[ Infrastructure ]
[ Infrastructure ]
whether it was possible to decrease the amount of chromium to lower the material cost while still meeting A709 specifications . None of the alternatives proved satisfactory , confirming 50CR ’ s dominance .
Duplex comes to the USA However , because of 50CR ’ s limitations ( it is a lean grade with low pitting resistance : see Table ), and also perhaps because 50CR was never marketed as a construction grade ( it started life as an alloy in salt truck liners , coal processing , power plants , etc .), US end users started to consider duplex stainless steel . According to Jason Provines , Senior Research Scientist at the Virginia Transportation Research Council , its advantages include “ greater availability , a smoother supply chain , the existence of several standards and best practices … Overall , there was a feeling that we didn ’ t have to reinvent the wheel .” Several US initiatives to assess duplex use in bridges were undertaken , including the establishment in 2022 of an AASTHO / NSBA Collaboration Task Group , TG18 , with the intent to “ develop a set of cohesive guide specifications that will allow for duplex stainless steel to be used for vehicular bridges in the United States ”. Perhaps the first time duplex was applied on a US bridge was the Harbor Drive Pedestrian Bridge , San Diego ( 2011 ). It is one of the longest selfanchored pedestrian bridges in the world , in which the cables are hidden inside welded pipes . The suspender cables and safety mesh were made in austenitic type 316 , while the connectors
Route 340 Bridge , Virginia , USA . Grade 50CR bent plates were used in the fabrication of the cross-frames . It was also the first time that a US bridge design specified stainless steel for all secondary members and fasteners . Low water clearance and industrial pollution were two factors determining the choice of material . Photos : Jason Provines .
for the cable system are in duplex 2205 . In 2013 , in the West 7th Street Bridge in Fort Worth , Texas , type 2205 was applied to the hanger bars . In 2020-22 , the Iowa- Illinois Memorial Bridge ( I-74 ) bridge used 2205 rebar and – apparently for the first time – super duplex grade 2507 for anchor rods as protection against chloride de-icing salts during the severe winters .
Duplex and 3D printing One final development concerning duplex bridges is the use of 3D printing . In 2021 a Dutch company , MX3D , completed the installation of a duplex stainless-steel bridge across a
small canal in the heart of Amsterdam ’ s old centre . It was made with robots , using the WAAM ( wire arc additive manufacturing ) process . However , it was intended only as a temporary replacement of an older bridge and was removed on 13 October 2023 . The future destination of the bridge is unknown , as also is the extent to which 3D-printing will be used to construct bridges .
Conclusion A publication of the ISSF dating from 2023 ( 1 ) lists 61 bridges made in stainless steel . The same document notes that there are 600,000 bridges in the USA alone . A great number of bridges all over the world need to be repaired or replaced . The bridges taking their place will require durable and sustainable materials . No marks for guessing which ones !
Acknowledgement I would like to thank Jason Provines , Senior Research Scientist of the Virginia Transportation Research Council of the VDOT ( Virginia Department of Transportation ) for his kind help in providing information and materials .
Construction of the Iowa-Illinois Memorial Bridge ( I-74 . Photo : Farragutful - Own work , CC BY-SA 4.0 , https :// commons . wikimedia . org / w / index . php ? curid = 107036960
References
( 1 ) “ Stainless Steel in Infrastructure : Bridges ”: https :// www . worldstainless . org / files / issf / nonimage-files / PDF / Stainless _ Steel _ in _ Infrastructure _ Bridges . pdf
18 Stainless Steel World December 2023 www . stainless-steel-world . net