Have you ever wondered why some things bend under pressure while others break? How do some buildings remain standing for centuries? <\/p>\n\n\n\n
In Structures<\/em>, scientist and engineer James Edward Gordon reveals why some materials and structures can withstand forces like gravity and wind while maintaining their form and stability, while others collapse under pressure.<\/p>\n\n\n\n Read more in our Structures<\/em> book overview.<\/p>\n\n\n\n\n\n\n\n What is structural integrity? According to scientist and engineer James Edward Gordon, it\u2019s how much force a structure can withstand without losing its form or collapsing<\/strong>. He explains that all structures<\/em>, both natural and man-made, are subjected to external forces that they must withstand to maintain their form and stability. For example, trees must counter forces such as wind and heavy rain, while buildings must withstand the weight of furniture and people. In his book Structures<\/em><\/a>, Gordon examines the factors that make some objects sturdy while others are vulnerable to failure. (Shortform note: Structures<\/em> was originally published in 1978. This overview is based on the 2003 updated edition.)<\/p>\n\n\n\n Gordon was a pioneering materials scientist who bridged the gap between theoretical physics and practical engineering. He served as head of plastic structures research at the Royal Aircraft Establishment and professor of materials technology at the University of Reading. In addition to Structures, <\/em>he authored several other books on engineering, including The Science of Structures<\/em> and Materials<\/em><\/a> <\/em>and <\/em>The New Science of Strong Materials<\/em><\/a>. His research was key to British military aircraft development during World War II and continues to influence generations of scientists and engineers.\u00a0<\/p>\n\n\n\n According to Gordon, a structure is only as stable as the materials it\u2019s made of. Therefore, to understand how a structure<\/em> can withstand external forces, you first need to grasp how its individual materials<\/em> respond to forces. Gordon suggests that three key properties determine how a material responds to external force: elasticity, energy storage, and strength. Let\u2019s explore each of these in detail.<\/p>\n\n\n\n A material\u2019s elasticity is its ability to return to its original shape after being misshapen by an external force. <\/strong>Gordon explains that every material has a given internal molecular structure\u2014the bonds between its molecules are organized in a specific way. When a force acts on a material, its internal molecular structure shifts as the bonds between molecules stretch. This may or may not impact the material\u2019s visible shape, depending on the material itself and the amount of force applied. In any case, elasticity is the material\u2019s ability to recover its original molecular structure after being subjected to force. (To picture elasticity on a larger scale, think of how a spring compresses when you squeeze it and expands when you release it.)<\/p>\n\n\n\n According to Gordon, some materials are naturally more elastic than others<\/strong> because their molecular bonds can withstand more force\u2014which means they can stretch further without breaking. If the force applied to the material isn\u2019t too strong, the change to the material\u2019s shape is just temporary. When you remove the force, the molecules return to their normal positions, and the material regains its original structure. But if the force is too strong for the material to withstand, the change becomes permanent. The force stretches the molecular bonds beyond their ability to recover, preventing them from returning to their original positions.<\/p>\n\n\n\n For example, think of stretching a rubber band. If you stretch it a little before letting go, the band deforms temporarily before bouncing back. However, stretching it too far permanently deforms the rubber band\u2014it becomes saggy or snaps. <\/p>\n\n\n\n As we just discussed, applying force to a material causes its molecular bonds to stretch. Gordon explains that this stretching process allows the material to absorb and store the force\u2019s energy<\/strong>\u2014in other words, once the force hits the material, the material stores its energy within its internal structure. The more force applied to the material, the more energy the material has to store\u2014and the further its molecular bonds have to stretch to accommodate the amount of energy. Put simply, the greater the force, the more energy it creates for molecular bonds to absorb. And the only way molecular bonds can store this energy is to keep stretching until they absorb it all.<\/p>\n\n\n\n But, as we explained before, molecular bonds can only stretch so far as their material\u2019s internal structure allows. It follows that a material\u2019s elasticity (how far bonds can stretch) determines its capacity for energy storage<\/em>\u2014how much energy its molecular bonds can safely store while maintaining their ability to return to their original positions.<\/p>\n\n\n\n Gordon explains that when the stored energy exceeds a material\u2019s storage capacity, the material must release that energy\u2014and this makes the material deform or break. <\/strong>This is because stored energy increases pressure within the material\u2019s internal structure (think of a balloon inflating). Eventually, the material must release that energy to relieve the building internal pressure (think of an over-blown balloon about to pop). This release manifests either through permanent deformation (where bonds stretch too far to recover) or through breakage (where bonds snap completely).<\/p>\n\n\n\n Gordon describes the energy release process: Excess energy concentrates at certain points within the material<\/strong>, creating areas of high internal pressure. Due to this high pressure, the molecular bonds in these areas stretch beyond their capacity and break, forming tiny cracks in the material\u2019s structure. These cracks then serve as paths of least resistance through which the stored energy escapes.