Introduction to Structural Engineering

1. Introduction to Structural Engineering Tony Freidman

2. Background • Graduate of University of Missouri – Rolla • B.S. in Civil Engineering • B.S. in Architectural Engineering • Research in Architectural specialties • Research on V-T-M diagram development for reinforced concrete column design • Currently enrolled as a Ph.D. student at Washington University – St. Louis • Research on MR Damper performance • Research on Structural Health Monitoring

3. http://www.youtube.com/watch?v=uKeENdyIluI&feature=related • http://www.youtube.com/watch?v=AsCBK-fRNRk&feature=related • http://www.youtube.com/watch?v=YCfgfccpHpc&feature=related • http://em-ntserver.unl.edu/Mechanics-Pages/Group1/sld001.htm

4. Structural Engineering is used so that the events in the preceding videos never take place. “Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties. “ - 1st Fundamental Engineering Canon

5. Structural Engineering Overview • What is a Structural Engineer? • What do they do? • What do they design?

6. Structural Engineering Overview • What is a Structural Engineer? • What do they do? • What do they design?

7. What is a Structural Engineer? • Engineer • Mathematics of design • Architect/Artist • Vision • Aesthetics of design • Mediator • Liason between parties on a project • Salesman • Must sell your idea, yourself

8. Structural Engineering Overview • What is a Structural Engineer? • What do Structural Engineers do? • What do they design?

9. What do SE’s do? • Designer • Consultant • Take a design, and fit a structural system to that • Expert witnesses in lawsuits • Inspector • Fieldwork, Job site inspections • Oversee the materials (concrete, steel, etc.) • Inspect the building – pre- and post-construction • Demolitions • Building deconstruction • Structural Retro-fits

10. Structural Engineering Overview • What is a Structural Engineer? • What do Structural Engineers do? • What do they design?

11. SE’s design/analyze Structures • What is a structure? • A system designed to resist or support loading and dissipate energy • Building Structures • Houses • Skyscrapers • Anything designed for continuous human occupation • Non-building Structures • Bridges • Tunnels • Dams

12. Forces • Influence on an object that causes a change in a physical quantity • Considered “vectors” – magnitude and direction • Static Force • Unchanging with time • Walls • Floors • Dynamic Force • Changing with time • People • Furniture

13. Forces • Axial Forces • Acting along one axis, directly on a point or surface • Momential (Bending) Force • Acting along an axis, at a certain distance from a point, causes a folding motion • M = F*d F

14. Forces • Tensile Force • Pulling on an object – stretching it • Steel shows “necking” when too much tensile force is applied • Compressive Force • Pushing on an object – collapsing it • Concrete crushes when too much compressive force is applied

15. Forces • Strain • Tensile-related property • Deformation / Length • Stress • Compression-related property • Force / Area • Compare using stress-strain graph

16. What constitutes loading? • Loading is a force being enacted on the structure • Many sources of load • Gravity/Weight • Wind • Snow • Earthquake • Man-made • Two Types of Structural Loading • Dead Loads – static, ever-present (i.e. Walls, Floors, etc) • Live Loads – dynamic, changing (i.e. People, Desk, etc)

17. What should we build our structures out of?? • Common Structural Materials • Timber • Masonry • Concrete • Steel • Composites

18. How do we judge the materials? • Common Material Properties • Strength – Tensile/Compressive • Density • Hardness • Ductility / Brittleness • Elasticity • Toughness

19. Strength • Ability of a material to withstand loading • Tensile strength – ability of a material to withstand a pulling force • Steel is good at this, but concrete performs very poorly. • http://www.youtube.com/watch?v=YdqvGGFIbfc • Compressive strength – ability of a material to withstand a pushing force • Wood, concrete, steel, and masonry perform well • http://www.youtube.com/watch?v=WC6AgX2N1Go&feature=related • http://www.youtube.com/watch?v=i5qwvtEqC5o&feature=related

20. Density • Mass per unit volume of a material • Units – mass/vol - kg/m3 or lb-m/ft3 • Typically, materials with a high density are very strong and offer great protection. • However, a high density means that they are heavy and difficult to work with $$$$$

21. Hardness • Ability of a material to resist permanent deformation under a sharp load • Relates to the elasticity of a material • Diamond is a very hard substance. If we built a wall out of diamond, we could be sure that very few things would scratch it. • However, Diamond is incredibly expensive and not as tough as other engineering metals. It wouldn’t stand up as well in impact loading versus other materials.

