14-15 September 2023 in Cambridge

Sebastiano Foti

Influence of scour of foundations on the seismic performance of bridges

Abstract

Infrastructure deterioration and aging are growing challenges, also because of budgetary constraints on bridge maintenance and retrofitting. Specifically, scour of foundations is a significant issue for many bridges, particularly in a situation where global climate change is causing an increase in extreme alluvial events. In fact, it not only is the primary cause collapse of existing bridges but also lowers the ability to withstand following catastrophic occurrences, such as earthquakes. For the limited financial resources available for retrofitting, it is crucial to analyze the residual static and seismic capacity of bridges with accurate models. In this regard, soil-structure interaction plays a crucial role both for the assessment of current conditions and for the appraisal of expected performances. In fact, a lot of emphasis has been paid in recent years to the use of dynamic testing on bridges to evaluate their current condition, specifically with regard to foundation scour. The fact that the dynamic response of the bridge is altered also when the scour hole is filled with sediment in the aftermaths of big events gives vibration-based monitoring approaches their principal benefit over conventional ones. On the other hand, scour of the foundation has a substantial impact on bridges dynamic response and ability to withstand future earthquakes. Modelling of these phenomena is often over-simplified by assuming homogeneous riverbed erosion as a reference condition, whereas the actual configuration of the scour hole can significantly affect the response of the pier. For a proper use of resources, not only from an economic perspective but also for environmental sustainability, a more realistic appraisal is required. To do this, physical models can supply information for the calibration of numerical models, which can subsequently be applied to a realistic evaluation of the static and seismic performances.

Biography

Sebastiano Foti is a Professor in Geotechnical Engineering and Vice-Rector for Education at Politecnico di Torino (Italy). His research activity is mainly devoted to geotechnical earthquake engineering and geophysical methods for geotechnical characterization. Author of the book “Surface wave methods for near-surface site characterization” and member of the Project Team for Eurocode 7 - Geotechnical design - Part 2: Ground investigation and testing. He was awarded the Geotechnical Research Medal (Bishop Medal) by the Institution of Civil Engineers (UK) and an Honorable Mention by the Society of Exploration Geophysics (USA) and the Outstanding Paper Award from Earthquake Spectra by the Earthquake Engineering Research Institute.

Stavroula Kontoe

Dynamic response of offshore foundations - from pile installation to seismic performance

Abstract

The growing demand for renewable energy has resulted in a rapid, worldwide expansion of offshore wind installations in deeper waters and in areas of medium to high seismicity (e.g. Taiwan, China, Japan, USA) with structures of higher energy capacity. The first generation of offshore wind farms were located in areas of low seismicity, mainly in northern Europe, and therefore there is limited experience worldwide on how this type of structure would respond to seismic loading or to combined environmental and seismic loading. Design performance requirements and code provisions with explicit reference to offshore structures under seismic loading conditions are yet to be developed, while the existing guidance for onshore foundations is not always transferable to offshore conditions. This lack of guidance also applies to the assessment of liquefaction at offshore sites. Most offshore wind turbines are founded on monopiles with geometries (length to diameter ratios) and functionality which differ substantially from end-bearing piles traditionally used in many onshore conditions with significant seismic design considerations. Furthermore, as monopiles are a relatively new type of foundation the assessment of their driveability at different ground conditions poses challenges. Most of the existing driveability assessment methods, which are critical in the selection of a suitable hammer and driving system, were developed based on driving records for piles of much smaller in diameter than the monopiles used in the offshore wind industry today, leading to unreliable predictions. The first part of the lecture will discuss the use of dynamic analysis of pile driving as a tool for the improvement of drivability predictions for monopiles. The discussion will extend to driven piles supporting jackets, where dynamic analysis of driving data combined with the analysis of restrike data can gives estimates of their long-term axial capacity. The second part of the lecture investigates the seismic response of monopiles in liquefiable soils, showing the impact of liquefaction on shifting the modal response the combined system (i.e. structure-pile-soil) to a frequency range in which resonance phenomena can occur. Finally, it will be shown that the traditional separation of seismic loading into kinematic and inertial components, which is often adopted in simplified pile analysis, is not necessarily applicable to monopiles.

