Structural Properties of Steels Subjected to Multiple Cycles of Damage Followed by Heating Repair

Experimental investigations were conducted to evaluate the effects of multiple cycles of damage followed by heating repair on the structural properties and fracture toughness of A36, A588, and A7 bridge steels. The test specimens were subjected to multiple cycles of tensile damage followed by compressive restraining stress and heat shortening repair. The damage and repair parameters considered were the damage strain $\left({\epsilon }_d\right)$ , the restraining stress $\left({\sigma }_r\right)$ , the number of damage-repair cycles $\left(N_r\right)$ , and the maximum heating temperature $\left(T_{\max }\right)$ . Seventy-five A36, A588, and A7 steel specimens were subjected to multiple damage-repair cycles with $T_{\max }$ limited to the recommended limit of $650°\mathrm{C}$ . Sixteen additional A36 steel specimens were subjected to multiple damage-repair cycles with $T_{\max }$ greater than the recommended limit ( $T_{\max }$ =760 or $840°\mathrm{C}$ ). Standard material specimens were fabricated from the damaged-repaired steel specimens and tested according to the applicable ASTM standards. The results from the standard material tests indicate that multiple damage-repair cycles have a relatively small influence $(\pm 15\%)$ on the elastic modulus, yield stress, and ultimate stress, and a significant influence on the ductility (percent elongation) and fracture toughness of damaged-repaired bridge steels. These effects of the multiple damage-repair cycles on the fundamental structural properties and fracture toughness of various bridge steels are summarized in the paper.