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Guide for Heat-Straightening of Damaged Steel Bridge Members
Table of Contents
1. Introduction
1.1 History of Heat Straightening
1.2 Typical Types of Damage
1.2.1 Category S
1.2.2 Category W
1.2.3 Category T
1.2.4 Category L
1.3 Classification Use
1.4 Objectives of This Guide
2. Heat Straightening Basics
2.1 What is Heat Strightening?
2.2 Why Heat Straightening Works
2.3 Fundamental Heating Patterns
2.3.1 Vee Heat
2.3.2 Edge Heats
2.3.3 Line Heats
2.3.4 Spot Heats
2.3.5 Strip Heats
2.4 Defining Basic Damage Patterns and Yield Zones
2.5 Basic Heating Patterns
2.5.1 Flat Plate Bent About the Major Axis (Category S)
2.5.2 Structural Members Bent About Their Strong (Major) Axis (Category S)
2.5.3 Structural Members Bent About Their Weak (Minor) Axes (Category W)
2.5.4 Structural Members Subject to Twisting Damage (Category T)
2.5.5 Flanges and Webs with Local Buckles (Category L)
2.5.6 Angles
2.6 Complex Damage
2.7 Equipment and Its Use
2.8 Safety Considerations
2.9 Temperature Control
2.10 Restraining Forces
2.11 Practical Considerations
2.11.1 Torch Tip Size and Intensity
2.11.2 Material configuration
2.11.3 Judging the Temperature
2.11.4 Jacking Forces
2.11.5 Heating Patterns
2.11.6 Sequencing of Heats
2.11.7 Lack of Movement
2.11.8 Cooling the Steel
3. Assessing, Planning and Conducting Successful Repairs
3.1 Role of Engineer, Inspector and Contractor
3.2 Keys to a Successful Repair
3.3 Steps in the Assessment Process
3.3.1 Initial Inspection and Evaluation for Safety and Stability
3.3.2 Detailed Inspection for Specific Defects
3.3.2.1 Signs of Fracture
3.3.2.2 Degree of Damage
3.3.2.3 Material Degradation
3.3.2.4 Geometry of the Structure
3.4 Steps in the Planning and Design Process
3.4.1 Analysis of Degree of Damage and Determination of the Maximum Strain due to Damage
3.4.2. Conduct a Structural Analysis of the System
3.4.3. Select Regions Where Heat Straightening is Applicable
3.4.4. Select Heating Patterns and Parameters
3.4.4.1 Vee Depth
3.4.4.2 Vee Angle
3.4.4.3 Number of Simultaneous Vee Heats
3.4.5. Develop a Constraint Plan
3.4.6 Estimate the Heats Required to Straighten the Members
3.4.7 Repair Plans and Specifications
3.5 Supervision of Repairs
3.5.1 Monitoring the temperature
3.5.2 Controlling restraining forces
3.5.3 Review of Proposed Heating Patterns
3.5.4 Checking Tolerances
3.5.5 Safety
3.5.6 Checklist of Procedures for Supervisors and Inspectors
4. Effects of Heat Straightening on the Material Properties of Steel
4.1 Introduction
4.2 Residual Stresses in Heat-straightened Steel
4.3 Effect of Heat Straightening on Material Properties of Steel
4.4 Limits on Jacking Force to Minimize Risk of Fracture
4.5 Limits on Maximum Damage Strains
4.6 Fatigue and Fracture Performance
5. Heat Straightening of Flat Plates
5.1 Introduction
5.2 Variables Affecting the Movement of Heat–straightened Plates
5.2.1 Temperature
5.2.2 Effect of Vee Angle
5.2.3 Restraining Forces
5.3 Analytical Development
6. Heat Straightening Rolled Shapes
6.1 Fundamental Damage Patterns
6.2 Composite Deck–Girder Bridges
6.2.1 Factors Affecting Heat–Straightening Behavior of Composite Girders
6.2.1.1 Heat Patterns
6.2.1.2 Residual Moments
6.2.1.3 Restraining Forces
6.2.1.4 Stiffening Effect of Web
6.2.2 Model for Heat–Straightening Response
6.2.3 Modeling Statically Indeterminate Spans with Intermediate Diaphragms
6.3 Trusses and Axially Loaded Members
6.3.1 Introduction
6.3.2 Response of Columns to Heat Straightening
7. Heat Straightening Repair of Localized Damage
7.1 Damage Classification
7.2 Heat Straightening Procedures for Unstiffened Local Damage
7.2.1 Phase I. Initial Heating Patterns and Jacking Locations
7.2.1.1 Restraining forces
7.2.1.2 Vee heats
7.2.1.3 Line heats
7.2.1.4 Web line heat
7.2.2 Phase II. Heating/Jacking Pattern if θ
n
= 0 or θ
f
= 0
7.2.3 Phase III. Heating Pattern if θ
f
= θ
w
7.2.4 Flange Damage in Opposite Direction
7.3. Heat straightening Procedures for Stiffened Elements
7.3.1 Initial Heating Pattern
7.3.2 Final Heating Pattern
7.4 Determination of Jacking Forces
7.5 Conclusions
Appendix I: Specifications for the Selection of Contractors and the Conduct of Heat-Straightening Repairs
A1 Selection of Contractor (or the Contractor's field supervisor)
A2 Technical Specifications for the Conduct of Heat-Straightening Repairs
Appendix II: Nomenclature
Appendix III: References and Other Sources of Information
Figures
Figure 1: Graphic illustration of Category S damage.
