CE 636 - Design of Multi-Story Structures
T. B. Quimby
UAA School of Engineering
• 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.
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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.
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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
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Use Manufacturer's Span Tables
Industry standards have been produced by
the Steel Joist Institute.
Most manufacturers build their joist to SJI
specifications
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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.
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Reference #1, pg. 164
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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.
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Reference #1, pg. 15
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Reference #1, pg. 161
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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.
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Reference #1, pg. 192
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Reference #1, pg. 168
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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.
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Reference #1, pg. 163
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Reference #1, pg. 169
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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.
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Reference #2, pg. 54
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Reference #1, pg. 198
1.
2.
3.
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.