SS 1

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SS 1
2013-07-22 16:02:01
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Structures Exam
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  1. Which of the following buildings employ bundled structural tubular framing system?
    I) World Trade Center, NY
    II)Pompidou Center, Paris
    III) Sears Tower, Chicago
    IV) John Hancock Bldg, Chicago
    V) Transamerica Pyramid, San Fran
    A) I and III
    B) I, II, III, IV
    C) I, III, IV
    D) I, II, III, IV, and V
    • A) I and III - World Trade Center and Sears Tower
    • Perimeter walls from a huge hollow tube cantilevering out of the ground to resist wind and seismic forces. Other examples are moment resisting frames.
  2. Which of the following buildings resists wind loads by acting as a huge trussed tube?
    A) Lake Point Tower in Chicago
    B) Kresge Auditorium at MIT
    C) John Hancock Bldg in Chicago
    D) Federal Reserve Bank in Minneapolis
    • C) John Hancock - has tubular construction with enormous exposed x-braces that truss the building
    • -designed by SOM
  3. Which of the following building best expressed the structure concept of the "bundled tube"?
    A) Sears Tower
    B) John Hancock Bldg
    C) CBS Bldg
    D) Knights of Columbus Bldg
    • A) Sears Tower consists of a "bundle" of 9 tubes that terminate at varying heights
    • designed by SOM
  4. True or False: Since truss joints are pure pins or hinges, there are no stresses caused by joint restraint
    • flanges/chords: increase towards center
    • webs: decrease towards center
  5. lateral forces cause what in shear walls?
    both shear and bending stresses
  6. spiral column supports
    • -spiral column supports more axial load than otherwise identical tied
    • -reinforcing in a spiral column is always circular pattern
    • -spiral column can support more load
  7. rigid frame
    joints are rigid and capable of transferring bending moment between members
  8. workability of concrete tests?
    • 1) slump
    • 2) Kelly ball test
  9. Do concrete systems have greater seismic loads than comparable steel systems?
  10. in seismic design - ductility of structure is its ability to
    absorb earthquake energy
  11. what does a camber is a glue-lam achieve?
    • -avoid appearance of sag
    • -eliminate ponding of water
    • -compensate for deflection
  12. for wind and seismic design, components of a building and connects are required to be...
    .. required to be designed for forces which are visually greater than those used in the design of the buildings lateral forces resisting system
  13. tilt-up walls
    often function as a deep beam spanning between footing pads
  14. Hooke's law
    up to elastic limit, unit stress is in direct proportion to unit strain
  15. hyperbolic paraboloid
    • -can be formed by a series of straight lines
    • -very stiff structure
    • -economical in use of material
    • -curved downward in one direction and up in other
  16. concrete floor framing systems
    • -pan jast floor system, shear stress near the support is often a controlling factor
    • -reinforced concrete slab 10ft x 25ft in plan is usually assumed to span 10ft direction only
    • -concrete floor framing system requiring simplest formwork is flat plate floor
    • -slab band construction requires more beam reinforcement than a conventional beam used for the same span and loading conditions
  17. order of increasing stiffness:
    • 1) shear (deflect the least)
    • 2) braced frame
    • 3) moment - resisting fr (deflect the most)
  18. specs for compacted fill include
    • -required density
    • -moisture content
    • -lift thickness
  19. Beam
    • -difference of bending moments between 2 sections of a beam is equal to the area of the shear diagram between 2 sections
    • -max. unit shear stress in a beam occurs at the neutral axis
  20. truss
    • -may have various configurations as long as it is comprised of triangles
    • -can support only load between panel points
    • -can resist any horizontal load
  21. stress
    internal resistance to an external force
  22. punching shear
    • -tendency of a column to punch through its supporting footing
    • -two-way shear
    • -investigated at a distance d/2 from face of column
  23. compared to a moment-resisting frame, a shear wall is...
  24. early Christian basilican churches
    timber trussed roof
  25. true of false: a rigid frame is more rigid than a braced frame of comparable dimensions
  26. why is composite construction economical?
    because of the savings in beam weight
  27. 1994 Northridge earthquake
    many moment-resisting frames had connection failures
  28. what is the wind relationship between wind velocity in mph and wind pressure in psf?
    wind pressure varies as the square of the wind velocity
  29. designed based on rxx or ryg?
    either, whichever results in lower value
  30. cost related to structure
    • -additional cost to provide seismic resistance for a building to conform to the IBC regulations for SDC D would vary between 5 to 25% with an average of 15% (because structural cost is about 25% of total construction cost, the addition seismic resistance would be roughly 15% of 25% which amounts to 3.75 of total cost
    • -providing seismic resistance may add 5 to 20% of the structural cost, which is 25% of total cost, therefore 1.25 to 5% of total construction cost
  31. staggered truss
    • -usually economical for spans greater than 45ft and hotel and residential occupancies
    • -story high trussed span the full width of the building are arranged in a staggered pattern: trusses in the odd-numbered column lines are erected in a given story, while those in even-numbered column lines are in the stories above and below
    • -floor system is supported alternately by the top chord of the next
    • -efficient framing system for the tall narrow buildings typically used for hotel and residential
    • -generally NOT economical for buildings of less than 8-10 stories
  32. typical rule of thumb for rebar
    # bars/8= inch diameter
  33. Ritcher scale magnitude
    each # is 10x ground motion or movement or 33x energy of lower #