22. Ductility / Brittleness • Ability of a material to deform without fracture • We want materials with high ductility, because they will indicate structural failure without a sudden collapse. • http://www.youtube.com/watch?v=BXpqW9B0eT4&feature=related – “Brittle failure”

23. Elasticity • Ability of a material to deform and return to it’s original shape. • Important quantity • Young’s Modulus • Ratio of stress to strain • Stress = Force / Area (lbs./in2 or N/m2) • Strain = Deformation / Length (unitless) • Generates a stress-strain graph • Related to the ductility of a material

24. Toughness • Ability of a material to resist fracture when stressed (amount of energy absorbed per unit volume) • Units – J/m3 or Lb-f/ft3 • Area under the stress-strain curve, evaluated from 0 to the desired strain.

25. So, we know what properties are important in structural materials. How do the common materials stack up against each other?

26. Timber • Advantages • Cheap, renewable resource • Good in Tension – ~40 MPa • Disadvantages • Susceptible to fire, nature • Not very hard • Not very strong • Limits on shape, size

27. Masonry • Concrete blocks, clay bricks • Advantages • Large compressive strength • Cheap • Good thermal properties – holds heat well • Disadvantages • Not a cohesive material. The strength could depend on the mortar, other factors • Poor tensile strength, unless reinforced • Heavy material, requires skilled laborers to use $$$$$ • Height restriction • Susceptible to the weather

28. Concrete • Combination of water, cement, small aggregate, and large aggregate. • Advantages • Very versatile – can be modified with admixtures for different effects • High compressive strength (4~7 ksi) • Fire resistant • Many diverse sizes and shapes - formwork

29. Concrete • Disadvantages • Long curing time • Low tension strength (~0.4 ksi) • Fails in shear, unless reinforced • Fairly heavy material to work with

30. Steel • Advantages • High tensile and compressive strength (A36 Steel ~ 60 ksi) • Many varieties, depending on your need • Carbon steel • Stainless steel • Galvanized steel • Elastic material • Ductile material • Many shapes, sizes

31. Steel • Disadvantages • Expensive – limited quantities / competition • Susceptible to fire, rust, impurities

32. Put them together and… • Reinforced Concrete • Concrete with steel reinforcement • Concrete handles compression • Steel takes the tension • Can handle nearly 4 times the loading that concrete alone can handle • More expensive material • http://www.youtube.com/watch?v=dGbrp7Mfp2w

33. Composites • Engineered compounds that have different physical or chemical properties • FRP – Fiber reinforced polymers • CFRP – Carbon-fiber reinforced polymers • Plastics • Categories of Glass • Categories of Wood

34. So, now we know what material will best suit our needs.. What should we build with it?

35. Structural Shapes • Rectangle / Square • Triangle • Interested in stability • Truss • Geodesic Dome

36. Shape Stability Exercise • Split into teams of 5 • Build a triangle and square • See which shape is the most stable • Can the unstable shapes be made stable? • How?

37. Rectangle • Advantages • Proficient in resisting vertical load. • Disadvantages • No lateral support

38. Triangle • Advantages • Able to withstand lateral & vertical loading • Many triangular shapes available • Disadvantage • Wide base = $$$$

39. Rectangle • Advantages • Proficient in resisting vertical load. • Disadvantages • No lateral (horizontal) load support Need another bar for lateral support! --BRACING--

40. Truss • Combination of square and triangle

41. Truss • Combination of square and triangle Squares

42. Truss • Combination of square and triangle Triangles

43. Truss • Combination of square and triangle • Both vertical and lateral support

44. Geodesic Dome

45. Domes

46. Domes • Advantages • Very strong shape, gets strong as the dome size increases • Perfect load distribution • No need for structural supports • Great aerodynamic performance

47. Structural Components • Beams • Girders • Columns • Floors • Foundations Column Girder Beam

48. Load Path • Floor • Beams • Girders • Columns • Foundation • Soil/Bedrock

49. Foundations • Support the building • Typically attached to columns • Types • Shallow • Spread footing – concrete strip/pad below the frost line • Slab-on-grade – concrete pad on the surface • Deep • Drilled Shafts • Piles