Seismic reliability implied by behavior‐factor‐based design

In the ongoing quest for improved seismic design codes, there is currently substantial focus on risk‐targeted design, which aims to achieve more uniform seismic risk across code‐compliant buildings. Such an approach has already been adopted in ASCE 7, which uses lognormal fragility functions, with a single assumed value for dispersion, to generate uniform risk spectra. One challenge to this approach is that fragility functions have been shown to vary depending on the site being considered. This article, therefore, explores the extent to which site location influences the dispersion of fragility functions through the study of inelastic single‐degree‐of‐freedom systems. Twenty‐four different sites across New Zealand are considered so that a diverse range of seismic hazard settings, including multiple tectonic region types, are examined. The resulting dispersion values for the cases examined range from 0.14 to 0.29 and they are shown to be influenced by both the spectral shape and variance of the target spectra used for ground motion selection. The study is then extended to the consideration of scenario‐based seismic risk analysis. It is shown that fragility functions derived using ground motions selected on the basis of probabilistic seismic hazard analysis are, in theory, not suitable for use in scenario‐based risk analyses. The potential ramifications of this work on other risk‐targeted design methods are also discussed. Overall, this work sheds important light on the importance and potential implications of site dependence for what concerns risk‐targeted design.

Section: Implications For Other Risk‐targeted Design Proceduresmentioning

confidence: 94%

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

Fox

O’Reilly

2022

“…This bias can be mitigated by iterating for risk‐targeted importance factors, similar to the conventional PEER framework, that is, by using the results of Step 7, redesigning and repeating from Step 1. Secondly, buildings in low seismic zones or very tall buildings can have gravity and wind load combinations as the most critical cases, where the uniformity of risk may not be achievable within a risk‐targeted design framework 74 . The proposed framework is applicable only for buildings where lateral load resistance requirement is governed by seismic forces.…”

Section: Proposed Risk‐targeted Seismic Design Frameworkmentioning

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.

“…This factor is 7.5, 7.5, and 6.0 for 4‐, 8‐, and 12‐story steel SMRF‐BRBs, respectively. Note that a reliable calibration of the R‐factor for application to entire steel SMRF‐BRBs requires further building archetypes at different seismic sites considering multishock events 136,115 . Moreover, LCC‐based optimized steel SMRF‐BRBs have larger yield and ultimate drifts (Δ y and Δ u ) than code‐based ones.…”

Section: Numerical Implementationmentioning

confidence: 99%

“…Note that a reliable calibration of the R-factor for application to entire steel SMRF-BRBs requires further building archetypes at different seismic sites considering multishock events. 136,115 Moreover, LCC-based optimized steel SMRF-BRBs have larger yield and ultimate drifts (Δ y and Δ u ) than code-based ones. This is owing to the proper distribution of SFRS elements along the building height when the strength increases, which allows the building to take full advantage of its higher strength.…”

Section: Evaluation Of Optimized Buildings and Quantification Of Targ...mentioning

confidence: 99%

Life cycle cost‐based optimization framework for seismic design and target safety quantification of dual steel buildings with buckling‐restrained braces

Amiri

Estekanchi

2023

This study proposes an efficient risk‐targeted framework for integrated optimal seismic design and quantifying target safety of Special Moment‐Resisting Frames (SMRFs) with Buckling‐Restrained Braces (BRBs) in the typical dual steel buildings. This framework provides an automated design procedure formulated as a constrained single‐objective optimization problem to achieve the minimum Life Cycle Cost (LCC) within the Particle Swarm Optimization (PSO) algorithm and can be the basis of current seismic codes for target safety calibration. LCC includes initial construction cost and lifetime seismic losses such as repair cost, repair time, and casualties. FEMA P‐58 methodology is employed for the LCC analysis of the building under possible earthquakes during its lifetime, which is able to take into account potential uncertainties in the hazard‐response‐damage‐loss relationship. An appropriate cost model is developed to estimate the initial and repair cost of the studied BRBs. Minimum requirements of ASCE and AISC codes are considered as design constraints. Nonlinear response history analysis through the Endurance Time (ET) method is utilized to estimate the structural responses versus seismic intensity. Three 4‐, 8‐, and 12‐story steel buildings with dual seismic force‐resisting system consisting of SMRF and BRB (called steel SMRF‐BRB) are selected as the case study. Each building is optimally designed with two approaches: (1) LCC‐based design within the proposed framework and (2) code‐based design to minimize initial construction cost. Comparison of optimized buildings with the two design approaches in terms of structural responses and seismic consequences demonstrates that fulfilling the minimum code requirements at a given seismic hazard level is not sufficient to minimize lifetime seismic losses of steel SMRF‐BRBs. This is because the optimal designs obtained from the code‐based approach are associated with damage concentration, irreparability, and high collapse probability, especially in seismic events more severe than the design level. The proposed LCC‐based approach provides useful information for improving the lifetime seismic performance of steel SMRF‐BRBs.