SUB-TASK 2.1: LABORATORY-SCALE INVESTIGATIONS. LABORATORY-SCALE DESCRIPTION Ninety one laboratory-scale specimens were subjected to multiple damage-heat

SUB-TASK 2.1: LABORATORY-SCALE INVESTIGATIONS

LABORATORY-SCALE DESCRIPTIONNinety one laboratory-scale specimens were subjected to multiple damage-heat straightening repair cyclesFocused on A36 and A588 steels due to the availability of material as apposed to older A7 and A373A36 - closest in chemical compositions as A7 and A373A588 - third most relevant steel type from databaseSome A7 steel specimens were acquired from the web of a W24x76 steel beamTest 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 (Pd) NOTES ON TESTING APPROACHRestraining Force (Pr) Two methods were considered(Method 1)t

PROBLEMS WITH METHOD 1The 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 2Strip HeatDamage Force (Pd )Repair Force (Pr )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

TEST MATRIX 91 TOTAL SPECIMENSA36 28 SpecimensThree damage strains (d) 30y, 60y , or 90yTwo restraining stresses (y) 0.25 y or 0.50y (0.40 y or 0.70 y for d = 30y)Number of damage-repair cycles (Nr) 1, 2, 3, 4, or 5A588 30 SpecimensThree damage strains (d) 20y, 40y , or 60yTwo restraining stresses (y) 0.25y or 0.50y Number of damage-repair cycles (Nr) 1, 2, 3, 4, or 5A7 17 Specimens Three damage strains (d) 30y, 60y , or 90yTwo restraining stresses (y) 0.25y or 0.50y Number of damage-repair cycles (Nr) 1, 3, or 5Three maximum heating temperatures Overheated A36 16 SpecimensTwo damage strains (d) 60y or 90yTwo restraining stresses (y) 0.25y or 0.50y Number of damage-repair cycles (Nr) 1 or 3Two maximum heating temperatures - 1400F or 1600F

TEST SPECIMEN DETAILS7.8752.063.752.063.383.755.003.753.383.2539.0013.25f = 1.1875Test specimen thickness = 0.45 in. A7 steel2.0013.252.002.133.752.131.633.383.3816.883.753.7516.881.633.383.383.258.0046.25Test specimen thickness = 1.00 in. A36 and A588 steelf = 1.1875f = 1.1875

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

TEST SETUPTop BeamBottom BeamConcrete BlocksTest SpecimenHydraulic ActuatorSplit-flow valveElectric PumpNeedle ValvePressure Gage

DAMAGE CYCLE-INSTUMENTATIONPressure transducers to measure actuator pressuresTwo longitudinal strain gages in test areaTwo displacement transducers to measure average strainGage front Gage -back3.25 in.5.0 in.Test-AreaTwo displacement transducers to measure average strains in test areaTEST AREA

EXPERIMENTAL DAMAGE BEHAVIORSpecimen A36-60-50-3 Target ed = 0.080 in/inCycle 1-Longitudinal Strain Gages (Back (gray) and Front (red))Cycle 1-Average StrainCycle 2 Average StrainsCycle 3-Average StrainsStress-strain of undamaged uniaxial tension test(SPECIMEN A36-60-50-3)Strain (in/in)

REPAIR CYCLE-INSTRUMENTATIONTwo displacement transducers to monitor movement during heat straighteningInfrared thermometer used to measure temperature on all sidesPressure transducers to measure actuator pressuresInfrared thermometer to measure surface temperatureTwo displacement transducers to measure displacement between top and bottom beam.

EXPERIMENTAL REPAIR BEHAVIORPressure (psi)Temperature (F)Right Displacement *10000 (in)Left Displacement*10000 (in) (SPECIMEN A36-60-50-3)

REPAIR DESCRIPTIONApplying the Strip HeatMonitoring the Surface Temperature

COLOR OF STEEL AT ELEVATED TEMPERATURES1400F1200F1600F

UNIAXIAL TENSION RESULTS (A36)ed = 30ey sr =0.40sy
ed = 30ey sr =0.70sy
Number of damage-repairs (Nr)ed = 30ey sr =0.40sy
Number of damage-repairs (Nr)Number of damage-repairs (Nr)ed = 30ey sr =0.40sy
ELASTIC MODULUSYIELD STRESSULTIMATE STRESSDUCTILITY % ELONGATION

DUCTILITY OF A36, A588, AND A7 STEEL ed = 30ey sr =0.40sy
Number of damage-repairs (Nr)ed = 30ey sr =0.40sy
A588 STEELNumber of damage-repairs (Nr)ed = 30ey sr =0.40sy
A7 STEELNumber of damage-repairs (Nr)A36 STEEL

CONCLUSIONSSTRUCTURAL 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 steelsThe yield stress and surface harness increase slightly and the ultimate stress and elastic modulus are always within 10% of the undamaged valuesHowever, the % elongation of damaged-repaired steel is influenced significantlyThe ductility (% elongation) of A36 and A588 steel decreases significantly but never lower than minimum values according to AASHTO requirementsThe ductility of A7 steel subjected to five damage-repair cycles is extremely low

FRACTURE TOUGHNESS RESULTS (A36) 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 ed, sr, and Nr are evaluated.

CONCLUSIONS - A36 FRACTURE TOUGHNESSThe fracture toughness of A36 steel is much lower than the undamaged fracture toughnessMean fracture toughness of specimens damaged to 30ey becomes less than 50% after two damage-repair cyclesThe fracture toughness of specimens damaged to 60ey becomes less than 50% after three damage-repair cyclesMean fracture toughness of specimens damaged to 90ey was found to have significant scatterHigher 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 casesThe fracture toughness never decreases below 50% (even after five damage-repair cycles)Increasing the restraining stress reduces the fracture toughness of A588 steel significantlyCONCLUSIONS - A588 FRACTURE TOUGHNESS

CONCLUSIONS - A7 FRACTURE TOUGHNESSThe fracture toughness of A7 steel decreases with an increase in sr and Nr and with a decrease edThe fracture toughness of steels damaged to 30ey reduces to 50% of the undamaged toughness after three damage-repairsThe fracture toughness of specimens damaged to 60ey and repaired with 0.25sy is excellent. However, increasing sr has a significant adverse effect on the fracture toughnessThe fracture toughness of specimens damaged to 90ey is close to the undamaged toughness after three damage-repair cycles

SUB-TASK 2.1: LARGE-SCALE INVESTIGATIONS

LARGE-SCALE DESCRIPTIONSix beam specimens were subjected to three damage-heat straightening repair cyclesTwo beam specimens were made of A7, two made of A36, and two made of A588Beams subjected to weak axis bending by applying concentrated forces at midspanSimilar to damage induced to the bottom flange of a composite beam impacted by an over-height truckTwo flanges could be used for the removal of material samples as apposed to one flangeEasier 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 beamResults of material testing used to validate the conclusions and recommendations of Sub-task 2.1

LARGE-SCALE TEST MATRIXed / ey is the ratio of the damage strain in the extreme tension fiber to the yield strainMr / Mp-y is the ratio of the restraining moment in the heated steel to the weak-axis plastic moment capacity of the sectionDp is the plastic displacement at the point of loading after unloadingTmax represents the maximum heat temperature at the vee heat locationFor 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 SETUPRotation MeterRotation MeterMidspan 12 in. Displacement TransducerQuarter 6 in. Displacement TransducerQuarter 6 in. Displacement TransducerInfrared ThermometerLongitudinal strain gage locationsp = 8.5 in ed = 90 eySuppo