Unit D Structures & Forces Presentation PDF

UNIT D STRUCTURES & FORCES FAMOUS STRUCTURES Click on image above 1.0 Structures are found in natural and human-made environments. 3 Biomimicry Biomimicry is the practice of emulating nature's designs to solve human problems. By studying nature's efficiency and resilience, engineers have developed i...

UNIT D STRUCTURES & FORCES FAMOUS STRUCTURES Click on image above 1.0 Structures are found in natural and human-made environments. 3 Biomimicry Biomimicry is the practice of emulating nature's designs to solve human problems. By studying nature's efficiency and resilience, engineers have developed innovative solutions that are both sustainable and effective. 4 Architecture has long drawn inspiration from nature's forms and patterns. Iconic buildings inspired by seashells, tree-like structures, and honeycomb patterns. Witness the harmony between human ingenuity and the beauty of nature, as architects push boundaries to create sustainable and visually stunning structures. 5 Sharkskin-inspired swimsuits These swimsuits received a lot of media attention during the 2008 Summer Olympics when the spotlight was shining on Michael Phelps. Seen under an electron microscope, sharkskin is made up of countless overlapping scales called dermal denticles (or "little skin teeth"). The denticles have grooves running down their length in alignment with water flow. These grooves disrupt the formation of eddies, or turbulent swirls of slower water, making the water pass by faster. Photo: Matt9122/Shutterstock; Michael Kappeler/AFP/Getty Images 6 Beaver Pelt = Wetsuits Beavers have a thick layer of blubber that keeps them warm while they're diving and swimming in their water environments. But they have another trick up their sleeves for staying toasty. Their fur is so dense that it traps warm pockets of air in between the layers, keeping these aquatic mammals not only warm, but dry. Photo: Rudmer Zwerver/Shutterstock;MIT 7 Termite Den = Building Cooling Termite dens look otherworldly, but they are surprisingly comfortable places to live. While the temperature outside swings wildly throughout the day from lows in the 30s to highs over 100, the inside of a termite den holds steady at a comfortable (to a termite) 87 degrees. 8 Mick Pearce, architect of Eastgate Centre in Harare, Zimbabwe, studied the cooling chimneys and tunnels of termite dens. He applied those lessons to the 333,000 square-foot Eastgate Centre, which uses 90 percent less energy to heat and cool than traditional buildings. The building has large chimneys that naturally draw in cool air at night to lower the temperature of the floor slabs, just like termite dens. During the day, these slabs retain the coolness, greatly reducing the need for supplemental air conditioning. Photo: fritz16/Shutterstock; David Brazier/Wikimedia Commons Burr = Velcro Velcro is widely known example of biomimicry. You may have worn shoes with velcro straps as a youngster and you can certainly look forward to wearing the same kind of shoes in retirement. Velcro was invented by Swiss engineer George de Mestral in 1941 after he removed burrs from his dog and decided to take a closer look at how they worked. The small hooks found at the end of the burr needles inspired him to create velcro. Photo: cpreiser000,Stocksnapper/Shutterstock 9 Birds = Jets Birds have been able to boost the distance they're able to fly by more than 70 percent though the use of the V-shape. Scientists have discovered that when a flocks takes on the familiar V-formation, when one bird flaps its wings it creates a small updraft that lifts the bird behind. As each bird passes, they add their own energy to the stroke helping all the birds maintain flight. By rotating their order through the stack, they spread out the exertion. 10 A group of researchers at Stanford University thinks passenger airlines could realize fuel savings by taking the same tactic. The team, lead by Professor Ilan Kroo, envisions scenarios where jets from West Coast airports meet up and fly in formation en route to their East Coast destinations. By traveling in a V-shape with planes taking turns in front as birds do, Kroo and his researchers think aircraft could use 15 percent less fuel compared to flying solo. Photo: Kevin Burkett/flickr; Ana Gram/Shutterstock Beetle = Water Collection The Stenocara beetle is a master water collector. The small black bug lives in a harsh, dry desert environment and is able to survive thanks to the unique design of its shell. The Stenocara's back is covered in small, smooth bumps that serve as collection points for condensed water or fog. The entire shell is covered in a slick, Teflon-like wax and is channeled so that condensed water from morning fog is funneled into the beetle's mouth. It's brilliant in its simplicity. MIT have crafted a material that collects water from the air more efficiently than existing designs. About 22 countries around the world use nets to collect water from the air, so such a boost in efficiency could have a big impact. Photo: Kevin Burkett/flickr; Ana Gram/Shutterstock 11 STRUCTURE: ANY object that provides support STRUCTURAL STRENGTH: The ability of a structure to hold itself up, over and above any weight that is added. STRUCTURAL STABILITY: The ability to maintain its position even if a FORCE is acting on it. FORCE: A push or a pull that tends to cause an object to change its movement or shape; measurement is Newtons. 