FEM1- An Introduction to Structural Health Monitoring

1. FEM1- An Introduction to Structural Health Monitoring Fundamentals Education Subunit- Structural Health Monitoring Education Unit

2. Purpose • To acquaint you with the fundamentals of Structural Health Monitoring (SHM) with specific application to bridges. • To develop a vocabulary of terms used in SHM and gain insight into the components and systems commonly used in SHM applications. • To identify the ways in which SHM systems are being used in contemporary bridge design and maintenance. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

3. Expected Learning Outcomes At the completion of this module you will be able to: • Identify and distinguish the components of SHM systems. • Relate the components of a viable SHM system in a schematic drawing. • Describe the benefits of implementing SHM. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

4. Your Assignment • After you have read and reviewed the content of FEM1, you will be required to: • Take an online readiness examination to determine if you have achieved a sufficient understanding of the content of FEM1 consistent with the stated learning outcomes to satisfactorily engage in the classroom discussion. • Submit an online response to a discussion question and list any questions you have concerning any topic you might not understand about the content of FEM1. • Your online discussion question response will be discussed in an interactive manner in a classroom setting on the date specified in the Master Schedule (via your institution’s LMS or hard copy) . Fundamentals Education Subunit- Structural Health Monitoring Education Unit

5. Definitions/Descriptions of Structural Health Monitoring (1) • A “Glossary of Uncommon Terms” (Bisby, 2004) is provided to assist your reading in this field of civil engineering. • This list is not necessarily comprehensive, so you may run across terms you don’t understand which are not included in the Glossary. If that’s the case, see if you can find the term by searching on the Internet. • If so, list the term and the definition you found on the discussion question submission form. • If not, simply list the term under “Questions” on the online response form. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

6. Definitions/Descriptions of Structural Health Monitoring (2) • Let’s start with the various ways in which practicing professionals define and/or describe SHM. • While the words may be different, you should be able to identify features/terms/concepts that are common to all the definitions. Think about that as you review the definitions. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

7. Definitions/Descriptions of Structural Health Monitoring (3) “SHM refers to the broad concept of assessing the on-going, in-service performance of structures using a variety of measurement techniques.” (Bisby, 2004) Fundamentals Education Subunit- Structural Health Monitoring Education Unit

8. Definitions/Descriptions of Structural Health Monitoring (4) “Structural Health Monitoring (SHM) aims to give, at every moment during the life of a structure, a diagnosis of the “state” of the constituent materials, of the different parts, and of the full assembly of these parts constituting the structure as a whole.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

9. Definitions/Descriptions of Structural Health Monitoring (5) “Thanks to the time dimension of monitoring, which makes it possible to consider the full history database of the structure, and with the help of Usage Monitoring, it can provide a prognosis (evolution of damage, residual life, etc.).” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

10. Definitions/Descriptions of Structural Health Monitoring (6) Considering the diagnosis function only, SHM “is a new and improved way to make a non-destructive evaluation (NDE).” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

11. Definitions/Descriptions of Structural Health Monitoring (7) Actually SHM is much more than a non-destructive evaluation. “It involves the integration of sensors, possible smart materials, data transmission, computational power, and processing ability inside the structures.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

12. Definitions/Descriptions of Structural Health Monitoring (8) SHM makes it possible “to reconsider the design of the structure and the full management of the structure itself and of the structure considered as part of a wider system.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

13. Definitions/Descriptions of Structural Health Monitoring (9) “The process of implementing a damage identification strategy for aerospace, civil and mechanical engineering infrastructure is referred to as structural health monitoring (SHM).” (Farrar and Worden, 2007) Fundamentals Education Subunit- Structural Health Monitoring Education Unit

14. Definitions/Descriptions of Structural Health Monitoring (10) SHM “can be defined as a non-destructive in-situ structural evaluation method that uses several types of sensors which are attached to, or embedded in, a structure.” The data collected “can be used to assess safety, integrity, strength or performance of the structure and identify damage at its onset.” (Bisby, 2004) Fundamentals Education Subunit- Structural Health Monitoring Education Unit

