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8/14/2019 BUILDING BESIDE A HIGHWAY
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BUILDING BESIDE A HIGHWAY
By Jonsig Eirik
The story I am about to tell you is true; it had serious
consequences, the cause was little understood by most, ridiculedby the know it all who wondered why he got wet if he stood inthe rain.
Shortly after WW2, Highway 401 was built through the FraserValley farming belt. A farmer close beside the highway decided tohave an implement shed built, using 8x8x16 concrete blocks,ideal for the building which was about 32 feet long with the endsabout 20 feet; the front facing the highway was open, to be a
series of sliding doors.A crew of several bricklayers had the blocks laid almost to aheight of 12 feet when suddenly the back wall collapsed killingone bricklayer. Nobody knew how such a tragic thing couldhappen. These bricklayers were qualified tradesmen; how couldsuch an unconscionable accident happen? The mortar wasproperly mixed. I doubt if anyone came up with the right answer. Inever heard.
Sound has tremendous energy: when I was playing around withradios, in the thirties when parts were cheap but I still had nomoney to buy any, I came across a very interesting article whereGeneral Electric built several large speakers into a wall, wiredthem all in phase, and then fed a low frequency sine wave tothese speakers. At a very low frequency they could knock out theopposite end of the building. A big piece of pie no matter how youcut it.
First visualize the setting; the 2 west lanes of 401 were not over a
hundred feet from the opening of the building. A semi would pullout and pass another of a similar make; normal traffic, exceptwhen one passed a situation might be created.
Lets say for example the trucks were the same make; if theywere both going 60 MPH the diesels theoretically would be
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running at the same speed where the sound of their exhaustwould be identical, say 50 hertz per second.
Then the truck following pulls out to pass; the frequency of hisexhaust will increase to, say 53-hertz/sec. Now we have a
phenomenon thats a fundamental component of any twofrequencies; the difference and the sum of the two. Using thehypothetical muffler sounds of 50 and 53, we would have 3 hertzand 103 hertz.
The 103 would do no harm to the building, but the 3-hertz couldstart that wall rocking, or it could create a standing wave where areflected sound meets one coming in which it can create enoughpressure to break the barely curing mortar bond and topple the
whole wall.This is my theory of why the building collapsed. The lowfrequency might have been anywhere in the very low range, wellbelow what the human ear could detect. My guess is that it wassomewhere between 1/4 and 5 CPS (hertz) considering the weightof the wall
Mortar can be easily disturbed until it sets, and if the weather iscold, and the blocks are laid quickly--then you have a recipe for
disaster. Increasing the cement a bit or cutting down on the limewill help speed up the set but only so much or it gets hard to workwith. I laid a lot of blocks but I was never fast. A hundred blocks aday was about all I could do; a couple of tons of 8x8x16 blocks? Iget tired thinking about it when now I can barely lift one blockwithout risking a hernia.
Jonsig Eirik.