A short footbridge crosses a stream at a quarry site in the middle of Northern Ireland.<\/p>\n
From above it is timber decking and a handrail, entirely unremarkable, the kind of thing a walking route gets given without ceremony.<\/p>\n
From underneath it is two long white shells, curved along their length.<\/p>\n
They came off a wind turbine and were headed for a landfill.<\/p>\n
Instead they are carrying the deck<\/strong>, and everything on it.<\/p>\n A test put 36 tons<\/strong> on them to see what would happen.<\/p>\n A bridge girder has one job. It spans a gap and resists bending without deflecting much.<\/p>\n That is close to the only job a rotor blade has ever done. It sticks out from a hub and resists bending in wind, for twenty years, in weather.<\/p>\n The material is right as well. Glass fiber composite does not rust, does not rot and needs no paint system to survive outdoors.<\/p>\n The shape is the awkward part. A blade tapers, twists and changes section along its length, which no standard girder does.<\/p>\n So the engineering work is not about strength. It is about geometry, bearing details and how to fix a deck to a curved shell.<\/p>\n Which is why the honest description is a repurposed girder<\/strong> rather than a recycled material<\/strong>.<\/p>\n The span uses two blades of about 44 feet, taken from a small three bladed turbine of an older generation.<\/p>\n The bridge itself is about 20 feet across and a little over 6 feet wide.<\/p>\n Around 20 inches of each blade rests on a concrete abutment at each end, which is the entire bearing.<\/p>\n There is no steel frame under the deck and no stiffening truss anywhere in the structure.<\/p>\n Five blades were donated in total. Four went to the quarry site and one went to a university laboratory to be tested on its own.<\/p>\n It is the second structure of its kind. The first went in at a site in Cork in January of 2022.<\/p>\n Neither is a prototype product<\/strong>. Both are research structures<\/strong> that people walk on.<\/p>\n The test ran in May of 2023, with both static and dynamic loading applied.<\/p>\n Teams from universities in Northern Ireland, Ireland, England and the United States took part in it, which is a lot of institutions for a footbridge over a stream.<\/p>\n The span carried about 36 short tons, roughly the weight of a loaded semitrailer parked on a footbridge.<\/p>\n Deflection at the middle under full load came to about 0.35 inches, a bit over a third of an inch.<\/p>\n For a 20 foot span that is a stiff structure by any standard, and stiffness rather than strength is what pedestrians feel.<\/p>\n The number that matters is not the load<\/strong> it took. It is how little<\/strong> it moved.<\/p>\n Every blade is different, so every bridge needs its own assessment, and that assessment costs more than a steel beam.<\/p>\n There is no material certificate for a used blade either. The composite came from a factory decades ago with no traceable record for a structural engineer to sign against.<\/p>\n Testing one blade to destruction, as the team did, gives numbers for that blade and only that blade.<\/p>\n A second blade off the same production line may behave the same way, and nobody can promise that on paper.<\/p>\n The technical result is not in doubt, and the test record<\/a> is public.<\/p>\n What is missing is a route from one span at a quarry to a catalog product, which the trade coverage<\/a> is candid about.<\/p>\n Until somebody standardizes the bearing detail, every blade bridge stays a bespoke object<\/strong> built by a research team<\/strong>.<\/p>\n The prize is real. Blades arriving for disposal are free at the gate and already engineered for exactly this kind of loading.<\/p>\n Small rural spans are the obvious market, because they are short, lightly loaded and expensive to build in steel.<\/p>\n What scaling needs is a sorting system, so blades of one model can be treated as one product line rather than as individual artifacts.<\/p>\n It also needs an owner willing to accept a structure whose material has no paperwork, which is a procurement problem rather than an engineering one.<\/p>\n Bridge decks are unforgiving about movement, which is why a Guizhou span closed with 93 steel pieces<\/a> fitted to tolerances measured in fractions of an inch.<\/p>\n Materials that look after themselves help the same argument, as with concrete that seals its own cracks using embedded bacteria<\/a> rather than a maintenance crew.<\/p>\n A blade needs neither, which makes the barrier entirely administrative<\/strong> rather than anything structural<\/strong>.<\/p>\n","protected":false},"excerpt":{"rendered":" A short footbridge crosses a stream at a quarry site in the middle of Northern Ireland. From above it is timber decking and a handrail, entirely unremarkable, the kind of thing a walking route gets given without ceremony. From underneath it is two long white shells, curved along their length. They came off a wind … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":2389,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-2385","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-wind-power"],"_links":{"self":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/2385","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/comments?post=2385"}],"version-history":[{"count":3,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/2385\/revisions"}],"predecessor-version":[{"id":2767,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/2385\/revisions\/2767"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/media\/2389"}],"wp:attachment":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/media?parent=2385"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/categories?post=2385"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/tags?post=2385"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}What a blade already has that a girder needs<\/h2>\n
What was actually built<\/h2>\n
What the load test measured<\/h2>\n
Why this has not turned into a business<\/h2>\n
What it would take to scale<\/h2>\n