Expected utility theory for monitoring-based decision making

The main purpose of structural health monitoring (SHM) is to obtain information about the state of a structure, in order to guide bridge management decisions. Nevertheless, in practice, once a rigorous estimate of the structural state is available, decisions are usually made based on the decision maker’s intuition or experience. In this paper, we present the implementation of expected utility theory (EUT) in those civil engineering decision problems in which decision makers have to act based on the output of SHM. EUT is an analytical quantitative framework that allows the identification of the financially most convenient decisions, based on the possible outcomes of each action and on the probabilities of each structural state occurring. The advantage of the presented implementation is the optimization of decision strategies in SHM. In the manuscript, we first formalize the solution of single-stage decision processes, in which the decision maker has to take only one action. Then, we formalize the solution of multi-stage decision processes, in which multiple actions may be taken over time. Finally, using an example based on a case study, we describe the variables involved in the analysis of SHM decision problems, discuss the possible results and address the issues that may arise in the application of EUT in real-life settings

FE modelling of the Streicker Footbridge

The Streicker footbridge was completed in 2010 at the Princeton University Campus, over the Washington Road. It is about 104 m long and consists of a central main span supported by a steel arch and four lateral approaching legs. The deck is a post-tensioned high-performance concrete girder. Steel columns with “Y” shape support four lateral legs that connect the bridge to the lateral bearings on the ground and the whole system results a slender varying cross section main girder. The original shape in the horizontal plane provides horizontal stability to the footbridge despite the intrinsic slenderness of the steel supporting columns. Vertical stability is provided also by the arch in the central main-span and by the supporting columns under the legs. Cross section width increases from the midpoint of the main span to the connections with the legs and then remains constant up to the ground bearings. This work is focused on the development of a finite element analysis of the footbridge at different levels of refinement from the essential implementation of beam elements to more refined FE solutions for the prestressed concrete deck. The models are identified with respect to the available operational modal parameters. This deck discretization could further allow simulating the motion of a running/walking pedestrian along different trajectories

Virtual Tour (VT), Informational Modeling (IM), and Augmented Reality (AR) for Visual Inspections (VI) and Structural Health Monitoring (SHM)

69A3551847102Existing infrastructure in the U.S. is deteriorating; the symptoms of overdue maintenance and underinvestment are ever-present in our society (rated with D+ by American Society of Civil Engineers, ASCE). To ensure the safety of existing infrastructure, on-site life-time inspections and monitoring are required. While these methods yield a great deal of raw and analyzed data, current methods for their simple and intuitive management, (i.e., simple and intuitive integration, documentation, access, and visualization), are severely lacking and can lead to mismanagement of infrastructure resources. To enable both on- and off-site documenting and viewing of infrastructure a novel method was developed in this project, which combines image-based documentation, Virtual Tours (VT) and informational modeling (IM), and augmented reality (AR). A cross-platform, client-server system for creating, saving, and viewing annotations was designed and implemented. The strengths and weaknesses of this implementation were addressed, and the accuracy of the approach was evaluated. The findings of this work show the promise of VT/IM/AR as a useful framework for documenting the built environment and assisting access and visualization of data and metadata related to SHM and visual inspections. This work presents a prototype and includes the proof of concept and real-life application

Combination of Image-Based Documentation and Augmented Reality for Structural Health Monitoring and Building Pathology

With the current deterioration rate of existing infrastructure, the importance of intervention and preservation efforts such as on-site visual inspections, non-destructive evaluation, structural health monitoring (SHM), and building pathology are on the rise. A critical aspect of these intervention and preservation methods is the visualization and accessibility of large, heterogeneous data sets. To enable diverse stakeholders to make informed choices, data and metadata for the built environment needs to be directly integrated into a user's viewing environment. To address this challenge, a human-machine interface which organizes these types of data and provides actionable information is necessary. The main aim of this work is to develop a preliminary framework for documenting and visualizing data about the built environment both on and off site using a combination of image-based documentation and augmented reality (AR). While this work illustrates preliminary annotation mechanisms such as drawing, the concept of projecting data between the image-based environment and the AR environment is the main contribution of this work. This method was applied to test objects as well as case studies in SHM and building pathology