Figure 2: Examples of Category W damage.
Figure 3: Examples of Category T damage.
Figure 4: Category L damage showing flange buckles on wind bracing on Mississippi River Bridge in Greenville, MS.
Figure 5: Conceptual example of shortening a steel bar.
Figure 6: Stages of movement during vee heat.
Figure 7: Schematic diagram of edge heats used to heat–curve a beam.
Figure 8: Line heat in progress on the web of a wide flange beam.
Figure 9: Schematic of line heat mechanism.
Figure 10: Strip heat in progress with a completed strip heat in the foreground.
Figure 11: Schematic of strip heat on the flange of a rolled beam.
Figure 12: Yield zones for basic damage patterns.
Figure 13: Yield zone and vee/strip heat layout for a category S damage to a rolled beam.
Figure 14: Plate vee heat pattern over yield zone.
Figure 15: Heating patterns for wide flange beams and channels bent about their major axes (Category S).
Figure 16: Heating patterns for wide flanges and channels bent about their minor axes (Category W).
Figure 17: Wide flanges and channels with twisting damage (Category T).
Figure 18: Typical heating patterns for local damage.
Figure 19: Heating patterns for angles.
Figure 20: Characteristics of plastic flow and restraint during heat straightening.
Figure 21: Brittle fracture during heat straightening.
Figure 22: Offset measurements to calculate degree of damage and radius of curvature.
Figure 23: Radius of curvature for a damaged beam of curvature and cord length.
Figure 24: Diaphragm damage due to vehicle impact on girder.
Figure 25: Jacking arrangements for global and local damage on a composite girder bridge.
Figure 26: Temperature sensing crayons.
Figure 27: Jacks in place on a Wisconsin bridge.
Figure 28: Iron–carbon equilibrium diagram.
Figure 29: Residual stress distribution for plates damaged and then vee heated
Figure 30: Typical residual stress distribution for a heat straightened angle
Figure 31: Typical residual stress distribution for a heat straightened angle
Figure 32: Typical residual stress distribution for a heat straightened channel
Figure 33: Typical residual stress distribution for a Category S wide flange beam
Figure 34: Typical residual stress distribution for a Category W heat straightened wide flange beam
Figure 35: Yield stress versus number of damage/repair cycles for heat straightened beam.
Figure 36: Tensile stress versus number of damage/repair cycles for heat straightened beam.
Figure 37: Percent elongation versus number of damage/repair cycles for heat straightened beam.
Figure 38: Influence of heating temperature on plastic rotation for 3/4 depth vee heats and a jacking ratio of 0.16.
Figure 39: Influence of jacking ratio on average plastic rotation for 650°C (1200°F) heating temperatures
Figure 40: Primary and stiffening plate elements for a channel bent about its major axis (Category S damage).
Figure 41: Weak axis bending resulting in a yield line in the plate element.
Figure 42: Typical deformed shape and yield zones in damaged composite girders.
Figure 43: Heating patterns for composite girder.
Figure 44: Diaphram stiffened composite girder.
Figure 45: Dead load conditions on a simply supported beam.
Figure 46: PΔ effect on an axially loaded column.
Figure 47: Plastic rotation versus jacking ratio for axially loaded Category W column.
Figure 48: Typical localized damage classified as Category L.
Figure 49: Typical Category L/U damage.
Figure 50: Heat straightening local flange damage (Category L/U).
Figure 51: Arrangement of restraining forces during various stages of repair.
Figure 52: Arrangement of vee and line heats.
Figure 53: Curvature and line heating patterns for category L/S damage.
Tables
Table 1: Recommended torch tips for various material thicknesses.
Table A1: Recommended Tolerances for Heat Straightening Repair.
Table A2: Recommended torch tips for various material thicknesses.
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This page last modified on 09/16/08