Fundamentals of structural analysis
- 1. Fundamentals ofFundamentals of Structural AnalysisStructural Analysis J. VoytillaJ. Voytilla
- 2. The Main Types ofThe Main Types of StressStress 1. Compressive1. Compressive 2. Elongation or Tensile2. Elongation or Tensile 3. Transverse or shear3. Transverse or shear
- 3. MechanicalMechanical STRESSSTRESS Stress is defined as theStress is defined as the perpendicularperpendicular force per unit areaforce per unit area applied to an object, inapplied to an object, in a way that compresses (compressivea way that compresses (compressive stress) or stretches (tensile stress) thestress) or stretches (tensile stress) the object.object. The units are N/mThe units are N/m22 (Pascal = Pa)(Pascal = Pa)
- 4. COMPRESSIVECOMPRESSIVE STRESSSTRESS If we stack a weight onIf we stack a weight on a pillar that is standinga pillar that is standing on a solid surface, iton a solid surface, it will be underwill be under compressive stresscompressive stress andand the length will decreasethe length will decrease by some distanceby some distance ΔΔL.L. If we double the weight,If we double the weight, it will compress twice asit will compress twice as much, 2much, 2 ΔΔ L.L.
- 5. COMPRESSIVECOMPRESSIVE STRESSSTRESS This linear property is common to almostThis linear property is common to almost all materials, provided you do not exceedall materials, provided you do not exceed thethe elastic limitelastic limit of the material.of the material. This is important information to knowThis is important information to know before you pour concrete pillars to supportbefore you pour concrete pillars to support an entire house.an entire house.
- 6. TENSILE STRESSTENSILE STRESS Also known asAlso known as tensiontension Tensile stress is just the opposite ofTensile stress is just the opposite of compression stress….it is the stress ofcompression stress….it is the stress of beingbeing stretched or pulledstretched or pulled .. The amount of tensile stress that aThe amount of tensile stress that a structure can withstand depends upon thestructure can withstand depends upon the material of the structure and its elasticitymaterial of the structure and its elasticity ..
- 7. TENSILE STRESSTENSILE STRESS Pure tension - strain is in one directionPure tension - strain is in one direction only. Standard example - bar of anyonly. Standard example - bar of any uniform cross section under tension load.uniform cross section under tension load. In all engineering materials, the elongationIn all engineering materials, the elongation produced by a tensile force is accompaniedproduced by a tensile force is accompanied by aby a contractioncontraction in the transversein the transverse directions.directions.
- 8. SHEAR STRESSSHEAR STRESS Also known asAlso known as TORSIONTORSION.. Shear stress, or just shear, is similar toShear stress, or just shear, is similar to other types of stress, except that the forceother types of stress, except that the force is applied in such a way that the material isis applied in such a way that the material is sheared or twistedsheared or twisted ..
- 9. SHEAR STRESSSHEAR STRESS The block is "glued" to the table and a forceThe block is "glued" to the table and a force F is applied to the top parallel to the table.F is applied to the top parallel to the table. The block distorts, the top surface moving aThe block distorts, the top surface moving a distancedistance ΔΔLL while the bottom remains inwhile the bottom remains in place.place.
- 10. SHEAR STRESSSHEAR STRESS Usually a material will distort more than itUsually a material will distort more than it will compress, but that is not always true.will compress, but that is not always true. The foundation and walls of a house willThe foundation and walls of a house will suffer shear forces during earthquakes andsuffer shear forces during earthquakes and high winds, but rarely do failures occur duehigh winds, but rarely do failures occur due to the wall or foundation materialsto the wall or foundation materials themselves.themselves. Typically, it is the "fasteners" that fail fromTypically, it is the "fasteners" that fail from shear.shear.
