The seismic design of structures according to current codes is generally carried out using a uniform-hazard spectrum for a fixed return period, and by employing a deterministic approach that disregards many uncertainties, such as the contribution of earthquake ground motions with return periods other than that assumed for the design. This results in uncontrolled values of the failure probability, which vary with the structure and the location. Risk targeting has recently emerged as a tool for overcoming these limitations, allowing achievement of consistent performance levels for structures with different properties through the definition of uniform-risk design maps. Different countries are implementing the concepts of risk targeting in different ways, and new methods have recently emerged. In the first part of this article, the most well-known approaches for risk targeting are reviewed, with particular focus on the one implemented in recent American design codes, the one based on the use of risk-targeted behaviour factors (RTBF), and an approach based on direct estimation of hazard curves for inelastic response of single-degree-of-freedom systems. The effect of the linearization of the hazard curve is investigated first. A validation of the RTBF approach is then provided, based on comparison with the results of uniform-risk design spectral accelerations for single-degree-of-freedom systems with elastic-perfectly plastic behaviour for two different sites. The effectiveness of the current risk-targeting framework applied in the United States is also investigated. In the last part of the paper, uniform-risk design maps for Europe are developed using the RTBF approach, showing how the seismic design levels may change when moving from a uniform-hazard to a uniform-risk concept.
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.
Over the past decade there have been various studies on the development of seismic design maps using the principle of "risk-targeting". The basis of these studies is the calculation of the seismic risk by convolution of a seismic hazard curve for a given location (derived using probabilistic seismic hazard analysis) with a fragility curve for a code-designed structure (ideally derived from structural modelling). The ground-motion level that the structure is designed for is chosen so that the structure has a pre-defined probability of achieving a certain performance level (e.g. non-collapse). At present seismic design maps developed using this approach are only widely applied in practice in the US but studies have also been conducted on a national basis for France, Romania, Canada and Indonesia, as well as for the whole of Europe using the European Seismic Hazard Model. This short article presents a review of the state of the art of this technique, highlighting efforts to constrain better some of the input parameters. In addition, we discuss the difficulties of applying this method in practice as well as possible paths forward, including an empirical method to estimate an upper bound for the acceptable collapse and yield risk.
Acknowledging the devastating consequences of past earthquakes, current research efforts focus on the development of tools for assessing and controlling the risk and losses associated with future earthquakes, in addition to trying to minimize construction costs. Apart from providing a control of these levels, earthquake engineering can also provide solutions to manage the financial implications of the expected hazardous events. The first part of this article focuses on the management of the expected losses through the mechanism of transfer of the financial risk via earthquake insurance. Various insurance models are explained and applied in different case studies, and numerous analyses are performed across Europe, for a benchmark four-storey reinforced-concrete frame building. The results highlight significant variation in the premiums with seismicity, design practices and properties of the insurance model. It is crucial that any mitigation or transfer framework should use probabilistic methods to consider the uncertainties inherent in the hazard and structural response estimates. For example, different studies for the same region often indicate considerable differences in seismic hazard estimates. The uncertainty inherent in the hazard input model is transferred to and affects the results of the structural design and the performance assessment. Thus, the second part of the article investigates the impact of the epistemic uncertainty in the hazard model on the structural design and consequently the estimated future losses and risk levels, again for the benchmark building. First, a comparison is performed between the hazard data from two studies for different locations in Italy, in order to assess the possible range of variation in estimated hazard levels amongst different studies. The effects of these hazard variations on the seismic design and risk and loss metrics for the benchmark building are also investigated for these locations. Finally, a simplified approach for modelling hazard uncertainty is introduced and various sensitivity analyses are performed to investigate the effects of the hazard uncertainty across Europe. It is shown that hazard uncertainty can be of differing importance for the various involved stakeholders.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.