EFFECTS OF MULTIPLE HEAT STRAIGHTENING REPAIRS ON THE STRUCTURAL PROPERTIES AND FRACTURE TOUGHNESS OF BRIDGE STEELS Keith Kowalkowski, Graduate Assistant and Ph.D. student Amit H. Varma, Assistant Professor Purdue University January 11, 2005 TRB 2005 Annual Meeting Session, 479 Advancements in Steel Bridge Fabrication Technology Sponsored by: Fabrication and Inspection of Metal Structures

PRESENTATION OUTLINE INTRODUCTION, BACKGROUND, AND TESTING APPROACH – Schematic of Typical Bridge Damage and Repair Procedure – Relevant Prior Experimental Investigations – Michigan High Load Hits Database – Testing Approach EXPERIMENTAL INVESTIGATIONS – Test Matrix – Specimen Designs – Test Setup – Procedure, Instrumentation, and Behavior EXPERIMENTAL RESULTS AND CONCLUSIONS – Elastic Modulus, Yield Stress, Ultimate Stress, % Elongation, Hardness – A36 Fracture Toughness – A588 Fracture Toughness – A7 Fracture Toughness RECOMMENDATIONS ACKNOWLEDGEMENTS

INTRODUCTION, BACKGROUND, AND TESTING APPROACH

INTRODUCTION Over-height trucks occasionally collide with and damage the fascia beams of steel bridge structures. The damage of the steel fascia beam primarily includes out-of-plane bending and twisting of the beam. Heat straightening is a cost-effective and efficient technique for repairing steel beam bridges damaged by collisions with overheight loads. Currently, there is a lack of knowledge on the effects of multiple damage-heat straightening repairs on the structural properties and fracture toughness of bridge steels. The Michigan Department of Transportation (MDOT) funded a research project to answer these questions relating the effects of multiple heat straightening repairs. The damage-repair parameters considered were the damage strain (  d ), the restraining stress (  r ), and the number of damage-repair cycles (N r ).

DAMAGE INDUCED TO FASCIA BEAMS Bottom Flange

HEAT-STRAIGHTENING REPAIR PROCEDURE a) Restraining force apparatus b) Strip heat to web c) Vee heat to flange d) Several Vee heats to flange

RELEVANT BRIDGE STEELS Relevant bridge steels were identified by analyzing the Michigan high load hits database from (Varma et al. 2004). A7 and A373 are the most relevant in this research project. A36 steel is the closest in chemical composition and is available commercially. Thus, the experimental investigations focused on A36 and A588 steels. Some A7 steel specimens were acquired from the web of a decommissioned W24x76 steel beam. When the same bridge is hit multiple times, the corresponding steel is counted multiple times When the same bridge is hit multiple times, the corresponding steel is counted once only.

Damage Force (P d ) TESTING APPROACH Restraining Force (P r ) Two methods were considered (Method 1) t

PROBLEMS WITH METHOD 1 The specimen cross-section and length are subjected to different magnitudes of damage strain, restraining stress, and heat straightening repair. Hinders obtaining several material specimens subjected to consistent damage-repair magnitudes and testing them to obtain statistically significant structural properties.

METHOD 2 Strip Heat Damage Force (P d )Repair Force (P r ) Specimen test-areas are subjected to consistent damage strains, restraining stresses, and heat straightening repair. Several material specimens are obtained from the test-areas and tested to obtain statistically significant structural properties. Method 2 was chosen in this research project. Test Area

EXPERIMENTAL INVESTIGATIONS

EXPERIMENTAL TEST MATRIX Steel Type Damage Strains (  d ) Restraining Stresses (  r ) Number of damage- repair cycles (N r ) No. of specimens (One spec. for each value of N r ) A36 30  y 0.40  y 1, 2, 3, 4,  y 1, 2, 3, 4,  y 0.25  y 1, 2, 3, 4,  y 1, 2, 3, 4,  y 0.25  y 1, 3,  y 1, 2, 3, 4, 5 5 A  y 0.25  y 1, 2, 3, 4,  y 1, 2, 3, 4,  y 0.25  y 1, 2, 3, 4,  y 1, 2, 3, 4,  y 0.25  y 1, 2, 3, 4,  y 1, 2, 3, 4, 5 5 A7 30  y 0.25  y 1, 3,  y 1, 3,  y 0.25  y 1, 3, 3 *,  y 1, 3,  y 0.25  y 1,  y 1, 3 2

REMOVAL OF A7 SPECIMENS 15 in. 39 in. 93 in in. Undamaged Material Testing Area A7 specimens were fabricated from the web of the acquired approximately 24-ft. long W24x76 steel beam. The 24-ft. long beam was cut into three 93 in. long segments. Six specimens were removed from each as shown below.