12 1.1 CLASSIFYING STRUCTURAL FORMS THREE STRUCTURAL FORMS 1. Mass (solid) Structure 2. Frame Structure 3. Shell Structure 13 1. Mass (solid) Structure Formed from a solid piece of strong material. Has little or no space between inside, relying solely on its own mass to resist any force that may be acted on it. Usually the strongest of the three types of structures. 2. Frame Structure Formed from a rigid component of parts or structural components fastened together. The strength of the frame comes from how these parts are put together. Lighter than a solid structure because they use less parts. Frame Structure 3. Shell Structure Has a solid outer surface, may be rounded or flat with a hollow inner area. Rounded outside is stronger due to the curved area distributing the load around the whole surface. Hollow interior allows it to be lighter. 1.2 THE FUNCTION OF STRUCTURES FUNCTION: ⬗ A structure's use or purpose Example: The function of an airplane or car is transportation. It has multiple functions, movement and shelter. ⬗ When a structure is built knowing the main function (i.e. comfort, transportation or shelter) of the structure will allow the designers to build it accordingly 18 Example: The function of a roof is to provide a cover and to protect what is inside. FUNCTION & EFFECTIVE DESIGN Technological problems can often be solved in a variety of ways, using many different structural designs, materials, and processes. What all successful solutions have in common, however, is that they pay close attention to function. Paint Roller Invented by Norman Breakey, a Torontonian who wanted to apply paint quicker without sacrificing a smooth finish. Up until his invention, which he developed in the 1940s, the only painting was done with paint brushes. 19 COMMON FUNCTION, DIFFERENT DESIGN Some structures, although they look very different from one another in their design, actually share a common function. 20 COMMON FUNCTION, DIFFERENT DESIGN A Gabled Roof: Gable roofs will easily shed water and snow, provide more space for the attic or vaulted ceilings and allow more ventilation. B Steep Pitch Steep pitch roofs are found in locations with large snow falls to shed snow more easily resulting in a decreased snow load that may damage the roof. 21 COMMON FUNCTION, DIFFERENT DESIGN C Gambrel Roof: Most barns and many stables in the United States use this design as a way to improve storage for agricultural products. Some churches use the concept to provide high ceilings. D Dome Shape Roof A dome allows for more storage than a silo with a comparable footprint. Because the hemispherical geometry of a dome provides strength at all points of the structure, the entire interior can be used to contain product, right up to the apex 22 COMMON FUNCTION, DIFFERENT DESIGN E Flat Roof: Flat roofs are generally versatile, easier to maintain, and more energy-efficient than most sloped roofs, so new home builders, in particular, enjoy the lower cost of long-term ownership. F Onion-Doe Roof Some scholars believe that onion domes first appeared in Russian wooden architecture above tent-like churches. According to this theory, onion domes were strictly utilitarian, as they prevented snow from piling on the roof. 23 COMMON FUNCTION, DIFFERENT DESIGN G Sail Roof: Used as a protective awning to shield people from the elements as they gather to learn, perform and celebrate their culture. A symbol of the west coast and its heritage. It is also aesthetically pleasing. 24 NATURAL vs. MAN-MADE STRUCTURES Structures can be interpreted and classified according to the materials and components they are made of. 25 AESTHETICS Aesthetics refers to the pleasing appearance or effect that an object has because of its design. Aesthetics is often in the “eye of the beholder”. Aesthetics has always played an important role in the structural designs of First Nations people. The design on teepees used by Plains First Nations reflected the environment as well as the 26owner’s personal spiritual beliefs. Section 1 Let’s review some concepts STRUCTURE: ANY object that provides support CLASSIFICATIONS OF STRUCTURAL FORMS 27 Mass Frame Shell STRUCTURAL STRENGTH: STRUCTURAL STABILITY: The ability of a structure to hold itself up, over and above any weight that is added. The ability to maintain its position even if a FORCE is acting on it. FUNCTION A structure's use or purpose AESTHETICS FORCE: A push or a pull that tends to cause an object to change its movement or shape; measurement is the Newton (N), Aesthetics refers to the pleasing appearance or effect that an object has because of its design. 