{"id":1402,"date":"2013-04-25T16:02:52","date_gmt":"2013-04-25T16:02:52","guid":{"rendered":"http:\/\/www.ericjorden.com\/blog\/?p=1402"},"modified":"2013-04-25T16:02:52","modified_gmt":"2013-04-25T16:02:52","slug":"investigating-a-vibrating-building","status":"publish","type":"post","link":"http:\/\/www.ericjorden.com\/blog\/2013\/04\/25\/investigating-a-vibrating-building\/","title":{"rendered":"Investigating a vibrating building"},"content":{"rendered":"<p>(<span style=\"color: #3366ff;\"><strong>This is not an East Coast ghost story<\/strong><\/span>)<\/p>\n<p>(The following is one in a series of cases I have investigated that illustrate the different <strong>forensic engineering methods I use to investigate<\/strong> <strong>the cause of failures<\/strong> <strong>and accidents<\/strong> <strong>that result in civil litigation.\u00a0 <\/strong>Knowledge of simple frost\u00a0heave was important in this case)<\/p>\n<p>The investigation of the\u00a0vibrating building\u00a0is reported under the following main headings with several sub-headings:<\/p>\n<ul>\n<li>The case (A description of: 1. The building and the problem experienced by the owner;\u00a02. The building&#8217;s\u00a0foundations,\u00a0and the problems with the building, 3. The legal\/technical issues, and, 4. My client)<\/li>\n<li>Forensic engineering investigation of the\u00a0problem and the methods used<\/li>\n<li>Findings of the investigation (conclusions with respect to the technical issues)<\/li>\n<li>Resolution<\/li>\n<li>Lessons learned<\/li>\n<\/ul>\n<h1><strong>The case<\/strong><\/h1>\n<p><strong>Description of\u00a0the building and\u00a0the problem\u00a0<\/strong><\/p>\n<p>The building was a large, well appointed\u00a0mobile home in the Halifax area that vibrated quite noticeably during the winter months.\u00a0 The vibration occurred when\u00a0the owner\u00a0and his family\u00a0walked the length of their home from one room to another.<\/p>\n<p>The owner also wanted to know why the interior partitions at some\u00a0locations were separating from the ceiling.<\/p>\n<p><strong>Legal\/Technical Issues<\/strong><\/p>\n<p>The main issues were the cause of the vibration and the cause of the gaps at the tops of the partitions.<\/p>\n<p><strong>Client<\/strong><\/p>\n<p>I was retained to investigate the problem by the company\u00a0who placed the mobile home on the site.<\/p>\n<p><strong>Forensic engineering investigation<\/strong><\/p>\n<p>My forensic engineering investigation involved the following methods:<\/p>\n<ol>\n<li>Take a briefing on the problem from the owner.<\/li>\n<li>Visually examine the building and the site it was on.<\/li>\n<li>Examine and determine how the building was supported and the foundations constructed.<\/li>\n<li>Sample and determine the type of foundation soils underlying the building site and their physical properties.<\/li>\n<li>Analyse the data collected during these examinations.<\/li>\n<\/ol>\n<h1>Investigations and Findings<\/h1>\n<p><strong>Briefing<\/strong>\u00a0 The owner was quite clear in describing how the building vibrated in winter in walking from one end of his home to the other.\u00a0 He also described the gaps at the top of the partitions.\u00a0 The building did not vibrate during the summer.<\/p>\n<p>I wasn&#8217;t on site during the winter but saw and measured gaps of about 1\/4 to 1\/2 inches during my visit.<\/p>\n<p><strong>Visual examination:\u00a0 <\/strong>The home was on a sloping site\u00a0with the length of the building\u00a0aligned up the slope.<\/p>\n<p><strong>Examine foundations:<\/strong>\u00a0 I crawled under the building and established that\u00a0the mobile home was supported on two continuous steel beams running the length of the mobile\u00a0home.\u00a0 The beams were\u00a0in turn supported\u00a0by concrete\u00a0block piers at regular intervals.\u00a0 The piers were supported on the sloping ground\u00a0a few inches\u00a0below\u00a0the surface.<\/p>\n<p>Because of the sloping ground,\u00a0the height of the piers and the home above the ground gradually increased from 1.5 feet at\u00a0the upslope\u00a0end to 3.5 feet at the downslope end.<\/p>\n<p><strong>Test foundation soils:\u00a0 <\/strong>I took samples of the soils supporting the\u00a0piers and had the samples\u00a0tested in a laboratory.\u00a0 I also researched the soil geology of the area &#8211; the surficial geology.<\/p>\n<p>The tests and research established that the foundation soils comprised a dense, silty glacial till typical of the many drumlins in the area.