Structures or Why Things Dont Fall Down Review
Cypher has fallen on me since I read this book.
What an incredible volume! The all-time layman's introduction to a scientific topic that I've read since Feynman's QED. The author is besides hilariously British and doesn't waste an opportunity to rag on the French. Much of what I write below is copied verbatim from the text, but am also lazy to identify what with advisable quotes. These notes plant about the first 175 pages, I should get around to documenting what I learned in the back half at some point. basic definitions cracks free energy anchient warfare nature fracture energy pressure vessels joints & fastenings surface tension
- Streess = southward= load / area = MegaNewtons / meter^2
- Stress measures how hard atoms in a textile are being pulled apart or pushed together
- Strain = e = increase of length / original length
- Strain is how far atams are beingness pushed or pulled
- Force is the stress needed to intermission a material
- Young's modulous of elasticity ('E') = stress/strain
- Immature's modulus aka stiffness
- Hooke's law says that all solids change their shape - past stretching or contracting - when a mechanical force is applied to information technology, and information technology is this change of shape that allows an object to push back
- Force is not the same thing as stiffness (e.g. a beige is stiff merely weak, steel is strong ad stiff, nylon is flexible (not stiff / depression E) and potent, raspbery jelly is flexible (not stiff / depression E) and weak
- resiliance is the ability to store train free energy and deflect elastically under a load without breaking/causing permanent damage
- ductile materials are those that, when pulled in tension, have stress-strain curves that depart from Hooke'south law, after which the fabric deforms plastically (call up chewing gum
- Critical Griffith crack length is the point when a crack goes from existence rubber and stable to beingness self-propagating and very dangerous. = 2WE/(pi*due south^2) where W=work of fracture in J/m^2, E = Young's modulous in Newtons/m^2, s = boilerplate tensile strength in the material near the crack in Newtons/m^2.
- piece of work of fracture (aka toughness) is the quantity of energy requried to break a given cantankerous-section of a material
- emulsions are drops of one liquid floating within antoehr liquid
- elastomers are materials who can extend to great strain, sometimes 800% (east.grand., rubber)
- Poisson's ratio says that every material has a constant ratio of strain in one management when a stress is practical creating strain in a perpindicular management. q=e2/e1 where e1 = strain in the direction of s1 and
- material has stress "trajectories" running through it, which become concentrated (jammed up) at cracks or divots
- If a textile has a stress s on it and develops a crack/notch with length/depth L and radius of r, and so the stress at the tip is no longer s but instead is south(1+2sqrt(L/r)), which ways a circular hole will accept stress of 3s just a corner, which has a low r and a large L can be much higher. This is why ships often intermission in two starting at corners in doors
- Cracks are even worse, because the radius of a fissure is tiny making stress at the tip of the crack much college than the stress elsewhere
- Sometimes yous can concentrate stress by calculation textile, making a sudden local increment in stiffness (call back new patch in old garment or thick plate of armor on the thin side of a warship). Stress trajectories here are diverted justas muchby an area which strains as well niggling equally information technology is past an are which strains besides much, like a pigsty
- one Joule is roughly the free energy with which an apple would hit the flooring if it fell from a table
- A palintonton or ballista is much more effective than a trebuchet in doing piece of work. trebuchets could only store about 30K joules of potential energy, while ballistas were ~10X that
- bows are unsafe to release without an arrow because in that location is nowhere for that energy to go simply back into the bow
- spiders webs have 2 different kinds of threads. long radial ones that carry the load of the structure and are 3X more strong than the circumfrential threads, which do the work of catching bugs. These more resiliant threads are known as tension members
- Piece of work of fracture is not the aforementioned as tensile strength, which is the stress (not the energy) needed to break a solid
- most structural solids (drinking glass,pottery, cement,brick,rock) which we use in technology simply require 1 Joule per square metre to break all the chemical bonds on any plane or cross section. these are known as breakable solids.
- we practice not employ breakable solids in applications where they are in tension for this reason. They don't take depression tensile strengths (i.e. they demand a low forcefulness to pause them) but because they need only a depression energy to break them.
