Structural Identification of Constructed Systems : Approaches, Methods, and Technologies for Effective Practice of St-Id by F. Necati Çatbaş, Tracy Kijewski-Correa, A. Emin Aktan.
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1 Structural Identification of Constructed Systems
2 A Priori Modeling
3 Experimental Considerations
4 Data Processing and Direct Data Interpretation
5 Structural Identification for Selection, Application, and Calibration of Physics-Based Models
6 Utilization of St-Id for Assessment and Decision Making
Appendix A: Case Studies on the Structural Identification of Buildings
Appendix B: Case Studies on the Structural Identification of Bridges
ASCE-SEI Performance of Structures Track established the current technical committee on “Structural Identification (St-Id) of Constructed Systems” in 2005. This was intended to continue with the unfinished work of an earlier ASCE Committee with the same name that was established over a decade ago but discontinued after 1999. The previous Committee issued a draft report that was circulated but not published, and many other contributions were made by the Committee in terms of bringing researchers from engineering mechanics and civil-structural engineering closer in the understanding of the powerful paradigm of St-Id especially in the context of applications to constructed systems. The contributors to the previous report included distinguished researchers such as James Yao, James Beck, Scott Doebling and Chuck Farrar amongst others, who are well-known as pioneers who have explored and contributed to St-Id of constructed systems, albeit mainly from an engineering mechanics world-view.
The current Committee, founded by the founding Chair of the earlier one, recognized that it is critical to understand and leverage the concept of St-Id mainly from a structural engineering world-view in order to advance the art of structural engineering. Differences between engineering mechanics versus structural engineering world-views is not often discussed, however, a review of the Table of Contents of the respective Journals of these sub-disciplines of civil engineering reveals a gap that is difficult to deny. One of the goals of the 2005 Committee was to try to bridge this gap. Given the above, the near-term purpose and objectives of the Committee were defined as follows:
Committee Purpose: Foster advances and dialogue to enable the collection of data, its analysis and interpretation, and ultimately the assessment of constructed system performance beyond the anecdotal observations that currently form our bases for judging the merits of our designs.
Committee Objectives: Given that the actual mechanical characteristics and performance of constructed systems have been shown to be very different from those considered during a specification-based code design, a principal focus will be on defining metrics and establishing measurement standards for constructed systems, which represents a prerequisite for a meaningful transition to Performance Based Civil Engineering. The Committee will also aim to develop guidelines for reliable field-calibrated analytical modeling and characterization of existing constructed systems. Field-calibrated analytical modeling leverages objective measurements of geometry, soil and structural material characteristics, responses during controlled experiments, and, long-term monitoring for establishing the loading environments and performance of a constructed system at critical performance limit-states.
To inform these two standards as well as the profession at large regarding the relevant issues and vast discrepancies between different applications of St-Id, the Committee will collect available data from existing tests, and interpret and archive case studies.
In addition to preparing and publishing guidelines, conference sessions will be organized and papers will be published in proceedings.
The following State-of-the-Art report on Structural Identification is the Committee’s first major product for the profession to fulfill the promise of both the earlier and the current Committee.
Background and the Drivers Shaping the Agenda of the Committee
Structural identification (St-Id) is an adaptation of the system-identification concept which originated in electrical engineering in relation to circuit and control theory. St-Id has been defined as: “the parametric correlation of structural response characteristics predicted by a mathematical model with analogous quantities derived from experimental measurements” (the 1995 draft report by the earlier Committee). The St-Id paradigm was first introduced to engineering mechanics researchers by Hart and Yao (1977) and to civil-structural engineering researchers by Liu and Yao (1978). These seminal papers gradually inspired many researchers to investigate various aspects of St-Id, and nearly 30 years later St-Id remains an active research area in both engineering mechanics and civil-structural engineering. Recent advances in IT has rendered FE modeling of large structures for new design, or condition and vulnerability assessment, rehabilitation or retrofit commonplace. Civil engineering consultants are routinely using FE modeling and simulation for practical applications. However, it has been well established that due to the uniqueness and significant epistemic uncertainty associated with our constructed systems, reliable simulations, either by a 3D microscopic FE model or by much simpler and greatly idealized macroscopic models, require calibration and validation based on actual observations and measured experimental data. Meanwhile, the paradigm of making meaningful observations and taking reliable measurements from actual operating constructed systems in the field is still an emerging art. Using field observations and measurements for calibrating and validating a FE model is also a highly challenging problem. An ASCE Committee was therefore warranted to bring together researchers and practicing engineers with experience and knowledge in practical applications of FE models, fundamentals of various approaches to FE modeling, simulations and scenario analysis, field research, and their integration
St-Id Application Scenarios
There are several scenarios, which may justify the construction and identification, based on the results of field experiments, of an analytical model for simulating an actual constructed system. Examples include:
1. Design verification and construction planning in case of challenging and/or ground-breaking new designs,
2. A means of measurement-based delivery of a design-build contract in a performance-based approach,
3. Documentation of as-is structural characteristics to serve as a baseline for assessing any future changes due to aging and deterioration, following hazards, etc.