Biography

Stavroula Kontoe is Associate Professor at the University of Patras and Visiting Reader at Imperial College London, specialising in the development and application of numerical methods to study the performance of geotechnical structures under static, dynamic and seismic loading. She has authored over 100 peer-reviewed publications, receiving the 2008 BGA Medal, the 2012 Computers & Geotechnics outstanding reviewer award, the 2017 Shamsher Prakash Foundation Excellence in Geotechnical Teaching prize and the 2019 and 2021 David Hislop ICE awards for the best paper on offshore matters. She has served as Chair of the UK Society for Earthquake and Civil Engineering Dynamics (SECED) (2020-2022), is co-editor for Computers and Geotechnics and serves on the editorial boards of Soil Dynamics & Earthquake Engineering and of the Journal of Earthquake Engineering.

Andrew Mair

The Need for a Controlling Mind in Seismic Engineering

Abstract

Within the wide range of engineering disciplines required to deliver a typical infrastructure project, seismic engineering is considered a specialism. Within this specialism there are a range of sub-disciplines, many, or all, of which will be required to deliver a major project, including geologists, seismologists, geophysicists, geotechnical, structural, mechanical and electrical engineers, and many other specialists in between. In recent years, the boundaries between these specialisms have become more distinct, perhaps reflecting an increase in knowledge and computational ability. The contribution of each specialism, as well as the relationship between seismic engineering and other professional disciplines, needs to be managed and controlled in way that the final product, e.g. a complete building, is designed and constructed as coherent whole, providing a safe, efficient engineering solution. The question emerges, ‘how do you keep control of this process?’ ‘How do you ensure that these experts work as a coherent whole, so that uncertainty and conservatism, inherent in the process, are addressed in an appropriate manner?’ In this paper, the need for a ‘controlling mind’ in seismic engineering projects is proffered as an essential ingredient in obtaining a safe, efficient engineering solution. Several examples are presented, illustrating the necessity for robust interface management and exploring the consequences of what can happen when robust project protocols are absent. If the design substantiation is to be robust, there must be internal consistency in the data, design assumptions and the treatment of uncertainty at all stages of the process, from the seismic hazard assessment, through the geotechnical and structural engineering to the design of plant, equipment and building services. With the increase in specialist skills within seismic engineering there is increasing need for the ‘seismic generalist’ who can provide oversight of an entire project and perform the role of the ‘controlling mind’. The skills required of a seismic ‘controlling mind’ on a major project are reviewed and recommendations made for the development of an Engineering Manager with this skillset.

Biography

Andrew Mair (PhD, CEng, FICE, FIStructE, FIES) has worked in Consulting Engineering for over 30 years, having been involved in the design and assessment of a wide range of structures, including bridges, maritime works, dams, airports and buildings. A significant part of his career has involved the seismic engineering of highly regulated facilities, including nuclear power plants and military facilities, both in the UK and overseas. His experience spans from site characterisation and hazard assessment through to the design and construction of buildings, infrastructure and plant. Andrew has worked as a seismic subject matter expert (SME) providing advice to clients in the nuclear industry, and acted as an Independent Peer Reviewer on several major projects. He was Chairman of SECED from 2012-14.

Eduardo Miranda

Recent Research on Directionality of Earthquake Ground Motions

Abstract

Earthquake ground motion intensity varies significantly with changes in orientation. Although historically this has been ignored or not properly accounted for, this variation is actually significant and has multiple, important, implications in earthquake resistant design and when evaluating the seismic performance of the built environment. A common misconception is that strong directionality only occurs in the near field, while, in reality, a strong directionality occurs even at large distances from the rupture where it cannot be attributed to directivity. Recent studies to quantify and model directionality will be presented. This includes probabilistic models of two different metrics to quantify directivity in earthquake ground motions. Novel results show an interesting negative correlation between the level of polarity in a ground motion and the duration of the ground motion, meaning the level of polarization tends to decrease as the duration of the motion increases. It will be shown that for most structures, which typically have two principal axes in the horizontal direction that are perpendicular to each other, the probability that orientation-independent measures of ground motion intensity such as RotD50 are exceeded in one of the principal axes of the structure is higher than 90% when RotD50 occurs at the site and therefore the mean annual rate of exceedance the ground motion intensity in the structure is actually significantly higher than the mean annual rate of exceedance of RotD50. An alternate measure on intensity referred to as MaxRotD50 will be presented and discussed. The new measure of intensity is particularly well suited for earthquake-resistant design where a major concern for geotechnical and structural engineers is the probability that the design ground motion intensity is exceeded in at least one of the two principal horizontal components of the structure. The presentation will also include new emerging orientation-dependent ground motion models that allow to make estimates of ground motion intensities at specific orientations and will show that the variability in these models in many cases is smaller than that of orientation-independent measures of intensity. Finally, some applications will be presented to illustrate the importance of directionality.

