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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58 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS SELECTION & DESIGN T This work discusses materials selec- tion and design factors related to the anchor rod failures and other issues that have plagued the new eastern span of the San Francisco-Oakland Bay Bridge. It is evident that some of the engineering decisions have con- tributed to these situations. The original San Francisco-Oakland Bay Bridge was completed in 1936. It actually consists of two bridges, the eastern and western spans (Figure 1). An earthquake in 1989 damaged the eastern span, and the Bay Bridge was closed for a month for re p a i r s . S e i sm i c re t r of i tt i n g p r o j e c t s ensued, followed by construction of a new eastern span. Construction began in 2002, and was scheduled for completion by 2007. After major delays, budget overruns, and high-strength steel anchor rod failures due to hydrogen embrittlement (HE), the new eastern span was finally opened to traffic in S e pt emb er 2013. C on c er n s ab out th e potential HE failures of the 3- to 4-in (76- to 1 0 2 - m m) d i a m e t e r a n c h o r r o d s t h a t support the traf fic decks are yet to be resolved. The California Department of Trans- portation (Caltrans) had the new eastern span designed to meet "the occurrence of up to a 1,500-year return period design earthquake." 1 This is equivalent to surviv- ing an 8.5 magnitude earthquake. Several seismic design innovations, such as "fusible links in the four-leg tower and hinge-pipe beams in the road decks" were utilized. At $6.5 billion for 2.2 miles (3.6 km) from Oak- land to Yerba Buena Island, the cost is more than $0.5 million/ft. This is the largest pub- lic works project in California. The new eastern span consists of the skyway and the self-anchored-suspension (SAS) span. The 1.2-mile (2-km) skyway consists of 452 precast concrete ortho- tropic box girders (OBGs). The SAS span is supported by a single 525-ft (160-m) high tower (T1), two piers (E2 and W2), a single continuous parallel wire strand (PW S) main cable, and 1,575 3- to 4-in diameter ASTM A354 2 Grade BD anchor rods. Hundreds of these anchor rods are 9- to 32-ft (2.7- to 9.7-m) long, with weights rang- ing from several hundred to more than 1,000 lb (450 kg ) each . Th ese massive anchor rods are critical to the structural integrity of the SAS span (Figure 2). This is the widest (72 ft [22 m]) between suspender ropes and longest (2,047 ft [624 m]) SAS span in the world that is supported by a single tower and one main cable. The SAS road decks consist of 14 steel OBGs in each direction. The OBGs, fabricated in China of ASTM A709M 3 Grade 345 (or 50) steel, were laid on a temporar y support bridge and joined together. The main cable is made of 137 PWSs. A strand is made of 127 steel wires, each 0.21 in (5.4 mm) in diameter. The wire is made of high-carbon (0.78-0.85%C) steel, hot-dip galvanized (HDG) with a minimum zinc coating thickness of 1.7 mils (42 ┬Ám or 300 g/m 2 ) . Corrosion on the New Eastern Span of the San Francisco- Oakland Bay Bridge Yun Chung, Alameda, California

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