1.3 HUMAN BUILT STRUCTURES AROUND THE WORLD Homes Homes developed by different cultures and at different times are just one example of how widely humans have adapted a basic form. 28 29 FAMOUS STRUCTURES Project Mr. Collins’ Sample Project 2.0 INTERNAL & EXTERNAL FORCES ACT ON STRUCTURES 31 2.1 Measuring Forces The actual effect of a force on a structure depends on three things: the magnitude, or size, of the force the direction of the force the location where the force is applied 32 THE NEWTON (N) NEWTON: Unit of Force is referred to as a NEWTON (N) 1 Newton (N) = amount of force needed to hold up a mass of 100 grams (g) Named after Isaac Newton. 33 2.2 EXTERNAL FORCES ACTING ON STRUCTURES EXTERNAL FORCE: A force is a push or pull that tends to cause an object to change its movement or shape. In order for an object to remain standing it must resist gravity. MASS: Mass is the amount of matter in an object. The more mass an object has, the greater the gravitational force. Weight is the pull of gravity on mass. 34 An external force is a force that is applied on a structure by something else. Center of Gravity Scientists have discovered that even though gravity acts on all parts of a structure, there is a point where we can think of the downward force of gravity acting on a structure. That imaginary point is called the centre of gravity. The main method of increasing a structure’s stability is to increase the width of its base relative to its height. One way to do this is to place most of the mass of the structure close to the ground. This lowers the centre of gravity. 35 CENTER of GRAVITY: Scientists have discovered that even though gravity acts on all parts of a structure, there is a point where we can think of the downward force of gravity acting on a structure. The main method of increasing a structure’s stability is to increase the width of its base relative to its height. One way to do this is to place most of the mass of the structure close to the ground. This lowers the centre of When a structure is supported at its centre of gravity gravity, it will stay balanced. Therefore, the location of the centre of gravity of a structure determines the structure’s stability. Center of gravity simulator 36 SYMMETRY Symmetry is a balanced arrangement of mass that occurs on opposite sides of a line or plane, or around a centre or axis. The force of gravity on either side of the centre point of the ruler (where the finger is supporting it) is the same. For a symmetrical structure to be stable, its mass must be distributed equally around the centre of the structure’s base. This means that the force of gravity around the centre is also equal, making the structure stable. 37 For a symmetrical structure to be stable, the mass of that structure must be distributed equally around the centre of the structure’s base, meaning force of gravity around the centre is also equal. 38 Load A load is an external force on a structure. The weight of a structure—and the non-moving load it supports—is called the static load. A dynamic load is an external force that moves or changes with time. Types of dynamic load include people, traffic, earthquakes, wind, waves, and blasts. Any structure can be subjected to dynamic loading and the changes that come with a dynamic load can be random, periodic or a combination of the two. 39 An elevator is an example where static loading occurs. When ten people stand in an elevator waiting for the doors to close, they are exerting a load on it that is static because the people and the elevator are not moving relative to each other. STATIC and DYNAMIC LOADS When structures are built the idea of having weight put on them is something every engineer or designer must think about. LOAD: External force on a structure. 40 STATIC and DYNAMIC LOADS 1. STATIC Weight of a structure and the non-moving load it supports. Example: books on a bookshelf 2. DYNAMIC External force that moves or changes with time. Example: moving students on a staircase at school 41 REQUIREMENTS FOR A STRUCTURE How well will a structure hold up under the load it was designed to carry out? Important for safety, cost and efficiency-Performance Requirements should always be expressed in Maximum Weight 42 SUPPORTING THE LOAD Engineers need two conditions to decide what type of bridge is suitable: 1. What the bridge is crossing (water/land) 2. What kinds of loads the bridge will be supporting 43 TYPES OF BRIDGES 1. Truss Bridge Is a lightweight but strong bridge, made of trusses (triangle-shaped frames) along its sides. 