IALCCE 2014 - Invited Lectures
Fazlur R. Khan Lecture
Life-cycle of structural systems: recent achievements and future directions
- Dan M. Frangopol
- Department of Civil and Environmental Engineering, ATLSS Engineering Research Center,
Lehigh University, Bethlehem, PA, USA
Structural systems are under deterioration due to aging, mechanical stressors, and harsh environment, among other threats. Corrosion and fatigue can cause gradual structural deterioration. Moreover, natural and man-made hazards may lead to a sudden drop in the structural performance. Under the combined effects of these threats, civil and marine infrastructure systems are expected to perform their intended function while maintaining acceptable safety, serviceability, and functionality levels. Inspection, repair, and maintenance actions are performed to monitor the structural safety and maintain the performance over certain thresholds. However, these actions must be effectively planned throughout the life-cycle of a system to ensure the optimum budget allocation and maximum possible service life without adverse effects on the safety of the structural system. In this context, life-cycle engineering provides rational means to optimize life-cycle aspects, starting from the initial design and construction to dismantling and replacing the system at the end of its service life. Within the last decades, several approaches have been proposed to provide decision-makers with rational life-cycle management strategies for deteriorating structural systems. This lecture presents a brief overview of the recent research achievements in the field of life-cycle engineering for civil and marine structural systems. Different aspects of the life-cycle engineering are presented. These aspects include the performance prediction under uncertainty, optimization of life-cycle cost and intervention activities, as well as the role of structural health monitoring and controlled testing techniques in supporting the life-cycle management decisions. Challenges related to risk-informed decision-making, resilience, and sustainability are also discussed.
An investigation of two methodologies to determine optimal life cycle activity profiles for bridges
- Bryan T. Adey
- Institute of Construction and Infrastructure Management (IBI),
ETH Zürich (ETHZ), Zurich, Switzerland
Bridges are vital objects in public road networks. They should be managed to ensure that they result in minimum costs for all stakeholders, e.g. intervention costs for the owner and travel time costs for the user. An important part of bridge management is, therefore, the determination of the optimal interventions to be executed on a bridge over its life cycle, i.e. the optimal life-cycle activity profile, which adequately takes these costs into consideration. This is challenging as some of the costs to be considered are related to the condition of the elements of which a bridge is composed, while others are related to the performance of the structure as a whole and only indirectly to the performance of the individual elements. In this paper, the possibility of using a state-of-the-art methodology and a state-of-practice methodology to determine optimal life cycle activity profiles is investigated. This is done by using them to determine the optimal life cycle activity profile for a multi-span weathering steel girder bridge. The strengths and weaknesses of each are discussed.
Failure times of concrete structures in aggressive environment
- Fabio Biondini
- Department of Civil and Environmental Engineering,
Politecnico di Milano, Milano, Italy
For concrete structures exposed to corrosion the identification of the local failure modes and of their occurrence in time can represent a crucial information to maintain a suitable level of system performance and to avoid collapse over the structural lifetime. In fact, repairable local failures can be considered as a warning of damage propagation and possible occurrence of more severe and not repairable failures. In particular, the ability of the system to redistribute the load after the occurrence of a local failure can be measured in terms of structural redundancy. However, this indicator refers to a prescribed point in time and does not provide a direct measure of the failure rate, which depends on the damage scenario and damage propagation mechanism. Failure times should be computed to this purpose and the investigation of all local failure modes up to collapse and their activation in time could be helpful to plan repair interventions and maintenance actions to protect, improve and/or restore the lifetime system performance in terms of redundancy and damage tolerance. In this study, failure times of concrete structures under corrosion are computed by means of a time-variant progressive collapse analysis conducted by removing components once they fail. For important structures, the computational cost of this type of analysis could be compensated by a more comprehensive knowledge of the redundancy resources of the system which allows to better identify weak components to be strengthened and damaged members to be repaired.
Time-dependent earthquake risk assessment modeling incorporating sustainability metrics
- Anne Kiremidjian
- Department of Civil and Environmental Engineering,
Stanford University, Stanford, CA, USA
Earthquake risk assessment methods have been the focus of research for the past several decades. Most of these models have treated the risk problem as static ignoring structural deterioration and regional infrastructure growth over time. The risk, however, is dynamic in nature for several reasons. First, occurrences of large earthquakes are time dependent. Second, the vulnerability of structure changes over time increasing due to deterioration of material and is in general lower for newer structures because of the introduction of more stringent earthquake resistance design requirements. In addition, various environmental factors contribute to the risk over the life of a structure, yet these environmental factors are typically not considered.
