MULTIPLE HEAT STRAIGHTENING REPAIRS OF STEEL BEAM BRIDGES

1
MULTIPLE HEAT STRAIGHTENING REPAIRS OF STEEL BEAM
BRIDGES
PHD Thesis - Preliminary Examination Keith J.
Kowalkowski School of Civil Engineering Purdue
University
COMMITTEE Amit H. Varma (Chair)-Civil Engineering
(Structures) Mark D. Bowman-Civil Engineering
(Structures) W. Jason Weiss-Civil Engineering
(Materials) Eric P. Kvam-Materials Engineering
2
PRESENTATION OUTLINE

• RESEACH PROBLEM STATEMENT
• BACKGROUND
• GOAL, OBJECTIVES, AND SIGNIFICANCE
• RESEARCH PLAN
• Task 1 - State of Knowledge and Practice
• Task 2 - Experimental Investigations of the
  Effects of Multiple Damage-Repair Cycles
  
• Task 3 - Analytical Investigations of the Damaged
  and Repaired Beams
• Task 4 - Develop Guidelines and Recommendations
• RESEARCH SCHEDULE
• CURRENT PROGRESS AND STATUS OF EACH TASK GROUP
  (ORGANIZED AS ABOVE)
• WORK REMAINING, TIME TO COMPLETION
• ACKNOWLEDGEMENTS

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RESEARCH PROBLEM STATEMENT

• Heat straightening - cost-effective and efficient
  technique for repairing steel members subjected
  to damage (plastic deformations)
• Most frequently used to repair the steel fascia
  beams of bridge girders damaged by overheight
  trucks
• Heat is applied with an oxygen-fuel torch. Steel
  yields at elevated temperatures due to material
  expansion and external restraining forces
• Significant research has been conducted on the
  heat straightening repairs of steel bridges.
• Most prior research has focused on development of
  empirical equations and guidelines for conducting
  effective heat straightening repairs in the field

4
RESEARCH PROBLEM STATEMENT

• Heat straightening can be very cost effective as
  compared to replacing portions of the steel
  bridge
• Occasionally, the same fascia beams of steel
  bridges are damaged and repaired multiple times
  in their service lives
• Limited research has been conducted on the
  effects single or multiple damage-heat
  straightening repairs on the structural
  properties, fracture toughness, and
  microstructure of typical bridge steels.
• Guidelines for evaluating and replacing (if
  necessary) steel beams subjected to multiple
  damage-repairs are lacking.
• Guidelines for evaluating the serviceability and
  load capacities of damaged and repaired steel
  beams are also lacking

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BACKGROUND

• Prior research on heat straightening has included
  the following topics
• Developing efficient heat straightening repair
  techniques
• Experimental studies measuring the plastic
  rotations and residual stresses due to heat
  straightening
• Effects of heat-straightening on the structural
  properties of undamaged steel plates

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BACKGROUND

• Limited research has been conducted on the
  effects of heat straightening on the structural
  properties of damage-repaired steel
• Avent et al. (2000a) experimentally determined
  the effects of a single damage-heat straightening
  repair cycle on the structural properties of A36
  steel plates
• Plates damaged by bending about the major axis
  and repaired using Vee heating patterns
• Results indicate that (a) the elastic modulus
  decreases by up to 30, (b) the yield stress
  increases by up to 20, (c) the ultimate stress
  increases by up to 10, and (d) the ductility (
  elongation) decreases by up to 30

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BACKGROUND

• Avent et al. (2000a) experimentally determined
  the effects on four A36 steel W6x9 beams
  subjected to 1, 2, 4, or 8 multiple
  damage-repairs
• Results indicated that damage-repair cycles
  progressively (a) increase sy and su, (b)
  increase the ratio of sy to su, (c) decrease E,
  and (d) reduce the ductility ( elongation) of
  the damaged-repaired steel
• The resulting fracture toughness, surface
  hardness, and the microstructure of
  damage-repaired steel were not investigated
• Avent and Fadous (1989) subjected a composite
  steel beam to multiple damage-heat straightening
  repair cycles
• Crack initiated during the fourth damage-repair
  cycle leading to a recommended limit of two
  damage-repair cycles for the same location in a
  steel beam

