9-10 September 2019 in Greenwich, London

A ground motion model to estimate nonlinear deformation demands from a recent pan European strong motion database

Paper co-authored with Abdullah M Sandikkaya.

Abstract

Estimating nonlinear deformation demands is essential in performance based seismic design and assessment. It becomes even more important as probabilistic damage (loss) assessment becomes an important component in taking critical decisions about the resilience-based performance of structural systems. Considering these issues as the primary source of motivation, we developed two ground-motion predictive models to estimating single-degree-of-freedom (sdof) inelastic deformation demands from their elastic counterparts. The models presented in the paper use constant ductility and strength reduction as the structural estimator parameters. The conventional source-site distance, magnitude, Vs30 and style-of-faulting estimators in the model account for the effect of physical earthquake process on inelastic deformation demands. The presented models also account for the period-dependent correlations between elastic and inelastic spectral displacement demands for a complete conditional probabilistic representation of inelastic deformation demands. The predictive models are used in probabilistic seismic hazard assessment (PSHA) to see how inelastic and elastic spectral displacement demands vary in terms of return periods. The PSHA case studies enable us to assess the design code formulations used in the estimation of nonlinear deformations from elastic spectral displacements. Our preliminary observations from the limited case studies suggest that there is still room to improve the code-based nonlinear deformation demand formulations used in simplified seismic design and assessment procedures.

Biography

Sinan Akkar has been the faculty member of the Earthquake Engineering Department at Bogazici University since 2013 and a faculty member at the Istituto Universiatrio di Studi Superiori of Pavia (Italy) since 2008. He has acted as the university representative and/or works co-ordinator of the 7th Framework and Horizon 2020 projects including SHARE & NERA. He has worked with the GEM funded EMME project and coordinated the NATO BSHAP project. He has served as a guest editor in the Bulletin of Earthquake Engineering and Earthquake Spectra journals. He co-authored “Basic Earthquake Engineering: From Seismology to Analysis and Design” with Prof. Dr. Haluk Sucuoğlu. Sinan was awarded the 2007 Prof. Dr. Mustafa N. Parlar Research Incentive Award.

Widening of existing motorway bridges: can pilegroup retrofit be avoided?

Abstract

The expansion of current motorway infrastructure often involves widening of existing bridges, calling for pier and foundation retrofit. While pier retrofit is relatively straightforward, pilegroup strengthening can be a challenging, costly, and time–consuming operation. A non-negligible excavation is necessary to reach the existing pilecap, followed by construction of additional piles, and of a new pilecap that needs to be connected to the existing one by doweling. Such major operation can be avoided by developing more rational methods to assess pilegroup moment capacity, and by taking advantage of nonlinear foundation response. Largely thanks to the inherent conservatism in pilegroup design, allowing such nonlinear response may offer a viable design alternative. Within this context, the paper presents a comparative assessment of current design practice, which is based on “elastic” foundation design, to an alternative design approach that allows nonlinear pilegroup response. This allows the conventionally-defined (elastic) moment capacity of the foundation to be temporarily exceeded and the loads to be redistributed between piles during seismic shaking. Inspired from the widening of an existing motorway bridge in Switzerland, a case study is conducted employing 3D finite element (FE) modelling. According to conventional “elastic” design, the initial pilegroup requires retrofitting. Such retrofit may be avoided by allowing full mobilization of pilegroup moment capacity. This is demonstrated by comparing the seismic performance of the widened bridge with the two design alternatives: (a) the pilegroup retrofitted according to the “elastic” design approach; and (b) the initial foundation without any retrofit measures. For moderate (Swiss) design–level seismic shaking, the performance is almost identical. For stronger shaking, substantially exceeding the design limits, the performance of the un-retrofitted foundation is advantageous, as it reduce structural damage by dissipating energy at the foundation level, at the cost of increased – but totally tolerable – settlements.

