{"id":4397,"date":"2016-03-15T13:11:24","date_gmt":"2016-03-15T16:11:24","guid":{"rendered":"http:\/\/www.ericjorden.com\/blog\/?p=4397"},"modified":"2016-03-15T13:11:24","modified_gmt":"2016-03-15T16:11:24","slug":"bridge-failure-in-litigation-due-to-inadequate-bracing-city-of-edmonton-but-inadequate-for-what","status":"publish","type":"post","link":"http:\/\/www.ericjorden.com\/blog\/2016\/03\/15\/bridge-failure-in-litigation-due-to-inadequate-bracing-city-of-edmonton-but-inadequate-for-what\/","title":{"rendered":"Bridge failure in litigation due to inadequate bracing – City of Edmonton. But, inadequate for what?"},"content":{"rendered":"

(Forensic investigations are carried out by hypothesizing the cause of a failure or accident based on the\u00a0evidence available at\u00a0the time\u00a0– as limited as this might be, and\u00a0revising the hypothesis as\u00a0more evidence comes in.\u00a0\u00a0This successive hypothesizing and revising might be done several times during an investigation<\/em>.\u00a0 <\/em>The following is an example of this process.<\/em><\/p>\n

Counsel benefits from a process like this early in a case – ideally before deciding to take the case, when an expert studies the evidence, then, based on the available evidence, identifies and evaluates the technical\u00a0issues and the cost to investigate these)<\/em><\/p>\n

***<\/p>\n

The cross bracing\u00a0was inadequate.\u00a0 I concluded that last\u00a0March, a few days after the failure.\u00a0(Ref. 1)\u00a0I used the bridge failure to illustrate how a hypothesis – an idea, could be formed\u00a0about the cause\u00a0of an engineering\u00a0failure based on very little evidence.\u00a0 In this case, all I had were some on-line photographs .<\/p>\n

But, inadequate for what?<\/strong>\u00a0 To\u00a0resist the service plus construction loads – weights and pressures on the bridge, as required by the Canadian Highway Bridge Design Code?\u00a0 If there’s no bracing at all –\u00a0none,\u00a0these loads would cause the girders to buckle sideways in the order of 375 mm,\u00a0not the approximately 1,000 mm or more seen in the photographs.<\/p>\n

The 1,000 mm was determined from the photographs by scaling like we do on maps.\u00a0 The known 3.0 metre depth of the girders at the middle section – see Sources<\/strong> below, is like a scale or ruler\u00a0in the photograph.\u00a0 This depth is about the same as the\u00a0spacing between the girders, maybe a little less.\u00a0 I decided\u00a0the spacing was\u00a03.5 metres.\u00a0 I saw that the girders had buckled about 1\/3 of the way into the 3.5 metre spacing – 1,000 mm or more.<\/p>\n

The\u00a01,000 mm\u00a0buckling indicates a greater load was acting on the girders than perhaps was\u00a0required to\u00a0be\u00a0resisted by\u00a0the Code.\u00a0 Where did the greater load come from to cause the 1,000 mm?<\/p>\n

The only thing\u00a0attached to the girder – at the top, that can be seen in the photographs is\u00a0a sling at the end of\u00a0a crane’s cable.\u00a0 The cable is attached to\u00a0a crane’s telescopic boom.\u00a0 The boom\u00a0would sway and flex\u00a0a little in the wind that was blowing that night which would cause the sling below to tug on the girder – a point load in engineering.\u00a0 Construction cameras show the girders\u00a0intact at 2:00 in the morning and buckled at 2:15.<\/p>\n

I hypothesized last March that this repetitive tugging caused the girders to buckle like they did.<\/p>\n

The 1,000 mm\u00a0magnitude of the buckling and the fact that crane booms sway in the wind supports this idea\u00a0that tugging on the girders was the source of the greater load.<\/p>\n

It would be of interest to know if the bracing that was in place – and seen bent in the photographs, was adequate to prevent buckling,\u00a0except for\u00a0the 1,000 mm\u00a0due to the tugging.\u00a0 There are simple calculations that bridge design engineers do to determine the bracing needed to prevent buckling in the order of 375 mm.<\/p>\n

I did think about\u00a0a sudden foundation soil failure causing the crawler crane to subside and the cable to tug on the girder as a result.\u00a0 I dismissed this\u00a0idea because the crane had been there a while lifting 40 tonne girders into\u00a0place.\u00a0 Foundation failure would have occurred\u00a0some time before\u00a0because of these heavy lifts if the foundation soils were inadequate.<\/p>\n