- tough materials can have the same strength every bit a brittle material, but they are able to deflect stress much deeper into their material, increasing dramatically the piece of work required to fracture the material. in other words, with tough materials, molecules living deep within the fabric blot some of the sstress
- The energy needed to abound a crack comes from the release of strain free energy in material that is separated past the crack. The release of strain energy tends to be over an surface area that is two triangles with one side the depth of the crack and the other side the exposed surface of the textile. The surface area of released strain is the square of the depth of the crack, which ways if a cleft is length L then the strain energy release grows as L^2. Therefore, equally a scissure length grows from 0, the kickoff of its life requires net consumption of free energy (more energy put into it than released), but later a while the cleft reaches a length where it net releases more than energy than information technology absorbs. This length is called "disquisitional Griffith scissure length".
- The local stress at a crack'due south tip can be very high - much college than the official tensile strength of the fabric. The structure will still be rubber and not break and so long as no crack or other opening is longer than the disquisitional Griffith length.
- The length of a safety crack depends upon the ratio of the value of the work of fracture to that of the strain energy stored in th cloth, or inversely proportional to its resilience.
- Rubber will store a lot of strain free energy simply its work of fracture is low then the disquisitional scissure length is very short, which explains why baloons pop the way they practice, in a breakable thing.
- One way to exist resilient and tough is to exist similar cloth or backet work and wooden ships and equus caballus-drawn vehicles. In these things the joints are more or less loose and flexibile and so free energy is absorbed in friction
- In a actually large structure like a ship or a span, we desire to be able to put up with a crack at least 1-two meters long with safe.
- the failure of a structure may be controlled, non past the strength, but past the brittleness of the material
- the toughness of well-nigh metals is reduced as the tensile strength increases. Y'all can cheaply double the strength of mild steel by increasing the carbon content, merely you would reduce the work of fracture past a cistron of ~fifteen. So if you double the working stress of a streucture this way, the critical fissure length will be reduced by a gene of 15x2^ii=60 (x2^2 is the ii triangles on each side fo the scissure). This means if the safe crack was originally one meter long, it will now measure 1.5cm
- But if yous have a small object (like a bolt) you are ok with crack lengths that are very small, so we can use high strength metals and high working stresses more safely in minor structures than in big ones. The larger the structure the lower the stress wch may have to be accepted in the interests of safety.
- the pressure inside a spherical vessel is rp/2t where r= the radius of the vessel, p = pressure, and 2 = the shell wall thickness
- for a cylinder, the stress along the shell (i.due east., longitudinally) is the same as that in a spherical vessel rp/2t
- teh circumferential stress in the shell of a cylinder is rp/t, meaning it is 2x the longitudinal stress, which explains why sausage skins dissever longitudinally when they are cooked because the skin can't handle the circumfrential stress
- this has upshot in sailing, where chinese junk sails are rigged so that equally wind pressure increasesthe radius of curvature diminishes and the tension force in the canvas remains roughly constant no affair how hard the winds may blow
- the only sort of elasticity which is stable nether fluid pressures at high strains follow an exponential stress~strain curve (our veins and arteries operat nether ~50% strain, and wouldn't piece of work if they were nether rubber-like straess-strain curves). This curve means y'all don't need much stress at first for any strain, but afterwards a while the gradient increases dramatically
- the heart works in that during the pumping (systolic) function of the cardiac cycle, much of the excess of high -pressure blood is accomodated past the elastic expansion of the aorta and of the larger arteries; this has the event of smoothing the fluctuations of our blood pressure level.
- the elasticity of the arteries therefore does the same task every bit the air-bottle thing which enegineers often attach to mechanical reciprocating pumps
- this is why, if artery walls stiff and harden with age, the blood-pressure is probable to rise
- a lapped joint creates stress concentrations at the 2 ends of the joint, which is why the force of such joints depends more often than not on their width and not the length of overlap between the ii parts. This makes uncomplicated rivets very effective
- for rods screwed into an anchorage, nearly all of the laod is taken out by the first 2 or 3 threads near the surface, making any extra length of rod within the socket ineffective
- this is true when two components of the joint accept simialr Young'south moduli or when the rod/tension bar is less still than the material of its socket/anchorage. Only if the rod or bar is substantially stiffer than the material into which one is trying to ballast it, the stress situation is often reversed and the concentration may exist mainly ata the bottom or inner end of the rod.
