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MULTIPLE HEAT STRAIGHTENING REPAIRS OF STEEL BEAM BRIDGES

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)

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MULTIPLE HEAT STRAIGHTENING REPAIRS OF STEEL BEAM BRIDGES

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  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

  3. 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

  5. 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

  6. 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%

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. RESEARCH SCHEDULE2002 and 2003 X = General time spent on sub-task P = Planning C = Construction E = Experiments

  23. RESEARCH SCHEDULE2004 and 2005 X = General time spent on sub-task A = Analysis C = Construction E = Experiments

  24. CURRENT PROGRESS AND STATUS

  25. 1.1 LITERATURE REVIEW • 100% complete • Discussed in the BACKGROUND section of this presentation

  26. 1.2 SURVEY OF STATE DOTs • 100% complete • Survey form sent – 23 DOTs responded

  27. 1.2 SURVEY OF STATE DOTs • Survey results

  28. 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

  29. 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

  30. DAMAGED AND REPAIRED BRIDGE (LANSING ROAD) 1.3 HEAT STRAIGHTENING PRACTICE • 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 Important findings

  31. 1.3 HEAT STRAIGHTENING PRACTICE From 1976-2001 corresponding to 183 steel bridges and 280 repair cases

  32. 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

  33. 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

  34. 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 Material coupons from test areas A36 and A588 steel 8.00 3.75 2.13 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.

  37. CONCLUSIONS–STRUCTURAL 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

  38. CONCLUSIONS–DUCTILITY 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

  39. 2.1 LABORATORY-SCALE TESTS CONCLUSIONS–FRACTURE 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 Tmax=1400F and Tmax=1600F

  40. 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

  41. 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 CONCLUSIONS–STRUCTURAL 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 CONCLUSIONS–FRACTURE TOUGHNESS • The fracture toughness of an A7 beam subjected to Nr=3 and ed = 30ey is much lower than the undamaged toughness. The mean fracture toughness of an A7 beam subjected to Nr=3 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 Tmax=1200F is comparable to the undamaged toughness. However, significant variability exists • The fracture toughness of an A36 beam subjected to Tmax=1400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, Tmax=1200F 2.3 EVALUATION OF MICROSTRUCTURE A36 Steel (240X) a) Undamaged b) After Damage of 90eyc) After Repair, Tmax=1200F A588 Steel (480X) a) Undamaged b) After Damage of 60eyc) After Repair, Tmax=1200F

  47. a) Undamaged b) After Damage of 90ey c) After Repair, Tmax=1200F 2.3 EVALUATION OF MICROSTRUCTURE A7 Steel (480X) a) Undamaged b) After Damage of 90eyc) After Repair, Tmax=1200F Overheated A36 Steel (480X) a) Undamaged b) After Damage of 90eyc) After Repair, Tmax=1600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)

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