A time-dependent earthquake risk model is developed by our research team that considers two key components of the problem – (a) the increasing vulnerability of structures due to corrosion and (b) contributions by various environmental factors typically used as metrics of sustainability over time. The Pacific Earthquake Engineering Research (PEER) performance based earthquake engineering formulation is used to identify key components that are time dependent. These include the earthquake hazard rate, the probability distribution of structural capacity given the earthquake demand and the decision variable dependence on monetary discount rates. Life-cycle cost analysis is used to evaluate the contribution of different repair components after every damaging earthquake event. Components in the life-cycle impact analysis include estimation of greenhouse gas potential, ozone depletion potential, acidification potential and several others. Results from applications of the methodology to a single reinforced concrete bridge column show that structural deterioration does contribute to the risk over time and if ignored can result in underestimation of that risk. Moreover, the risk significantly decreases with improved seismic design. Similarly, the contribution of various life-cycle impacts is most pronounced for older structures that have greater potential for deterioration.
Big-data based infrastructure management: Toward assetmetrics
- Kiyoshi Kobayashi
- Graduate School of Engineering,
Department of Urban Management, Kyoto University, Kyoto, Japan
The asset management for infrastructures has been conducted based on implicit knowledge, such as the experience and knowledge of professional engineers, for each process. Asset metrics is aimed at converting the decentralized decision making process based on implicit knowledge to the systematic decision making process based on formal knowledge. Especially, methodologies are developed based on the data that can be obtained through daily and regular inspections, under the thoroughgoing hands-on policy. In the field of asset management, the authors emphasize the importance of intellectual technologies for analyzing existing data rather than the hardware technologies for collecting new data, and indicate that this is consistent with the concept of big data analysis. In addition, the authors mention ideal monitoring methods in this field and the perspective for comprehensive risk management, by introducing the latest researches into assetmetrics.
Exploring reliability based bridge design framework against accidental loads - ship collision
- Hyun-Moo Koh
- Department of Civil & Environmental Engineering,
Seoul National University, Seoul, Korea
The inherent uncertainty of the frequency and magnitude of accidental loads such as ship collisions, as well as the approximate nature of accidental load effects, makes it difficult to minimize safety and economical risks in the design process. In this regard, current bridge design practices against ship collisions are critically appraised and a new reliability-based design framework using multiple collision scenarios with various uncertainties are proposed.
Climate change risks and climate adaptation engineering for built infrastructure
- Mark G. Stewart
- Centre for Infrastructure Performance and Reliability,
The University of Newcastle, New South Wales, Australia
A changing climate may result in more intense tropical cyclones and storms, more intense rain events and flooding, and other natural hazards. Moreover, increases in CO2 atmospheric concentrations, and changes in temperature and humidity, may reduce the durability of concrete, steel and timber structures. There is increasing research that takes into account the changing climate risks and life-cycle costs in engineering to reduce the vulnerability or increase the resiliency of infrastructure - we define this as ‘climate adaptation engineering’. The paper will describe how risk-based approaches are well suited to optimising climate adaptation strategies related to the design of new infrastructure. Stochastic methods are used to model infrastructure performance, risk reduction and effectiveness of adaptation strategies, exposure, and costs. These concepts will be illustrated with state-of-the research of risk-based life-cycle assessment of climate adaptation strategies including (i) design of new houses subject to severe storms, (ii) effects of climate change on corrosion of reinforced concrete structures, and (iii) measures to reduce vulnerability of power distribution infrastructure. Uncertainties of climate projections are also discussed. This will pave the way for more efficient and resilient infrastructure, and help 'future proof' new and existing infrastructure to a changing climate.
Practical application of life-cycle management system for shore protection facilities
- Hiroshi Yokota
- Faculty of Engineering,
Hokkaido University, Sapporo, Japan
Shore protection facilities, mainly made of concrete or reinforced concrete have a long lifetime and must be expected to meet demands for providing people living coastlines with safety and security. The principal demands for those facilities seem to be simple but have not been practically so easy to be kept over the requirements. The reasons for those are that facilities are rather long and are exposed to severe environments for materials. In addition, as it would be very important, rise of the seawater level etc. due to global warming may affect the function and performance, which has to be taken into account rehabilitation planning. To meet such difficulties, it is important to pursue coordination between design and maintenance based on the procedure of the life-cycle management through which sustainability indicators would be maximum/minimum. The author presents the concept and the framework of the life-cycle management system for those facilities, and introduces methodologies of the management system particularly feasible to practical maintenance. Assessment, prioritization of interventions, and functional update of facilities are also covered in the lecture.