr. Department of Civil and Environmental Engineering

(ABSTRACT)

Vibrations resulting from earthquakes, machinery, or unanticipated shocks may be very damaging and costly to structures. To avoid such damage, designers need a structural system that can dissipate the energy caused by these vibrations. Using elastically buckled struts may be a viable means to reduce the harmful effects of unexpected vibrations. Post-buckled struts can support high axial loads and also act as springs in a passive vibration isolation system by absorbing or dissipating the energy caused by external excitation. When a base excitation is applied, the buckled strut may act to reduce the dynamic force transmitted to the system, thus reducing the structural damage to the system.

Several models of buckled and pre-bent struts are examined with different combinations of parameters and end conditions. The models include pinned or fixed columns supporting loads above their buckling load, and columns with an initial curvature supporting various loads. The varying parameters include external damping, internal damping, and stiffness. The columns will be subjected to simple harmonic motion applied at the base or to a multi-frequency base excitation. The response of each model is measured by the deflection transmissibility of the supported load over a large range of frequencies. Effective models reduce the motion of the supported load over a large range of frequencies.

لينک دانلود: http://scholar.lib.vt.edu/theses/available/etd-12122003-123751/unrestricted/ETD_1.pdf

Analysis and Modeling of Snap Loads on Synthetic Fiber Ropes

Type of Document Master's Thesis
Author Hennessey, Christopher Michael
URN etd-11092003-135228
Title Analysis and Modeling of Snap Loads on Synthetic Fiber Ropes
Degree Master of Science
Department Civil Engineering
Advisory Committee Advisor Name Title
Raymond H. Plaut Committee Chair
Finley A. Charney Committee Member
Thomas M. Murray Committee Member

Keywords Snap Loads
Cables
Synthetic Fiber Ropes
Drop Tests
Hysteresis

Date of Defense 2003-11-07
Availability unrestricted
Abstract
Analysis and Modeling of Snap
Loads on Synthetic Fiber Ropes

by

Christopher Michael Hennessey

Raymond H. Plaut, Committee Chairman

Civil Engineering

(ABSTRACT)

When a rope quickly transfers from a slack state to a taut state, a snapping action occurs and produces a large tensile force which is known as a snap load. Energy is dissipated during this snap load, and it is proposed to use synthetic fiber ropes as a type of passive earthquake damper in order to take advantage of this phenomenon. This thesis is the second phase of a multi-stage research project whose goal is to investigate and develop what will be known as Snapping-Cable Energy Dissipators (SCEDs).

The experimental data that was collected in the Master?s Thesis of Nicholas Pearson was organized and analyzed as a part of this research in order to evaluate the behavior of the ropes during the snapping action. Additional tests were also conducted for this project under more controlled conditions in order to better understand how the ropes change throughout a sequence of similar snap loadings and also to determine the amount of energy that is dissipated. The data from both projects was then used as input parameters for a mathematical model that was developed to characterize the behavior of the ropes during a snap load. This model will be utilized in subsequent research involving the finite element analysis of the seismic response of structural frames containing SCEDs.

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