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BACKGROUND

• Till (1996) determined the influence of elevated
  temperatures on fracture critical steel members
• A36 steel specimens were heated to specific
  elevated temperatures, held for one minute, and
  then cooled
• Parameters included in the study were the heating
  temperature and the cooling method
• Results indicated that
• Chemical composition does not change
• Grain size decreases with an increase in the
  heating temperature up to 1400?F and then begins
  to increase
• Fracture toughness increases with an increase in
  temperature up to 1400?F and then begins to
  decrease
• Surface hardness generally decreases due to
  elevated temperatures

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RESEARCH GOAL

• DEVELOP RECOMMENDATIONS AND GUIDELINES FOR
  EVALUATING AND REPLACING (IF NECESSARY) STEEL
  BEAMS SUBJECTED TO SINGLE OR MULTIPLE CYCLES OF
  DAMAGE FOLLOWED BY HEAT STRAIGHTENING REPAIRS

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RESEARCH OBJECTIVES

• Investigate the current state-of-knowledge of
  heat straightening repair of damaged steel
  bridges, and evaluate the heat straightening
  procedures, guidelines, and specifications used
  by various state DOTs in the U.S.
• Experimentally investigate the effects of single
  and multiple damage-heat straightening repair
  cycles on the structural properties and fracture
  toughness of bridge steels
• Analytically investigate the effects of damage
  and heat straightening repair on the
  serviceability performance and load capacity of
  fracture critical and non-fracture critical steel
  bridges
• Develop recommendations and guidelines for
  evaluating (and replacing if necessary) fracture
  and non-fracture critical steel bridges subjected
  to single or multiple damage-repair cycles

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RESEARCH SIGNIFICANCE

• Guidelines are lacking for the maximum number of
  multiple damage-heat straightening repairs a
  steel member can sustain before replacement
• Heat straightening is cost effective alternative
  to replacing steel bridge members
• Therefore, there is significant research interest
  in evaluating the structural properties and
  fracture toughness of steels subjected to
  multiple damage-heat straightening repairs
• Engineers have limited guidance for estimating
  the damage strains and net restraining stresses
  due to external restraining loads.
• Engineers have limited guidance for evaluating
  the serviceability and design capacity of
  fracture and non-fracture critical members
  subjected to damage and repairs

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RESEARCH PLAN

• State-of-Knowledge and Practice
• 1.1 Comprehensive Literature Review
• 1.2 Survey and review of DOT heat straightening
  guidelines and specifications
• 1.3 Review of heat straightening practice
• Experimental Investigations of the Effects of
  Multiple Damage-Heat Straightening Repair Cycles
• 2.1 Laboratory-scale experimental investigations
• 2.2 Large-scale experimental investigations
• 2.3 Effects of damage-repair cycles on steel
  microstructure
• Analytical Investigations of the Damaged and
  Repaired Beams
• 2.1 Behavior of damaged beams
• 2.2 Behavior of repaired beams
• Develop Guidelines and Recommendations

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1.1 LITERATURE REVIEW

• Review of heat straightening topics included in
• U.S. and international journals
• Conference proceedings
• Research reports by DOTs, FHWA, NCHRP
• Theses and dissertations
• Review will summarize
• Current state-of-knowledge on heat straightening
  repair of damaged steel members
• Effects of single and multiple heat straightening
  on steel material properties
• Current guidelines for conducting effective heat
  straightening in the field

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1.2 SURVEY OF DOT GUIDELINES

• Survey form containing seven multiple choice
  questions will be sent to DOTs across the U.S.
• Goal is to determine the various heat
  straightening guidelines and specifications
• Focus on multiple heat straightening

