Comprehensive Introduction To Recommendation For The Design Of Base Isolated Buildings

Recommendation for the Design of Base Isolated Buildings (Chinese title: 隔震结构设计), compiled by the Architectural Institute of Japan (AIJ) and translated by Liu Wenguang with proofreading by Feng Demin, was first published by Earthquake Press in December 2005. As a landmark work in seismic isolation engineering, this book systematically presents the design principles, technical details, practical cases, and supporting data of base-isolated buildings, serving as a core reference for structural engineers, researchers, and students globally-especially those in earthquake-prone regions like Japan, the U.S., and Europe.

The book is structured into four parts, each with clear functional positioning:

1. Part 1: Design of Base Isolated Structures: Focuses on fundamental concepts, including the characteristics of isolated structures, overview of isolation devices, design general principles, input ground motion, and structural design. It lays the theoretical foundation for practical design.
2. Part 2: Explanatory Volume: Deepens the understanding of key technologies, such as the effectiveness of isolated structures, design of isolation bearings (e.g., laminated rubber bearings), damper performance evaluation, and ground motion prediction.
3. Part 3: Design Examples: Provides 7 practical cases (e.g., high-rise office buildings, hospitals, data centers) to demonstrate how to apply theoretical methods to real-world scenarios, including solutions for soft soil foundations and seismic retrofitting of existing buildings.
4. Part 4: Design Data Volume: Offers detailed technical parameters for isolation bearings, dampers, and ground motion, including material properties, stiffness calculations, and performance test methods-essential for precise design.

The book emphasizes that the performance of base-isolated buildings depends primarily on isolation devices and energy dissipation components. Below is a detailed introduction to core products, their working mechanisms, and design criteria.

2.1 Isolation Bearings

Isolation bearings are the core of the isolation layer, responsible for supporting vertical loads and decoupling horizontal seismic motion. The book focuses on three main types:

2.1.1 Laminated Rubber Bearings

Composed of alternating layers of rubber and steel plates, they feature high vertical stiffness and low horizontal stiffness-enabling them to isolate horizontal seismic motion while stably supporting the building's weight. They are classified into three subtypes based on functionality:

1. Natural Rubber Bearings (NRB): Use natural rubber with excellent elasticity and low damping. They require matching with independent dampers to absorb seismic energy.
2. High-Damping Rubber Bearings (HDRB): Blend natural/synthetic rubber with damping-enhancing additives (e.g., carbon black). They integrate spring and damping functions, eliminating the need for additional dampers. However, their stiffness and damping are sensitive to temperature and strain (e.g., equivalent damping ratio decreases with increasing temperature).
3. Lead-Core Rubber Bearings (LRB): Insert a lead core into the center of NRBs. The lead core yields plastically under seismic motion to absorb energy, forming a stable bilinear hysteretic curve. Key specifications: Yield force and post-yield stiffness; lead core diameter is usually 10–20% of the bearing diameter.

2.1.2 Sliding Bearings

Rely on sliding between materials (e.g., PTFE and stainless steel) to isolate seismic motion, using friction to dissipate energy. They are divided into:

1. Rigid Sliding Bearings: Lack elastic recovery force; mainly used for low-load components (e.g., staircases). They require matching with elastic elements (e.g., NRBs) to restore position after an earthquake.
2. Elastic Sliding Bearings: Combine a sliding layer with a laminated rubber bearing. The rubber layer provides small-deformation elasticity, while the sliding layer isolates large seismic motion. Friction coefficient is critical-typically 0.02–0.12 for PTFE-stainless steel combinations.

2.2 Dampers

Dampers supplement isolation bearings by absorbing seismic energy and limiting isolation layer displacement. The book categorizes them based on energy dissipation mechanisms:

2.2.1 Hysteretic Dampers

Dissipate energy through plastic deformation of metals or friction:

1. Steel Bar Dampers: Use mild steel's plastic deformation; hysteretic curves are spindle-shaped. They have high durability but require large deformation to exert effects.
2. Lead Dampers: Rely on lead's plastic flow; stable hysteretic characteristics and low sensitivity to temperature. Yield force is adjustable by changing lead diameter.
3. Friction Dampers: Use friction between contact surfaces (e.g., spring-loaded steel plates). Hysteretic curves are rectangular, suitable for small-to-moderate earthquakes.