44 TYPES OF BRIDGES 2. Suspension Bridge 45 TYPES OF BRIDGES 3. Arch Bridge Dynamic loads are transferred to the end supports, which are embedded in the ground. The ground pushes back (resists), and this resistance is passed back through all the pieces creating the arch. 46 2.3 INTERNAL FORCES WITHIN STRUCTURES Internal Force: An internal force is a force that one part of a structure exerts on other parts of the same structure. In other words, internal forces are forces that act within a structure. 47 Compression: Is a force that acts to squeeze an object or push parts within an object together. Tension: Is a force that acts to stretch and pull apart something. Shear: Is a force that acts to push parts that are in contact with each other in opposite directions 48 Complementary Forces: When different kinds of internal forces act on a structure at the same time. Bending is one example. 49 2.4 Designing Structures to Resist Forces and Maintain Stability 50 Arch An arch is a common shape in structures such as bridges. The arch can support a large load because the force of the load is carried down through the arch to the foundation. This spreads out the load. 51 Beam A beam is a flat structure supported at both ends. I-Beam: Have less mass and make it stronger. Girder (box beam): are long beams in the shape of hollow rectangular prisms 52 Truss A truss is a framework of beams joined together. Trusses are usually in the form of interlocking triangles Cantilever A cantilever is a beam that is supported only at one end. When weight is placed on the beam, the beam bends in an N-shape to resist the load. 53 Column A column is a solid structure that can stand by itself. Columns can be used to support beams. 54 Structural Stress, Fatigue or Failure Sometimes too great a combination of external and internal forces acting on a structure can weaken it. The result can be structural stress. A strong, stable structure is designed and built to be able to resist stress without any damage happening. However, repeated abnormal use of the structure could cause structural fatigue. This is a permanent change in a structure caused by internal forces such as compression, tension, and shear. Structural failure, such as the collapse of a bridge, occurs when a structure can no longer stand up to the forces acting on it. 55 3.0 Structural strength and stability depend on the properties of different materials and how they are joined together. 56 1. What materials can you see around you? What is holding them together? 2. What are example of fasteners? Make a list of each of the above in your notes. 57 3.1 Materials and Their Properties Classifying Material Properties The materials used in structures can be evaluated according to many properties. How well the designer, engineer, or builder analyzes those properties determines how well the resulting structures will do what they’re supposed to. It also determines how long the structures will last before giving in to the forces acting on them. Deformation Deformation is a change of shape in a structure or any structural component, because the material is unable to resist the load acting on it. When too much deformation occurs, a component or the entire structure might fail. Flexibility Flexibility is the ability of a material to be bent under force without breaking. How much an object can change shape under a given load without breaking is an indication of how flexible it is. 3.2 Joining Structural Components Just as design and materials are important to a structure’s strength and stability, so is how the parts of the structure are fastened together. The place at which structural parts are joined is called the joint. Some joints need to be rigid, or fixed, for the structure to work as intended. Others need to be flexible, or movable. Friction Which of the following statements is incorrect? 61 1. A camper spreads a rubber tarp on slightly sloping ground, then puts a backpack on top of the tarp. When the camper returns a moment later, the backpack has slid several centimetres down the slope. 2. It is easier to open a jar lid if your hands are dry than if they are wet. 3. A hockey skater reduces speed by digging in the tip of each skate when striding forward. 