Seismic isolators are crucial components in earthquake-resistant structures. They come in various types, each with unique properties and performance characteristics. Understanding these differences is key to selecting the right isolator for a specific building and site.

Choosing the ideal seismic isolator involves considering structural factors, site conditions, and performance objectives. The selection process requires careful analysis and optimization to ensure the best protection against seismic forces while meeting practical constraints and budget limitations.

Types of Seismic Isolators

Types of seismic isolators

• Elastomeric bearings absorb seismic energy through material deformation
  • Natural rubber bearings (NRB) provide flexibility and moderate damping
  • High-damping rubber bearings (HDRB) offer enhanced energy dissipation
• Lead-rubber bearings (LRB) combine elastomeric layers with lead core for increased damping
• Friction pendulum systems (FPS) utilize sliding motion and gravity for isolation
  • Single friction pendulum (SFP) uses one concave surface
  • Double friction pendulum (DFP) employs two surfaces for improved performance
  • Triple friction pendulum (TFP) incorporates three surfaces for adaptive behavior
• Other types provide alternative isolation mechanisms
  • Ball and roller bearings use rolling elements to reduce friction
  • Spring-damper systems combine mechanical springs with viscous dampers

Properties of seismic isolators

• Elastomeric bearings exhibit distinct mechanical characteristics
  • Vertical stiffness supports gravity loads
  • Horizontal flexibility allows lateral displacement
  • Energy dissipation occurs through material damping (hysteresis)
• Lead-rubber bearings display unique force-displacement relationship
  • Bilinear behavior with initial stiffness and post-yield stiffness
  • Energy dissipation achieved through lead core yielding
• Friction pendulum systems rely on sliding interface properties
  • Friction coefficient determines initial resistance
  • Effective stiffness depends on radius of curvature
  • Re-centering capability ensures return to original position
• Mechanical properties characterize isolator behavior
  • Equivalent stiffness represents overall lateral resistance
  • Equivalent damping ratio quantifies energy dissipation
  • Characteristic strength defines yield point
  • Post-elastic stiffness ratio indicates stiffness change after yielding

Seismic isolator performance comparison

• Horizontal displacement capacity varies among isolator types
  • Elastomeric bearings allow moderate movement
  • Lead-rubber bearings accommodate moderate to high displacements
  • Friction pendulum systems permit high lateral displacements
• Energy dissipation capabilities differ
  • Elastomeric bearings provide low to moderate damping
  • Lead-rubber bearings offer high energy dissipation
  • Friction pendulum systems achieve high damping through friction
• Vertical load capacity ranges across isolator types
  • Elastomeric bearings support moderate loads
  • Lead-rubber bearings carry high vertical loads
  • Friction pendulum systems handle very high vertical forces
• Durability and aging effects impact long-term performance
  • Elastomeric bearings may degrade due to environmental factors
  • Lead-rubber bearings show moderate resistance to aging
  • Friction pendulum systems demonstrate high durability with minimal aging
• Cost considerations influence selection
  • Elastomeric bearings generally have lower initial costs
  • Lead-rubber bearings present moderate cost options
  • Friction pendulum systems often incur higher costs, especially for larger sizes

Selection of seismic isolators

• Structural factors guide isolator choice
  • Building weight and mass distribution determine required capacity
  • Desired isolation period influences isolator stiffness
  • Allowable lateral displacement limits isolator size and type
• Site conditions affect isolator performance
  • Seismic hazard level dictates required isolation effectiveness
  • Soil characteristics impact foundation-isolator interaction
  • Environmental factors (temperature, humidity) influence material behavior
• Performance objectives shape design criteria
  • Target reduction in seismic forces sets isolator efficiency goals
  • Acceptable level of structural and non-structural damage defines limits
• Practical considerations influence final selection
  • Available space for isolator installation constrains size and type
  • Maintenance requirements affect long-term costs and feasibility
  • Budget constraints limit options and materials
• Design process ensures optimal isolator selection
  1. Conduct preliminary sizing and selection based on initial criteria
  2. Perform iterative analysis and optimization to refine choices
  3. Finalize design and create detailed specifications for chosen isolators