ce 636 design of multi story structures t b quimby uaa school of engineering
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CE 636 - Design of Multi-Story Structures T. B. Quimby UAA School of Engineering. Gravity Force Resisting Systems. Basic Elements. • Horizontal Systems (Floors & Roofs) – Joists, purlins , girders – One-way slabs – Two-way slabs – Waffle Slabs – Flat plates – Space Trusses

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basic elements
Basic Elements
  • • Horizontal Systems (Floors & Roofs)
  • – Joists, purlins, girders
  • – One-way slabs
  • – Two-way slabs
  • – Waffle Slabs
  • – Flat plates
  • – Space Trusses
  • • Vertical Components
  • – Columns
  • – Load Bearing Walls
  • • Horizontal systems are generally unaffected by lateral loads
  • • Vertical components often are affected by both gravity and lateral loads.
joists girders purlins
Joists, Girders, Purlins
  • The system consists of:
    • a horizontal slab or sheathed surface.
    • a system of beams (i.e. joists, purlins, girders) supporting the bearing surface.
    • columns or walls that support the beam system.
steel deck
Steel Deck
  • Use manufacturers load tables.
  • Used without concrete for roof decks
  • Used with concrete for floor decks.
  • Lots of different profiles and gage thicknesses.
  • Design connection to supports for diaphragm shears
steel joists
Steel Joists
  • Use Manufacturer\'s Span Tables
  • Industry standards have been produced by the Steel Joist Institute.
  • Most manufacturers build their joist to SJI specifications
one way slabs
One-Way Slabs
  • Slab spans between supports on two opposite sides
  • Generally true for slabs with an aspect ratio of 3:1 or more.
  • Analyzed and Designed as a beam without shear reinforcement.
one way slab and beam behavior
One-Way Slab and Beam Behavior
  • Reference #1, pg. 164
two way slabs
Two-Way Slabs
  • Support on all edges.
  • May be “fixed” or “free” at supports.
  • Moments and shears are somewhat less than seen in one-way slabs of comparable span.
  • Precise analysis is somewhat complex.
approximate flat slab behavior
Approximate Flat Slab Behavior
  • Reference #1, pg. 15
may use stiff beams for support
May use Stiff Beams for support
  • Reference #1, pg. 161
waffle slabs
Waffle Slabs
  • A grid consisting on beams running in two directions.
  • Slab spans between joists.
  • Easy to construct with reusable “pans”.
  • Fairly common in areas that use lots of concrete.
concrete waffle slab
Concrete Waffle Slab
  • Reference #1, pg. 192
waffle slab behavior
Waffle Slab Behavior
  • Reference #1, pg. 168
flat plates
Flat Plates
  • Slabs supported by columns only.
  • Slab is divided into strips.
  • Each strip is designed as a beam to carry a portion of the load.
  • Punching shear at columns is often a critical problem.
  • The problem becomes very complex if the columns are not laid out on a rectangular grid.
punching shear resistance
Punching Shear Resistance
  • Reference #1, pg. 169
space trusses
Space Trusses
  • Generally steel, sometimes wood or concrete.
  • Used mostly for exposed for roof structures.
  • Can be used to achieve many different shapes.
  • Often used for long span roof structures.
roof for a high school gym
Roof for a High School Gym
  • Reference #2, pg. 54
alternative truss layouts
Alternative Truss Layouts
  • Reference #1, pg. 198
references
References
  • Lin, T.Y., and Stotesbury, S.D., Structural Concepts and Systems for Architects and Engineers, 2nd edition, Van Nostrand Reinhold, 1988.
  • Ambrose, J., Building Structures, Wiley Interscience, 1988.
  • Council on Tall Buildings & Urban Habitat, Advances in Tall Buildings, Van Nostrand Reinhold, 1986.
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