- riveted joints are heavier than welded joints, but they are as well easier to inspect, and often act equally crack-stoppers. Near importantly, riveted joints tin slip a piddling and so redistribute the load
- rivet holes unremarkably are punched then reamed. The reaming at the end makes the hole stronger and with fewer cracks that were made during the punch
- in theory a welded joint should be watertight, but seldom is. In do, rivets are cheaply caulked, but that can't be donee with a welded articulation, so instead a liquid sealing chemical compound is injected under pressure into the weld.
- tension in a liquid surface differs from Hookean tension in three aspects: i. the tension force does non depend on the strain/extension only is constant nonetheless far the surface is stretched, 2. unlike a solid, the usrface of a liquid tin can be extended without breaking, three. the tension force does non depend on the cross-sectional area merely simply upon the width of teh surface. The surface tension is just the same in a deep or "thick" liquid as it is in a shallow or "thin" ane.
- so if two droplets join up to make i droplet of twice the volume, there is a net reduction in the surface surface area of the liquid and therefore the surface free energy. And then there is an energy incentive for drops in an emulsion to coagulate and for the system to segregate into to continuous liquids.
- if you want the droplets to remain divide and not coalesce, and so you have to "stabilize the emulsion" then they repel each other. This can be done with electricity, which is why emulsions are afflicted past electrolytes similar acids and alkalis
Overall, I liked but did not love this book. The author'due south purpose is to innovate the basic principles of structural applied science in a way that leaves the reader with skilful intuitions well-nigh how structures piece of work, an appreciation for how the field has evolved (and, in turn, how we've evolved with it), and optimism for what the hereafter holds. On the basis of fulfilling its purpose, the author does a peachy job. The author breaks down difficult concepts into understandable chunks. He uses math judiciously to make principles more than relatable. By the end of the volume, you can walk around a structure site and have a much amend understanding of what'southward going on. More and then, you lot're going to have a humility for all that you don't know. One of my biggest takeaways, personally, was how little we empathise of why structures work and how much of our recent experience with airplanes and bridges has been only after structures failed catastrophically. I detested the author's tone. To the author'south credit, he wrote in what certainly seemed to be a sincere tone, then I suppose that I may just hate him. He writes in the style of a charming, elderly British professor. What makes that more grating than charming to me are:
- His obfuscation at times by relying on obscure celebrated or British references
- His prejudices, including rhetorical asides that repeatedly propose that lilliputian boys go engineers and fiddling girls become frivolous targets for fiddling boys to woo and that those who question whether British imperialism had downsides should exist summarily dismissed
With no real relevant educational or vocational background, I came to this volume for the championship and inspired chapter headings ("Strain energy and mod fracture mechanics--with a digression on bows, catapults, and kangaroos") and stayed for the captivating asides: "All over the world bridge-building used to be associated with children's dances...and with human sacrifices which are non just legends. At least one child'south skeleton has been discovered immured in the foundations of a span." Along the mode, Gordon's casual and attainable manner of discussing how structures work--which happens to employ to pretty much everything, including the human body and its tiniest parts, east.k. blood vessels (an observation that, to me at least, wasn't already so obvious)--made for unexpectedly compelling and effective reading on a variety of topics that may sound somewhat specialized to those of us without engineering backgrounds. (I never thought I'd think so much about torsional stiffness, for example, or detect my life marginally improved past knowing more most it.) Merely Gordon'southward prose has a style of making y'all step away from the book and into your environment with fresh eyes, newly enlightened that things may or may not autumn downwardly all considering of a few fundamental facts about tension and compression, stress and strain. Information technology's a preoccupying worldview; I tin encounter why people end up structural engineers. Recommended to anyone who is a structure or interacts with structures (one doesn't necessarily have to live a structured life), and is above say grade six--there is some math here and there. Mileage may vary for those prone to anxiety; equally it turns out, yes, your house *might* collapse without warning, merely at least you'll know, should you be out when it happens, that information technology was nearly certainly because the cranium floor gave out and not that the roof caved in.
