SKYSCRAPER STRUCTURAL SYSTEMS

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SKYSCRAPERSTRUCTURAL SYSTEMS

• 1) Gravity Load System
• 2) Lateral Load System

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GRAVITY LOAD SYSTEM

• 1) Residential / Hotels
• 2) Office Buildings
• Flooring system
• Column/wall system
• Load path to the foundation

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RESIDENTIAL / HOTELS

• Small room size ? close bearing walls
• Flat slab floors lt 10in thick
• Small span lengths lt 30ft
• One-way or two-way slabs
• Small story heights lt 12ft
• No utility space between floors
• No ceiling lights in hotel rooms
• Periodic mechanical levels

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OFFICE BUILDINGS

• Large open room size
• Non-structural / temporary partitions
• Waffle slabs
• One-way slabs on beams
• Floor trusses
• Utilities between floors
• Greater story heights

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LATERAL LOAD SYSTEM

• Skyscraper is a vertical cantilever beam
• Low-rise buildings resist lateral load with shear
  stiffnessSkyscrapers resist lateral load with
  flexural stiffness
• Most buildings have a walled core(s) containing
  elevator and utility shafts

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LOW-RISE BUILDINGS

• Frame stiffness is strong in long direction
• End shear walls and braces provide stiffness in
  short direction
• Window openings in long side rather than in end
  shear walls

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EMPIRE STATE BUILDING 1931

• Braced and moment resisting frame
• Many columns and braces obstruct space

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WORLD TRADE CENTER 1973

• Framed tube
• Maximum moment of inertia
• Long-span steel floor trusses between core and
  external tube (60ft)
• Columns obstruct window space

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SHEAR LAG PROBLEM

• Plane sections do not remain plane
• Axial force in columns does not vary linearly
• Caused by vertical shearing in girders

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JOHN HANCOCK BUILDING 1969

• Braced tube to overcome shear lag

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SEARS TOWER 1974

• Bundled tube to overcome shear lag

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MODERN SKYSCRAPERS

• Mega-columns up to 18 ft wide
• Belt, cap, and outrigger trusses

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IFC2 HONG KONG 2003
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SHANGHAI WFC 2008
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