15. Definitions/Descriptions of Structural Health Monitoring (11) “The SHM process involves the observation of a system over time using periodically sampled dynamic response measurements from an array of sensors, the extraction of damage-sensitive features from these measurements, and the statistical analysis of these features to determine the current state of system health.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

16. Definitions/Descriptions of Structural Health Monitoring (12) “For long term SHM, the output of this process is periodically updated information regarding the ability of the structure to perform its intended function in light of the inevitable aging and degradation resulting from operational environments.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

17. Definitions/Descriptions of Structural Health Monitoring (13) “After extreme events, such as earthquakes or blast loading, SHM is used for rapid condition screening and aims to provide, in near real time, reliable information regarding the integrity of the structure.[1]” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

18. Definitions/Descriptions of Structural Health Monitoring (14) The Illinois SHM Project describes SHM as “The ability to continuously monitor the integrity of civil infrastructure in real time” as a means “to reduce maintenance and inspection costs, while providing for increased safety to the public.” They cite that it is particularly imperative for evacuation routes and facilities be evaluated for safety after natural disasters. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

19. Definitions/Descriptions of Structural Health Monitoring (15) These definitions/descriptions have introduced a couple words which should be defined. • Damage • Sensor Fundamentals Education Subunit- Structural Health Monitoring Education Unit

20. Definitions/Descriptions of Structural Health Monitoring (16) DAMAGE: “Defined as changes to the material and/or geometric properties of a structural system, including changes to the boundary conditions and system connectivity, which adversely affect the system’s performance.” https://en.wikipedia.org/wiki/Structural_health_monitoring Fundamentals Education Subunit- Structural Health Monitoring Education Unit

21. Definitions/Descriptions of Structural Health Monitoring (17) SENSOR: “A device whose purpose is to detect events or changes in its environment, and then provide a corresponding output. A sensor is a type of transducer; sensors may provide various types of output, but typically use electrical or optical signals.” https://en.wikipedia.org/wiki/Sensor Fundamentals Education Subunit- Structural Health Monitoring Education Unit

22. Questions to Think About 1. What are the common features of the definitions/descriptions? 2. Thinking about your Mechanics of Materials Laboratory course, what kind of sensors could you (or did you) use to measure… (a) load? (b) deflection? (c) strain? (d) temperature? Fundamentals Education Subunit- Structural Health Monitoring Education Unit

23. Purposes of Structural Health Monitoring (1) SHM can be used for a variety of purposes, including but not necessarily limited to… • “Determine actual behavior and compare to assumptions used in the analysis.” • “Determine actual loading and compare to design loading.” • “Evaluate durability of structure to environmental, operational, and load conditions.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

24. Purposes of Structural Health Monitoring (2) and… • “Assess secondary design issues such as temperature, joints, movements, and vibrations.” • “Identify deterioration or damage of the structure and its components.” • “Evaluate safety and reliability of structure at any stage of its service life.” • “Assess the impact of maintenance or rehabilitation on future performance.” Fundamentals Education Subunit- Structural Health Monitoring Education Unit

25. Purposes of Structural Health Monitoring (3) While the listings on the two previous slides are reasonably exhaustive, they do not necessarily identify all the possible purposes of SHM. Question: Can you think of other possible uses? Fundamentals Education Subunit- Structural Health Monitoring Education Unit

26. Purposes of Structural Health Monitoring (4) One particular unique application involved the widening of the Huey P. Long Bridge near New Orleans during the period, 2006-2013 (Bassam and Schulze, 2011). • The specific issue was the transfer of construction loads from new structural members to old bridge truss members during construction. • The concern was the possibility of overloading the old truss members. • To address this concern, a SHM system was designed to monitor the changes in stresses and deformations continuously at all stages of the project. https://www.campbellsci.com/louisiana-bridge-avw206 • A photo of the original and rendering of the renovated Bridge are provided in the following slide. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

27. The Old and Renovated Huey P. Long Bridge Fundamentals Education Subunit- Structural Health Monitoring Education Unit

28. Fundamental Axioms of SHM (1) Worden, et. al. (2007) asserted that the progress in the development of SHM over the previous 20 years had matured to the point that several fundamental principles or axioms had emerged. Note: Some of these axioms apply to principles and conditions beyond the scope of the SHM Fundamentals Education Subunit. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