Underwater Communication Acoustic Transducers: A Technology Review

This paper provides a comprehensive review on transducer technologies for underwater communications. The popularly used communication transducers, such as piezoelectric acoustic transducers, electromagnetic acoustic transducers, and acousto-optic devices are reviewed in detail. The reasons that common air communication technologies are invalid die to the differences between the media of air and water are addresses. Because of the abilities to overcome challenges the complexity of marine environments, piezoelectric acoustic transducers are playing the major underwater communication roles for science, surveillance, and Naval missions. The configuration and material properties of piezoelectric transducers effects on signal output power, beamwidth, amplitude, and other properties are discussed. The methods of code and decode communication information signals into acoustic waves are also presented. Finally, several newly developed piezoelectric transducers are recommended for future studies

Influence of mechanical and geometrical properties of embedded long-gauge strain sensors on the accuracy of strain measurement

In many civil and geotechnical applications it is of interest to monitor the strain deep inside the structure; consequently, it is necessary to embed the sensors into the structure's material. Construction and geotechnical materials, such as concrete and soil, can be affected by local defects, e.g. cracks, air pockets and inclusions. To monitor these materials at a structural level it is necessary to use long-gauge sensors. As the sensor has to be embedded in the host material, its presence causes perturbation of the strain field and influences the accuracy of the strain measurement. The aim of this research was to identify the critical parameters that influence the accuracy of the strain measurement, to study how these parameters affect the accuracy, and to give recommendations for sensor users. The study was based on finite element analysis and all involved materials were assumed to have the MöhrCoulomb elastic, perfectly plastic behavior. A suitability of the numerical model for the analysis was verified using the experimental results of two cases reported in the literature and one on-site application. The study revealed that the most important parameters that influence the accuracy of the strain measurement are the goodness of interaction (strain transfer) between the host material and the anchor pieces of the sensor, the ratio between equivalent Young's modulus of the sensor and the Young's modulus of the host material, the radius of the anchor piece and the gauge length. The numerical model and parametric study are presented in detail along with practical recommendations. © 2012 IOP Publishing Ltd.The authors would like to thank the Spanish Ministry of Education, with support received under the National Program for Mobility of Researchers (O.M. EDU/1456/2010, ref. PR2010-0293) which enabled the joint work that made this study possible. The Streicker Bridge project was realized with help of Turner Construction Co., HNTB, AG Construction Corp., Vollers Excavating & Constr., SMARTEC SA, Micron Optics, Princeton Facilities, and staff and students of CEE department of Princeton University.Calderón García, PA.; Glisic, B. (2012). Influence of mechanical and geometrical properties of embedded long-gauge strain sensors on the accuracy of strain measurement. Measurement Science and Technology. (23):1-15. https://doi.org/10.1088/0957-0233/23/6/065604S11523Glišić, B., & Inaudi, D. (2007). Fibre Optic Methods for Structural Health Monitoring. doi:10.1002/9780470517819Ansari, F. (2007). Practical Implementation of Optical Fiber Sensors in Civil Structural Health Monitoring. Journal of Intelligent Material Systems and Structures, 18(8), 879-889. doi:10.1177/1045389x06075760Li, H.-N., Zhou, G.-D., Ren, L., & Li, D.-S. (2009). Strain Transfer Coefficient Analyses for Embedded Fiber Bragg Grating Sensors in Different Host Materials. Journal of Engineering Mechanics, 135(12), 1343-1353. doi:10.1061/(asce)0733-9399(2009)135:12(1343)Torres, B., Payá-Zaforteza, I., Calderón, P. A., & Adam, J. M. (2011). Analysis of the strain transfer in a new FBG sensor for Structural Health Monitoring. Engineering Structures, 33(2), 539-548. doi:10.1016/j.engstruct.2010.11.012Kesavan, K., Ravisankar, K., Parivallal, S., Sreeshylam, P., & Sridhar, S. (2010). Experimental studies on fiber optic sensors embedded in concrete. Measurement, 43(2), 157-163. doi:10.1016/j.measurement.2009.08.010Azenha, M., Faria, R., & Ferreira, D. (2009). Identification of early-age concrete temperatures and strains: Monitoring and numerical simulation. Cement and Concrete Composites, 31(6), 369-378. doi:10.1016/j.cemconcomp.2009.03.004Glisic, B. (2011). Influence of the gauge length on the accuracy of long-gauge sensors employed in monitoring of prismatic beams. Measurement Science and Technology, 22(3), 035206. doi:10.1088/0957-0233/22/3/035206Leng, J. S., Winter, D., Barnes, R. A., Mays, G. C., & Fernando, G. F. (2006). Structural health monitoring of concrete cylinders using protected fibre optic sensors. Smart Materials and Structures, 15(2), 302-308. doi:10.1088/0964-1726/15/2/009Calderón, P. A., Adam, J. M., Ivorra, S., Pallarés, F. J., & Giménez, E. (2009). Design strength of axially loaded RC columns strengthened by steel caging. Materials & Design, 30(10), 4069-4080. doi:10.1016/j.matdes.2009.05.014Adam, J. M., Ivorra, S., Pallarés, F. J., Giménez, E., & Calderón, P. A. (2009). Axially loaded RC columns strengthened by steel caging. Finite element modelling. Construction and Building Materials, 23(6), 2265-2276. doi:10.1016/j.conbuildmat.2008.11.014Adam, J. M., Ivorra, S., Pallares, F. J., Jiménez, E., & Calderón, P. A. (2008). Column–joint assembly in RC columns strengthened by steel caging. Proceedings of the Institution of Civil Engineers - Structures and Buildings, 161(6), 337-348. doi:10.1680/stbu.2008.161.6.337Adam, J. M., Ivorra, S., Pallares, F. J., Giménez, E., & Calderón, P. A. (2009). Axially loaded RC columns strengthened by steel cages. Proceedings of the Institution of Civil Engineers - Structures and Buildings, 162(3), 199-208. doi:10.1680/stbu.2009.162.3.199Johansson, M., & Gylltoft, K. (2001). Structural behavior of slender circular steel-concrete composite columns under various means of load application. Steel and Composite Structures, 1(4), 393-410. doi:10.12989/scs.2001.1.4.393Johansson, M., & Gylltoft, K. (2002). Mechanical Behavior of Circular Steel–Concrete Composite Stub Columns. Journal of Structural Engineering, 128(8), 1073-1081. doi:10.1061/(asce)0733-9445(2002)128:8(1073