4. Load-capacity rating for inventory, operations or special permits,
5. Evaluation of possible causes and mitigation of deterioration, damage and/or other types of performance deficiencies (e.g. vibrations, cracking, settlement, etc.),
6. Structural intervention, modification, retrofit or hardening due to changes in use-modes, codes, aging, and/or for increasing system-reliability to more desirable levels,
7. Health and performance monitoring for operational and maintenance management of large systems,
8. Asset management of a population of constructed systems such as RC TBeam bridges,
9. Advancing our knowledge regarding how actual structural systems are loaded (during construction and after commissioning), how they deform, i.e. their kinematics at supports, joints, connections, and how they transfer their forces through the members to foundations and to soil.
There is sufficient evidence that our current knowledge base on the loading, behavior and performance of constructed systems is greatly incomplete, especially when new construction materials and systems are considered. The significant epistemic uncertainty prevailing in the actual loading mechanisms, intrinsic force distributions, kinematics, failure modes and capacities of existing constructed systems, especially after aging may lead to discrepancies between predicted responses and capacities that are different by more than an order of magnitude, and not always in a conservative way. Many members, joints and connections may be loaded less than assumed while many others may be loaded with demands that are far greater than anticipated. Some of the mechanisms that may control the distribution of demands and the corresponding capacity at the critical regions of constructed systems are often very difficult to discover and quantify even with measurements unless a rigorous St-Id is carried out by experts. Therefore, systematic applications of St-Id to well selected samples of constructed systems is considered important if civil engineering in the USA will move from specification-based project delivery to a performance-based one with long-term warranty.
Observations in the field, followed by properly designed, executed and interpreted experiments are the only definitive approach for reducing epistemic uncertainty that clouds constructed system behavior. Further, it is not possible to reliably design, execute and interpret field experiments without first studying, observing, conceptualizing, and modeling a constructed system, so that sensing and loading can be designed effectively and data can be interpreted. These are some of the reasons that make advancing St-Id and conducting applications important and in fact necessary for civil engineers if we are to respond to the needs of the society regarding improving the lifecycle performance and sustainability of our constructed systems. The Committee has developed the following long-term work-plan to accomplish its goals:
1. Recruiting Champion Experts: The first step has been to bring together as many of the champions and experts as possible from academe, industry and government who have been advocates in changing the way we teach and practice civil engineering. Such experts would be the first to recognize the importance of St-Id as a paradigm offering an effective path to integration and discovering the reality of constructed systems and infrastructures. Civil engineers knew of this reality before the 20th Century through intuition and heuristics. After losing this to a proliferation of university programs and prescriptive codes; and to the shift to applied science in the 1950’s without distinguishing the differences between constructed and mechanical systems, we now have a chance to rediscover reality. The most important long-term goal for the Committee would be to establish reality of civil engineered systems in a factual and quantitative manner, as accurately and completely as possible, comparing the assumed-predicted and true reality, and to disseminate this information. In this manner we may contribute to changing the way we teach and practice by basing it on ground truth which we can discover through St-Id of existing systems. The Committee membership has been endowed with the best possible global expertise.
2. Establishing the State-of-the-Art: The first deliverable identified by the Committee is a state-of-the-art report that is now complete and that recognizes the distinctions between constructed and mechanical systems.
3. Organizing/Coordinating Research on Lab Benchmarks: Well-designed physical laboratory models are invaluable benchmarks for exploring and demonstrating the St-Id process, and the many possible products that may come out of the process. Such models also serve as excellent case-study based learning opportunities for students and practicing engineers interested in continuing education. Recognizing that there is no unique characterization for a constructed system, but a ground truth that we can approach only as close as uncertainty permits, the art of St-Id becomes how we deal with the challenges of managing uncertainty. The age-old strategy in civil engineering analysis has been investing only as much into modeling and computation that is commensurate with what the uncertainty will permit us to predict within some confidence. The issue is in how we may reduce the uncertainty by virtue of having a physical model that does NOT have many of the uncertainties we face in the field, and one that may be tested as many times, by as many persons, and, in as many different ways as needed.
4. Organizing/Coordinating Demonstrations on Real Systems: A long-term goal is to leverage the expertise of the Committee in St-Id demonstration projects on real bridges and buildings. Such an effort may be initiated in NIST’s leadership for buildings and FHWA’s leadership for bridges, with ASCE and other agencies such as NSF’s participation and support.
Structural Identification of Constructed Systems : Approaches, Methods, and Technologies for Effective Practice of St-Id by F. Necati Çatbaş, Tracy Kijewski-Correa, A. Emin Aktan pdf
⏩Editors: F. Necati Çatbaş, Tracy Kijewski-Correa, A. Emin Aktan
⏩Copyright © 2013 by the American Society of Civil Engineers.
⏩ISBN 978-0-7844-1197-1 (paper)
⏩ISBN 978-0-7844-7647-5 (PDF)
Manufactured in the United States of America.
⏩Size: 10 MB
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