Comparison of methods to develop risk-targeted seismic design maps

The current design approach recommended by seismic codes is often based on the use of uniform-hazard response spectra, reduced to account for inelastic structural behaviour. This approach has some strong limitations that have been highlighted in many studies, including not allowing a direct control of the seismic risk and losses. This study aims at quantifying the levels of safety and the costs associated with this design approach, and to investigate alternative design approaches that have been developed in the last decades. In particular, a risk-targeting approach and a minimum-cost approach are considered. The first one, allowed by US codes, aims at designing structures with the same risk of collapse throughout regions of different seismicity. The second one aims to minimize the sum of the initial construction cost and the cost of expected losses due to future earthquakes. The comparison of the three approaches is performed by considering, as an example structure, a fourstorey reinforced concrete frame building located in different areas in Europe, and by looking at the implications in terms of achieved safety levels, initial costs, and future losses. The study's results provide useful information on how the design criteria and the different hazard levels throughout Europe affect the cost and safety levels of seismic design.

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“…It is noteworthy that this approach leads to non-uniform levels of risk for different locations, as discussed in e.g. Gkimprixis et al (2019).…”

Section: Uniform-hazard Designmentioning

confidence: 99%

“…This risk-targeting methodology has been investigated and applied by many researchers (e.g. Douglas and Gkimprixis 2018;Silva et al 2016;Tsang and Wenzel 2016;Douglas et al 2013;Luco et al 2007), while alternative techniques of risk targeting have also been proposed in the literature (Gkimprixis et al 2019;Tsang et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Evaluating alternative approaches for the seismic design of structures

Gkimprixis

Tubaldi

Douglas

2020

Bull Earthquake Eng

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“…Nevertheless, the MAF of exceedance is higher than the reference MAF of collapse that is targeted by the risk-based design approaches in the US [63]. In Europe, lower values of the MAF of collapse are sought for new structures, (about 10 -5 -10 -6 1/year [60], [63]. Accounting for the presence of the infills results in further reductions of the IDR demand.…”

Section: Seismic Demand Hazard Curvesmentioning

confidence: 97%

“…The discrepancy may be due to the simplifying assumptions of the design procedure, particularly the fact that the isotropic hardening behavior of the BRBs is neglected when evaluating the pushover curve of the retrofitted frame. Nevertheless, the MAF of exceedance is higher than the reference MAF of collapse that is targeted by the risk-based design approaches in the US [63]. In Europe, lower values of the MAF of collapse are sought for new structures, (about 10 -5 -10 -6 1/year [60], [63].…”

Section: Seismic Demand Hazard Curvesmentioning

confidence: 98%

Seismic performance of an existing RC structure retrofitted with buckling restrained braces

Castaldo

Tubaldi

Federico

et al. 2021

Journal of Building Engineering

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The use of buckling restrained braces (BRBs) represents one of the best solutions for retrofitting or upgrading the numerous existing reinforced concrete framed buildings in areas with a high seismic hazard. This study investigates the effectiveness of BRBs for the seismic retrofit of reinforced concrete (RC) buildings with masonry infills. For this purpose, an advanced non-linear threedimensional model of an existing building in L'Aquila is developed in OpenSees, by accounting for the effect of infill walls through an equivalent strut approach, and by using a recently developed hysteretic model for the BRBs. The seismic performance of the building before and after the retrofit with BRBs is evaluated by performing both non-linear static analyses and incremental dynamic analyses under a set of real ground motion records. Seismic demand hazard curves are built for different response parameters before and after the retrofit, by accounting for and by disregarding the contribution of the infill walls. The study results shed light on the effect of the BRBs and of the infill walls on the seismic performance of the various components of the system, and on the effectiveness of the retrofit with BRBs for a real case study.

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“…Risk targeting has recently emerged in the seismic design of structures; it considers many uncertainties that are disregarded in the uniform-hazard spectrum method and allows the achievement of consistent performance levels for structures with different properties through the definition of uniform risk design maps [25]. The 50-year collapse probability, which is derived from the average annual collapse probability, is suggested to be less than 1% in FEMA P-750 [20] as a uniform collapse risk target.…”

Section: Introductionmentioning

confidence: 99%

Assessing Seismic Collapse Safety and Retrofitting Low-Ductility RC Frame Structures on the Basis of the Acceptable Collapse Safety Margin in China

et al. 2020

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The relationship between the average annual collapse probability and collapse safety margin of structures is identified to evaluate structural collapse performance quantitatively. A method is then proposed to determine the acceptable collapse margin ratio (CMR) with a certain annual collapse probability. Two methods, namely adopting steel braces and enlarging column cross sections, are used to retrofit a four-story, low-ductility reinforced concrete (RC) frame structure. On the basis of the acceptable CMR, the seismic collapse resistance of the structure is assessed before and after strengthening. Furthermore, a four-story RC frame structure, which is designed in conformity to the minimum design criteria of the building code, is constructed. The incremental dynamic analysis method is used in consideration of collapse uncertainties. Results show that when the acceptable annual collapse probability is equal to 1.24 × 10−4, which is calculated using the collapse probability at maximum considered earthquake (5%, as proposed in CECS 392), the collapse safety margin of the four structures does not satisfy the seismic collapse resistance requirements with large collapse uncertainty. The structures that are retrofitted and designed in conformity to the code can satisfy the collapse safety margin requirements when the acceptable annual collapse probability is increased to 2 × 10−4. The comparison of the two retrofitting schemes used to improve the seismic collapse resistance of the structure indicates that the steel brace-retrofitting method is better than increasing the column section. This work is an important reference for the reinforcement of the seismic resistance of structures and for corresponding research on collapse resistance.

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Comparison of methods to develop risk-targeted seismic design maps

Cited by 58 publications

References 42 publications

Evaluating alternative approaches for the seismic design of structures

Evaluating alternative approaches for the seismic design of structures

Seismic performance of an existing RC structure retrofitted with buckling restrained braces

Assessing Seismic Collapse Safety and Retrofitting Low-Ductility RC Frame Structures on the Basis of the Acceptable Collapse Safety Margin in China

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