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1.3 HEAT STRAIGHTENING PRACTICE

• Three heat-straightening repair sites in Michigan
  will be visited
• Heating temperatures, patterns, and restraining
  forces used by the MDOT Statewide Bridge Crew
  will be monitored
• Effects on the surface hardness and
  microstructure will be evaluated
• Analyses will be conducted to identify the steel
  and beam types most frequently subjected to
  single and multiple damage-heat straightening
  repairs

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2.1 LABORATORY-SCALE TESTING

• Several laboratory-scale specimens will be
  fabricated from three relevant bridge steels and
  subjected to multiple damage-heat straightening
  repair cycles
• Damage and repair parameters will be the damage
  strain (ed), the restraining stress (sr), the
  number of damage-repair cycles (Nr), and the
  maximum heating temperature (Tmax)
• Several material coupons will be fabricated from
  each damaged-repaired specimen do determine the
  structural properties and fracture toughness of
  the damaged-repaired steels
• Results will be compared and evaluated using the
  undamaged steel material properties

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2.2 LARGE-SCALE TESTING

• Large-scale beam specimens will be tested to
  validate the conclusions and recommendations from
  the laboratory-scale results (Sub-task 2.1)
• Beam specimens will be made from the relevant
  bridge steels and each specimen will be tested
  according to the heat straightening repair
  procedures identified from Sub-task 1.3
• Several material specimens will be fabricated
  from the damage-repaired area and tested to
  determine the structural properties and fracture
  toughness of damaged-repaired steel beams

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2.3 MICROSTUCTURE EVALUATION

• Focuses on evaluating the effects of damage and
  heat straightening repair cycles on the
  microstructures of the relevant bridge steels
• Microstructures of the undamaged, damaged, and
  repaired (heat straightened) steels from
  Sub-tasks 2.1 and 2.2 will be examined (ASTM E3)
• Grain sizes and the percentage of pearlite in the
  microstructure will be computed (ASTM E112)
• Metallurgical theories will be used to explain
  the changes in steel microstructure, and thus the
  changes in structural properties and fracture
  toughness

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3.1 BEHAVIOR DAMAGED BEAMS

• Focuses on simulating the damage due to impact of
  overheight trucks and evaluating the
  serviceability performance and load capacity of
  composite steel beams using 3D finite elements
• Damage will be simulated by applying
  monotonically increasing lateral force to the
  bottom flange of the beam
• Results will include the plastic strains and the
  residual stresses in the damaged beams
• The model of the damaged beam will be subjected
  to live load (truck) to evaluate its
  serviceability performance, namely, deflections,
  sway, and stress ranges at fatigue critical
  connections
• Load carrying capacities will be determined

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3.2 BEHAVIOR REPAIRED BEAMS

• Focuses on simulating the heat-straightening
  repair and evaluating the serviceability
  performance and load capacity of the repaired
  steel beams using 3D finite elements
• Repair will be simulated by applying the
  restraining force to the bottom flange of the
  damaged beam, and by applying vee-heats in
  specific patterns to the bottom flange of the
  damaged beam
• The model of the repaired beam will be subjected
  to live load (truck) to evaluate its
  serviceability performance
• Load carrying capacities will be determined
• Effects of restraining stress, location, and
  maximum heating temperature on the serviceability
  performance and load capacity will be evaluated

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4 RECOMMENDATIONS, GUIDELINES

• Results from the experimental investigations
  (Task 2) will be used to develop recommendations
  for evaluating the structural properties and
  fracture toughness of steel beams subjected to
  multiple damage-heat straightening repairs
• Results from the analytical investigations (Task
  3) will be used to develop guidelines for
  evaluating the serviceability performance and
  load capacity of damaged and repaired beams

