Transcript Introduction to Lateral Force Resisting Systems

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
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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.