Science 7: Structures and Forces Overview Key Concepts - structural forms - material strength and stiffness - joints - forces on structures (loads) - forces within structures (stresses) - direction of forces - deformation - structural stability - modes of failure - performance requirements - margin of safety Allison’s You Tube Video Playlist: https://www.youtube.com/playlist?list=PLLFNQ_MiA9w0L_LTaDMu5pZmejtW1_I3G Topics 1-2: Structural Design What is a structure? Can you classify a structure according to its origin? What is structural “strength” and “stability”? Can you classify a structure according to its form? What is design? What is function? What is aesthetics? What is margin of safety? Section 3-5: Forces Acting on Structures What is force? ● (mass vs. weight: https://youtu.be/1whMAIGNq7E ) How do we measure force? What are the external forces (loads) acting on a structure? https://youtu.be/qPkCFEPvP68 What are the internal forces (stresses) acting within a structure? https://youtu.be/So6dh0-W0jc What is failure? What is deformation? ● https://youtu.be/mXTSnZgrfxM Bridges & Tacoma Narrows Failure ● What are some methods of joining materials together? https://youtu.be/sd-hgMw7YmM ● What are some ways to improve material strength? ○ https://youtu.be/UspM9qOdAmI - make an I beam ○ https://youtu.be/kL8PQWWtsOU - how you build it… stronger structures ○ https://youtu.be/zKq2rfY4DrE - great summary - all types of shapes (YYC based) What are some considerations for building safe structures in different environments? Section 6-7: Designing for Strength and Stability How can we design strong and stable structures that resist forces? Group project: Design and Build a Structure Group project reflection: Revise and improve your design Can you analyze your structure in order to make improvements in strength, stability, aesthetics, etc.? Science 7: Structures and Forces Detailed Outline Topics 1-2: Structural Design What is a structure? - An object that has a definite size and shape that serves a purpose. Can you classify a structure according to its origin? - Origin (where did they come from?): (a) natural structures – an object or structure not made by people Examples: (b) manufactured structures – object or structure that is made by humans Examples: What is structural strength? - Strength is a structure’s ability to hold it's shape when forces act on it. - Give some examples of structures that are strong. What is structural stability? - Stability is a structure’s ability to hold it's position when forces act on it. - Give some examples of structures that are stable. Can you classify a structure according to its form? - Form: there are three main types of forms: (a) Solid: A solid structure is formed from solid pieces of a strong material that are piled on top of each other. What are some examples of manufactured solid structures? (b) Frame: A frame structure is formed from pieces that have been joined together to create a skeleton of support. (c) Shell: A shell structure is formed from a solid outer material that creates a large hollow inner space. For each form: What are some examples (natural or manufactured)? What would be some advantages? What might be some disadvantages? What are some of the things that must be considered when designing a structure? - function (form follows function!) - aesthetics - safety (margin of safety) - cost of parts and labour - forces acting in/on a structure - materials (strength, weight, cost) - joining structural components - environmental impact - structural strength - structural stability - culture - available technology What is function? - Function is a structure’s purpose. - List the purpose of various structures (buildings, statues, vehicles, chairs, etc.) - The function of a structure needs to be determined before the structure is designed. - Form follows function! What is aesthetics? - Aesthetics is "beauty" in a structure's design. - However, each person may have a different idea about beauty depending upon their personal experiences. What is “margin of safety”? - Safety is important to all designers. However, since it is impossible to make anything perfectly safe, designers work with a margin of safety. This refers to the limits within which a structure’s safety performance is felt to be acceptable. It balances safety with material or building costs. - Some structures are designed to fail at specific times or along certain spots. What are some methods of joining materials together? (1) Friction is the force that results when the surface of one object moves against the surface of another object. What are some ways that we can create friction? (a) Fasteners such as nails and screws (b) Interlocking pieces such as Lego or puzzle pieces (c) Mass creates weight that pushes pieces together (2) Glues can join different materials together. (3) Welding melts two separate pieces together. - When different parts of the structure are joined, they form two main types of joints: (a) Fixed joints are rigid to prevent any movement. (b) Movable joints are flexible or mobile so that parts of the structure can move as required. What are some ways to improve material strength? - Corrugation is the process of forming a material into wave-like ridges or folds. - Gluing layers of a material together to create a strong bond is called lamination. Topics 3-5: Forces Acting on Structures What is force? - Weight is the force your body pushes down with. It is caused by the force of gravity from our planet pulling down on you. - weight can change depending upon where you are - weight is measured in Newtons (N) - weight is measured using a Spring Scale - Mass refers to the amount of matter in your body. - mass does not change as your location changes - mass is measured in Kilograms (Kg) - mass is measured using a Balance - Gravity is one of the main forces that act on a structure. Weight is how we measure this force caused by gravity. As the mass of a structure increases, gravity will cause its weight to increase as well. - Force is a push or pull that acts on an object. - The effect of a force depends on three things: - the strength of the force, the direction of the force, where the force is applied What are the external forces (loads) acting on a structure? - external forces – are loads that act on a structure from the outside. They are divided into two groups: (1) static loads – the weight of a structure upon itself - it is an external force because it is due to gravity - it is permanent Examples: (2) dynamic loads – the forces that act in or on a structure but are not part of the structure - it is temporary Examples: What are the internal forces (stresses) acting within a structure? - internal forces – are stresses that act on an object from the inside - internal forces are often caused by external forces acting on a structure (1) Compression is a force that acts to squeeze an object or push parts within an object together. (2) Tension is a force that acts to stretch and pull apart something. (3) Shear is a force that acts to push parts that are in contact with each other in opposite directions. (4) Torsion is twisting force that results when the ends of a material turn in opposite directions. (5) Bending is an example of two different forces acting at the same time. What is failure? - Failure is when a structure is permanently damaged because it can no longer stand up to the internal or external forces acting on it; there are two main types of failure: (1) deformation: when a structure is permanently damaged but still maintains some aspect of its original design or (2) collapse: when a structure no longer maintains any aspect of its original design or is no longer able to perform its intended function - flexibility is the ability of a material/structure to withstand forces without collapsing or being permanently deformed - Causes of failure: (1) shear failure – when a structure collapses because one section of a material/structure slides over another section along a weak point because of compression or shear force (2) buckle (bending) failure – when a structure is deformed or collapses due to folding that is caused by compression and tension (bending) forces (3) torsion failure – when a structure is deformed or collapses due to torsion force (4) snapping failure – when a structure is deformed or collapses due to tension force Topics 6-7: Designing for Strength and Stability How can we design strong and stable structures that resist forces? - design a wide base for stability - keep most weight low to the ground - design a structure that has symmetry (balanced weight) - consider the shape of your structure or the shapes within your structure (triangles, rectangles, circles, etc) - arches, beams, columns, trusses, cantilevers and braces can be used to strengthen your structure - consider your materials and their properties - consider how you will hold all of the materials together - consider the joints within your structure What are some considerations for building safe structures in different environments? - climate (precipitation, wind, temperature) - earthquakes, hurricanes, etc. - terrain (stability of the land)