29. Fundamental Axioms of SHM (2) • Axiom I: All materials have inherent flaws and defects. • Axiom II: The assessment of damage requires a comparison between two system states. • Axiom III: Identifying the existence and location of damage can be done in an unsupervised learning mode, but identifying the type of damage present and the damage severity can generally only be done in a supervised learning mode. • Need definitions Fundamentals Education Subunit- Structural Health Monitoring Education Unit

30. Fundamental Axioms of SHM (3) • Axiom IV: Sensors cannot measure damage. Feature extraction through signal processing and statistical classification is necessary to convert sensor data into damage information. • Axiom V: The length- and time- scales associated with damage initiation and evolution dictate the required properties of the SHM sensing system. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

31. Fundamental Axioms of SHM (4) • Axiom VI: There is a trade-off between the sensitivity to damage of an algorithm and its noise rejection capability. • Axiom VII: The size of damage that can be detected from changes in the system dynamics is inversely proportional to the frequency range of excitation. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

32. Schematic of Structural Health Monitoring Systems (1) • Now that you have been introduced to qualitative descriptions of SHM systems and the range of their purposes, let’s take a look at a schematic of a typical system and discuss the functions of the various components of the system. • Recognize that this is a generic system presented for illustrative purposes. • Actual systems will likely vary in their specific design but will generally consist of the components (subsystems) and functionalities herein discussed. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

33. Schematics of Typical SHM Systems Note that the system depicted on the RHS has a much more elaborate system for processing and evaluating data. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

34. Schematic of Structural Health Monitoring Systems: Sensors (2) • Acquisition of data is achieved by an array of sensors selected to acquire the data needed to assess and, ultimately, analyze the performance of the bridge consistent with the purpose of the SHM system. • Functionally, sensors can be used to measure the response of the bridge to its primary force- traffic and dead load and secondary forces such as temperature and wind. • Thus, the sensor array generally encompasses sensors to measure both bridge behavior and the external environment (e.g., temperature and wind speed and direction). Fundamentals Education Subunit- Structural Health Monitoring Education Unit

35. An example of an elaborate sensor array Take some time and examine the types of sensors deployed. Do you understand the function of each? Fundamentals Education Subunit- Structural Health Monitoring Education Unit

36. Schematic of Structural Health Monitoring Systems: Data Acquisition Unit (DAU) (3) • This onsite unit receives the inputs of the sensor array; converts the input signals (either analog or digital) to engineering parameters such as strain, load or deflection; and stores the data temporarily. • Since the sensors must communicate with the DAU, either a wired or wireless connection is needed between the sensors and the DAU. • Note: The sensors combined with the DAU and the signal transmission system may be referred to as the Data Acquisition System (DAS). Fundamentals Education Subunit- Structural Health Monitoring Education Unit

37. Schematic of Structural Health Monitoring Systems: Data Transmission System (DTS) (4) • The onsite DAU generally has limited storage capacity for data, so data are either continuously or intermittently transmitted to a central computer with both data processing and data storage capabilities. • Alternatively, the data could be transmitted to a data storage unit or server which would provide long term secure storage of the data for access by a data processing unit. • As with the sensor to DAU connection, either a wired or wireless connections are used. • The wired connection is generally achieved through the use of existing telephone lines. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

38. Schematic of Structural Health Monitoring Systems: Data Processing Unit (DPU) (5) • The function of this unit is to process (eliminate or minimize “noise”) and organize the data into a format amenable for analysis and diagnosis. • See following slide for definition of “noise”. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

39. Schematic of Structural Health Monitoring Systems: Data Processing Unit (DPU) (6) NOISE: can consist of spurious readings. • These are data points that could be anywhere, and are sometimes ridiculously far from where the real data should have been. • With small data sets, these are often pruned by hand. • With large sensed datasets, these need to be automatically dealt with. • In high dimensions they are often impossible to physically “see.” • Other forms of “noise” include measurement error and background datawhich are described on the following two slides. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