Biography

Prof. Ioannis Anastasopoulos has been Full Professor of Geotechnical Engineering at ETH Zurich since 2016. He specializes in geotechnical earthquake engineering and soil–structure interaction, combining numerical with experimental methods. He holds a PhD from the National Technical University of Athens (NTUA), an MSc from Purdue University, and a Civil Engineering Diploma from NTUA. His research interests include the development of innovative seismic hazard mitigation techniques, faulting and its effects on infrastructure, site effects and slope stabilization, railway systems and vehicle–track interaction, seismic response of monuments, offshore geotechnics, and earthquake crisis management systems. He has been involved as a consultant in a variety of projects of significance in Europe, the US and the Middle East. His consulting work ranges from special seismic design of bridges, buildings, retaining walls, metro stations and tunnels, to harbour quay walls, and special design against faulting–induced deformation applying the methods he has developed. He currently has sat on the panel of Géotechnique and of the ICE Geotechnical Engineering Journal, and currently serves as Associate Editor of Frontiers in Earthquake Engineering. He is the inaugural recipient of the Young Researcher Award of the ISSMGE in Geotechnical Earthquake Engineering, and winner of the 2012 Shamsher Prakash Research Award.

Advances in simulating post-earthquake recovery for performance-based engineering and resilience

Abstract

The performance-based earthquake engineering paradigm has enabled a dramatic shift in the way that some damage-resistant buildings are being designed. By enabling the more explicit targeting and verification of performance in large earthquakes, building owners have an increased opportunity to achieve enhanced performance with limited additional cost. And ongoing research is extending this paradigm to encompass a broader set of performance metrics related to the impacts of regional damage and post-earthquake recovery activities. This presentation will highlight developments in performance-based engineering research and practice in the United States. Progress has depended upon advancements in developing standards of practice, standardized performance metrics, practical software tools, and fundamental research. Recent developments related to resilience assessment, and exemplary successful projects, will be presented.

Biography

Jack Baker's work focuses on the development and use of probabilistic and statistical tools for managing risk due to extreme loads on the built environment. He has investigated seismic loads on spatially distributed systems, characterization of earthquake ground motions, performance of damaged infrastructure systems, and probabilistic risk assessments of a number of types of structures. Prof. Baker joined the Stanford faculty in 2006 from the Swiss Federal Institute of Technology (ETH Zurich), where he was a visiting researcher in the Department of Structural Engineering. In 2015-2016 he was a Visiting Erskine Fellow at the University of Canterbury. He has degrees in Structural Engineering (Stanford, M.S. 2002, Ph.D. 2005), Statistics (Stanford, M.S. 2004) and Mathematics/Physics (Whitman College, B.A. 2000). He has industry experience in seismic hazard assessment, ground motion selection, probabilistic risk assessment, and modelling of catastrophe losses for insurance and reinsurance companies. His awards include the Shah Family Innovation Prize from the Earthquake Engineering Research Institute, the CAREER Award from the National Science Foundation, the Early Achievement Research Award from the International Association for Structural Safety and Reliability, the Walter L. Huber Prize from ASCE, and the Eugene L. Grant Award for excellence in teaching from Stanford.

Towards self-aware infrastructure

Abstract

Engineers are today faced with a conundrum. On one hand an ageing building stock and on the other novel materials and digital building technologies reshaping the landscape of construction. The life-cycle management of both existing and new structural systems operating under diverse loads demands a better understanding of how these systems respond. This involves the tasks of simulation (forward engineering), identification (inverse engineering) and the organization of maintenance/control actions. The efficient and successful implementation of these tasks is however non-trivial, due to the ever-changing nature of these systems, and the variability in their interactive environment. Two defining factors in understanding and interpreting such large-scale systems are nonlinear behavior and structural uncertainty. The former is related to the external dynamic loading that might shift the structural response from purely linear to nonlinear regimes, while the latter is related to erroneous modeling assumptions, imprecise sensory information, ageing effects, and lack of a priori knowledge of the system itself.

