This code provides guidelines for the seismic design of buildings using base isolation systems. It covers the design principles, analysis methods, design of the isolated structure and the isolation system, and mandatory testing requirements for isolator units to ensure performance during an earthquake.
Specifies criteria for the seismic design of buildings incorporating base isolation systems.
Quick Reference Values
Minimum Effective Period Ratio (Ti/Tf)≥ 3.0
Response Modification Factor for Isolation System (R I)2.0
Maximum Response Modification Factor for Superstructure (R)≤ 2.5
Minimum Separation (Seismic Gap)≥ Total Maximum Displacement (DTM)
Minimum Restoring ForceForce at Dd should be greater than force at 0.5Dd by W/80
Key Formulas
Ti = 2π * sqrt(W / (Keff * g)) — Effective period of isolated structure
Dd = (g / (4 * π^2)) * SaD * Td^2 — Design displacement of isolation system
Vb = (W * Ah) / R_I — Design seismic base shear for the superstructure
DTM = Dm * [1 + y * (12e / (b^2 + d^2))] — Total Maximum Displacement including torsion
Practical Notes
Strict adherence to the prototype and quality control testing protocols in Clause 11 is critical for the success of a base-isolated project.
The 'seismic gap' or 'moat' around the building must be carefully detailed to accommodate large design displacements and prevent pounding, including provisions for services and access.
Base isolation is most effective for stiff, low to mid-rise buildings on firm soil; its effectiveness diminishes for tall, flexible structures or buildings on very soft soil.