<\/p>\n<p>Drumlins are teardrop shaped glacial soil deposits.\u00a0 The Citadel in Halifax is on a drumlin.<\/p>\n<p><strong>Analyse data:\u00a0<\/strong>The fact that the\u00a0mobile home vibrated in winter but not in summer was interesting, and took some reflection on my part.<\/p>\n<p>The shallow\u00a0depth of the pier foundations\u00a0supporting the\u00a0mobile home &#8211; a few inches, was not typical\u00a0for foundations in this area.<\/p>\n<p>We\u00a0dig our\u00a0foundations down typically about 3.5 to 4.0 feet in the Halifax area to get below the depth of frost penetration and the effects of frost heave.<\/p>\n<p>A\u00a0characteristic of the fine grained soils found beneath the piers is that they are very frost susceptible &#8211; water collects in the soils easily and freezes in winter.\u00a0 The mixture of water and soil expands on freezing &#8211; frost heave to everyone.\u00a0 The more soil freezes &#8211; the greater the depth of freezing, the greater the frost heave.<\/p>\n<p>The pier foundations would have heaved in winter for certain considering they were only a few inches below the ground surface, not 3.5 to 4.0\u00a0 feet..<\/p>\n<p>The depth to which the soil freezes depends on the severity of the winter.\u00a0 Deeper in cold winters, shallower in warmer\u00a0winters.<\/p>\n<p>A source of heat\u00a0from an external source other than\u00a0the weather can also affect the depth of frost penetration in the ground and the amount of frost heave.<\/p>\n<p>Regardless of how well we typically insulate our homes,\u00a0heat is lost in winter to the surrounding air.\u00a0 The air is warmed in the process and in turn warms other surfaces in contact where it is protected from the wind.<\/p>\n<p>That was the case at the upslope end of the mobile home where the building was closer to the ground &#8211; 1.5 feet.\u00a0 The depth of frost penetration and heave could be expected to be less at this end\u00a0of the building than at the\u00a0downslope end where the home was 3.5 feet above the ground.\u00a0 It was also\u00a0exposed to the wind at this downslope location.<\/p>\n<p>Frost was penetrating the ground to an increasing depth from the\u00a01.5 foot end of the mobile home to the 3.5 foot end.<\/p>\n<p>All the piers along the length of the home would heave due to frost action but not necessarily a proportionate amount.\u00a0 This is because conditions at each pier\u00a0could be expected to vary a little: Foundation soil conditions could vary, also heat loss from the\u00a0mobile home, protection from the wind, etc.<\/p>\n<p>The steel beams could be expected to be lifted off the piers completely at some locations &#8211; and &#8220;suspended&#8221; between adjacent piers, because of the disproportionate amount of heave at the adjacent piers.<\/p>\n<p>Steel beams deflect between piers.\u00a0 The greater the suspended distance between\u00a0piers\u00a0providing support to a mobile home the greater deflection.\u00a0 Walking along a floor supported on such beams causes the floor and the beam to deflect\u00a0and vibrate.\u00a0 I\u00a0think a good many of us have walked along wooden planks supported at each end and\u00a0felt the deflection and\u00a0vibration.<\/p>\n<h1><strong>Conclusion<\/strong><\/h1>\n<p>I concluded that the mobile home was\u00a0vibrating as much as it was because it was not properly supported\u00a0by the piers in the winter\u00a0time.\u00a0 Because of the magnitude of the\u00a0vibration, I\u00a0believed that the mobile home was only supported by the piers at the ends of\u00a0the two beams.<\/p>\n<p>The gaps formed at the top of the partitions because the joints between the tops of partitions and\u00a0the ceiling are relatively weak\u00a0and would separate when the supporting beams deflected.\u00a0 I suspect\u00a0that small gaps would have formed at the bottom of the partitions as well but\u00a0went unnoticed.<\/p>\n<h1><strong>Resolution<\/strong><\/h1>\n<p>I recommended digging and founding the piers deeper and below the depth of frost penetration and heave.<\/p>\n<h1>Lessons learned<\/h1>\n<ol>\n<li>Always look at the weather conditions along different parts\u00a0of a foundation when unusual problems are\u00a0occurring in the structure above.<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>(This is not an East Coast ghost story) (The following is one in a series of cases I have investigated that illustrate the different forensic engineering methods I use to investigate the cause of failures and accidents that result in &hellip; 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