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SKYSCRAPER LOADS

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LATERAL SEISMIC LOADING. MULTISTORY BUILDING. Sum of story forces = base shear V ... SEISMIC LOADING IS COMPLEX. Inertial effects. Damping effects. Inelastic ... – PowerPoint PPT presentation

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Title: SKYSCRAPER LOADS


1
SKYSCRAPER LOADS
  • Reference Minimum Design Loads for Buildings and
    Other Structures ASCE 7-05

2
GRAVITY DEAD LOADS
  • Reinforced Concrete 150 pcf
  • Lightweight Concrete 110 pcf
  • Structural Steel 490 pcf
  • Timber 32 pcf
  • Glass 160 pcf
  • Rain 62.4 pcf
  • Snow 10 pcf

3
GRAVITY LIVE LOADS
  • Offices 50 psf
  • Hotel/Residential 40 psf
  • Lobbies 100 psf
  • Libraries 150 psf
  • Schools 40 psf
  • Stadiums 100 psf

4
LATERAL WIND LOAD
  • Bernoulli's Equation
  • state 1 wind before it hits building, p 0
  • state 2 air after it hits building, v 0
  • Both states have same elevation y

5
AIR AT 60 DEGREES (F)
  • p pressure in psf
  • v velocity in mph

6
ASCE 7-05 FORMULA
  • h height
  • Exposure
  • closely spaced obstructions 7.0 1200ft
  • scattered obstructions 9.5 900ft
  • open terrain, unobstructed 11.5 700ft

7
DESIGN WIND SPEED
  • Salt Lake City, Chicago 90mph
  • New York 100mph
  • Miami, Hong Kong 150 mph

8
WIND LOADING IS COMPLEX
  • Pressure on windward side
  • Suction on leeward side
  • Drag and Lift
  • Vortex Shedding -- vibration
  • Acceleration due to sudden gusts
  • Wind tunnel tests are performed for most
    skyscrapers

9
LATERAL SEISMIC LOADING
10
MULTISTORY BUILDING
  • Sum of story forces base shear V

11
ASCE 7-05 STORY FORCES
  • weight of ith story (no live load)
  • height of ith story from the ground
  • If , k 1 (T building period)
  • If , k 2 (T of stories/15)
  • Otherwise, k 0.75T/2

12
ASCE 7-05 BASE SHEAR
  • M total mass of building
  • W total weight of building Mg

13
DUCTILITY FACTOR R
  • R 8 for special eccentrically braced frame
  • R 1.5 for ordinary concrete building
  • All other buildings somewhere in between
  • It is assumed that the maximum inelastic
    displacement equals maximum elastic displacement

14
SPECTRAL ACCELERATION Sa
15
PEAK DESIGN ACCELERATION
  • Flat part of design spectrum
  • High seismicity (California, Beijing) 1.4g
  • Medium Seismicity (Utah) 0.9g
  • Low seismicity 0.5g
  • Also depends on soil conditions at site

16
SEISMIC LOADING IS COMPLEX
  • Inertial effects
  • Damping effects
  • Inelastic effects
  • Site effects
  • Higher modes
  • Uncertainty
  • Most skyscrapers analyzed under multiple records
  • Some are modeled on a shake table
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