- 11. Materials vs.Materials vs. StressStress Certain materials are better equipped toCertain materials are better equipped to handle certain kinds of stress than others.handle certain kinds of stress than others. This depends on the material’s ability toThis depends on the material’s ability to withstand being squashed by compression,withstand being squashed by compression, or stretched out by tensile stress, oror stretched out by tensile stress, or twisted by torsion.twisted by torsion. THINK: How would you best matchTHINK: How would you best match materials according to stress resistancematerials according to stress resistance ??
- 12. What about Structures?What about Structures? What are the basic structural elements that humansWhat are the basic structural elements that humans use? Wait……What is a structural element??????use? Wait……What is a structural element?????? Look around the room that you are in or the buildingLook around the room that you are in or the building that you are close to. How does it stay “up” and notthat you are close to. How does it stay “up” and not fall apart?fall apart? The most common basic structural elements are:The most common basic structural elements are: beams, columns, arches, fasteners, and cables.beams, columns, arches, fasteners, and cables. THINK:THINK: What kind of stress are each of theseWhat kind of stress are each of these designed for?designed for?
- 13. See for YourselfSee for Yourself Here is a very simple flash based lab on PBS’s websiteHere is a very simple flash based lab on PBS’s website that you can use to examinethat you can use to examine Forces, Loads, Materials,Forces, Loads, Materials, and Shapesand Shapes. Try it out.. Try it out. http://www.pbs.org/wgbh/buildingbig/lab/http://www.pbs.org/wgbh/buildingbig/lab/ materials.htmlmaterials.html
- 14. Good or Bad??Good or Bad?? (fill this in)(fill this in) MATERIALMATERIAL CompressionCompression TensileTensile ShearShear PolymersPolymers MetalsMetals CeramicsCeramics CompositesComposites
- 15. What aboutWhat about Structures??Structures?? StructureStructure CompressionCompression TensileTensile ShearShear BeamsBeams ColumnsColumns ArchesArches CablesCables
- 16. The Bridge ProjectThe Bridge Project Your first construction projectYour first construction project will be a virtual bridgewill be a virtual bridge using Bridge Designer software.using Bridge Designer software. However, before you are able to build something likeHowever, before you are able to build something like this, you need to do a littlethis, you need to do a little researchresearch on bridgeon bridge design…..design…..
- 17. Main Bridge TypesMain Bridge Types 1.1. SuspensionSuspension 2.2. BeamBeam 3.3. ArchArch
- 18. Types of BridgesTypes of Bridges 1.1. Arch bridgesArch bridges 2.2. Box Girder BridgesBox Girder Bridges 3.3. Simple Beam Girder BridgesSimple Beam Girder Bridges 4.4. Slab BridgesSlab Bridges 5.5. Cable-StayedCable-Stayed 6.6. CantileverCantilever 7.7. TrussTruss 8.8. SuspensionSuspension
- 19. Bridge PartsBridge Parts Some units of bridge construction are similar to thoseSome units of bridge construction are similar to those of building construction and serve a similar purpose.of building construction and serve a similar purpose. These areThese are footings, piers, caissons, walls, columns,footings, piers, caissons, walls, columns, beams, slabs, girdersbeams, slabs, girders..
- 20. Bridge ResearchBridge Research You first need to research theYou first need to research the different types ofdifferent types of bridgesbridges, and their, and their uses, strengthsuses, strengths, and, and weaknessesweaknesses You need to analyze the components that are anYou need to analyze the components that are an integral part of a bridgeintegral part of a bridge’s construction’s construction You need to analyze what materials are used in bridgeYou need to analyze what materials are used in bridge construction and WHY they are used…stress factorsconstruction and WHY they are used…stress factors and $$$and $$$ Check outCheck out thisthis website.website.
