Tall Buildings: Shear Wall & Core Systems

• Study notes on Shear Wall, Core, Outrigger, Belt Truss, and Buttress Core Systems for Tall Buildings

Introduction to Structural Designs for Tall Buildings

• Tall buildings need a sophisticated design process for safety, stability, and efficiency
• Engineers address challenges like wind loads and seismic forces
• They must also use advanced technologies, computer modeling, and performance-based design
• Lateral load-resisting systems like shear walls, core systems, outriggers, and belt trusses enhance structural stability
• These systems minimize displacement under dynamic loads
• Modern structural solutions, case studies, and material advancements help engineers tackle high-rise construction challenges

Understanding Shear Wall Core Systems

• Shear walls enhance the structural stability of tall buildings against lateral loads
• This ensures safety during seismic activity and adverse weather
• Core systems house elevators and stairwells
• They provide critical safety pathways and structural integrity during emergencies
• The use of concrete for shear walls and cores reduces construction costs
• This is especially true in regions where steel is less accessible or economically viable

Shear Wall Characteristics and Functions

• Shear walls provide lateral stability by resisting forces from wind and seismic activities
• Walls ensure the structural integrity of tall buildings during adverse conditions
• Strategically placed shear walls improve seismic protection
• They effectively dissipate energy and prevent structural failure during earthquakes
• This is crucial for tall buildings in seismic zones

Types of Core Systems

• Reinforced concrete cores provide greater stiffness, cost efficiency, and fire resistance
• Concrete cores are a common choice for high-rise buildings
• Constructing them typically precedes steel framing
• This allows for efficient sequencing and use of climbing cranes(Fu, 2018).
• Modern steel-framed cores improve structural efficiency and seismic performance
• Innovations like Speed Core reduce construction time
• Diagrid systems enhance stability and aesthetic appeal in tall buildings(Dowell & Adcock, 2022; Silva et al., 2022; Patel & Shah, 2024)

Introduction to Outrigger, Belt Truss and Buttress Core Systems

• The core stabilizes tall buildings, but relying solely on it for lateral resistance becomes inefficient as height increases.
• Outriggers, belt trusses, and buttress walls connect the core to exterior columns.
• This improves structural efficiency by about 30%(Fu, 2018)
• Outriggers reduce drift by distributing lateral loads.
• Belt trusses enhance resistance to overturning.
• Buttress walls stabilize the core(Kamble, 2024; Mayur et al., 2024).
• These systems are used in skyscrapers like the Shanghai Tower and Burj Khalifa.
• They are essential for high-rise structural integrity.

Types of Outriggers

• Steel outriggers improve lateral stability in tall buildings
• Innovations like SP-RCF provide superior strength, stiffness, and ductility (Habrah et al., 2024)
• Concrete outriggers offer high stiffness and cost efficiency
• They are effective in resisting wind loads through deep beams or concrete walls (Fu, 2018)
• Hybrid outriggers combine steel and concrete
• They enhance structural performance by using a composite system that balances stiffness and ductility (Fu, 2018)
• Damped outriggers reduce angular displacements
• They convert motion into linear motion, dissipating energy to minimize vibrations (Salazar, 2023; Liu et al., 2022)

Pros and Cons of Outriggers

• Outriggers effectively reduce building sway and lateral displacement
• Overall structural performance is improved during wind and seismic events
• By connecting the core to exterior columns, outriggers distribute loads efficiently
• They reduce material requirements and optimize design
• Installing outriggers requires precise engineering and coordination
• This can complicate construction sequencing and increase costs
• Outriggers occupy valuable interior space
• They potentially limit usable floor area
• Outriggers also affect architectural design flexibility

Shard’s Structural Innovation

• The Shard's lateral stability relies on a central concrete core
• It was built using slip-form techniques, ensuring strength and efficiency
• A combined piled raft foundation was used
• This optimizes load distribution and stability, along with plunge columns for efficient top-down construction
• The Project Team consisted of:
  • Renzo Piano Building Workshop (Designer)
  • WSP (Engineer)
  • MACE (construction)
  • Sellar Property (Client).

Introduction to Belt Truss and Ring Truss Systems

• Belt truss and ring truss systems are essential structural components
• Used to enhance stability and load distribution for buildings
• Belt trusses are commonly found in skyscrapers
• They improve lateral stability by connecting the core to perimeter columns
• Ring trusses provide circumferential strength
• They are ideal for domes, stadiums, and cooling towers
• Both systems play a crucial role in modern structural engineering
• They ensure safety and efficiency in various architectural designs

Understanding Belt Truss Concept

• Belt trusses streamline construction by reducing connection complexities between the outrigger and core structures
• They maximize use of interior space by minimizing structural impediments associated with conventional outriggers
• Belt trusses enhance overall building strength by effectively distributing lateral loads and reducing excessive sway

Ring Truss System Overview

• Ring trusses improve structural performance in high-rise buildings without adding unnecessary weight
• They distribute loads effectively and enhance stability
• Ring trusses reduce stress concentrations
• Ring trusses maximize interior usable space by minimizing structural elements in the layout
• Ring trusses streamline construction processes
• They ensure quicker project completion and reduced downtime

Comparison of Truss Systems:

• Belt Truss System:
  • Shape: Rectangular, surrounds a building
  • Function: Enhances lateral stability in high-rise buildings
  • Applications: Skyscrapers and tall buildings (with outriggers)
  • Load Distribution: Transfers loads between core and perimeter columns
• Ring Truss System:
  • Shape: Circular, supports a dome or cylinder
  • Function: Provides circumferential strength and load distribution
  • Applications: Domes, stadiums, cooling towers
  • Load Distribution: Distributes loads evenly in a circular form

Belt Trusses vs Conventional Outriggers

• Belt trusses simplify design
• They eliminate connection difficulties between outrigger and core structures
• Making the construction process more efficient and reducing structural complexities
• Belt trusses maximize free interior space
• They minimize obstructions caused by conventional outrigger systems
• This allows for more flexible floor layouts.
• Belt trusses contribute to structual stability
• They remove the need to consider differential shortening between the core and outer columns
• Provides a more uniform and stable structural performance

Buttressed Core System

• A buttressed core system is an evolution of the buttress structure
• Features used in ancient structures like churches and bridges
• The buttressed core structural stability system is based on the buttress structural system concept
• Skidmore, Owings & Merill LLP (SOM) first developed it for the Burj Khalifa project

Structural System of a Tower

• A 3D model was built in ETABS to demonstrate the structural system.
• The primary structural material is concrete.
• Concrete strength varies:
  • 85 MPa from the base to level 95
  • 75 MPa up to the spire
  • 65 MPa in the spire
• Reinforcing bars have a yield strength of 420 and 520 MPa
• Diameters of up to 40 mm
• There are three groups of walls:
  • End walls
  • Corridor walls
  • Fin walls
• The central core plays an essential role
• Wall thicknesses are:
  • 1200 mm at the base
  • 600 mm in the spire
• Coupling beams' depth are at 1500 or 1600 mm