Exploring the site dependency of fragility functions in risk‐targeted design

The risk‐targeted seismic design framework is used to set design intensities, based on achieving a target risk level (e.g., collapse or fatality risk) with respect to an assumed building collapse response. This paper assesses the distribution of fatality risk associated with the risk‐targeted design intensity, considering uncertainty in both the hazard and the variety of buildings that can satisfy the minimum design requirement. The randomness among buildings and their response is due to other design decisions (aleatory variability with respect to the design intensity) and can be represented by a distribution of fragility curves that quantify the collapse probabilities of as‐built, code‐conforming buildings. First, a single design intensity is calculated based on a “design fragility,” the mean hazard curve, and a risk target. The design fragility is taken as a conservative estimate from the distribution of collapse fragilities and the selected risk target approximates the risk associated with New Zealand's previous (non‐risk‐targeted) criteria for design intensities. Then the risk distribution is assessed, considering the aleatory variability in as‐built fragilities and the epistemic uncertainty in the new National Seismic Hazard Model. Accounting for variability in design decisions and uncertainty in the hazard model produces a risk distribution that more fully represents the potential risk associated with a given design intensity. This distribution can be compared to guidance on tolerable risk ranges, which suggest that risk can be variable among buildings but should fall within acceptable bounds. Sensitivity studies consider epistemic uncertainty in the assumed model for the distribution of as‐built fragilities. This inclusion of uncertainty to assess the risk distribution offers a powerful extension to the risk‐targeted framework. While this extension would not affect engineering practice (as the output is still a single design intensity), it allows building code developers to better understand and consider the risk implications associated with the selected design intensity.

Section: Selecting a Design Fragilitymentioning

confidence: 99%

Considering uncertainty in the collapse fragility of New Zealand buildings for risk‐targeted seismic design

Hulsey

Horspool

Gerstenberger

et al. 2023

“…Thus, this approach assumes an idealized fragility and does not address performance objectives corresponding to non‐collapse. The issue of assuming fixed dispersion and its repercussions on the risk‐targeted design, as in Luco et al., 35 was investigated in great detail by Fox and O'Reilly 41 . Žižmond and Dolšek 28 proposed a seismic action for force‐based design.…”

Section: Introductionmentioning

confidence: 99%

“…The issue of assuming fixed dispersion and its repercussions on the risk-targeted design, as in Luco et al, 35 was investigated in great detail by Fox and O'Reilly. 41 Žižmond and Dolšek 28 proposed a seismic action for force-based design. Seismic loss estimation was further integrated into the process.…”

Section: Introductionmentioning

confidence: 99%

Risk‐targeted importance factors for prescriptive seismic design of critical buildings

Badal

Sinha

2023

The post‐earthquake recovery of a community depends on the ability of important buildings to perform their functions. Lifeline and other critical buildings that meet a predictable enhanced seismic performance increase the community's disaster risk management capacity. In prescriptive force‐based design standards, the seismic design force for these buildings is typically enhanced using an importance factor depending on the risk category. The present paper proposes an innovative framework based on performance‐based seismic design (PBSD) principles using risk‐targeted importance factors suitable for use with prescriptive standards. The framework decouples probabilistic assessments of building typologies to experts, while the structural designers can continue the conventional design approach. The framework explicitly considers probabilistic seismic demand, uncertainty in the performance of the building, and the inter‐building variation within a particular building typology in seismic performance. Six special reinforced concrete (RC) frame buildings conforming to Indian standards are selected to illustrate the framework. Sensitivity studies on parameter selection are used to establish the framework's robustness. An expression for the importance factors is also proposed. The use of the proposed importance factor expression is shown to meet a wide range of risk targets corresponding to different performance levels. The paper also proposes design factors for enhanced performance objectives suitable for the risk‐targeted prescriptive design. Further, the framework is implemented to estimate the seismic risk associated with existing building typology conforming to prevalent design standards. The assembly‐ and critical‐category RC buildings are found to require higher importance factors for achieving enhanced performance objectives than currently prescribed.

“…The topic of design methods alone occupies one‐third of the papers, which is not surprising given the scope of the SI. The papers by Ahmadie Amiri and Estekanci, 11 Chen et al., 12 and the two by Dolsek and co‐workers, 13,14 deal with the risk‐targeted design of specific structural types, while those of Fox and O'Reilly, 15 Kourehpaz et al., 16 Clemett et al., 17 and Hulsey et al., 18 with the role of seismic vulnerability (i.e., fragility) in risk‐targeted design. A few papers deal with more specific issues, such as non‐structural elements (i.e., Merino et al.…”

mentioning

confidence: 99%

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

Iervolino

2023

Risk-targeted seismic design: Prospects, applications, and open issues, for the next generation of building codesSeismic design targeting a specific failure risk (i.e., seismic structural reliability) has been invoked as the desired landing of building codes for over than half a century now. 1 On one hand, it has been missed, as most codes worldwide are still based on the seismic adaptation of load-resistance factor design, whose limitations are known. Most notably, it does not enable explicitly controlling the failure probability of the designed construction and does not necessarily warrant comparable seismic structural safety among sites with different seismic design hazards. 2 Since reaching a broad consensus around performance-based earthquake engineering (PBEE) 3 more than two decades ago, research is increasingly proposing results about risk-targeted design, suggesting it is a now-viable approach for earthquake practice. On the other hand, the development of building codes may be slow in implementing scientific innovations, waiting for enough time to transpire after these results have been consolidated and formalized.Earthquake Engineering and Structural Dynamics (EESD) dedicates selected issues of the journal, normally no more than two per year, to special topics. The special issue (SI) publication is planned to be attractive to authors and readers. To authors, it should provide a forum to present their work in a publication of related papers on one subject. To readers, it should give a comprehensive overview of a topical subject. The objective of this SI was to be a venue to review the stateof-the-art research about risk-targeted design, present new advancements and/or extensions, set objectives, and propose calibration for application-ready use, and finally discuss open issues. The SI was expected to be a reference about design based on target seismic reliability and risk. It ideally connects to the EESD SI on PBEE of more than twenty years ago, 4 which has published some among the landmarking papers of contemporary earthquake engineering.After the call for papers launched in March 2022, over thirty-five manuscripts were submitted to the issue within the deadline, confirming the current interest in the topic. Eighteen papers were finally accepted after the usual, multipleround, rigorous review process enforced by the journal. The accepted papers come from four of the five dwelled continents, with Africa being the only one not represented, and are authored by some of the most reputed researchers among those currently active in the field, feeding the hope of an impactful issue.The accepted papers revolve around several topics that can be roughly grouped as follows. The works of Badal and Sinha, 5 Ordaz et al., 6 Bodenmann et al.,7 Heresi and Miranda, 8 Bahnu et al., 9 and Franchin and Noto 10 (who present the re-calibration of partial safety factors for the second generation of the European building code), explicitly deal with risk-and reliability-based design methods for the various facets of risk-targete...