comparative load rating study under lrfr and lfr methodologies for alabama highway bridges

336 Pages·2009·5 MB·English

by  Michael Murdock

COMPARATIVE LOAD RATING STUDY UNDER LRFR AND LFR
METHODOLOGIES FOR ALABAMA HIGHWAY BRIDGES

Except where reference is made to the work of others, the work described in this thesis is
my own or was done in collaboration with my advisory committee. This thesis does not
include proprietary or classified information.

________________________
Michael Murdock

Certificate of Approval:

________________________ ________________________
Robert W. Barnes Hassan H. Abbas, Chair
Associate Professor Assistant Professor
Civil Engineering Civil Engineering

________________________ ________________________
J. Michael Stallings George T. Flowers
Professor Dean
Civil Engineering Graduate School
COMPARATIVE LOAD RATING STUDY UNDER LRFR AND LFR
METHODOLOGIES FOR ALABAMA HIGHWAY BRIDGES

Michael Brawner Murdock

A Thesis
Submitted to
the Graduate Faculty of
Auburn University
in Partial Fulfillment of the
Requirements for the
Degree of
Master of Science

Auburn, Alabama
August 10, 2009
COMPARATIVE LOAD RATING STUDY UNDER LRFR AND LFR
METHODOLOGIES FOR ALABAMA HIGHWAY BRIDGES

Michael Brawner Murdock

Permission is granted to Auburn University to make copies of this thesis at its discretion,
upon request of individuals or institutions and at their expense. The author reserves all
publication rights.

________________________
Signature of Author

________________________
Date of Graduation
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VITA

Michael Brawner Murdock, son of Harry Mike and Judy Kay (Moore) Murdock,
was born November 21, 1984, in Cornwall, England. He graduated from Apopka High
School with honors in May, 2003. In September of 2003, Michael entered Auburn
University where he received the Bachelor of Science in Civil Engineering in May, 2007.
He married Jennifer Short on December, 16 2006, also a graduate of Auburn University.
Michael entered the graduate school of Auburn University in September, 2007 to seek the
Masters of Science in Civil Engineering, focusing on structural engineering.

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THESIS ABSTRACT
COMPARATIVE LOAD RATING STUDY UNDER LRFR AND LFR
METHODOLOGIES FOR ALABAMA HIGHWAY BRIDGES

Michael Murdock
Master of Science, August 10, 2009
(B.S., Auburn University, 2007)

336 Typed Pages
Directed by Hassan H. Abbas

Currently, the Alabama Department of Transportation (ALDOT) uses the load
factor rating (LFR) methodology of the American Association of State Highway and
Transportation Officials (AASHTO) Manual for Condition Evaluation (MCE) of Bridges
(1994) in load rating of highway bridges across the state. With the introduction of the
new AASHTO MCE and Load and Resistance Factor Rating (LRFR) of Highway Bridges
(2003), the need arose to assess the impact of implementing the new manual on
ALDOT’s current bridge rating practices. To this end, a comparative study was
performed between ALDOT’s current rating practices utilizing the older LFR
methodology, according to the AASHTO MCE (1994), and the new LRFR methodology.
This comparative study was performed on a representative sample of 95 bridges
from Alabama’s state and county owned bridge inventory at all three primary levels of
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LRFR rating: Design, Legal and Permit rating levels. The load models that were utilized
in the rating analysis were the AASHTO design load models, AASHTO standard legal
loads, ALDOT state legal loads, and a sample of ALDOT overweight loads. The bridges
were modeled in AASHTO BridgeWare’s Virtis version 5.6 (2007) and analyzed in
BRASS-GIRDER LRFR and LFR analysis engines (2007). Rating results were
generated for interior and exterior girders of each bridge analyzed as well as for moment
and shear load effects.
The rating data at all three primary levels of rating indicated that the LRFR
methodology produces lower rating factors than the LFR. It was therefore concluded that
adopting the AASHTO MCE LRFR (2003) can have a significant impact on the rating
practices of ALDOT.
Comparisons were additionally made between the LRFR and LFR rating data, at
the Design rating level, in the context of estimated probability of failure for a bridge
based on the Monte Carlo simulation technique. This comparison showed that rating
factors produced under the LRFR methodology have strong correlation to a bridge’s
estimated probability of failure, whereas rating factors under the LFR methodology
showed only sporadic correlation to a bridge’s estimated probabilities of failure.
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ACKNOWLEDGMENTS