    • ex. 4.0 to an 8.0
    • 4/5/6/7/8
    • 33x33x33x33
    • about 1,000,000 times more energy
  34. stirrups
    in reinforced concrete provide web reinforcement where the concrete is overstressed in shear
  35. stub girder system
    • -steel floor beams sit on top of a stub girder, instead of framing into a girder
    • -because the beams are clear of the girder, they may be designed for simulate continuity
    • -the space between floor beams can be used for the mechanical and electrical distribution systems
    • -short lengths of filler beams are welded to the top of the stub girder to provide a connection between the girder and the slab for composite action
    • -main advantages: reduced weight of steel, reduced story height, simplified steel erection
  36. wind forces
    are real exterior surface applied forces
  37. seismic forces
    • -are simulated forces resulting from a buildings inertia
    • -seismic design forces are based on inelastic behavior of the structure
  38. flat slab
    • -drop panels and column capitals used in flat slab are used to reduce shear stress in the slab near the columns and to provide greater effective depth for negative bending moment
    • -two-way concrete slab, without the use of beams and girders
    • -in this system, a portion of the slab at the columns is thickened, which is termed a drop panel
    • -tops of columns are flared and known as column capitals
    • -drop panels and column capitals are used to reduce shear stress in the slab near the columns and provide greater effective depth for negative bending
  39. shell structures
    • -a shell or thin shell is a structure with a curved surface that resists load by compression, shear, or tension in its own plane
    • -too thin to resist any appreciable bending stresses
    • -shells are strong in resisting uniform loads but cannot resist any substantial concentrated loads, which tend to induce bending
  40. cable roof structures
    • -a cable is always under tension
    • -high strength cable is about four times as strong as structural steel
    • -the dynamic behavior of cable-supported roofs is more critical than that of conventionally framed roofs
    • -the largest part of the structural framing cost is in the fittings, connections, and anchorage members
    • -drapped cable will assume the shape of a parabola
  41. height-to-width ratio
    short, squat building=low height-to-width, less likely to overturn than a tall building

    tall, slender building=high height-to-width ratio
  42. strength design method for reinforced concrete
    • -margin of safety for reinforced concrete is provided by the load factor and strength reduction factor
    • -load factor is 1.4 for dead load and 1.7 for live load, is based on the possibility that sometime during the life of the structure, the service loads may be exceeded
    • -the strength reduction factor allows for variation in material strengths and actual construction dimensions, as well as in accuracies and approximation in design calculations
    • -depending on the type of stress, varies from 0.65 to 0.90
  43. base plate under steel column
    • -the base plate under steel columns spreads the column load over a large area of the supporting foundation
    • -the base plate must be thick enough to resist the resulting bending
    • -anchor bolts transfer horizontal shear to the footing by the shear in the bolts
  44. tied columns
    • -usually square or rectangular
    • -longitudinal bars with separate lateral ties
    • -same as spiral: longitudal bars carry compressive load - ties hold bars in position and prevent buckling out
    • -usually an even number of bars is used with code requirement at least four for bars with reaction ties
    • -longitudal bars may be bundles in 2,3, or 4 bars each, must be tied or wired together
    • -SPC C and higher: hoops are required and spacing is more stringent
  45. spiral columns
    • -square or round
    • -longitual bars help carry the compressive load
    • -spiral braces the longitudal bars against buckling and confines the concrete
    • -held firmly in place and true to line by vertical spacers
    • -min. size of spiral reinforcement is 3/8" clear spacing between spirals must be at least 1" and not more than 3"
  46. a building with a long period is associated with...
    • ... flexibility, low acceleration, low seismic force
    • -every building has a natural or fundamental period of vibration, which varies inversely with its stiffness
    • -the acceleration of a building during an earthquake and the resulting seismic force depend on the building's stiffness: the stiffer the building, the greater the acceleration and seismic force
    • -overturning moment is not directly related to a building's period
  47. composite design
    • -a concrete slab is connected to a steel beam with shear connectors that can develop the ultimate capacity of the concrete or the steel, whichever is less
    • -because the concrete and steel act together than in conventional steel framing, which generally results in a more economical system, however when a small steel beam is used, deflections tend to become greater, and thus more critical in composite design than in conventional steel framing
    • -conventional steel framing can always be designed to carry the required loads
  48. factor of safety
    ratio of the ultimate strength of a material to its working stress (also called allowable stress)
  49. trusses
    • -number of members to be joined, as well as the complexity of the joints, usually make truss fabrication expensive, but this is often  offset by the economy of the material
    • -truss members are usually subject to axial stress only, unless they support loads between panel points
    • -stress in chord members depends on depth, but stress in web members is a function of their slope
  50. if a member is inadequate in shear, increasing...
    ... the area (either width or depth) is effective
  51. if a member is adequate in deflection, increasing...
    ...the moment of inertia (width) is ok, but depth (d) is cubed and is much more effective reducing deflection
  52. if a member is inadequate in bending, increasing...
    ...the section modulus (width b) is okay, but depth (d) is square and is much more effective in reducing bending
  53. point of inflection (P.O.I)
    • -point on the moment diagram where M=0
    • -only happens when a beam has an overhang
    • -point in a beam or other flexural member where the bending moment changes sign and has a value of zero
  54. moment
    tendency of a force to cause rotation about a given point or axis
  55. yield point
    unit stress at which a material deforms with no increase in load
  56. point of inflection
    point in a beam or other flexural member where the bending moment changes sign and has a value of zero
  57. moment of inertia
    sum of the products obtained by multiplying each unit of area by the square of its distance to the neutral axis
  58. flexure
  59. hardwoods
    • broad leaves
    • deciduous (shedding their leaves)
  60. softwoods
    • scalelike or needlelike
    • conifers (evergreen)
    • *most structrual woods