Biography

Eduardo Miranda obtained his Civil Engineer degree from the National Autonomous University of Mexico, UNAM. He obtained his MSc and PhD degrees in Structural Engineering at the University of California at Berkeley. From 1993 to 1999 he was a Professor at the Graduate School of Engineering at UNAM. He has been a faculty member at the Department of Civil and Environmental Engineering at Stanford University since 2000 where he is currently a full professor. He is the author of more than 100 peer-reviewed publications and recipient of several awards one of which is the Moisseff award from the American Society of Civil Engineering His research focuses on Earthquake Engineering with emphasis on Performance-Based Design.

Ellen Rathje

Applying the SSHAC Framework to Site Response Analysis for Critical Facilities

Abstract

Probabilistic seismic hazard analysis (PSHA) is the standard approach for developing earthquake ground motions for critical facilities because it account for the important sources of uncertainty and variability associated with the earthquake source and with ground motion prediction. The Senior Seismic Hazard Analysis Committee (SSHAC) process was initiated in 1997 by the US Nuclear Regulatory Committee to provide guidance on uncertainty and the use of experts in PSHA, and since then the SSHAC framework has been used for PSHA projects for critical facilities around the world. Site response analysis traditionally has been performed outside of the PSHA and, thus, the SSHAC process has not been utilized, despite the fact that significant uncertainties and judgments are associated with site response analysis. More recently, site response analysis has become part of the PSHA and guidance for applying the SSHAC process to site response analysis has been developed. This presentation will introduce the SSHAC process and its application to site response analysis in recent projects. The approach to developing site adjustment factors will be described, along with the main sources of epistemic uncertainty and aleatory variability. The logic tree approach to incorporate epistemic uncertainty will be demonstrated and examples provided.

Biography

Dr. Ellen M. Rathje is the Janet S. Cockrell Centennial Chair in Engineering in the Department of Civil, Architectural, and Environmental Engineering at the University of Texas at Austin (UT), and Senior Research Scientist at the UT Bureau of Economic Geology. She has expertise in the areas of geotechnical earthquake engineering, engineering seismology, induced seismicity, field reconnaissance after earthquakes, and remote sensing. She has participated in seismic hazard assessments and site response studies for nuclear facilities in South Africa, Taiwan, the United Kingdom, and the United States. Dr. Rathje is the Principal Investigator for the DesignSafe-ci.org cyberinfrastructure for the NSF-funded Natural Hazards Engineering Research Infrastructure (NHERI). She has been honored with various research awards, including the 2022 Ralph Peck Award from the ASCE Geo-Institute, the 2018 William B. Joyner Lecture Award from the Seismological Society of America and the Earthquake Engineering Research Institute, and the 2010 Huber Research Prize from the ASCE. She was elected Fellow of the American Society of Civil Engineers in 2016.

Irmela Zentner

How to make best use of numerical simulation, experience feedback and expert judgement in seismic fragility analysis for nuclear installations

Abstract

In nuclear engineering practice, the so-called safety factor (or separation of variables) approach is generally used to develop fragility curves due to its systematic applicability and the possibility to deal with a large number of SSCs (Structure, Systems and Components). With increasing computational capabilities, it becomes now feasible and more and more common to develop numerical models representing complex and possibly nonlinear behavior for components at stake. This talk addresses different aspects related to the numerical evaluation of fragility curves, including the choice of intensity measures, uncertainty propagation, reliability of numerical models, possible surrogates and the introduction of knowledge through expert judgement and in-situ experience data. Different sources of information such as expert judgement, numerical simulation, qualification tests and experience feedback can be combined in a Bayesian framework to develop best-informed fragility curves. Here, we present an approach that allows for the consideration of generic fragility parameters and simulation to develop priors and update fragility curves using experience feedback considering both epistemic and aleatory uncertainty. In particular, we use a database that contains failure data collected in industrial plants that have experienced an earthquake. We discuss opportunities and difficulties of this approach, related to the lack of specific data for nuclear equipment despite growing experience feedback and awareness. The PGA is generally used as intensity measure when developing fragility and hazard curves. Eventually, we consider an approach to deal with vector hazard and vector fragility curves and discuss possible benefit for seismic risk assessment of nuclear plants. Indeed, while PGA proves to be a very good damage or failure indicator for a large number of SSCs, there are a few with low frequency behavior that could be better characterized by introducing a second intensity measure such as low frequency spectral acceleration.

