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Cracking in Stud-Welded Stainless Steel Bolts for Bridge Expansion Joints
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LJG is a Corrosion Engineer, Metallurgical Engineer with world-class expertise in structural materials and relationships to design construction, and failure, properties and fabrication of materials used in transportation structures and bridges, research projects concerning use of metals and alloys, concrete and plastic composites, fatigue, welding, and materials testing
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Neoprene-composite expansion joints are widely used on bridges to accommodate thermal contraction and expansion. The expansion joints are anchored to metal plates secured by threaded studs. SAE 304 stainless studs were specified by bridge designers to stop corrosion for easy removal of nuts. Provisions for their use were specified in Illinois Standard Specifications for Road and Bridge Construction per Article 1052.02 (d).
In the contract to rehabilitate the Old Cairo Warren-style cantilever bridge over the Mississippi River, 7/8”-9 UNC threaded rods made of 304 stainless steel were stud-welded to steel deck plates at various panel points and piers. After stud welding and torquing to 125 ft-lbs, the studs broke off within a few days.
The causes of cracking were due to the formation of a brittle martensitic phase in the weld metal. X-ray analysis showed the composition to be approximately 10% chromium, 4.5% nickel, 1.3% manganese, 0.4% silicon, and 0.10% carbon. The yield strength was determined to be about 200,000 psi, which renders the weld zone susceptible to hydrogen embrittlement.
The failed studs were re-welded with AWS E309L electrodes. Afterwards, no cracking was reported. To test for any potential cracking due to hydrogen pickup from deicing salt water, the E309L welded studs were torqued to 450 ft-lbs and coupled with galvanized spacers and immersed in a 1% sodium chloride solution. After 127 days, no cracking occurred. The decrease of preload torque to 300 ft-lbs to loosen the nuts was attributed to corrosion of the zinc and creep relaxation of the initial load on the zinc-coated spacers.
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Cracking in Stud-Welded Stainless Steel Bolts for Bridge Expansion Joints
| Corrosion Engineer, Metallurgical Engineer, structural materials and relationships to design construction, and failure, properties and fabrication of materials used in transportation structures and bridges, research projects concerning use of metals and alloys, concrete and plastic composites, fatigue, welding, and materials testing | |
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| Resume of DAD | component corrosion failure, fatigue failure expert consultant |
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