The only way I would revise my hypothesis is to note that the crane operator did not contribute to the failure because he was not working.<\/p>\n

The initial hypothesis<\/strong><\/p>\n

The bridge failed because the middle crane’s boom moved in the wind – possibly also due to the crane operator’s actions, causing the cable\u00a0to periodically tug at the middle section of\u00a0beam #6 and eventually cause it to bend.\u00a0 This caused\u00a0the middle sections of\u00a0beams #5 and #4 to bend as well because they were connected to #6 by\u00a0some cross-bracing.\u00a0 The cross-bracing was inadequate to resist the force from the tugging\u00a0indefinitely and eventually failed too.\u00a0 The middle sections of beams #3, #2, and #1 did not bend and fail because they were adequately cross-braced.<\/em><\/p>\n

Revised hypothesis<\/strong><\/p>\n

The bridge failed because the middle crane’s boom moved in the wind causing the cable\u00a0to periodically tug at the middle section of\u00a0beam #6 and eventually cause it to bend.\u00a0 This caused\u00a0the middle sections of\u00a0beams #5 and #4 to bend as well because they were connected to #6 by\u00a0some cross-bracing.\u00a0 The cross-bracing was inadequate to resist the force from the tugging\u00a0indefinitely and eventually failed too.\u00a0 The middle sections of beams #3, #2, and #1 did not bend and fail because they were adequately cross-braced.<\/em><\/p>\n

Sources<\/h1>\n

I studied various photographs on-line including construction photographs taken at the time of the failure.<\/p>\n

I\u00a0spoke with Barry Bellcourt,\u00a0the Road Design and Construction Manager for the City of Edmonton, a few weeks ago, also Bryon Nicholson, Manager of Special Projects. Barry\u00a0mentioned the litigation and the city’s position.<\/p>\n

I also learned from him that the bridge consists of seven, 40-tonne girders.\u00a0\u00a0Each girder consists of two 7.5 metre long end sections and a 43 metre middle section.\u00a0 The end sections are 4.5 metres deep arching up to 3.0 metres at the middle section.\u00a0 The sizes are approximate.<\/p>\n

I\u00a0saw and photographed the underside of the repaired bridge girders\u00a0from Groat Road in early August when I was in Edmonton.<\/p>\n

I understand it was windy the night the girders buckled and that was the reason workers were not on the job.<\/p>\n

I spoke with four\u00a0companies in Nova Scotia that operate cranes.\u00a0 I learned that crawler crane booms move\u00a0in the wind; flex and sway.\u00a0\u00a0There is\u00a0greater movement\u00a0sideways because there is less strength that way.\u00a0 Telescopic booms move more than lattice booms because of the greater surface area.\u00a0 Booms are lowered to the ground in strong winds.\u00a0 One company doesn’t operate its cranes in winds of 50 km\/hr or more.<\/p>\n

I also talked with Amjad Memon, a structural engineer with the Nova Scotia Department of Transportation, about the Canadian Highway Bridge Design Code.<\/p>\n

References<\/strong><\/h1>\n
    \n
  1. Wind, construction crane and inadequate cross-bracing caused Edmonton bridge failure: An initial hypothesis.\u00a0 Posted March 27, 2015<\/li>\n
  2. Why, in a recent blog, didn’t I seem to consider foundation failure as a possible cause of the Edmonton bridge failure?\u00a0 Posted April 3, 2015<\/li>\n
  3. Bridge beams that fail are sometimes like balloons filled with water – squeeze them and they pop out somewhere else.\u00a0 Posted May 20, 2015<\/li>\n
  4. Google: Edmonton bridge failure, Groat Road, Buckling, etc.\u00a0to see\u00a0photographs of the buckled girders.<\/li>\n<\/ol>\n

     <\/p>\n","protected":false},"excerpt":{"rendered":"

    (Forensic investigations are carried out by hypothesizing the cause of a failure or accident based on the\u00a0evidence available at\u00a0the time\u00a0– as limited as this might be, and\u00a0revising the hypothesis as\u00a0more evidence comes in.\u00a0\u00a0This successive hypothesizing and revising might be done … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts\/4397"}],"collection":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/comments?post=4397"}],"version-history":[{"count":43,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts\/4397\/revisions"}],"predecessor-version":[{"id":4579,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts\/4397\/revisions\/4579"}],"wp:attachment":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/media?parent=4397"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/categories?post=4397"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/tags?post=4397"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}