{"id":221,"date":"2018-05-15T19:57:55","date_gmt":"2018-05-15T17:57:55","guid":{"rendered":"https:\/\/blogs.futura-sciences.com\/lehning\/?p=221"},"modified":"2018-06-16T11:14:39","modified_gmt":"2018-06-16T09:14:39","slug":"les-ponts-himalayens","status":"publish","type":"post","link":"https:\/\/blogs.futura-sciences.com\/lehning\/2018\/05\/15\/les-ponts-himalayens\/","title":{"rendered":"Les ponts himalayens"},"content":{"rendered":"

Les ponts himalayens sont des ouvrages souples suspendus par leurs deux extr\u00e9mit\u00e9s.\u00a0L\u2019ancrage \u00e9tant essentiel, leur altitude d\u00e9pend de la qualit\u00e9 de la roche. Les deux extr\u00e9mit\u00e9s doivent \u00eatre approximativement \u00e0 la m\u00eame hauteur et ind\u00e9racinables.<\/span><\/p>\n

La courbe du pont<\/h2>\n

Globalement, le pont se comporte comme une cha\u00eene suspendue par ses deux extr\u00e9mit\u00e9s. Autrement dit, il prend la forme d\u2019une courbe appel\u00e9e cha\u00eenette pour cette raison. Les lignes \u00e9lectriques hautes tensions ainsi que les c\u00e2bles de t\u00e9l\u00e9ph\u00e9riques en donnent d\u2019autres exemples. Galil\u00e9e pensait qu\u2019il s\u2019agissait d\u2019une parabole, sans doute parce qu\u2019elle est presque indiscernable de l\u2019arc de parabole de m\u00eame longueur suspendu entre les m\u00eames points. En fait, son \u00e9quation est li\u00e9e \u00e0 la fonction exponentielle.<\/span><\/span><\/p>\n

\"\"
Parabole (en rouge) et cha\u00eenette (en bleu) de m\u00eame longueur suspendue entre les m\u00eames points.<\/figcaption><\/figure>\n

Minimiser la tension<\/h2>\n

En tendant fortement les c\u00e2bles soutenant le pont, il serait possible que cette courbe se confonde avec une droite. L\u2019observation montre que ce n\u2019est jamais le cas. Pourquoi\u00a0? Tout simplement pour r\u00e9duire la tension exerc\u00e9e aux extr\u00e9mit\u00e9s qui, \u00e0 terme, pourrait faire c\u00e9der le pont. Pour la minimiser, la forme id\u00e9ale est celle utilis\u00e9e pour suspendre les lignes haute tension.<\/span><\/span><\/p>\n

\"\"
Minimisation de la tension. Le rapport entre la fl\u00e8che et la distance doit \u00eatre \u00e9gal \u00e0 1 \/ 3.<\/figcaption><\/figure>\n

Pour cela, le calcul montre que la fl\u00e8che doit \u00eatre \u00e9gale au tiers de la distance entre les points d\u2019appui, s\u2019ils sont \u00e0 la m\u00eame altitude. Bien entendu, dans la pratique, il suffit que la tension reste \u00e0 un niveau raisonnable. La fl\u00e8che est donc rarement aussi importante. Au d\u00e9part, la descente serait d\u2019ailleurs dangereuse\u00a0! En pratique, on d\u00e9passe rarement une fl\u00e8che de l\u2019ordre du dixi\u00e8me de la distance.<\/span><\/span><\/p>\n

Stabiliser le pont<\/h2>\n

Un pont fabriqu\u00e9 ainsi est sujet \u00e0 des mouvements de roulis et de tangages, ce qui rend sa travers\u00e9e d\u00e9licate d\u00e8s que plusieurs utilisateurs l\u2019empruntent. Le vent a \u00e9galement une influence non n\u00e9gligeable sur sa stabilit\u00e9. Pour \u00e9viter ces inconv\u00e9nients, le plus simple est de le stabiliser par des c\u00e2bles exer\u00e7ant une tension lat\u00e9rale.<\/span><\/span><\/p>\n

\"\"
Cette photographie montre les c\u00e2bles tendant lat\u00e9ralement le pont de chaque c\u00f4t\u00e9. Ils sont r\u00e9guli\u00e8rement espac\u00e9s le long de deux courbes sym\u00e9triques, de forme parabolique. \u00a0 \u00a9 Herv\u00e9 Lehning<\/figcaption><\/figure>\n

La courbe tendant ces c\u00e2bles \u00e9pouse la forme d\u2019une parabole afin que la tension exerc\u00e9e soit constante le long du pont. Dans les ponts himalayens, on retrouve donc simultan\u00e9ment deux courbes\u00a0: la cha\u00eenette et la parabole.<\/span><\/span><\/p>\n

\"\"
Cha\u00eenette et parabole se trouvent dans ce pont himalayen. \u00a9 Herv\u00e9 Lehning<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

Les ponts himalayens sont des ouvrages souples suspendus par leurs deux extr\u00e9mit\u00e9s.\u00a0L\u2019ancrage \u00e9tant essentiel, leur altitude d\u00e9pend de la qualit\u00e9 de la roche. Les deux extr\u00e9mit\u00e9s doivent \u00eatre approximativement \u00e0 la m\u00eame hauteur et ind\u00e9racinables. La courbe du pont Globalement, le pont se comporte comme une cha\u00eene suspendue par ses deux extr\u00e9mit\u00e9s. Autrement dit, il … Continuer la lecture de Les ponts himalayens<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":12,"featured_media":222,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_links_to":"","_links_to_target":""},"categories":[29,13,10],"tags":[108,26,107,105,106],"class_list":["post-221","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-maths-2","category-photographies","category-voyages","tag-chainette","tag-himalaya","tag-parabole","tag-ponts","tag-ponts-himalayens"],"yoast_head":"\nLes ponts himalayens, par Herv\u00e9 Lehning<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blogs.futura-sciences.com\/lehning\/2018\/05\/15\/les-ponts-himalayens\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Les ponts himalayens, par Herv\u00e9 Lehning\" \/>\n<meta property=\"og:description\" content=\"Les ponts himalayens sont des ouvrages souples suspendus par leurs deux extr\u00e9mit\u00e9s.\u00a0L\u2019ancrage \u00e9tant essentiel, leur altitude d\u00e9pend de la qualit\u00e9 de la roche. Les deux extr\u00e9mit\u00e9s doivent \u00eatre approximativement \u00e0 la m\u00eame hauteur et ind\u00e9racinables. La courbe du pont Globalement, le pont se comporte comme une cha\u00eene suspendue par ses deux extr\u00e9mit\u00e9s. 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