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RESEARCH SCHEDULE2002 and 2003
Task Group Task Group 2002 2002 2002 2002 2002 2002 2002 2002
Description May June July Aug. Sept. Oct. Nov. Dec.
Literature Review 1.1 X X X X X X X
Survey Analysis 1.2 X X X X X
Heat Straightening Practice 1.3 X X X
Laboratory-Scale Testing 2.1 P P P P C
Task Group Task Group 2003 2003 2003 2003 2003 2003 2003 2003 2003 2003 2003 2003
Description Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Survey Analysis 1.2
Heat Straightening Practice 1.3 X X X X
Laboratory-Scale Testing 2.1 C C C E E E E E E E E E
Large-Scale Testing 2.2 P P P
Microstructure Evaluation 2.3 X X X X X X X
X General time spent on sub-task P Planning
C Construction E Experiments
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RESEARCH SCHEDULE2004 and 2005
Task Group Task Group 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004
Description Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Literature Review 1.1 X X X
Laboratory-Scale Testing 2.1 E/A A A
Large-Scale Testing 2.2 C C E E E E A A
Microstructure Evaluation 2.3 X X X X X X
FEM Heat Straightening 3.2 X X
Develop Recommendations 4 X
Task Group Task Group 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005
Description Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Microstructure Evaluation 2.3 X X
FEM Damaged Beams 3.1 X X X X
FEM Heat Straightening 3.2 X X X X X X X
Develop Recommendations 4 X X X X
X General time spent on sub-task A Analysis
C Construction E Experiments
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CURRENT PROGRESS AND STATUS
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1.1 LITERATURE REVIEW

• 100 complete
• Discussed in the BACKGROUND section of this
  presentation

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1.2 SURVEY OF STATE DOTs

• 100 complete
• Survey form sent 23 DOTs responded

1) Does your DOT have special provisions and guidelines for heat straightening?
___ Yes (Please provide) ___ No
2) What is the basis for these heat straightening provisions?
___ DOT Research ___ FHWA Research ___ Other (Please provide info)
3) Are these provisions available from the Internet?
___ Yes (Please provide link__________________) ___ No
4) Does your DOT have special provisions for multiple heat straightening of the same beam?
___ Yes (Please provide) ___No
5) Which parameter governs the maximum number of multiple heat straightening repairs of the same beam?
___ No. of repairs ___ Structure type ___ Damage magnitude ___ Combination of parameters
6) How many times does your DOT allow multiple heat straightening of the same beam?
___ One ___ Two ___ Three ___ Four ___Other (Please provide number)
7) Would you be interested in the results of our research project?
___ Yes ___ No
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1.2 SURVEY OF STATE DOTs

• Survey results

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1.3 HEAT STRAIGHTENING PRACTICE

• 100 Complete.
• Three heat straightening repair sites in Michigan
  were visited
• In all three cases, the MDOT Statewide Bridge
  Crew (SBC) repaired damage to composite beams
  damaged by overheight trucks
• Heating patterns, temperatures, and restraining
  forces were monitored

Lake Lansing Road Bridge Elm Road
Bridge Lansing Road
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1.3 HEAT STRAIGHTENING PRACTICE
a) Restraining force apparatus
b) Strip heat to the web
c) Vee heat to flange
d) Several Vee heats to flange
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DAMAGED AND REPAIRED BRIDGE (LANSING ROAD)
1.3 HEAT STRAIGHTENING PRACTICE

• Important findings

• Overheating in the range of 1300-1400?F was
  witnessed
• The MDOT codes and guidelines were not always
  taken into consideration
• Cold-working residual stresses were not taken
  into consideration

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1.3 HEAT STRAIGHTENING PRACTICE
From 1976-2001 corresponding to 183 steel bridges
and 280 repair cases


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1.3 HEAT STRAIGHTENING PRACTICE

• CONCLUSIONS FROM DATABASE
• A7 and A373 are the steel types most frequently
  damaged and heat straightened in Michigan
• The steel types in their order of importance are
  A7, A373, A588, A36, and A572
• Structure type 332 (simply supported composite
  wide-flange steel beam) is most frequently
  damaged and heat straightened in Michigan
• Structure types 332, 382, and 432 represent 82
  of all repair cases. All three correspond to
  composite steel girders

