I recently mentioned how you can think – hypothesize, about the cause of a failure or accident based on very little evidence, then\u00a0modify your thoughts as\u00a0more comes in.\u00a0(Ref. 1)\u00a0\u00a0This is\u00a0the\u00a0nature and technique of forensic engineering investigation.\u00a0 Some of the evidence can be as brief as a chance remark years ago, as happened to me.\u00a0 Following is another example of this process.<\/p>\n
(Counsel benefits from a process like\u00a0this<\/strong> – ideally when the merits of the case are assessed.\u00a0 But also when you think you have enough technical evidence to go forward and want to\u00a0cut costs\u00a0by stopping the forensic investigation)<\/em><\/em><\/p>\n ***<\/p>\n There are a lot of multistory buildings in the Halifax area.\u00a0 I learned that at least one is defective because\u00a0the floors are sagging – the floors are “wavey” to use one person’s description.\u00a0 A defect is a failure in engineering.<\/p>\n The floor in one of the rooms\u00a0on the 10th floor slopes down 1.5% to 2.5% from the\u00a0end to the middle.\u00a0 It sags in the middle.\u00a0 The room is 22 feet long by 12 feet wide. \u00a0That means the floor\u00a0sags 2 to 3 inches.\u00a0 That’s a lot for a commercial building.\u00a0\u00a0It’s far more than a construction tolerance of 1\/4 inch.\u00a0 You can see the slope in the length of the conference tables.\u00a0\u00a0I\u00a0measured the floor\u00a0with a tape and a digital level.<\/p>\n In another large, square\u00a0room chairs with casters roll to\u00a0the left side of the\u00a0room when you’re sitting in one.\u00a0 That happened to me.\u00a0 The floor slopes down to the left\u00a0in this room compared to the middle in the other room.\u00a0 At least on\u00a0the left\u00a0half of the room where I was sitting.\u00a0\u00a0Quick measurements in three places in the room and also in the reception area indicated slopes of 0.1% to less than 1.0%.\u00a0 Staff in the office on this floor report that the floors slope in all the rooms.<\/p>\n I saw that the floors were not level on the 12th floor of the\u00a0building.\u00a0 Office staff were\u00a0not conscious of this but\u00a0they did say that\u00a0previous tenants reported that the floors were\u00a0not level. \u00a0I also saw the floor\u00a0sloping down from a concrete column in an office on the 4th floor.<\/p>\n A staff\u00a0member familiar with four floors in the\u00a0lower part\u00a0of the building reported that the floors were “Wavey.\u00a0 Not very, very, very level.\u00a0 We have to level when we do renovations”.<\/p>\n Building construction<\/strong><\/p>\n The building is made of concrete – concrete foundations, columns and floors.<\/p>\n The foundations are supported on bedrock which is very strong.\u00a0 I learned this from a friend who saw the foundations being constructed when his company worked on the\u00a0building site.\u00a0 He also said multistory buildings like this are erected quickly<\/em> so they can be rented as soon as possible and make money.<\/p>\n Construction technique<\/strong><\/p>\n The construction technique\u00a0used to erect multistory concrete buildings\u00a0is sensitive to construction schedule.<\/p>\n A\u00a0concrete floor in a multistory building is constructed by placing\u00a0concrete in forms that are supported on jack posts.\u00a0 The jack posts\u00a0are in turn supported on a\u00a0previously constructed concrete floor below.\u00a0 The floor below will also be supported on jack posts below it.\u00a0 Jack posts are steel posts whose length can be adjusted – jacked up<\/p>\n You can see this construction technique\u00a0in different places in Atlantic Canada – a\u00a0number of jack posts at\u00a0each floor level – usually three or four levels, below the floor under construction.\u00a0 There are at least two\u00a0buildings under construction now in Halifax using this technique, one\u00a0on Jos. Howe Drive\u00a0and the other on Young Street.<\/p>\n The technique involves removing the jack posts from the lowest floor and leap-frogging\u00a0over the upper floors\u00a0to support the\u00a0forms for the next floor under construction above.<\/p>\n Construction schedule<\/strong><\/p>\n I knew the construction manager who directed the work crews erecting the defective building years ago.\u00a0 He told me one time – the chance remark, that he was on a<\/em> very tight<\/em> schedule<\/em> to\u00a0construct the building<\/em> – had to\u00a0get\u00a0it up in a hurry.\u00a0\u00a0Just like\u00a0my friend said for multistory buildings, in general, but this one sounds like it was rushed even more.<\/p>\n Concrete strength<\/strong><\/p>\n The jack posts are removed from the lowest level when the strength of the\u00a0concrete forming the floor being supported just above is\u00a0high enough.\u00a0 The strength of concrete floors is specified by the design engineer according to the planned construction and use of the building.\u00a0 Concrete\u00a0sets up – gains in strength,\u00a0over a number of days\u00a0from the wet concrete\u00a0when\u00a0placed in forms\u00a0to the\u00a0rock-hard\u00a0concrete later.\u00a0 The quality of the concrete delivered to a building construction site is checked by testing companies to ensure it will set up to the design strength.<\/p>\n Analysis of the\u00a0cause of the “wavey” floors<\/strong><\/p>\n Building components<\/em><\/span><\/p>\n The defective, multistory building had\u00a0five components when\u00a0it was\u00a0under construction:<\/p>\n Limited information<\/em><\/span><\/p>\n The\u00a0limited information\u00a0for a hypothesis in this case is:<\/p>\n Possible causes<\/strong><\/p>\n Analysis of the limited\u00a0information<\/em> suggests the following possible causes\u00a0<\/em>associated with\u00a0one\u00a0or the other of the building\u00a0components<\/em>.