Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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59 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 Each PWS was shop fabricated to an exact predetermined length, ~1.0 mile (1.6 km), with a steel socket at each end. One socketed end is connected to a 3.5-in (89- mm) di am et er A STM A354 Gra d e BD anchor ro d and anchored to th e east anchor wall (Figure 3). The other socketed end is pulled over the tower cable saddle, looped around the west end, and anchored to the west anchor wall. Thus, the PWS main cable, which sustains the entire load of the steel OBG decks of the SAS span, is anchored in the two splay chambers that are part of the structure (Figure 3). Therein lies the name, self-anchored-suspension. The SAS span has ~1.4 million fasteners (bolts and studs): 1,000 fabricated to ASTM A307; 4 1.25 million to ASTM A325; 5 100,000 to ASTM A490; 6 13,000 to ASTM A354 Grade BC; and 2,300 to ASTM A354 Grade BD. All but those meeting ASTM A490 were HDG. ASTM A490 prohibits HD G b ecause it increases HE cracking susceptibility. ASTM A354 warns that HE cracking "may occur on hot dip galvanized Grade BD bolts." Hydrogen Embrittlement Failures of Grade BD Anchor Rods As part of seismic engineering, four bearings (B1 to B4) and four shear keys (S1 to S4) were installed between the concrete cap beam of Pier E2 and the steel OBG decks. In March 2013, 32 of the 96 HDG ASTM A354 Grade BD anchor rods for shear keys S1 and S2 failed under static loading within two weeks after being pre- tensioned. The failures occurred in the bot- tom threads inside the concrete cap beam. The remediation of the 32 Grade BD anchor rod failures cost $25 million because the anchor rods for S1 and S2 were neither repairable nor replaceable. HE is the only cracking mechanism that can cause high-strength steel to fail under static loading below yield stresses when exposed only to water, including atmo- spheric condensates. Hydrogen in the steel is one of three principal factors that can cause a crack to initiate and grow under static stress. The other two factors are stress and a material's susceptibility to HE FIGURE 1 San Francisco-Oakland Bay Bridge (2016 est.). FIGURE 2 Self-anchored-suspension (SAS 2,047-ft long overall in 2013). FIGURE 3 Splay chambers where the main cable is anchored.

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