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2.1 LABORATORY-SCALE TESTS

• LONG TASK 100 COMPLETE
• Ninety one laboratory-scale specimens were
  subjected to multiple damage-heat straightening
  repair cycles
• Focused on A36 and A588 steels due to the
  availability of material as apposed to older A7
  and A373
• A36 - closest in chemical compositions as A7 and
  A373
• A588 - third most relevant steel type from
  database
• Some A7 steel specimens were acquired from the
  web of a W24x76 steel beam
• Test specimen-test areas were damaged by uniaxial
  tensile forces and repaired with uniaxial
  compressive forces and by applying strip heats
• Material samples taken from the test areas to
  obtain statistically significant structural
  properties and fracture toughness

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2.1 LABORATORY SCALE TESTS

• A36 28 Specimens
• Three damage strains (?d) 30?y, 60?y , or 90?y
• Two restraining stresses (?y) 0.25 ?y or 0.50?y
  (0.40 ?y or 0.70 ?y for ?d 30?y)
• Number of damage-repair cycles (Nr) 1, 2, 3, 4,
  or 5
• A588 30 Specimens
• Three damage strains (?d) 20?y, 40?y , or 60?y
• Two restraining stresses (?y) 0.25?y or 0.50?y
• Number of damage-repair cycles (Nr) 1, 2, 3, 4,
  or 5
• A7 17 Specimens
• Three damage strains (?d) 30?y, 60?y , or 90?y
• Two restraining stresses (?y) 0.25?y or 0.50?y
  
• Number of damage-repair cycles (Nr) 1, 3, or 5
• Three maximum heating temperatures
• Overheated A36 16 Specimens
• Two damage strains (?d) 60?y or 90?y
• Two restraining stresses (?y) 0.25?y or 0.50?y
• Number of damage-repair cycles (Nr) 1 or 3
• Two maximum heating temperatures - 1400?F or
  1600?F

35
TEST SETUP
Concrete Blocks
Top Beam
Test Specimen
Hydraulic Actuator
Split-flow valve
Bottom Beam
Electric Pump
Pressure Gage
Needle Valve
36
TEST SPECIMEN DETAILS
A36 and A588 steel
8.00
2.13
3.75
2.13
1.63
3.38
f 1.1875
3.38
16.88
3.75
3.25
46.25
3.75
16.88
3.38
f 1.1875
3.38
1.63
Test specimen thickness 1.00 in.
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CONCLUSIONSSTRUCTURAL PROPERTIES
2.1 LABORATORY-SCALE TESTS

• Multiple damage-heat straightening repair cycles
  have a slight influence (15) on the elastic
  modulus, yield stress, ultimate stress, and
  surface hardness of A36, A588, and A7 bridge
  steels
• For specimens heated to the recommended limit of
  1200?F, the yield stress and surface harness
  increase slightly and the ultimate stress and
  elastic modulus are always within 10 of the
  undamaged values
• For specimens heated to overheated temperatures
  of either 1400?F or 1600?F, the yield stress and
  tensile stress increase more significantly, the
  surface harness decreases slightly, and the
  ultimate stress and the elastic modulus is always
  within 10 of the undamaged values

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CONCLUSIONSDUCTILITY
2.1 LABORATORY-SCALE TESTS

• However, the elongation of damaged-repaired
  steel is influenced significantly
• The ductility ( elongation) of A36 and A588
  steel decreases significantly but never lower
  than minimum values according to AASHTO
  requirements
• The ductility of A7 steel subjected to five
  damage-repair cycles is extremely low
• The ductility of overheated A36 decreased as well
  but to the same magnitudes as A36 steel heated to
  the recommended limit of 1200?F

