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CCTV Structural Analysis

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by

ewing leong

on 26 November 2013

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Transcript of CCTV Structural Analysis

Introduction
- China Central Television

Concept & Design Development

Evolution of the Braced Tube System

Suggestion in Increasing Stability

Steel – Wide Flanges

Advantages
Weight & size are optimized to resist bending loads experienced by the members
Has reduced structure weight & flexibility of size
Prefabricated in multi-plane section; allowing for quick erection by crane & reducing labor cost

Disadvantage
Prefabrication took a longer lead time

Materials Used for CCTV Diagrid

Assist in load transfer
Located beneath the overhang, and platform
Connected to the internal core & external columns



Other Structural Elements
– Transfer Trusses

Diagrid Elements – Node Construction

Horizontal member
Typical 1500mm x 500mm that is fused with a structural floor slab
Supports a raised floor system above it
Services a diaphragm floor below it; housing the sprinklers and air return from façade
Supports a suspended luminous ceiling
Supports extruded aluminum closer plate; for glazing & cladding


Structural Elements
– Perimeter Edge Beam

Under vertical loading (Gravity; dead and live loads) – Compression

Diagrid Forces on Node

Sideways horizontal force / Overturning moment, MW causes vertical forces in the apex joint of the diagrid modules
Max intensity in upward direction on windward façade (NW)
Max intensity in downward direction in leeward façade (NW)
Gradual decreasing values in modules along the sides

Structural Action in a Diagrid Module - Lateral Loading

Optimal Angle, Height & Base

Optimal angle is highly dependant on the building’s height
Optimal angle of columns (for max bending rigidity) - 90’
Optimal angle of diagonals (for max shear rigidity) - 35’
Optimal angle of diagonal members of diagrid range - 60’ to 70’
which rises with the building height
Height - 2 to 6 stories stacked per diagrid module with floor height varying from 3.5 to 4.15 m
Base - Depends on the height and optimal angle of the diagrid


Diagrid Module Geometry

Classification of Structure - Diagrid
Principal state-run broadcaster of 13 channels
Planning to expand to 200 channels by 2008
Compete in global market with big players like CNN, NBC, BBC & Sky
Steel – Rectangular Hollow Steel Section (HSS)

Advantage
Prefabricated in multi-plane section; allowing for quick erection by crane & reducing labor cost

Disadvantages
Prefabrication took a longer lead time
Changes in floor layout as beams will need to frame into the node points; reducing floor efficiency & flexibility


Materials Used for CCTV Diagrid

The meeting of vertical columns, diagonal members & perimeter beams at nodes
Butterfly plates will be welded to bring all these 3 members together
Enabling the vertical and horizontal elements to remain comparatively unstressed in an earthquake.


Structural Elements – Butterfly Plates

Structural Elements – Diagrid

Vertical member
Fire protected & top coated
Collects gravity & lateral load from diagonal members and transfer them to the ground
Fused with the floor slab

Structural Elements – Column

Global shear, VW causes horizontal force in the apex joint of the diagrid modules, vW
Intensity depends on the position of the module in respect to the direction of the wind
Absorbed by the modules parallel to the load direction
Structural Action in a Diagrid Module

Downward vertical force, NG
Diagonals in compression
Horizontal chord in tension

Structural Action in a Diagrid Module - Gravity Loading

It’s modeled as a beam, subdivided longitudinally into modules along the diagonal patterns (Fig 1)
Diagonal carry shear and moment
Uses building plan dimension to counteract overturning moment through flexural / elasticity of the axial action in the diagonal members acting as inclined columns
But, cannot fully achieved due to the shear deformation experienced by the building’s network of webs as opposed to the bending moment of the traditional columns / beam structure
Thus, the geometry of a single module plays a major role in the internal axial force distribution & giving shear lag and bending rigidity to the building structure


Diagrid Module Geometry

Design Issues

Instability due to weight (a lot of steel used)
Instability due to form - cantilever overhang, continuous loop & sloping tower

Site Issues

Beijing is earthquake prone
High settlement risk
Shallow subsoil condition
Porosity and underground water in large amount

Problems

Continuous loop like a Möbius strip
Cantilever overhang
CCTV Structural Analysis
March 2003
Sept 2004
2008
Mid-2007
August 2002
OMA + ARUP won the design competition organized by CCTV
Project commence with schematic & conceptual design
Groundbreaking on site
Construction of overhang
Final completion of CCTV
Design Solution
Diagrid System
Uses 20% less steel as opposed traditional braced tube system
Lighter & efficient in load transference
Adjusted Demand Ratio
Structural beams & diagrids are modified to its maximum carrying capacity
Performance-based Analysis
MSC/NASTRAN program to evaluate the stress magnitude and the degree of stress concentration
Piled Raft Foundation
Building sit on top of a piled raft foundations.
Typical piles are 1.2m in diameter and about 52m long.
Raft is up to 7.5m thick in places and extends beyond the footprint of the Towers to act as a toe, distributing forces more favourably into the ground.
Basement
3-storey basement with retaining walls & with the help of the piled raft resist the upward force of the water pressure around the site
Stress modeled on the fastening node
CCTV's Diagrid Structural Elements
floor slab
vertical column
diagrid
orthogonal steel structure
perimeter beam
glazing
cladding
Forces Acting on the Structural Elements
Perimeter steel involves in bending resistance / rigidity
compression
tension
Triangulation also minimizes shear racking effects because internal axial forces are within the members
Diagonalized modules acting as inclined columns & bracing elements carry gravity & lateral load resistance
Triangular modules with diagonal beams diffusion of forces along the façade (hence, the elimination of large vertical columns)
In-place steel shop welding
Lifting up piece by piece
Trial shop assembly of parts with high strength bolts
In-place welding
High strength bolts assembly
Setting up perimeter girders

Under lateral loading (Seismic & Wind) – Shearing
Doorway into China
water pressure
piled raft & retaining walls
dia
gonal
grid
Concealed Diagrid System
1
Diagonal member
Typical 660mm thick member with 30mm thick film intumescent fire protection with top coat
Fronting a prefabricated, insulated structural steel cladding / panel


perimeter beam
vertical members
diaphragm floor
Very stable :)
compression
compression
tension
bending rigidity
shearing
raft
pile
Menara Tabung Haji
John Hancock
Building
St. Mary Axe
Timeline
Full transcript