Japanese attitudes toward risk control in seismic design in light of observation, prediction, and actual performance of building structures

Abstract

Despite recent international efforts toward a risk‐conscious approach to advancing seismic design, Japan, a country very prone to earthquakes, remains conservative regarding the consideration of risk‐based seismic hazards in developing seismic designs. This article attempts to interpret the reasons. First, the evolution of Japanese seismic design codes and specifications is introduced, noting that the design seismic loads have remained essentially the same since the revisions implemented in 1981. Second, Japanese efforts in providing and renewing seismic hazard maps are briefly introduced and discussed. The maps have been developed using the data recorded by Japanese strong motion networks. Some unique challenges in preparing seismic hazard maps for the territory of Japan are presented, in light of the observations of actual earthquakes in the past three decades. On many occasions, the damage disclosed in modern buildings remained limited even when the recorded ground motions significantly exceeded the design earthquake level. An inherent conservatism is embedded in the performance criteria imposed on structural systems and elements. Third, political‐legal and sociocultural aspects are discussed. Centralized operation is commonly exercised in Japan for post‐disaster relief efforts, and the general public also values “equality” for such support. The factors naturally encourage cautiousness for the revision of relevant seismic codes and specifications.

On the fragility of non‐structural elements in loss and recovery: Field observations from Japan

“…Using a decision variable like monetary loss has provided engineers with much more apt ways of communicating seismic risk to clients and stakeholders over the past two decades. When considering the recent reflections for Japan by Suzuki et al., 17 it is clear there is still work to be done on some fronts worldwide regarding the adoption of risk‐based approaches in seismic design practice. The PEER PBEE framework has been formalised via the provision of the FEMA P‐58 guideline 16 initially published in 2012 by the Federal Emergency Management Agency in the US, where quantities like expected loss are now commonplace among seismic engineers.…”

Risk‐targeted fragility functions considering a system performance requirement and domino effects

“…The nonuniform risk for structures designed by seismic code was recently confirmed for Italy. 17 A risk-targeted approach was followed by Douglas et al 18 and Silva et al, 19 who developed risk-targeted design maps for mainland France and Europe, respectively, but Japan remained conservative regarding risk-based seismic hazards due to reasons recently discussed by Suzuki et al 20 In parallel, many variants of seismic design procedures based on risk metrics were introduced. Franchin and Pinto 21 presented a method for seismic design of reinforced concrete structures to meet performance requirements expressed in terms of risk.…”

“…A risk‐targeted approach was followed by Douglas et al 18 . and Silva et al., 19 who developed risk‐targeted design maps for mainland France and Europe, respectively, but Japan remained conservative regarding risk‐based seismic hazards due to reasons recently discussed by Suzuki et al 20 . In parallel, many variants of seismic design procedures based on risk metrics were introduced.…”

Risk‐targeted seismic design: Prospects, applications, and open issues, for the next generation of building codes

“…20 . The paper by Suzuki et al., 21 provides opinions on the forces opposing seismic design paradigm shifts in Japan, which is certainly interesting beyond Asia, and is likely applicable to all countries of advanced technical culture. Finally, the work of Spillatura et al 22 .…”

“…A few papers deal with more specific issues, such as non-structural elements (i.e., Merino et al), 19 or go beyond targeting risk, that is, considering seismic resilience (i.e., Blowes et al). 20 The paper by Suzuki et al, 21 provides opinions on the forces opposing seismic design paradigm shifts in Japan, which is certainly interesting beyond Asia, and is likely applicable to all countries of advanced technical culture. Finally, the work of Spillatura et al 22 provides a comprehensive overview of risk-targeted ground motion (RTGM).…”