\u00a0 The causes are listed\u00a0beginning\u00a0at the top surface of the new floor:<\/p>\n Cause #1.<\/strong> The floor forms\u00a0were constructed level but the concrete\u00a0was not placed and troweled level\u00a0by the concrete finishers<\/p>\n I believe the concrete was placed and troweled level – or to the level of the forms, an important qualifier.\u00a0 I’ve seen concrete finishers at work often enough.\u00a0 They are proud of their craft.\u00a0 And besides, the concrete form they must place and trowel the concrete to is right there in front of their eyes\u00a0a few\u00a0feet away.\u00a0 It would be difficult to make a mistake.<\/p>\n Cause #2.<\/strong> The floor forms were not level because mistakes were made in measuring the\u00a0position of the new floor\u00a0on the concrete columns.\u00a0 These marks are the starting point\u00a0for leveling the forms<\/p>\n Similarly, it would be difficult to make a mistake measuring the position of the new floor on the concrete columns.\u00a0 This is a simple measurement with a tape.\u00a0\u00a0I can imagine it being\u00a0checked and rechecked.\u00a0 “Measure twice, cut once” like a carpenter does.<\/p>\n Cause #3.<\/strong> The floor forms\u00a0were not level, either because of the leveling method or because the posts\u00a0were not jacked up properly<\/p>\n The jack posts would be\u00a0placed according to the level of the forms and adjusted up or down a little as required by the form leveling technique.<\/p>\n Based on what I’ve seen<\/span> on construction sites, I can easily imagine a carpenter’s level with a spirit bubble being used to check the level of the forms and the need to adjust the jack posts.\u00a0 Cheap and quick on a job that’s in a\u00a0hurry, also inaccurate.\u00a0 Inaccurate in different directions too depending on where you put the carpenter’s level.\u00a0This would result in different slopes\u00a0to the floor forms – and different slopes and sags to the finished concrete floor like\u00a0I saw in the defective building.<\/p>\n What I’ve seen<\/span>\u00a0<\/strong><\/em>–\u00a0the\u00a0plumb of concrete columns being\u00a0set with a carpenter’s level –\u00a0floor after floor after floor on one 20\u00a0story building.\u00a0 Very crude.\u00a0 It’s not too great a leap of faith to believe that the floor forms were set “level” in the same way in the 20 story building.<\/p>\n Cause #4.<\/strong> The forms sagged when the heavy concrete was poured because the distance between the jack posts was too great<\/p>\n This might be possible but unlikely because jack posts would be placed at the construction joints between concrete floor forms.\u00a0 The forms themselves would be more than rigid enough to support a layer of concrete a few inches thick.\u00a0 The forms are likely to be reusable – certainly from floor to floor, but also from job to job.<\/p>\n Cause #5.<\/strong> The floors sagged because the jack posts were removed before the concrete set up and was strong enough<\/p>\n This is possible.\u00a0 I can’t dismiss it.\u00a0 Particularly if low strength concrete was accepted at the construction site and there were only three floors of jack posts in place.\u00a0 However, I\u00a0might expect sloping and sagging to be more broadly distributed across the new floor rather than quite variable like in the defective building.<\/p>\n The floor in the long, narrow room on the 10th floor that tweaked my interest sagged 2 to 3 inches over about 10 feet.\u00a0 And the slope was in a different direction in the square room about 25 feet away from the narrow room.<\/p>\n I also can’t imagine low\u00a0quality concrete being accepted at a construction site – truck load after truck load and floor after floor.<\/p>\n But this cause is possible because I just don’t have enough information on how deflection three or four floors down would affect a new floor way up above.<\/p>\n Cause #6.<\/strong> The floors sagged because an inadequate number of the lower floors were supported with jack posts beneath the upper floor that was under construction<\/p>\n This cause might be possible if\u00a0jack posts were placed at only two levels rather than the three or four that\u00a0seem to be\u00a0normal.\u00a0 I see four in the two buildings I drove\u00a0by recently.\u00a0 It seems like a risky decision for a construction manager on a very tight schedule and in a real hurry to get the building up even if he’s prepared to accept low strength concrete.\u00a0 I also don’t know as mentioned above on how deflection\u00a0two or three floors down would affect a new floor.<\/p>\n ***<\/p>\n What do I think is the likely cause of the “wavey”, sagging floors based on the limited evidence?<\/strong><\/p>\n I think – my initial hypothesis,\u00a0<\/strong>that the floors slope and sag – because the forms were not leveled properly –\u00a0Cause #3\u00a0<\/strong>–\u00a0in the rush to get the building up.<\/p>\n ***<\/p>\n The following is what we do in forensic engineering when we think about the cause of a failure or personal injury for Counsel and the justice system:<\/p>\n More evidence in the case of the defective, multistory building would be a precise elevation survey and contouring of many or all of the floors in the building. \u00a0Basically quantify the nature and extent of the problem, the defect whose cause you must determine. \u00a0But this is not likely to happen\u00a0because the building although defective\u00a0is functioning quite okay.\u00a0 I’m sure there are others like it in Atlantic Canada.<\/p>\n References<\/strong><\/p>\n I recently mentioned how you can think – hypothesize, about the cause of a failure or accident based on very little evidence, then\u00a0modify your thoughts as\u00a0more comes in.\u00a0(Ref. 1)\u00a0\u00a0This is\u00a0the\u00a0nature and technique of forensic engineering investigation.\u00a0 Some of the evidence … Continue reading \n
\n
\n
\n