- 21. The following series ofThe following series of slides contain a glossaryslides contain a glossary that you might find usefulthat you might find useful
- 22. Factors affecting properties ofFactors affecting properties of materialsmaterials 1.1. TemperatureTemperature - Material properties- Material properties often behave as functions ofoften behave as functions of temperaturetemperature 2.2. LoadingLoading - The strength of some- The strength of some materials depends on the speed ofmaterials depends on the speed of application of force. Wood, forapplication of force. Wood, for example, is stronger when testedexample, is stronger when tested slowly than quickly.slowly than quickly. 3.3. MoistureMoisture - Absorption of moisture in- Absorption of moisture in some porous materials up to thesome porous materials up to the saturation point greatly lowers both thesaturation point greatly lowers both the modulus of elasticity and the yieldmodulus of elasticity and the yield stress.stress.
- 23. Factors affecting propertiesFactors affecting properties of materialsof materials 4.4. CorrosionCorrosion - Corrosion involves physical- Corrosion involves physical changes in the geometry and molecularchanges in the geometry and molecular composition of a structure. It is mostcomposition of a structure. It is most important for fatigue considerations.important for fatigue considerations. 5.5. ImperfectionsImperfections - irregularities in- irregularities in material, such as air bubbles inmaterial, such as air bubbles in castings, can contribute to prematurecastings, can contribute to premature failure, often resulting in brittle fracture.failure, often resulting in brittle fracture. It is often assumed for mathematicalIt is often assumed for mathematical analysis that such imperfections are notanalysis that such imperfections are not present.present.
- 24. Here are some commonHere are some common terms that you should knowterms that you should know brittle - type of material that exhibits fracture without plastic behavior.brittle - type of material that exhibits fracture without plastic behavior. Exhibits elastic behavior up until point of failure.Exhibits elastic behavior up until point of failure. buckling - a type of structural behavior that exists when a thin objectbuckling - a type of structural behavior that exists when a thin object collapses under compression, quickly folding over onto itself. Also knowncollapses under compression, quickly folding over onto itself. Also known as elastic buckling.as elastic buckling. coefficient of thermal expansion - the amount of strain that a material willcoefficient of thermal expansion - the amount of strain that a material will undergo when subjected to a unit change in temperature.undergo when subjected to a unit change in temperature. conduction - mode of heat transfer that occurs in a solid (like heat throughconduction - mode of heat transfer that occurs in a solid (like heat through a pot handle).a pot handle). convection - mode of heat transfer that occurs between a fluid and a solidconvection - mode of heat transfer that occurs between a fluid and a solid (like wind blowing over a house).(like wind blowing over a house).
- 25. deformation - deflection that occurs when structural body is underdeformation - deflection that occurs when structural body is under an external loadan external load ductility - the ability for a material to become permanentlyductility - the ability for a material to become permanently deformed without fracturedeformed without fracture elastic - capable of sustaining stress without permanentelastic - capable of sustaining stress without permanent deformation. Also used to denote conformity to the law of stress-deformation. Also used to denote conformity to the law of stress- strain proportionality.strain proportionality. fatigue - the gradual deterioration of a material when subjected tofatigue - the gradual deterioration of a material when subjected to repeated loads.repeated loads. fracture - type of failure exhibited by brittle materials, where therefracture - type of failure exhibited by brittle materials, where there is no deviation from elastic theory until the point of failure.is no deviation from elastic theory until the point of failure.
- 26. homogeneous - a material whose properties are the same at any locationhomogeneous - a material whose properties are the same at any location loads - in structural analysis, these are applied to the model to represent anyloads - in structural analysis, these are applied to the model to represent any external forces that are acting on the structure.external forces that are acting on the structure. plasticity - the phenomenon of sustaining permanent deformation without rupture.plasticity - the phenomenon of sustaining permanent deformation without rupture. strain - stretching of material that causes deflection, represented as a percentagestrain - stretching of material that causes deflection, represented as a percentage of sizeof size stress - measure of force per area, used to predict failure for a given materialstress - measure of force per area, used to predict failure for a given material torsion - load that tends to twist a member, rather than bend or elongate ittorsion - load that tends to twist a member, rather than bend or elongate it