List of bridges in Bhutan

Cantilever beams were developed in order to cross increasingly wide streams or rivers, where simple wooden beams had a limited range of about 10 meters. Two arms with timber superimposed are built on either side of the river, above the highest flood-level point, while being weighted to allow an increasingly large cantilevering, and solid wooden beams are then fixed on each end of the arms with wooden pegs. Bridges of this type were very common in mountainous region of India, Nepal and Tibet with an average span of {{convert|20|m|ft}}, but those from Bhutan have the particularity of being more elaborate with stone masonry bridge towers, roofed with wooden shingles above the abutments or bridge head structures.Gerard, 1841, p.35Deloche, 1984, p.72 The main purpose of these towers was to act as a counterweight to stiffen the structure.

File:Tamchog Chakzam, Bhutan 01.jpg

The use of more layers of wooden beams with more pronounced inclinations permit to achieve greater spans, one of the most significant example is the Wangdue Zam with a span reported from {{convert|112|to|180|ft|m|1}} according to different sources.Gerner, 2007, p.60 The renovation of the Punakha Bridge in the city of the same name in 2008 by a Swiss company{{cite web |url=https://www.waltgalmarini.ch/en/portfolio/wooden-bridge-punakha-bhutan/ |title=Reconstruction of wooden bridge in Punakha, Bhutan |website=Waltgalmarini.ch |access-date=December 9, 2022}} made it possible with this technique to reach a span of {{convert|55|m|ft}}, the largest for this type of bridge in Bhutan.

All these bridges are called Bazam, a word composed of Ba which means Cattle and Zam who is the traduction of Bridge in Dzongkha, the national language of Bhutan. This comes from the resemblance of the cantilever beams that sit opposite each other with two noses of cattle.

A major innovation was created by Thang Tong Gyalpo regarding the crossing of large spans, he developed iron chains working techniques and adapted them to the construction of bridges. By adding arsenic to the iron (a bit more than 2.8%),Kalmus, 2015, p.21 it was easier to work with and had good resistance against rust, some of these chains are still functional today. This made it possible to reach spans to over a hundred meters which had not yet been reached in Europe at this time, the Chushul Chakzam in Tibet is reported to be {{convert|150|yd|m}} long.

After making more than a hundred such bridges in Tibet, Thang Tong Gyalpo came to Bhutan in 1433 where he found big iron ore deposits and locals blacksmiths, many chains forged here were shipped from Bhutan to Tibet. He build 8 bridges in the country, oftentime near ore deposits, and some of them were still in use in the 20th century, the last existing bridges are Tamchog Chakzam, Doksum Chakzam, Dangme Chakzam, and Khoma ChakzamGerner, 2007, p.97-98 (Chakzam literally means "iron bridge" in standard Tibetan).

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This table presents the structures with spans greater than {{convert|100|m|ft}} (non-exhaustive list).

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• Transport in Bhutan
• Geography of Bhutan
• List of rivers of Bhutan
• Architecture of Bhutan

• Notes

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• {{cite web | url=https://structurae.net/en| title=International Database for Civil and Structural Engineering |author=Nicolas Janberg |website=Structurae.com}}