4. A very thin film of water on a road is less slippery to a moving car or truck than a dry road. Joints that Rely on Friction Friction of any structure is affected by: - Mass (weight) - Gravity - Force - Type of surface (rough or smooth) Nails, Screws, Rivets, Tacks, Staples It is the friction between the metal and the material surrounding it that does the job. One advantage of screws, tacks, and staples is that they can be easily removed to dismantle a structure if necessary. Interlocking Pieces Since friction is the force as two surfaces rub against one another, you can increase the amount of friction by increasing the area in contact. Mass The pyramids were designed by friction with the base of the block using friction to stabilize with the block below it. Joints that Rely on Bonding Another form of joining actually changes the two surfaces being joined so that they are connected by a common material—whatever bonding substance is spread on them. Glue, Tape, Cement, Welds The pyramids were designed by friction with the base of the block using friction to stabilize with the block below it. Fixed Joints vs. Moveable Joints Fixed joints are rigid to prevent any movement. They result, for example, from welding, cementing, gluing, or nailing parts firmly together. welding cementing gluing which results in the parts of the structure being firmly secured Movable joints are flexible or mobile so that parts of the structure can move as required. Hinges, pin joints, and flexible rubber tubing are examples of movable joints. So are your knees, elbows, and shoulders. hinges on a door knees elbows shoulders (can move however, still able to withstand force or the stress of repeated movements 3.3 Properties of Materials in Plant and Animal Structures Think about your body as a structure. Each of the components in the human body is a unique material with special properties suited to the function of that part. Bones, Ligaments, and Cartilage of the Frame Structure BONES: Hard/rigid forming a structural frame which can support and protect the other parts of the body LIGAMENTS: Flexible connective tissue which allows for movement, connect bone with bone CARTILAGE: Reduces friction providing smooth surfaces for movement MUSCLES: Semi-solid fibrous tissue (contracts/relaxes) TENDONS: Attaches the muscles to the bones (strong/flexible) Types of Moveable Joints 1. 2. 3. Ball and Socket (shoulder/hip joints) Hinge (elbows/knees) Pivot (wrists/spine) Skin, the Human Shell Tough, flexible (waterproofs the body and protects it from bacteria) as well it works to regulate temperature (perspire and shiver). Materials in a Tree’s Structure A tree trunk may seem to be made of just one material (“wood”), but in fact, it is a structure composed of several layers of different materials. 4.0 Structures are designed, evaluated, and improved in order to meet human needs. Margin of Safety Limits within which a structure’s safety performance is felt to be acceptable. Example – limits on roads and highways, tire pressure, elevator capacity Testing for Structural Safety The best way to determine if a structure is safe we test it to the extremes. Testing occurs at all stages from the components used to the design to the final product before putting it on the market Example – Cars are driven in to brick walls to test the materials used for safety purposes Monitoring for Structural Safety Scientist continually look at how often the structure will fail and why. Experts keep track of how well the structure performs. Accounting for Environmental Factors Terrain Conditions Unstable soils and steep terrain may be a poor choice for a structure, therefore when constructing a structure within these areas special techniques are required. Climate Conditions Builders must take into account the climatic-related factors that outdoor structures must face. Example – Permafrost (solid frozen layer of soil during winter, however upper portions melt in the summer making the ground spongy, therefore a solid foundation is needed). Earthquake Risk The structures built within these areas must be able to resist external and internal forces that act on them during the shifting of the earth’s plates Monitoring for Structural Safety Scientist continually look at how often the structure will fail and why. Experts keep track of how well the structure performs. 4.2 Strengthening Materials to Improve Function and Safety THROUGH NUMEROUS TESTS, NEW DESIGNS AND MATERIALS ARE APPLIED THEREFORE RESULTING IN IMPROVED PRODUCTS. ADVANCES IN THE KNOWING WHAT WORKS BETTER OR DISCOVERING NEW MATERIALS ALSO LEADS TO A CHANGE IN WHAT METHODS MAY BE USED TO INCREASE STRENGTH OF MATERIALS. Altering Materials for Strength One way to solve structural problems is to combine materials/components in a new way therefore allowing you to take advantage of the best characteristics of each area. Example - Lightening Holes in a airplane's wing. Corrugation: Process of forming a material into wave-like ridges or folds. Ex. cardboard Lamination: Process of forming a material into wave-like ridges or folds. Ex. laminate kitchen countertops Build It Week “ Day 1 - Paper Towers Day 2 - Building in the Rain Day 3 - Bridge Over Troubled Water Day 4 - Spring Fling 83