This talk discusses implementation of methods and tools able to tackle the aforementioned challenges. Among other topics, the use of parametric surrogate representations and Bayesian-type filters for the reduced representation and identification of uncertain and time-varying or nonlinear structural systems is discussed. It is further demonstrated how construction of data-driven performance indicators (PIs) stemming from the previous analysis may be exploited to support decisions on optimal management of infrastructure.

Biography

Eleni Chatzi received her PhD from the Department of Civil Engineering and Engineering Mechanics at Columbia University, New York. She is currently an Associate Professor and Chair of Structural Mechanics at the Institute of Structural Engineering of the Department of Civil, Environmental and Geomatic Engineering of ETH Zürich. She leads an international team of researchers working on data-driven monitoring, automated condition assessment and intelligent decision support for engineered systems, with applications spanning across civil, mechanical and aerospace infrastructure. She serves as editor of numerous peer reviewed journals, and as scientific committee member of international conferences in the field of SHM. Her research has been supported by the European Commission, the Swiss National Science Foundation, and the ETH Research Foundation. She is currently leading the ERC Starting Grant WINDMIL on Smart Life-Cycle Assessment of Wind Turbines. She serves as director of the Computational Science Zurich PhD Program, and a Core Group member of COST Actions TU1402, TU1406 focusing on assessment of infrastructure.

Cumulative damage to masonry structures due to repeated earthquakes and effectiveness of strengthening provisions

Abstract

The quantification of the response of buildings to consecutive shaking from strong motions occurring at the same site in relatively rapid succession, and before repairs can be implemented, is not a recent problem. Examples are documented from at least the late 1990’s. However, after major swarms of earthquakes at the beginning of this decade, the Maule Chile earthquake, 2010, Christchurch, New Zealand earthquake, 2011, and the Tohoku, Japan earthquake, 2011, the scientific and technical community has been paying more attention to this issue with a significant number of studies devoted to this problem with the intent of providing design guidance for structures exposed to repeated shaking.

Such studies rely on:

• more accurate documentation and reliable records of seismic sequences, thanks to denser and more sensitive arrays of sensors;
• better understanding and modelling of fault ruptures and relationship among consecutive strong motions;
• more detailed post elastic modelling of structures, with improved characterization of degrading capacity phenomena.

Designing for multiple earthquakes is a logical extension of the performance-based design, responding to the necessity of minimizing damage, so as to reduce recovery times and costs, improve resilience and render the building stock more sustainable.

The paper summarizes key developments in this field within the framework of probabilistic risk assessment and illustrates the fundamental elements of such analyses with reference to the case of the 2016 Central Italy earthquake sequence, with particular attention to masonry structures.

Using accurate data collected in situ for building affected by the earthquake in Norcia and in Amatrice, the mechanics approach coded in FaMIVE is used to determine initial and residual capacities of a large number of buildings under repeated shaking. Cloud of performance points are generated for each event to be used to determine fragility curves, representative of the percentage of buildings undergoing certain damage levels under the specific seismic scenario. A discussion on the obtained results and the capability of the method to represent the observed damage extents concludes the paper.

Biography

Dina D’Ayala is the Professor of Structural Engineering at University College London, within the Department of Civil, Environmental and Geomatic Engineering. She is head of Civil Engineering and Co-Director of the Earthquake and People Interaction Centre, EPICentre. She is a director of the International Association of Earthquake Engineers and Fellow of the ICE. Her specialism is Structural Resilience Engineering with particular emphasis on the assessment, strengthening, preservation and resilience of existing buildings, structures, transport infrastructure and cultural heritage. Her current research focusses on resilience of structures and infrastructure to natural hazards, supported through research grants from EU FP7, INFRARISK, and the UK RC, PARNASSUS, STORMLAMP, SCOSSO, PRISMH. She has 25 years’ experience working with international agencies, the World Bank, ODA, UNDP, British Council, in countries such as Nepal, Jordan, Turkey, Iraq, Philippines etc., and leading interdisciplinary projects on enhancing resilience against natural hazards. She has produced Guidelines for DfID on assessment and strengthening of hospitals and reconstruction efforts in Nepal. She is the chief scientist for the World Bank on the Global Programme for Safe Schools (GPSS) and leads the development of the World Bank GLoSI project. She is a member of the Management Board of the International Centre for Collaborative Research on Disaster Risk Reduction (ICCR-DRR) at Beijing Normal University.