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2.1 LABORATORY-SCALE TESTS
CONCLUSIONSFRACTURE TOUGHNESS

• The fracture toughness of A36 steel is much lower
  than the undamaged fracture toughness. The
  fracture toughness increases for specimens
  subjected to higher ed
• The fracture toughness of damaged-repaired A588
  steel is greater than or close to the undamaged
  fracture toughness in several cases. Increasing
  the restraining stress reduces the fracture
  toughness of A588 steel
• The fracture toughness of A7 steel increases for
  specimens subjected to higher ed
• The fracture toughness of overheated A36 is much
  higher than the undamaged toughness. There was
  not a significant difference for Tmax1400?F and
  Tmax1600?F

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2.2 LARGE-SCALE TESTS

• 100 Complete
• Six beam specimens were subjected to three
  damage-heat straightening repair cycles
• Beams subjected to weak axis bending by applying
  concentrated forces at midspan
• Similar to damage induced to the bottom flange of
  a composite beam impacted by an over-height truck
• Two flanges could be used for the removal of
  material samples as apposed to one flange
• Easier to conduct, control, and repeat in a
  laboratory type setting as compared to the
  composite beam damage
• Repair conducted by applying half-depth Vee heats
  along the damaged area of the beam
• Results of material testing used to validate the
  conclusions and recommendations of Sub-task 2.1

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2.2 LARGE-SCALE TESTS
?p 8.5 in ed 90 ey
42
MATERIAL COUPSONS FROM BEAMS

• Three flat tensile coupons removed from the back
  flange (Flange A) of each beam specimen
• Twelve charpy specimens removed from the mid
  thickness of the front flange (Flange B) along
  the center of Vee heats L1, C, and R1

43
2.2 LARGE-SCALE TESTS
CONCLUSIONSSTRUCTURAL PROPERTIES

• Damage-heat straightening repair cycles do not
  have a significant influence on the yield stress,
  elastic modulus, ultimate stress, or surface
  hardness of steel (??15)
• Damage-repair cycles reduce the percent
  elongation (ductility) of A7 and A36 steel
• For A588, damage-repair cycles slightly increase
  the elongation at the flange edges and decrease
  the ductility of material closer to web-flange
  junction

44
2.2 LARGE-SCALE TESTS
CONCLUSIONSFRACTURE TOUGHNESS

• The fracture toughness of an A7 beam subjected to
  Nr3 and ed 30ey is much lower than the
  undamaged toughness. The mean fracture toughness
  of an A7 beam subjected to Nr3 and ed 90ey
  compares favorably with the undamaged toughness.
  However, some variability is seen in the result.
• The fracture toughness of A588 steel increases
  significantly. The fracture toughness values were
  smaller for charpy specimens closer to the
  flange-web junction
• The overall fracture toughness of an A36 beam
  subjected to Tmax1200?F is comparable to the
  undamaged toughness. However, significant
  variability exists
• The fracture toughness of an A36 beam subjected
  to Tmax1400?F increases significantly. The
  increase ranges from 101-460 of the undamaged
  toughness.

45
2.3 EVALUATION OF MICROSTRUCTURE

• 95 Complete
• Metallographic investigations were conducted on a
  charpy specimen fabricated from each
  damaged-repaired laboratory specimen
• Each was polished and etched according to ASTM E3
• Grain sizes were determined using the grain line
  intercept procedure outlined in ASTM E112
• Metallographic photographs were taken of
  undamaged steel, the damaged steel at all three
  damage strain levels, and after the
  heat-straightening repair of each damage strain
  level
• Changes in the microstructure were related to
  changes in the structural properties and fracture
  toughness of steel

46
a) Undamaged b)
After Damage of 90ey c)
After Repair, Tmax1200?F

2.3 EVALUATION OF MICROSTRUCTURE
A36 Steel (240X) a) Undamaged
b) After Damage of 90ey c) After
Repair, Tmax1200?F

A588 Steel (480X) a)
Undamaged b) After Damage of 60ey
c) After Repair, Tmax1200?F