TEST SPECIMEN DETAILS  Test specimen thickness = 0.45 in. A7 steel Test specimen thickness = 1.00 in. A36 and A588 steel  =  5.00

MATERIAL COUPONS FROM TEST AREAS (A36 and A588 Specimens) Charpy Specimens Tension Coupons

TEST SETUP Top Beam Bottom Beam Concrete Blocks Test Specimen Hydraulic Actuator Split-flow valve Electric Pump Needle Valve Pressure Gage

DAMAGE CYCLE-INSTUMENTATION Pressure transducers to measure actuator pressures Two longitudinal strain gages in test area Two displacement transducers to measure average strai Gage – front Gage -back 3.25 in. 5.0 in. Test-Area Two displacement transducers to measure average strains in test area TEST AREA

Specimen A Target  d = in/in Cycle 1-Longitudinal Strain Gages (Back (gray) and Front (red)) Cycle 1-Average Strain Cycle 2 Average Strains Cycle 3-Average Strains Stress-strain of undamaged uniaxial tension test EXPERIMENTAL DAMAGE BEHAVIOR (SPECIMEN A ) Strain (in/in)

Focused on shortening the specimen test area to the original length. The length is monitored using digital calipers and two punch marks at the edges. Lengths, widths, and thickness were monitored in between each heating cycle to maintain uniformity in the test area. Maximum heating temperature of 1200  F was enforced while repairing REPAIR CYCLES

REPAIR CYCLE-INSTRUMENTATION Two displacement transducers to monitor movement during heat straightening Infrared thermometer used to measure temperature on all sides Pressure transducers to measure actuator pressures Infrared thermometer to measure surface temperature Two displacement transducers to measure displacement between top and bottom beam.

Pressure (psi) Temperature (F) Right Displacement *10000 (in) Left Displacement*10000 (in) EXPERIMENTAL REPAIR BEHAVIOR (SPECIMEN A )

REPAIR DESCRIPTION Applying the Strip HeatMonitoring the Surface Temperature

EXPERIMENTAL RESULTS

UNIAXIAL TENSION RESULTS (A36)  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y Number of damage-repairs (N r )  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y Number of damage-repairs (N r )  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y ELASTIC MODULUS YIELD STRESS ULTIMATE STRESS DUCTILITY % ELONGATION

DUCTILITY OF A36, A588, AND A7 STEEL  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y Number of damage-repairs (N r )  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y A588 STEEL Number of damage-repairs (N r )  d = 30  y  r =0.40  y  d = 30  y  r =0.70  y  d = 60  y  r =0.25  y  d = 60  y  r =0.50  y  d = 90  y  r =0.25  y  d = 90  y  r =0.50  y A7 STEEL Number of damage-repairs (N r ) A36 STEEL

CONCLUSIONS–STRUCTURAL PROPS. 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. The yield stress and surface harness increase slightly and the ultimate stress and elastic modulus are always within ±10% of the undamaged values. 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.

FRACTURE TOUGHNESS RESULTS (A36)  d = 30  y  r = 0.40  y  d = 30  y  r = 0.70  y Number of damage-repairs (N r ) 95% low 95% high Mean 95% high Mean 95% low 0 = undamaged 95% high Mean 95% low 95% high Mean 95% low  d = 60  y  r = 0.25  y  d = 60  y  r = 0.50  y Number of damage-repairs (N r ) 0 = undamaged 95% high Mean 95% low 95% high Mean 95% low  d = 90  y  r = 0.25  y  d = 90  y  r = 0.50  y Number of damage-repairs (N r ) 0 = undamaged Fracture toughness of damaged-repaired specimens analyzed statistically  mean toughness and 95% confidence interval (CI) high and low toughness values The 95% CI Low, mean, and 95% CI high toughness values of the damaged-repaired specimens were normalized with respect to the undamaged mean toughness of the corresponding steel. The normalized fracture toughness values for the damaged-repaired specimens are shown and the effects of parameters  d,  r, and N r are evaluated.

CONCLUSIONS – A36 TOUGHNESS The fracture toughness of A36 steel is much lower than the undamaged fracture toughness. The mean fracture toughness of specimens damaged to 30  y becomes less than 50% after two damage-repair cycles. The fracture toughness of specimens damaged to 60  y becomes less than 50% after three damage- repair cycles. The mean fracture toughness of specimens damaged to 90  y was found to have significant scatter. Higher restraining stress appear to decrease the fracture toughness slightly.