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• Others references

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• {{cite book |ref=Aris |url=https://archive.org/details/ViewsOfMedievalBhutanTheDiaryAndDrawingsOfSamuelDavis1783MichaelAris |title=Views of Medieval Bhutan, The Diary and Drawings of Samuel Davis - 1783 |last1=Aris |first1=Michael |author-link1=Michael Aris |publisher=Smithsonian Institution Press |date=1982 |isbn=0-87474-210-2 |location=Washington D.C. }}
• {{cite book |ref=Deloche |title=The Ancient Bridges of India |last1=Deloche |first1=Jean |author-link=Jean Deloche |publisher=Sitaram Bhartia Institute of Scientific Research |location=New Delhi |date=1984 }}
• {{cite book |ref=Gerard |url={{GBurl|id=GZVeAAAAcAAJ}} |title=Account of Koonawur in the Himalaya, Etc. ... |last1=Gerard |first1=Alexander |author-link=Alexander Gerard (explorer) |publisher=James Madden |date=1841 |location=London }}
• {{cite book |ref=Gerner |url=http://www.bhutanstudies.org.bt/publicationFiles/OccasionalPublications/Chakazampa/chakzampa.pdf |title=Thangtong Gyalpo: Architect, Philosopher and Iron Chain Bridge Builder |last1=Gerner |first1=Manfred |translator-first=Gregor |translator-last=Verhufen |publisher=Centre for Bhutan Studies |date=2007 |isbn=978-99936-14-39-5 |website=Bhutanstudies.org.bt }}
• {{cite report |ref=Kalmus |chapter-url=https://www.researchgate.net/publication/352908621 |title=Journal of Comparative Cultural Studies in Architecture |chapter=Remarks on selected bridges of Thangtong Gyalpo |last1=Kalmus |first1=Marek |date=November 2015 |pages=20–32 |website=ResearchGate }}
• {{cite book |ref=Stearns |url={{GBurl|id=tqZ9CAAAQBAJ}} |title=King of the Empty Plain: The Tibetan Iron Bridge Builder Tangtong Gyalpo |last1=Stearns |first1=Cyrus |publisher=Shambhala Publications |date=2007 |isbn=978-1-5593-9837-4 |location=Boston }}
• {{cite book |ref=Turner |url={{GBurl|id=tPTVnyOGSxgC}} |title=An Account of an Embassy to the Court of the Teshoo Lama in Tibet: Containing a Narrative of a Journey Through Bootan, and Part of Tibet |last1=Turner |first1=Samuel |author-link=Samuel Turner (diplomat) |publisher=W. Bulmer and Co |date=1800 |location=London }}

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• {{cite web |url=https://www.timbresponts.fr/types_de_ponts/ponts_couverts_dossiers/asie_ponts_couvert.htm |title=Des Ponts couverts en Asie |trans-title=Covered Bridges in Asia |language=fr |website=Timbresponts.fr }}
• {{cite web |url=http://bhutanphilately.blogspot.com/2010/07/stamps-on-bridges-of-bhutan.html |title=Stamps On Bridges of Bhutan |date=July 8, 2010 |website=Bhutanphilately.blogspot.fr }}
• {{cite web |url=https://www.nsb.gov.bt/GIS/map/WANGDI/WANGDUE%20BRIDGES.pdf |title=Bridges Map of Wangdue Phodrang District - scale :1:300 000 |archive-url=https://web.archive.org/web/20201116114529/https://www.nsb.gov.bt/GIS/map/WANGDI/WANGDUE%20BRIDGES.pdf |archive-date=November 16, 2020 |website=Nsb.gov.bt - National Statistics Bureau }}
• {{cite web |url=http://www.nsb.gov.bt/GIS/xl/wangdue/bridge.xls |title=Bridges table of Wangdue Phodrang District |archive-url=https://web.archive.org/web/20201116114553/http://www.nsb.gov.bt/GIS/xl/wangdue/bridge.xls |archive-date=November 16, 2020 |format=xls |website=Nsb.gov.bt - National Statistics Bureau }}
• {{cite book |url=https://www.yumpu.com/en/document/read/3091992/good-governance-in-bridge-building-helvetas |title=Good Governance in Bridge Building, Suspension Bridge Programme - Sharing Experiences from Bhutan |last1=Rosenberg |first1=Katrin |publisher=Helvetas Bhutan |date=August 2009 }}
• {{cite report |ref=DCSRCKB |url=https://openjicareport.jica.go.jp/pdf/12183323_01.pdf |title=Data collection survey on road connectivity in the Kingdom of Bhutan |date=September 2014 |website=Openjicareport.jica.go.jp - Japan International Cooperation Agency }}
• {{cite web |url=http://www.en.yokogawa-bridge.co.jp/04_structures/index7.html |title=Arch Bridges - Bhutan |website=Yokogawa-bridge.co.jp}}

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Bhutan

Bridges

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