47
a) Undamaged b)
After Damage of 90ey c)
After Repair, Tmax1200?F

2.3 EVALUATION OF MICROSTRUCTURE
A7 Steel (480X) a) Undamaged
b) After Damage of 90ey c) After
Repair, Tmax1200?F

Overheated A36 Steel (480X) a)
Undamaged b) After Damage of 90ey
c) After Repair, Tmax1600?F






48
3.1 BEHAVIOR OF DAMAGED BEAMS

• FEM Models in development
• High load hits database of Sub-task 1.3 indicated
  that 66 of all heat straightening repair cases
  in the state of Michigan were on composite
  wide-flange beams
• Three-dimensional FEM models will simulate the
  damage of composite wide-flange beams damaged by
  overheight trucks
• Results from the analysis will include the
  plastic strains and the residual stresses in the
  damaged beams
• The steel beams (web and flange members) will be
  modeled using 4-node S4 shell elements
• The concrete deck will be modeled using 8-node
  C3D8 solid elements

49
3.1 BEHAVIOR OF REPAIRED BEAMS

• Analysis in planning
• Models of the laboratory-scale specimens are
  being analyzed first due to simplicity in
  validating material properties at elevated
  temperatures and the heat straightening
  applications using finite elements
• Limitations of these finite element models will
  be noted for further FEM heat straightening
  applications
• 3D FEM models of the damaged composite
  wide-flange beams will be the starting point for
  simulating the heat-straightening repair
• Repair simulated by applying the restraining
  force to the bottom flange of the damaged beam,
  and by applying Vee-heats to the bottom flange

50
FEM ANALYSIS IN ABAQUS
(A heat flux is being applied to the nodes)
51
FEM ANALYSIS IN ABAQUS
52
4 RECOMMENDATIONS AND GUIDELINES

• Recommendations from the results of Task 2
• Based on fracture toughness and ductility results
  of Sub-tasks 2.1 and 2.2, A7 and A36 steel beams
  should not be subjected to more than three
  damage-repair cycles. Smaller damage strains are
  more detrimental to A7 and A36 steel as compared
  to larger damage strains
• Overheating the A36 steel during the repair
  improves its material properties and fracture
  toughness significantly. Therefore, it is
  recommended to use a maximum heating temperatures
  of 1400?F for repairing A36 steel
• A588 steel is an extremely resilient material
  that can undergo several (up to five)
  damage-repair cycles without significant adverse
  effects on the structural properties and fracture
  toughness
• Lower restraining stresses should be used
  preferably
• Recommendations need to be made considering
  fracture and non-fracture critical members

53
WORK REMAINING, TIME TO COMPLETION

• Planned graduation is December 2005
• Most of the work remaining involves the
  analytical finite element modeling of damaged and
  repaired beams (Task 3)
• Due to a busy course schedule, this work should
  be completed by August, 2005
• Task 1 and Task 2 have been written but the
  report still needs to be converted into the
  thesis format
• The fall semester will be used to make
  recommendations and guidelines, finish writing
  the thesis, and prepare for graduation

54
ACKNOWLEDGEMENTS

• Tasks 1 and 2 conducted within the Department of
  Civil and Environmental Engineering at Michigan
  State University
• Funded by the Michigan Department of
  Transportation. The MDOT program manager (Roger
  Till) and the research advisory panel are
  acknowledged for their help and support

• Significant contribution was provided at MSU by
  the following
• Jason Shingledecker (MSU Undergraduate Student)
• Siavosh Ravanbakhsh (MSU Civil Engineering Lab
  Manager)
• Sig Langenberg (Langenberg Machine Products)

• Amit Varma is acknowledged for allowing me to
  work on this research project, for his continuous
  support in my PhD. studies, and for bringing me
  to this University
• Mark Bowman, Jason Weiss, and Eric Kvam are
  acknowledged as members of my PhD. committee at
  Purdue University. Their views and support are
  greatly appreciated