Readers in Edmonton and Halifax commented on\u00a0an item I posted last Friday about the Edmonton bridge failure – and my initial hypothesis as to the cause of the failure. (Ref. 1)<\/p>\n
I concluded the bridge failed because a crane supporting a middle section of\u00a0one\u00a0of\u00a0the bridge beams moved in the wind pulling the beam sideways and causing it to buckle.\u00a0 Cross-bracing was not adequate enough to prevent this movement.<\/p>\n
Gary in Halifax<\/strong><\/p>\n Gary in Halifax wondered why I didn’t give links to the photographs and video that I studied and mentioned in my blog.\u00a0\u00a0He thought\u00a0this would make it easier for the reader.\u00a0\u00a0He\u00a0is quite right because we learn more visually than we do\u00a0verbally or from text.<\/p>\n Basically, I was anxious to get the item out there while it was\u00a0current news – and while some readers\u00a0might still have the newspapers around that carried\u00a0the story.<\/p>\n Googling “Edmonton bridge failure” quickly took me to a good number of sites with text, photographs and at least one good video.\u00a0 I looked at a number of them in forming my initial hypothesis.<\/p>\n It would have been an exercise in itself reviewing all this material\u00a0and selecting three or four links, and in the process possibly omit some that might have been included.\u00a0 It seemed easier to let readers google.\u00a0 But, I might have suggested readers google in lieu of providing specific links rather than unconsciously assuming they would.\u00a0 I’ll do\u00a0that next time.<\/p>\n Albert in Edmonton<\/strong><\/p>\n Albert in Edmonton noted the lack of\u00a0comment in my blog\u00a0about the possibility of foundation failure causing the beams to buckle.\u00a0 He knew that as a civil engineer I had specialized in geotechnical and foundation engineering for a number of years.\u00a0 Why didn’t I mention the foundations?<\/p>\n Why\u00a0I didn’t mention the foundations<\/strong><\/p>\n Typical structural damage due to foundation failure<\/em><\/p>\n I didn’t mainly because I’ve seen a lot of structures damaged by foundation failure and what I saw in the pictures and video didn’t fit what I’ve learned over the years.<\/p>\n Most foundation failures – not all, mind you,\u00a0result in typical damage to the structure above.\u00a0 You come to know\u00a0the character\u00a0of this damage after seeing quite a lot of it.\u00a0 Also, after seeing the different structures, foundations and\u00a0sub-surface soils and rocks involved.<\/p>\n This damage is due to marked vertical movement of parts of the structure – inches,\u00a0and a little horizontal movement – fractions to maybe inches.\u00a0\u00a0It’s characterized by cracking\u00a0and distortion of the structure.\u00a0\u00a0The damage is\u00a0differential in nature – more here and less there, not uniform throughout the structure.<\/p>\n (For certain, there are exceptions to this typical failure and\u00a0distortion of a structure.\u00a0 I investigated a\u00a054 foot long structure one time that had\u00a0“settled” – moved vertically, 11\u00a0inches from one end to the other.\u00a0 Turned out it was mistakenly built this way)<\/p>\n Edmonton bridge damage<\/em><\/p>\n The middle sections of three of the Edmonton bridge beams\u00a0moved sideways\u00a0several feet, not inches<\/strong>.\u00a0 The end sections where the foundations are located did not move sideways hardly at all.\u00a0\u00a0And all of\u00a0this movement was\u00a0quite uniform, not differential.\u00a0 Quite unlike the typical damage\u00a0associated with\u00a0foundation failure.<\/p>\n Did the two end sections of each beam\u00a0move towards one another and cause the beams to buckle and to do this uniformly?\u00a0 If so, where did the force come from to push on the ends of the beams?\u00a0 There’s nothing showing in the pictures and video.<\/p>\n Did the foundations beneath\u00a0the two end sections move towards one another causing the beams to buckle, uniformly?\u00a0 I can’t see the foundations but I’ve never\u00a0known foundations to move sideways several inches causing the structure above to move sideways too.\u00a0 Landslides and retaining wall failures possibly excepted, but that’s not the situation here.\u00a0 And where did the forces come from to push on the sides of the foundations?\u00a0 To the extent you can see the soil near the level of the foundations in some of the pictures, there’s nothing there.<\/p>\n Intuition?\u00a0 Engineering experience?<\/strong><\/p>\n Sub-conscious thoughts like these\u00a0would have been running through my head as I looked at the pictures.\u00a0 They resulted in me not considering\u00a0the foundations as the cause of the problem.\u00a0\u00a0Intuition?\u00a0 Engineering experience?<\/p>\n But Albert in Edmonton made me think and next time I’ll\u00a0draw attention to the fact\u00a0that something in what I was seeing didn’t fit, didn’t look right.<\/p>\n Similarly, the structural engineer I chatted with about this bridge failure quickly dismissed wind forces on the sides of the beams as being anywhere near strong enough to cause the beams to buckle.\u00a0 That would be his intuition, his engineering experience kicking in.<\/p>\n Initial hypothesis of bridge failure validated to some extent by others\u00a0<\/strong><\/p>\n Barry Belcourt, manager of Edmonton’s road design and construction branch, was reported recently in the Globe and Mail as saying it was a construction procedure failure.\u00a0 This\u00a0would suggest\u00a0the failure is\u00a0not\u00a0due to\u00a0inadequate design.\u00a0 I don’t know what\u00a0Mr. Belcourt\u00a0is\u00a0basing that opinion on but he’s on the ground\u00a0in Edmonton\u00a0and all I’ve got are pictures and video.<\/p>\n Mr. Belcourt’s comments to some extent validate my initial hypothesis of the cause of the bridge failure.<\/p>\n Albert, who is also a civil engineer,\u00a0also considered “careless handling\u00a0during construction” as one of\u00a0several\u00a0possible causes<\/p>\n Reader’s questions are important<\/strong><\/p>\n Questioning is\u00a0how we revise hypothesis so keep them coming.<\/p>\n References<\/strong><\/p>\n \u00a0<\/span><\/strong><\/p>\n Readers in Edmonton and Halifax commented on\u00a0an item I posted last Friday about the Edmonton bridge failure – and my initial hypothesis as to the cause of the failure. (Ref. 1) I concluded the bridge failed because a crane supporting … Continue reading \n