2. Structures and Materials

3. General Terms Force: A push or pull applied to some object. –Examples: gravity, you, wind Gravity: the attraction that any two objects have for each other even if the objects separated by large distances. Weight: a measure of the force of gravity; specifically, the measure of the Earth’s gravitational pull on the mass of an object. Mass: the amount of matter an object contains.

4. Force Units of Force –Standard system: pounds (lbs) or ounce (oz) –Metric system: Newton (N)-can be mN or kN –Conversion factor: 4.45 N = 1 lb -Vectors-Vectors: -same direction : add -opposite direction: subtract -At an angle: draw triangles or use trig

5. Tension vs. Compression Tensile force or Tension: an external force that creates a pulling or stretching action on a material. –Examples: Compressive Force or Compression: an external force that creates a push or squeezing action on a material. –Examples:

6. Properties of Solids Strength –Strength = ability to resist an action without breaking. –Tensile strength: ability of a material to resist a pulling or stretching action without breaking. –Compressive strength: ability of a material to resist a pushing or stretching action without breaking.

7. Stress Stress: an internal force applied to each square inch of the cross sectional area of a material. Internal pressure. –Stress can be applied due to a variety of forces: Tensile force Compression force Twisting force: applying rotational force or torque Bending force: force on middle of an object that is supported on its ends.

8. Stress Formula Formula for calculating: –Stress (S)=Force (F) Area (A) Units: lbs/in 2 (psi) or Pascal (Pa) Area (A) = Force (F) Stress (S) Units: in 2 or cm 2 Force (F)=Stress (S) x Area (A) Units: lbs or N Note: Area in formula must be the area perpendicular to the applied force.

9. Mechanical Properties of Solids Second Property of Solids: Deformation Deformation is the change in length of a material due to exposure to tensile or compressive forces. Hook’s Law is the deformation of an object is directly proportional to the applied force.

10. Mechanical Properties of Solids Third Property of Solids: Strain Strain is the change in length for each inch (or meter) of an object. –Formula for calculating Strain: Strain: Original length: Deformation: Units: e – no units L and ∆L – cm, in, m, ft, yds (must use same units for both

11. Stress and Strain Relationship Stress and strain are proportional – can predict on from the other. Modulus of elasticity (E) = a constant value for each material that relates stress to strain (unit of psi or Pa) –Formula for Stress-strain relationship Modulus of Elasticity: Stress : S=E x e Strain: Tables exist of values of E for different materials

12. Table of E values MaterialUltimate stress (lbs/in 2 ) Modulus of Elasticity (lbs/in 2 ) Cast iron (class 30)30,00015,000,000 Structural steel64,00030,000,000 Stainless steel90,00028,000,000 Ultrastrength steel220,00030,000,000 Copper32,00015,600,000 Aluminum45,00010,000,000 Douglas fir12,2001,760,000 PVC7,000410,000

13. Example Problem The stress placed on a rod is 42,000 lbs/in 2 and the resulting strain is 0.0014. What is the modulus of elasticity? What material is this?

14. Mechanical Properties of Solids Fourth Property of Solids: Elasticity –Elasticity = the ability to stretch under tensile force (or compressive force) and then return to its original dimensions when force is removed. Fifth Property of Solids: Plasticity –Plasticity = a failure to return to original dimensions when a force is removed (opposite of elastic). Materials will stretch or compress to a point and remain elastic, and then beyond that point, they will not retract or expand.

15. Mechanical Properties of Solids Elastic limit = limit that represents the maximum stress that can be applied to a material and still have the material retain its elastic properties. Plastic range = the range of stress values above the elastic limit. If these forces are applied, the material will be permanently deformed. Elastic range = the range of stress values for which a material remains elastic and the stress- strain formula works. Ultimate strength = the maximum stress value that a material can withstand. An attempt to go beyond this value will result in breaking.

16. Stress-Strain Curve

17. Mechanical Properties of Solids Ductility = the measure of the plasticity of metals involving the ability of a material to stretch under a tensile force. –Example of high ductility: Structural steel, brasses, gold, silver, copper. Malleability = a measure of the plastic property of metals involving the ability of a material to be squeezed or hammered by a compressive force. –Example of high malleability: gold –http://www.24carat.co.uk/whyeighteencaratgol disbetter.htmlhttp://www.24carat.co.uk/whyeighteencaratgol disbetter.html

18. Mechanical Properties of Solids Brittleness = the inability of a material to deform very much before breaking. The shorter the deformation required for rupture, the more brittle the material. Short plastic range. –Example of high brittleness: cast iron, high strength steel, concrete, clay products, glass Hardness = the ability of a material to resist scratching or denting –Example of high hardness: diamonds, high- carbon steel, ceramic material –Example of low hardness: lead, copper

19. Structural Loads: Types of Loads Notes Dead load = weight of materials permanently part of a structure. Includes weight of: –Columns, beams, exterior walls, interior walls, floors, ceiling, insulation, plumbing, heating and cooling equipment. Live load = weight of nonpermanent objects within a structure that may change over time. Includes weight of: –Furniture, people, equipment, and stored goods. Static load = dead load + live load. Loads that remain relatively constant over time or change relatively slowly.

