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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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Ce 636 design of multi story structures t b quimby uaa school of engineering

CE 636 - Design of Multi-Story Structures

T. B. Quimby

UAA School of Engineering

Gravity Force Resisting Systems


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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