Consistently illuminating - I read this book with the intention of seeing how learning about physical/engineering structures would translate/resonate for Organisational Development. And information technology does. Gordon doesn't come across a 'clear distinction between material and structure', for example - which I think is a really interesting insight. It's fun, there's lots of interestingly powerful new words to acquire, and, although it'south very engineer-ish, I managed to grok well-nigh of it.
!!! J.E. Gordon makes everything sooo interesting
Shelved as 'could-not-conduct-to-finish'
March 18, 2017This book was so interesting, actually really interesting, but... always is a "but" in the unfinished books shelf isn't?, well the starting time was amazing and it maintained the pace -at least to 36% when i drop it- but the thing that bug me was the parallelism that the autor made of how the structures work with the human being anatomy. I take instruction in basic mechanics -I am an engineer- and i love all that stuff of stress and strain in structures and objects, merely when you lot beginning saying that a lot of strain on veins tissue can provoke an Aneurism... well, or excess of vibrations can provoke that your veins get zig zag on your torso, and you say that tendons tin be cut with a trivial knife but can sustain greats weight loads, all of this makes you start thinking most thinks that you lot should not think about. Of grade all of this things are true, at least the behavior of this structures knowing their composition is predictable to some caste, the book is honest, but mixing what i know of engineering with tissues and the middle, and the tendons, and the arteries, well i don't desire to lose my mind, no give thanks you.
Хорошая разминка для мозгов. Инженерия это все-таки отчасти наука, отчасти искусство. Поэтому книга получилась с поэзией. Читал из списка Илона Маска, поэтому настроен был с большим интересом, чем если бы сам нашел. Это помогло дочитать книгу, хоть и после нескольких месяцев медленного прогресса. По результату - обещание книги выполняется, намного лучше понимаю как обеспечивается прочность конструкций. Здания, мосты, корабли, самолеты - нашлось место всему
Very interesting volume, I learned a lot. Gordon'south prose is readable. He is also opinionated and throws in only the right number of anecdotes. I read this book while also watching the "Keen Courses" class, "Understanding the World's Greatest Structures," by Stephen Ressler, and recall those lectures covered a lot of the same fabric but with more than compelling examples, buildings and bridges.
Structures is, in terms of classes at the University of Florida, Mechanics of Materials and its lab, besides as Mechanical Design one and two. Annihilation that is covered in these classes is covered hither with a fleck less math. Yet, while the textbooks for these classes may exist dry out and direct, Gordon is willing to make jokes, get on tangents, and explore his opinions. This makes an engineering book- beyond all expectations- a folio turner. More than one of my professors at UF used to exist a consultant. When things blew upward or went wrong, information technology was there job to get to courtroom and indicate fingers afterward having studied the shit out of any blew up. And these stories were always the best stories. Tension? Compression? Fatigue failure? The best examples are not-examples. "Look on this wreckage, ye mighty, and despair-- delight don't practice this or our college gets a bad rap." Structures has tons of these examples, and as the book goes from the basic principles of factors of safety and critical crack lengths up to arches, nosotros get more and more of them. The last few capacity are calls to action: Failures in structures are almost e'er due to lazy designers or lazy manufacturing and these are critical moral failures of Biblical proportions. Parallel to this is failures in aesthetics: an engineer is by and large likely designing something that many people will use. Therefore, it is absolutely critical that what they're designing /is dainty/. The Spartan ethic of functionalism is as well narrow and shut-minded. Structures is a practiced book for the young engineer or the layman. It gives a -forgive me- structure to one'south thoughts nearly structures. Because it deals with non but buildings, but vehicles, tools, and living things --similar usa-- it is important for the construction worker, the mechanic and the doctor.
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Source: https://www.goodreads.com/book/show/245344.Structures
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