Achievements and Results

  • Failed studs re-evaluated
  • Cracking of expansion joints halted
  • Bridge rehabilitation proceeded


The Problem

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. For this particular project, which was a contract to rehabilitate the Old Cairo Warren-style cantilever bridge over the Mississippi River, SAE 304 stainless studs were specified by bridge designers to stop corrosion, aiding with easy removal of nuts. Provisions for their use were specified in Illinois Standard Specifications for Road and Bridge Construction per Article 1052.02 (d).

During the bridge rehabilitation, 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 expert was tasked with figuring out the cause behind this.


The Solution

Several tests of yield strength determined the yield strength to be about 200,000 psi, which renders the weld zone susceptible to hydrogen embrittlement. X-ray analysis showed the composition to be approximately 10% chromium, 4.5% nickel, 1.3% manganese, 0.4% silicon, and 0.10% carbon. 

Combining these results led to the expert concluding that various causes of cracking were due to the formation of a brittle martensitic phase in the weld metal.

The failed studs were re-welded with AWS E309L electrodes. 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 then they were immersed in a 1% sodium chloride solution.


Benefits Realized

After 127 days, no more cracking had 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.


To see the resume of the expert associated with this case study, see the link below.

Resume of LJG Materials Selection, Failure, Fatigue, Fracture Expert Consultant Resume


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Peter Habicht, Lead Consultant
Peter specializes in welding and metallurgical engineer with 40 years industry experience in commercial nuclear power plant construction.


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