FRACTURE TOUGHNESS RESULTS (A588) Number of damage-repairs (N r ) Quarter Average Mid Average Quarter Average Mid Average  d = 20  y  r = 0.25  y  d = 20  y  r = 0.50  y 0 = undamaged Quarter Average Mid Average Quarter Average Mid Average  d = 40  y  r = 0.25  y  d = 40  y  r = 0.50  y 0 = undamaged Number of damage-repairs (N r )  d = 60  y  r = 0.25  y Quarter Average Mid Average Quarter Average Mid Average  d = 60  y  r = 0.50  y 0 = undamaged Fracture toughness of damaged-repaired specimens analyzed statistically  mean quarter and mid thickness values were used The mean values of the damaged-repaired specimens were normalized with respect to the undamaged mean toughness (quarter or mid) of the corresponding steel. The normalized fracture toughness values for the damaged-repaired specimens are shown and the effects of parameters  d,  r, and N r are evaluated.

CONCLUSIONS – A588 TOUGHNESS The fracture toughness of damaged-repaired A588 steel is greater than or close to the undamaged fracture toughness in several cases. The fracture toughness never decreases below 50% (even after five damage-repair cycles). Increasing the restraining stress reduces the fracture toughness of A588 steel significantly.

FRACTURE TOUGHNESS RESULTS (A7) Number of damage-repairs (N r ) 95% high Mean 95% low Mean 95% low 95% high  d = 60  y  r = 0.25  y  d = 60  y  r = 0.40  y 0 = undamaged 95% high Mean 95% low Mean 95% low 95% high  d = 30  y  r = 0.25  y  d = 30  y  r = 0.40  y 0 = undamaged  d = 90  y  r = 0.25  y  d = 90  y  r = 0.40  y 95% high Mean 95% low Mean 95% low 95% high 0 = undamaged Fracture toughness of damaged-repaired specimens analyzed statistically  mean toughness and 95% confidence interval (CI) high and low toughness values The 95% CI Low, mean, and 95% CI high toughness values of the damaged-repaired specimens were normalized with respect to the undamaged mean toughness of the corresponding steel. The normalized fracture toughness values for the damaged-repaired specimens are shown and the effects of parameters  d,  r, and N r are evaluated.

CONCLUSIONS – A7 TOUGHNESS The fracture toughness of A7 steel decreases with an increase in  r and N r and with a decrease  d. The fracture toughness of steels damaged to 30  y reduces to 50% of the undamaged toughness after three damage-repairs. The fracture toughness of specimens damaged to 60  y and repaired with 0.25  y is excellent. However, increasing  r has a significant adverse effect on the fracture toughness. The fracture toughness of specimens damaged to 90  y is close to the undamaged toughness after three damage-repair cycles.

Based on the changes in fracture toughness and ductility (% elongation), it is recommended that A36 and A7 steel beams should be limited to three damage-heat straightening repair cycles. Smaller damage strains are more detrimental to A36 and A7 steel as compared to larger damage strains. A588 steel is an extremely resilient material that can be subjected to several (up to five) damage-repair cycles without significant adverse effects on the structural properties, ductility, and, fracture toughness. Lower restraining stresses should be used preferably. RECOMMENDATIONS

ACKNOWLEDGEMENTS Conducted within the Department of Civil and Environmental Engineering at Michigan State University. Funded by the Michigan Department of Transportation. The MDOT program manager and the research advisory panel are acknowledged for their help and support. – Roger Till(Program Manager) – Christopher Idusuyi (Bridge Maintenance) – Corey Rogers(Bridge Maintenance) – Steve Cook (MDOT Engineer) – Steve Beck (MDOT Engineer) 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)

QUESTIONS

RELEVANT EXPERIMENTAL TESTS Avent et al. conducted experimental investigations to determine the effects of one damage-heat straightening repair cycle on the structural properties of ASTM A36 steel plate specimens. – The plates were damaged by bending about the major axis and repaired using Vee heat patterns. – The experimental results indicated 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 % elongation decreases by up to 30%. Avent et al. also conducted experimental investigations on four W6x9 beams made from A36 steel by subjecting them to 1, 2, 4, and 8 damage-heat straightening repair cycles. – The experimental results indicated similar relationships as for the plate specimens.

MATERIAL COUPONS FROM TEST AREAS (A7 Specimens) Charpy Specimens Tensile Coupons 0.45 in 3.25 in.