Biography

Dr Irmela Zentner is a civil engineer specialized in structural dynamics and earthquake engineering with a focus on probabilistic assessments. She is currently research engineer at EDF R&D Lab Paris-Saclay where she acts as an expert for probabilistic seismic risk assessment. She holds a PhD carried out at the French Aerospace Lab in the area of aeroelasticity and stochastic dynamics, after working in consulting and receiving master degrees at Ecole Centrale Paris and RWTH Aachen. She is member of IMSIA laboratory and SEISM institute Paris-Saclay. She is currently coordinator of the H2020 funded project EURATOM METIS and has been involved in several national and international research projects such as the recent SIGMA-2 and ANR EXAMIN projects.

Dimitrios Vamvatsikos

Stranger things in seismic response and statistical tools to resolve them

Abstract

Demogorgons, monsters, and mythical creatures do not appear only in Soviet research labs, secretive government facilities or just plain Hawkins, Indiana. They frequently cross-over to earthquake engineering in the form of questions that conform to the paradigm of “Does X matter in seismic response?”. X can be a seismological characteristic, such as duration, vertical component, incident angle, or near-field directivity; it can also be a structural property, such as building period, rocking block size, or plan asymmetry. We, as investigative structural engineers, are vastly more familiar with the latter set of queries and we are clearly better equipped to handle them. We can even provide definitive answers that most, if not all of us, would agree upon. Instead, questions involving seismological characteristics seem to leave us baffled and stuck in an Upside Down world that resembles structural engineering but it is not exactly the same. Wading through its murk, it is good to have some investigative tools and processes that will help us find our way home. In the end, though, we may end up equal parts enlightened and confused, as most questions of whether something of the seismologist world matters for the structural one are nearly-universally answered by uttering “It depends”.

Biography

Dimitrios arrived by way of Greece, California, Cyprus and Greece again. His life is of great food, tasteful drinks, good friends, far travels and colorful commentaries. His work is of earthquakes, winds, weather, probability, and risk, presently confined to Earth but hopefully going to outer space. He enjoys writing software, codes, Eurocodes, FEMA standards, research papers, and whimsical paragraphs. Feel free to ask him questions about Life, the Universe, and Everything, but be prepared to receive answers way longer than 42 words.

Emily So

Building for safety from earthquakes: the global challenge

Abstract

This paper contributes to the ongoing debate about progress in global earthquake safety. Drawing on personal experience and insights from earthquakes of the last 30 years, a survey of experts and practitioners from around the world, and our review of global building types and standards, we highlight key areas of progress and concern. We present empirical evidence to describe the successes of earthquake engineering and disaster preparedness, as well as the failures that may have had tragic consequences, and how we can learn from them. What we have learned is that technological advancements and knowledge cannot be relied on alone to deliver earthquake safety. With affordable protection actions, buildings collapsing and people dying from earthquakes are largely preventable, and perhaps of equal importance is advocacy that complements building codes. Advocates in the field have shown how a careful balance of local knowledge, cultural sensitivity, wit, communication skills, and resolve is the essence that shifts the status quo. Based on our assessment of earthquake initiatives and the actions of game changers around the world, we point to some of the actions that have made a difference in their local context.

Biography

Professor Emily So is a chartered civil engineer with specialist experience in loss assessments and earthquake engineering. She is Director of the Cambridge University Centre for Risk in the Built Environment. She has actively engaged with earthquake‐affected communities in different parts of the world, focusing on applying her work towards making real‐ world improvements in seismic safety. She has been involved in interdisciplinary and international collaboration through her work with the UK’s Earthquake Engineering Field Investigation Team (EEFIT), Global Earthquake Model (GEM), the World Bank and the USGS, and actively participates in the international debate on the way forward for disaster risk mitigation