2.2.2 Viscous Dampers

Dissipate energy through viscous resistance of fluids or viscoelastic materials:

1. Oil Dampers: Use fluid flow resistance in a piston-cylinder structure. Damping force is proportional to velocity. They are effective for long-period seismic motion.
2. Viscoelastic Dampers: Use shear deformation of viscoelastic materials (e.g., rubber blends). They work under small deformations, making them suitable for wind vibration control and small earthquakes.

The book's design methods are rooted in Japanese standards, but for global application, it is critical to compare them with U.S. and European codes. Below is a comparison of core provisions (a detailed Excel table is provided separately, listing clause-by-clause differences).

3.1 Fundamental Design Philosophies

3.2 Design Ground Motion

1, Japan:

Uses "energy spectrum" (velocity equivalent value ) to characterize ground motion, considering long-period components (critical for isolation structures with periods of 3–5s).

Requires considering bidirectional ground motion input; total energy is the sum of NS and EW components.

2, U.S.:

Adopts "design response spectrum" (ASCE 7) with 5% damping; adjusts for site class (A–F) and seismic hazard level (S_DS, S_D1).

For isolation structures, mandates at least 3 ground motion records (2 historical, 1 synthetic) for time-history analysis.

3, Europe:

Defines "elastic design spectrum" and "inelastic design spectrum"; site classification is based on average shear wave velocity.

Considers seismic hazard zones (Z1–Z3) and building importance classes (I–IV); adjusts ground motion parameters accordingly.

3.3 Isolation Device Performance Requirements

1, Laminated Rubber Bearings:

Japan (AIJ): Requires S_1 > 30 , S_2 > 5 ; maximum long-term compressive stress ≤15 N/mm²; shear strain ≤250% under rare earthquakes.

U.S. (FEMA 356): Mandates cyclic load tests for prototypes; horizontal stiffness deviation ≤±15%; durability test for 50 years of service.

Europe (Eurocode 8): Specifies S_1, S_2 ; compressive stress ≤20 N/mm²; shear strain ≤200% for HDRB.

2, Dampers:

Japan: Requires damping energy absorption capacity ≥1.5 times the design seismic input energy.

U.S.: For hysteretic dampers, mandates fatigue tests (≥200 cycles at design displacement).

Europe: Requires dynamic tests to verify damping ratio and force-displacement characteristics at different velocities.

3.4 Structural Analysis Methods

1, Japan:

Promotes "envelope analysis" (simplified method based on energy conservation) for preliminary design; uses time-history analysis for verification.

For torsion, assumes upper structure as a rigid body to simplify calculation.

2, U.S.:

Requires time-history analysis for all isolation structures; models isolation devices with bilinear or trilinear hysteretic curves.

For high-rise isolation buildings, mandates considering P-Δ effects and higher-mode vibrations.

3, Europe:

Allows equivalent linearization method for elastic isolation structures; requires inelastic time-history analysis for inelastic devices.

Emphasizes soil-structure interaction (SSI) analysis for soft soil sites.

3.5 Construction and Maintenance

1, Japan:

Mandates 100% inspection of isolation bearings (vertical stiffness, horizontal stiffness); post-earthquake inspection only requires visual checks.

Requires marking isolation buildings to prevent obstruction of isolation layer displacement.

2, U.S.:

Requires third-party inspection during construction; maintenance plans include annual visual checks and 5-year detailed tests.

3, Europe:

Specifies durability requirements (e.g., rubber bearings must resist ozone and temperature cycles); mandates maintenance records for 30 years.

Recommendation for the Design of Base Isolated Buildings provides a comprehensive framework for seismic isolation design, with in-depth coverage of devices, analysis methods, and practical cases. For engineers in Japan, the U.S., and Europe, the book offers:

Insights into Japanese isolation technology (e.g., long-period isolation for high-rises and soft soil sites).

A basis for comparing and optimizing local codes (e.g., integrating Japan's energy spectrum into U.S. or European performance-based design).

Guidance for cross-border projects, ensuring compliance with multiple standards.

This book remains a vital resource for advancing seismic isolation practice globally, bridging theoretical innovation and engineering application.