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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.
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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
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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
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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
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lateral forces cause what in shear walls?
both shear and bending stresses
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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
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rigid frame
joints are rigid and capable of transferring bending moment between members
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workability of concrete tests?
- 1) slump
- 2) Kelly ball test
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Do concrete systems have greater seismic loads than comparable steel systems?
true
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in seismic design - ductility of structure is its ability to
absorb earthquake energy
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what does a camber is a glue-lam achieve?
- -avoid appearance of sag
- -eliminate ponding of water
- -compensate for deflection
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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
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tilt-up walls
often function as a deep beam spanning between footing pads
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Hooke's law
up to elastic limit, unit stress is in direct proportion to unit strain
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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
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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
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order of increasing stiffness:
- 1) shear (deflect the least)
- 2) braced frame
- 3) moment - resisting fr (deflect the most)
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specs for compacted fill include
- -required density
- -moisture content
- -lift thickness
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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
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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
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stress
internal resistance to an external force
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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
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compared to a moment-resisting frame, a shear wall is...
...stiffer
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early Christian basilican churches
timber trussed roof
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true of false: a rigid frame is more rigid than a braced frame of comparable dimensions
false
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why is composite construction economical?
because of the savings in beam weight
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1994 Northridge earthquake
many moment-resisting frames had connection failures
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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
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designed based on rxx or ryg?
either, whichever results in lower value
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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
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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
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typical rule of thumb for rebar
# bars/8= inch diameter
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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
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stirrups
in reinforced concrete provide web reinforcement where the concrete is overstressed in shear
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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
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wind forces
are real exterior surface applied forces
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seismic forces
- -are simulated forces resulting from a buildings inertia
- -seismic design forces are based on inelastic behavior of the structure
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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
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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
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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
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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
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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
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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
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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
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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"
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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
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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
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factor of safety
ratio of the ultimate strength of a material to its working stress (also called allowable stress)
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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
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if a member is inadequate in shear, increasing...
... the area (either width or depth) is effective
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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
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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
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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
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moment
tendency of a force to cause rotation about a given point or axis
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yield point
unit stress at which a material deforms with no increase in load
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point of inflection
point in a beam or other flexural member where the bending moment changes sign and has a value of zero
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moment of inertia
sum of the products obtained by multiplying each unit of area by the square of its distance to the neutral axis
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hardwoods
- broad leaves
- deciduous (shedding their leaves)
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softwoods
- scalelike or needlelike
- conifers (evergreen)
- *most structrual woods
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