Summary of Comparison of Japanese Seismic Isolation Design Code with Overseas Codes

In October 2022, ISO 23618:2022 (Bases for design of structures - General principles for seismically isolated structures) was published. This document compares the detailed seismic isolation design procedures of four regions/countries-Japan (MLIT Notification No. 2009), China (GB/T 51408-2021), the USA (ASCE 7-16), and the Eurocode (EC8)-to propose a common design workflow for engineering practice. Key comparison dimensions include seismic loads, analysis methods, major load combinations, and isolation device testing methods. A 7-story reinforced concrete (RC) building model is used to demonstrate design procedures, with results from the equivalent linear method (ELM) and response history analysis (THA) summarized.

Core differences in seismic loads, analysis methods, load combinations, and device testing across the four codes are summarized in Table 1 (general provisions) and Table 2 (ultimate limit state, ULS, requirements).
Table 1: Key Provisions of Seismic Isolation Design Codes

Table 2: ULS Seismic Load and Super-Structure Response Requirements

Key code-specific notes:

1. Design philosophy: Japan uses the allowable stress design method; China, the USA, and EC8 use the limit state design method.
2. Tension loads: China and the USA have critical tension load designs (with more tension-resistant devices used) compared to Japan.
3. Device quality control: All codes require strict prototype testing; Japan and the USA test 100% of production devices, while China and EC8 allow sampling.

3.1 Analysis Model
A modified 7-story RC building (based on Saito 2011 and Feng 2022) is used. Key parameters:
1. Fixed-base fundamental periods: Frame direction (Tx): 0.564, 0.190, 0.107s; Shear wall direction (Ty): 0.238, 0.105, 0.087s.
2. Isolation device: Lead Rubber Bearings (LRB) (selected for restoring force and damping).
Diameter: 650–750mm (Japan, China, EC8); 900mm (USA, due to large MCER seismic loads).
Table 3: Nominal Design Properties of Isolation System

3.2 Seismic Load
1. Target sites: Tokyo (Japan), Beijing (China), San Francisco (USA), Reggio Calabria (EC8).
2. Soil condition: Fixed profile; average shear wave velocity (top 30m): 209 m/s.
3. Spectra characteristics:
1) 5% damping: USA has the largest acceleration/pseudo velocity spectra (≈1.5x Japan's).
2) Pseudo velocity spectra: Increases with period (China); constant/decreases (Japan, USA, EC8).
3) ULS damping for isolated buildings: ~20%.
3.3 Response Analysis Results
Two main methods are compared: ELM (equivalent linear method) and THA (response history analysis).
3.3.1 Equivalent Linear Method (ELM)
All codes define ELM for single-degree-of-freedom (SDOF) systems, but with varying applicability. China uses 85% equivalent mass and calculates responses for 475-year and 2475-year loads (no boundary properties considered).
Table 4: Key ELM and THA Response Results

3.3.2 Response History Analysis (THA)
1. Ground motions: 6 pairs (Japan, max values); 10 pairs (China, USA, EC8, average values); all match 5% design spectra.
2. Modeling:
a) 3D frame; LRB idealized as bilinear.
b) Horizontal analysis: Rayleigh damping (isolation system damping=0; super-structure 1st/2nd period damping=3%).
c) Super-structure: Non-linear (Japan, China); elastic (USA, EC8).
3. Software: SERA3D Ver10.8 (THA); PKPM (China, RSA); ETABS V18 (vertical RSA).
4. Vertical analysis: RSA with Rayleigh damping (1st/2nd vertical period damping=3%); beam vibration modes are prominent (due to high isolation vertical stiffness).
3.3.3 Main Findings
1. Japan: ULS isolation drift > SLS drift; ELM and THA are selected independently (20% ELM, 80% THA in practice); Kobe NS near-field ground motion produces the largest shear (exceeding ELM); ELM predicts larger isolation deformation.
2. China: 475-year load (RSA) designs the super-structure; 2475-year load (THA) checks drift; design load uses the maximum of RSA/THA results.
3. USA: THA results are limited by ELM; ELM shear is slightly larger than seismic design (due to Rᵢ=1.875 for isolation vs. R=5 for normal seismic design).

This document compares seismic isolation design procedures of Japan, China, the USA, and EC8, focusing on seismic loads, analysis methods, and device testing. A 7-story RC building model demonstrates design workflows, with ELM and THA results compared. The goal is to propose a common design procedure for engineering practice, addressing code-specific differences in design philosophy, load combinations, and analysis requirements.

All the above content is sourced from "Comparison of Japanese Seismic Isolation Design Code with Overseas Codes" JSSI April 2024.