<\/p>\n\n\n\n As the energy escapes through these paths, it breaks more molecular bonds<\/strong>, causing them to violently release their stored energy and weaken or break neighboring bonds. The more energy stored within the material before this process begins, the faster and more catastrophic the breakage becomes. Gordon says this chain reaction explains why materials often break suddenly rather than gradually\u2014once released, the stored energy provides the force needed to rapidly spread damage through the material.<\/p>\n\n\n\n For example, consider a glass window that\u2019s struck by a small stone. Initially, the glass absorbs and stores the energy from the impact. However, this energy quickly concentrates at the point of impact, creating a high-pressure area that exceeds the glass\u2019s energy storage threshold. This causes a crack to form, providing a path for the stored energy to escape. The sudden release of this energy causes the crack to spread rapidly across the entire window, resulting in a shattered pane rather than just a small chip at the point of impact.<\/p>\n\n\n\n A material\u2019s strength determines how much force it can withstand before its molecular structure permanently deforms or breaks.<\/strong> As we discussed, applying force to a material changes its internal structure (depending on its elasticity<\/em>) and creates internal pressure (depending on its capacity for energy storage<\/em>). The combination of these two effects can cause the material to deform both internally and externally. Gordon writes that the extent of this deformation depends on the material\u2019s strength<\/em>.<\/p>\n\n\n\n In simple terms, materials that can respond to force while maintaining their original molecular structure have more strength<\/strong> than those that can\u2019t maintain their structure. <\/p>\n\n\n\n However, Gordon clarifies that materials unable to maintain their original structure don\u2019t always collapse. Rather, the way materials respond to excess force depends on their elasticity and capacity for energy storage. This response can play out in multiple ways: <\/p>\n\n\n\n We\u2019ve just explained the properties that determine how individual materials respond to force: elasticity, energy storage, and strength. Since structures tend to be composed of different materials, each with its own molecular composition, we\u2019ll now explore how the combination of different materials impacts a structure\u2019s ability to withstand force and maintain structural integrity. <\/p>\n\n\n\n Structures composed of multiple materials respond <\/strong>collectively<\/em><\/strong> to force.<\/strong> Gordon explains that applying force to a structure doesn\u2019t just affect each constituent material in isolation. Rather, the energy of the force moves through all the materials that make up the structure, triggering complex interactions between them. How a structure responds to this moving energy depends on two key factors:<\/p>\n\n\n\n Let\u2019s examine how each of these factors impacts a structure\u2019s response to force.<\/p>\n\n\n\n As we\u2019ve established, applying force to a material causes the material\u2019s molecular bonds to stretch and absorb the energy carried by a force. Gordon explains that in a structure made of multiple materials, the differences between each material\u2019s capacity for energy storage determine how energy flows through that structure.<\/strong> Energy doesn\u2019t flow through a multi-material structure evenly from one material to the next. Rather, it interacts with one material at a time and only moves to another when the current material reaches its capacity for energy storage. <\/p>\n\n\n\n However, Gordon states that energy doesn\u2019t move to a neighboring material at random. Instead, it takes the quickest path through the structure.<\/strong> To clarify, let\u2019s examine how different energy storage capacities impact the speed at which energy flows:<\/p>\n\n\n\n Of course, a force can\u2019t \u201cchoose\u201d what material it interacts with first. Think of a boulder rolling into a house\u2014whatever material it happens to land on is the first material it interacts with. However, Gordon explains that after the initial impact, the force\u2019s energy<\/strong> always moves to materials with the lowest capacity for energy storage<\/strong> because these materials channel energy through structures more efficiently. In simple terms, materials that can\u2019t absorb a lot of energy help it flow faster through a structure than materials that can absorb more. <\/p>\n\n\n\n To visualize this, imagine setting a sponge and a sheet of smooth plastic next to each other and pouring water over both. In this scenario, the sponge is a high-capacity material because it can absorb water, and the plastic is a low-capacity material because it can\u2019t. When you pour water (which represents a force) onto these materials, the water will race across the surface of the plastic, flowing outward and away. Some goes into the sponge, where it quickly slows and gets absorbed. The sponge soaks up the water, holding it in place, while the plastic does nothing to stop or contain the flow.<\/p>\n\n\n\n By opting for the most efficient path, energy flows unevenly through the structure, concentrating more on materials with a low capacity for energy storage. Gordon says this concentration of energy creates areas of high internal pressure within those materials. While energy initially veers toward these materials because they\u2019re efficient channels, this high concentration of pressure can quickly exceed their capacity for energy storage, causing them to deform or break. This uneven energy flow creates weak points in the structure, undermining its integrity.<\/strong><\/p>\n\n\n\n Additionally, Gordon explains that structural weak points tend to occur where two materials join.<\/strong> This is due to two reasons: <\/p>\n\n\n\nOverview of Structures<\/em> by J.E. Gordon<\/strong><\/h2>\n\n\n\n
Principle 1: Material Properties<\/strong><\/h3>\n\n\n\n
Material Property #1: Elasticity<\/strong><\/h4>\n\n\n\n
Material Property #2: Energy Storage<\/strong><\/h4>\n\n\n\n
How Materials Release Excess Energy<\/h5>\n\n\n\n
Material Property #3: Strength<\/strong><\/h4>\n\n\n\n
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Principle 2: Force Distribution<\/strong><\/h3>\n\n\n\n
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Factor #1: Each Material\u2019s Capacity for Energy Storage<\/strong><\/h4>\n\n\n\n
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Uneven Energy Flow Creates Weak Points<\/h5>\n\n\n\n