I would like to sincerely thank Dr Hassan H. Abbas for his continuous support,
encouragement and insights throughout my time working with him at Auburn University.
I would like to thank my committee members Dr. J. Michael Stallings and Dr. Robert W.
Barnes for their time and invaluable advice.
I would like to additionally thank the Alabama Department of Transportation for
their support and guidance. In practical I would like to thank James Boyer, Daniel Jones,
Eric Christie, and George Conner for their help on this project.
I would additionally like to convey my sincere thanks and love for my wife
Jennifer S. Murdock for her never-ending love and support throughout my time at
Auburn University.
The research described herein has been sponsored by Auburn University Highway
research Center (Dr. Frazier Paker, Director). The findings, opinions, and conclusions
expressed in this thesis are those of the author and not necessarily reflect the views of the
sponsor or others acknowledged herein.
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Style manual or journal used The Chicago Manual of Style 15th Edition

Computer software used Microsoft Word, Microsoft Excel, Adobe Photoshop CE,
BRIDGEWares Virtis, Mathcad, MatLab, Microsoft Visual Basic 2008 Express,

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TABLE OF CONTENTS
LIST OF TABLES...........................................................................................................xiv
LIST OF FIGURES.......................................................................................................xxiii
Chapter 1 INTRODUCTION......................................................................................1
1.1 Overview...........................................................................................................1
1.2 Motivation.........................................................................................................2
1.3 Research Objectives and Scope........................................................................3
1.4 Approach...........................................................................................................4
1.5 AASHTO Specifications...................................................................................4
1.6 Thesis Organization and Presentation...............................................................5
Chapter 2 BACKGROUND........................................................................................7
2.1 Overview of Bridge Rating...............................................................................7
2.2 Rating Methodologies.......................................................................................7
2.3 Rating Equations...............................................................................................8
2.4 LRFR Condition and System Factors.............................................................13
2.5 Live Load Factors...........................................................................................15
2.6 Load Combinations.........................................................................................17
2.7 Rating Levels..................................................................................................19
2.7.1 LRFR Design Load Rating....................................................................22
2.7.2 LRFR Legal Load Rating.......................................................................22
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2.7.3 LRFR Permit Load Rating.....................................................................23
2.8 Posting.............................................................................................................23
2.9 Live Load Models...........................................................................................25
2.9.1 Design....................................................................................................25
2.9.2 Legal......................................................................................................27
2.9.3 Permit.....................................................................................................29
2.10 Previous Research...........................................................................................31
2.10.1 Lichtenstein Consulting Engineers (2001).............................................32
2.10.2 Mertz (2005)..........................................................................................34
2.10.3 Rogers and Jáuregui (2005)...................................................................38
Chapter 3 BRIDGE SAMPLE...................................................................................40
3.1 Determining Bridge Sample..............................................................................40
3.1.1 Standard Bridge Sample........................................................................45
3.1.2 Unique Bridge Sample...........................................................................46
3.1.3 Permit Bridge Sample............................................................................47
3.2 Bridge Sample Information................................................................................48
Chapter 4 ANALYSIS TOOLS.................................................................................50
4.1 Analysis Software..............................................................................................50
4.1.1 Virtis......................................................................................................50
4.1.2 In-House Rating Tools...........................................................................52
4.1.2.1 AASHTO Rating Example Comparisons...........................................53
4.1.2.2 Output Sorting Programs....................................................................59
Chapter 5 RATING RESULTS.................................................................................62
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