40. Schematic of Structural Health Monitoring Systems: Data Processing Unit (DPU) (7) MEASUREMENT ERROR: • This is the small amount of error that can occur on all data points and in every dimension. • It can occur because a sensor is not accurate or precise enough, a rounding or approximation error occurs before the data reach you, or a truncation error in a conversion to an abstract data type. • This type of data noise may have little effect on the structure you are trying to measure, but can violate noiseless assumptions and should be understood. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

41. Schematic of Structural Health Monitoring Systems: Data Processing Unit (DPU) (8) BACKGROUND DATA: • These data are from something other than what you are trying to measure. • This could be unlabeled data (like unrated movies on Netflix) or people who don’t have the disease you are trying to monitor. • The problem is that it sometimes gets mixed in, and is then indistinguishable from the actual data of the phenomenon you are trying to monitor. https://www.cs.utah.edu/~jeffp/teaching/cs5140/L19-Noise.pdf Fundamentals Education Subunit- Structural Health Monitoring Education Unit

42. Schematic of Structural Health Monitoring Systems: Data Storage Unit (DSU) (9) • This unit is generally a server which can be used to receive and store data directly from the DAU or the DPU or both. • Further, the DSU can also be used to store the results of the analysis and diagnosis of the processed data. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

43. Schematic of Structural Health Monitoring Systems: Diagnosis Process (DP) (10) • This is the process whereby the processed data are analyzed to: • detect damage. • compare bridge behavior with design and analysis predictions. • assess the bridge for any of the purposes cited. • This is a function or a component of the SHM system which involves knowledgeable professionals and whereas it makes use of computers, it is not a device. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

44. Schematic of Structural Health Monitoring Systems: Decision Making Process (DMP) (11) • This function attempts to answer the question, what do the results of the Diagnosis Process mean in terms of the safety of the bridge or the current level of damage to the bridge or its actual vs. predicted behavior or any number of questions for which the SHM system was designed to answer. • As you might expect, this function must involve knowledgeable and experienced analysis, design and, possibly, construction professionals in collaboration with SHM specialists in other relevant disciplines. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

45. Schematic of Structural Health Monitoring Systems: Decision Making Process (DMP) (12) • The interrelation and interaction between these units and functions can be found on page 5 of the ISIS Canada document. • While this represents a reasonably generic and common system, other configurations and interactions are possible depending on the specific purpose of the SHM system. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

46. Question to Think About Before reading the next section, take your eyes off the screen, take a piece of paper and respond to the following question. • List the possible advantages/benefits of SHM. • Now compare your responses with those provided in the following four slides.How did you do? Fundamentals Education Subunit- Structural Health Monitoring Education Unit

47. Possible Benefits/Advantages of Structural Health Monitoring Systems (1) Development of a better understanding of actual structural behavior because the analysis and design of structural elements and systems are based on… • idealized theoretical models • adherence to the provisions of structural design codes (e.g., ACI for concrete, PCI for pre-stressed concrete, and AISC for steel) • results of testing of coupon samples of structural materials • use of assumed or prescribed loads. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

48. Possible Benefits/Advantages of Structural Health Monitoring Systems (2) • SHM allows collection of information that allow us to measure the behavior/performance of actual structures under actual loading conditions. • The information collected from SHM system installations can be used to improve future analysis and design practices. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

49. Possible Benefits/Advantages of Structural Health Monitoring Systems (3) Earlier Detection of Damage • Early detection of damage allows remedial action to be taken before the level of damage reaches a critical state. • Thus, possibly timelier and less costly repairs can be undertaken. • Should the level of damage detected suggest the possibility of near-term collapse of the bridge, action can be taken to remove the structure from service. Fundamentals Education Subunit- Structural Health Monitoring Education Unit

50. Possible Benefits/Advantages of Structural Health Monitoring Systems (4) Continuous monitoring eliminates or minimizes the need for and cost of periodic inspections which require manpower and bridge closures. • Assurances of a structure’s strength and serviceability • Reduction in down time • Improved maintenance and management strategies • Encourages use of innovative materials and structural systems Fundamentals Education Subunit- Structural Health Monitoring Education Unit