Towards improved seismic design procedures for steel structures

Abstract

European seismic design procedures are currently undergoing a process of evolution and development. This process is guided by improved understanding of structural behaviour based on new research findings, coupled with the need to address issues identified from the practical application in real engineering projects. Developments in design guidance however need to balance technical advancements with the desire to maintain a level of stability and simplicity in codified rules. To this end, this paper summarises the main changes proposed in the imminent revision of Eurocode 8 with respect to the design of steel framed structures. Proposed code modifications in terms of seismic loading, behaviour factors, ductility considerations, capacity design verifications, as well as drift-related requirements, are outlined and discussed. In order to illustrate the implications of several of the main suggested code modifications on key performance aspects, a set of moment frames satisfying Eurocode 8 are utilised within a series of nonlinear static and dynamic analysis. It is shown that several of the proposed code changes lead to fundamentally improved seismic performance, whilst others result in more efficient design at the expense of safety margins at the design and ultimate levels. Importantly, the results emphasise the imbalance between the focus given to ductility supply compared to assessing the expected inelastic demand considering salient seismic loading characteristics such as frequency content and duration effects. The paper concludes with an appraisal of proposed code modifications and highlights areas in which further developments are still required to improve the reliability of seismic design procedures.

Biography

Professor Ahmed Elghazouli is Head of the Structural Engineering Section and Director of the MSc programme in Earthquake Engineering at Imperial College London. He has over 25 years of research and consulting experience in seismic design and structural robustness under extreme loads, and has published over 250 papers in related areas. He is a Fellow of the Royal Academy of Engineering, a Chartered Engineer and a Fellow of the Institutions of Civil and Structural Engineers. He has participated in key national and European code development activities. He is also a past chairman of SECED and currently chairs the BSI B/525/8 committee on seismic design.

Performance-based geotechnical earthquake engineering – How can we use it in practice?

Abstract

Since the publication of SEAOC Vision 2000 in 1995 the topic of performance-based earthquake engineering has been a key subject for earthquake engineers. This has principally been focussed on structural aspects of design and less so on geotechnical aspects. The framework of performance-based design was adopted some 15 years ago in the International Standard ISO 23469 for seismic design of geotechnical structures. However, very little useful and pragmatic guidance is provided for the practising engineer. The one area in which strides have been made is for the design of ports and harbours. How can we best utilise this disparate guidance for real design work? It is well understood that the seismic performance of geotechnical works is significantly affected by ground displacement. Therefore, there is a requirement to accurately model the behaviour of geotechnical structures and estimate ground displacements. This leads to concern relating to the adequacy and accuracy of computer models to estimate soil behaviour and associated settlements or displacements. This paper reviews the current state of the practice in performance-based geotechnical earthquake engineering. It looks at key questions and concerns in implementing this approach. It also provides examples of how the approach has been applied to projects including ports, bridges and offshore structures and hence attempts to provide some practical design guidance.

Biography

Ziggy is a geotechnical earthquake engineer with over 30 years’ experience working at Arup. He has carried out seismic design, analysis and assessment for a range of structures in the energy, infrastructure, manufacturing and humanitarian sectors. He has acted as the seismic specialist for major projects such as offshore platforms in New Zealand and Caspian Sea, the proposed Çanakkale Bridge in Turkey, and the seismic and tsunami hazard assessment for the new Wylfa Newydd NPP. Ziggy was recently appointed a Royal Academy of Engineering Visiting Professor in Geotechnical Earthquake Engineering at UCL. He has been Chair of SECED and is heavily involved in the development of Eurocode 8.