[ExI] david statue coincidence

spike spike66 at att.net
Sun Aug 21 15:37:59 UTC 2016



From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of William Flynn Wallace
Sent: Sunday, August 21, 2016 7:58 AM
To: ExI chat list <extropy-chat at lists.extropy.org>
Subject: [ExI] david statue coincidence


In today's NYTimes:


"The world's most famous statue may someday topple, done in by hairline cracks in its ankles and tremors from a quake, traffic or millions of tourists' feet."


Can you hard science guys get moving faster on antigravity, please?





No need for mysterious physics BillW; I have an idea, rather two of them, neither requiring anti-gravity.  Allow me to offer a mechanical engineer’s perspective please rather than a physics-based solution.


We know that stone is very strong in compressive load; that stuff is great for making mountains.  This explains why nearly all mountains are made of it.  Stone is good in shear stress, which is why rock fractures look the way they do (review your mechanical engineering books, that chapter on Mohr’s Circle and measuring ratios of shear to compressive stress using Cauchy stress tensor.)  Marble (and stone in general) is not good at resisting bending moment, which is why stone arches are arches instead of one block going across horizontally: arches are in compression, straight across stone would be in bending stress.  


But rock is in general terrible at tensile stress, really lousy at that.  This is why it is never used for tension elements.  The old Greeks were smart guys, but all they had for building material was stone.  So… the old timers didn’t build any structures anywhere which require tension elements.


OK so the real problem here is that David’s ankles are in slight bending moment loading, and might fail. 


First idea: calculate the center of gravity of the sculpture, then slightly tilt the base so that both ankles are in compression loading only.  Or get it as close as we can.  It is over-constrained, so we can’t get both ankles in perfect compression-only loading, but it can be improved by slightly tilting the base.  The necessary tilt would scarcely be noticed, and tourists would never know Michel didn’t plan it that way to start with, perhaps at Mrs. Angelo’s suggestion.   


Second idea:  Consider what David was about to do in that sculpture.  Faced with this enormous adversary (Goliath) most of us would piss.  So, we add on a urine stream in the form of structural steel painted yellow to reinforce the statue and reduce bending moment at the ankles.



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