SUB-TASK 2.1: LABORATORY-SCALE INVESTIGATIONS

LABORATORY-SCALE DESCRIPTION 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 damage 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

Damage Force (P d ) NOTES ON 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

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 (N r ) – 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 (N r ) – 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 (N r ) – 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 (N r ) – 1 or 3 Two maximum heating temperatures  F or 1600  F TEST MATRIX – 91 TOTAL SPECIMENS

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

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 strain 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)

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

COLOR OF STEEL AT ELEVATED TEMPERATURES 1400  F1200  F1600  F

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 FRACTURE TOUGHNESS The fracture toughness of A36 steel is much lower than the undamaged fracture toughness 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 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

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 CONCLUSIONS - A588 FRACTURE TOUGHNESS

CONCLUSIONS - A7 FRACTURE 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

SUB-TASK 2.1: LARGE-SCALE INVESTIGATIONS

LARGE-SCALE DESCRIPTION Six beam specimens were subjected to three damage- heat straightening repair cycles Two beam specimens were made of A7, two made of A36, and two made of A588 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

LARGE-SCALE TEST MATRIX Specimen ID  d /  y M r / M p-y  p (in)T max (  F) Cycle #  , 2, 3 A7-Beam A7-Beam A588-Beam A588-Beam A36-Beam A36-Beam  d /  y is the ratio of the damage strain in the extreme tension fiber to the yield strain  M r / M p-y is the ratio of the restraining moment in the heated steel to the weak-axis plastic moment capacity of the section  p is the plastic displacement at the point of loading after unloading  T max represents the maximum heat temperature at the vee heat location For each steel type, one damage-repair parameter was altered among the two specimens. The parameters were chosen from the results of laboratory-scale testing.

LARGE-SCALE TEST SETUP Rotation Meter Midspan 12 in. Displacement Transducer Quarter 6 in. Displacement Transducer Infrared Thermometer Longitudinal strain gage locations  p = 8.5 in  d = 90  y Support Column Beam Specimen (A7-Beam 2) Threaded Rod Loading Beam Hydraulic Actuator Before damage - indicating instrumentation After damage – indicating key elements of test setup

LOADING FRAME a)Top Plates b)Semi-Circular Contact Shafts c)0.75 in. Threaded Rods g)Hydraulic Actuator h)2.5 in. Threaded Rod i)Structural Plates and Nuts d)Beam Specimen e)Semi-Circular Contact Shafts f)Loading Beam ELEVATION VIEW SIDE VIEW

DAMAGE CYCLES The damaging (upward) force was applied by the hydraulic actuator pushing the loading beam against the flanges Load was applied monotonically until the strain in the extreme tension fiber reached  d from earlier table Instrumentation included: – Pressure transducers to measure actuator pressures – Six longitudinal strain gages at midspan to measure strains at the top, bottom, and at b f / 3 from the top on both flanges – Four displacement transducers to measure midspan and quarter deflections – Four rotation meters used to measure the end rotations

DISPLACEMENT DATA AT MIDSPAN WHILE DAMAGING (A36-Beam 1)

REPAIR CYCLES The restraining (downward) force was applied by the hydraulic actuator pulling down on the loading beam with additional attachments Two researchers applied Vee heats simultaneously to both flanges, spaced along the entire damaged region Heats were applied until the deflection of the beam was within 1/16 in. of the deflection before damage Instrumentation included: – Pressure transducers to measure actuator pressures – Infrared thermometer used to measure the surface temperature of the Vee heat – Four displacement transducers to measure midspan and quarter deflections – Four rotation meters used to measure to measure end rotations

VEE HEAT LOCATIONS AND NOMENCLATURE

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

NORMALIZED STRUCTURAL PROPERTIES Results are normalized to the statistical mean structural properties of undamaged steel from the same plate

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 percent elongation of the outmost (X) specimen and decrease the percent elongation of the middle (Y) and innermost (Z) specimens

NORMALIZED FRACTURE TOUGHNESS Results are normalized to the statistical mean fracture toughness of undamaged steel from the same flange plate

CONCLUSIONS – FRACTURE TOUGHNESS The fracture toughness of A7-Beam 1 subjected to N r =3 and  d =30  y is much lower than the undamaged toughness. The mean fracture toughness of A7-Beam 2 compares favorably with the undamaged toughness. However, some variability is seen in the results and the toughness of material closer to the flange-web junction (k-region) is much lower Damage-repair cycles increase the fracture toughness of A588 steel significantly to the ranges of % for the outermost two rows of charpy specimens. The fracture toughness values were smaller for charpy specimens closer to the flange-web junction The overall fracture toughness of A36-Beam 1 is comparable to the undamaged toughness. However, significant variability exists The fracture toughness of A36-Beam 2 increased significantly. The increase ranges from % of the undamaged toughness. There was one low value (40%) None of the significant conclusions and recommendations from the laboratory-scale testing (Sub-task 2.1) were altered by the results from the large-scale testing

QUESTIONS, COMMENTS, AND DISCUSSION?