20. Loads cont. Dynamic loads= loads that change value rapidly and abruptly. Includes pressure of wind gusts or storms or an object dropped on floor. Resonance = a rhythmic force that is applied to a structure in the same period as that of the structure. Builds slowly over time to have a dynamic effect on structures. Earthquakes = jerking forces of earth moving over its hot liquid core.

21. Loads cont. Wind load = the static or dynamic effect of the wind on a structure. Creates a pressure on the windward side and an area of suction on the opposite side. May cause wind drift which is the swaying of tall buildings. –Tall buildings contain a Tuned Mass Damper (large concrete weight) in the top to counteract wind drift.

22. Loads cont. Locked in Loads: Thermal load= force placed on structure by daily and seasonal change in air temperature. ( winter verses summer). Solid materials expand when heated. Settlement load= forces placed on structure by settling of soil beneath structure.

23. Structures Structural Components of Buildings  Foundation (footer, pad, or basement)- solid base to build on.  Skeleton (load bearing columns and beams)- carry weight of structure to foundation.  Shell/envelope (exterior walls and roof) – keep out weather.  Interior (floor, ceiling, interior, walls) divide up space and make it usable (functional)

24. Structures Structure vs. Function –Structural and functional parts of building are usually made from different materials. Structural- high strength Functional- transparent, light, cheap, easy to maintain. –Traditional brick or stone buildings – brick walls are both structural and functional.

25. Architectural terms –Columns – vertical (up and down) components. –Beams – horizontal (sideways) components –Cantilever - vertical or horizontal components with only 1 end attached. –Arch - compression of blocks gives strength to this form. –Dome – half of a sphere with no internal supports.

26. Properties of Construction Materials Masonry Materials: –Concrete Composition –Portland cement – composed of lime, silica, iron oxide, and alumina. –Water – high ratio of water to cement = decreases strength. –Aggregates – make up 60 to 80% of mixture –Sand –Small stones or gravel – size and surface texture affect strength. High compressive strength Low tensile strength Fireproof, water tight, cheap

27. Concrete Ratio

28. Concrete cont Reinforced concrete: –Concrete + steel reinforcement (rebar) –Increase tensile strength –High compressive strength –Allows use for beams. Mortar- concrete made without gravel or small stones. Strength determined by water to cement ratio. Natural Stone limestone, granite, or marble. –High compressive strength –Low tensile strength

29. Concrete cont Cast Stone = composed of Portland cement, fine coarse aggregates (granite, quartz, or limestone), natural or manufactured sands and chemical additives. May contain steel reinforcements and chemical additives. May contain steel reinforcements. –High compressive strength –Relatively high tensile strength if reinforced

30. Concrete cont Brick made of clay molded and fired –Color depends on mineral composition of clay. –Relatively high compressive strength – but varies with firing method and composition Concrete block –High compressive strength –Strength depends on density – degree of aeration and composition of mix. Monuments in DC area. –Stones and MortarStones and Mortar

31. Steel Structural steel: –High tensile strength –High compressive strength –Cheap –Made from Iron and Carbon Iron contains impurities in the form of silicon, phosphorus, sulfur, and manganese Steel making involves the removal of impurities (slag) and the addition of desirable alloying elements

32. Types of steel: Plain steel = iron and carbon with mg, P, S, Si –Higher carbon content = higher strength Low – carbon = contains less than 0.3% carbon Medium – carbon = between 0.3 and 0.8% carbon High – carbon = between 0.8 and 2.11% carbon. Alloy steels = contains other elements (Al, Cr, Ni) Stainless = Chromium added (rust proof) Cast iron = more than 2.11% carbon (relatively impure iron) –Brittle Wrought iron = refined metallic iron with 1 to 3% slag (relatively pure) and 0.05% carbon

33. Wood Products Lumber (hardwoods and softwoods) –With grain: high tensile strength and average compressive strength –Across grain: low tensile and compressive strength –Strength varies with variety of wood (pine vs. oak) Veneer = thin layers or sheets of wood (1/100 inch – ¼ inch) –Very thin pieces are fragile Plywood = uneven number of thin sheets of wood glued together with grains of the successive layers at right angles. –Increase tensile strength from all sides –Noted for durability lightness, rigidity, and resistance to splitting and warping.

34. Wood Products Composite panels = produced in the form of a board or sheet, formed of cellulose fibers or particles derived from wood or other sources. –Particleboard – wood particles sprayed with adhesive, formed into a mat and compressed –Wafer board and oriented strand board (OSB) – larger pieces of wood imbedded with adhesive –Fiber-based panels- hardboard, medium density fiberboard (MDF), insulation board –Consistent composition makes strength and rigidity uniform

35. Other Metals: Aluminum –High tensile strength –High compressive strength –Changes shape when stressed more than steel

36. Plastics Plastics: tensile and compressive strength vary with formulation Changes shape and size a lot in response to stress Inexpensive

37. Properties of Components: Foundation: Compressive strength Columns: Compressive strength Beams:Tensile strength, not brittle Shell:High hardness, water resistant, transparent, ect.

38. Materials for components Foundation: concrete, block, brick, stone Columns: concrete, block, brick Beams: steel, wood, reinforced concrete Shell: glass, plywood, or composite panels, plastic.