IWSHM 2017 : Quantifying the benefit of structural health monitoring : what if the manager is not the owner?

Only very recently our community has acknowledged that the benefit of structural health monitoring can be properly quantified using the concept of value of information (VoI). The VoI is the difference between the utilities of operating the structure with and without the monitoring system. Typically, it is assumed that there is one decision-maker for all decisions, that is, deciding on both the investment on the monitoring system and the operation of the structure. The aim of this work is to formalize a rational method for quantifying the value of information when two different actors are involved in the decision chain: the manager, who makes decisions regarding the structure, based on monitoring data; and the owner, who chooses whether to install the monitoring system or not, before having access to these data. The two decision-makers, even if both rational and exposed to the same background information, may still act differently because of their different appetites for risk. To illustrate how this framework works, we evaluate a hypothetical VoI for the Streicker Bridge, a pedestrian bridge in Princeton University campus equipped with a fiber optic sensing system, assuming that two fictional characters, Malcolm and Ophelia, are involved: Malcolm is the manager who decides whether to keep the bridge open or close it following to an incident; Ophelia is the owner who decides whether to invest on a monitoring system to help Malcolm making the right decision. We demonstrate that when manager and owner are two different individuals, the benefit of monitoring could be greater or smaller than when all the decisions are made by the same individual. Under appropriate conditions, the monitoring VoI could even be negative, meaning that the owner is willing to pay to prevent the manager to use the monitoring system

The conditional value of information of SHM : what if the manager is not the owner?

Only very recently our community has acknowledged that the benefit of Structural Health Monitoring (SHM) can be properly quantified using the concept of Value of Information (VoI). The VoI is the difference between the utilities of operating the structure with and without the monitoring system, usually referred to as preposterior utility and prior utility. In calculating the VoI, a commonly understood assumption is that all the decisions to concerning system installation and operation are taken by the same rational agent. In the real world, the individual who decides on buying a monitoring system (the owner) is often not the same individual (the manager) who will actually use it. Even if both agents are rational and exposed to the same background information, they may behave differently because of their different risk aversion. We propose a formulation to evaluate the VoI from the owner's perspective, in the case where the manager differs from the owner with respect to their risk prioritisation. Moreover, we apply the results on a real-life case study concerning the Streicker Bridge, a pedestrian bridge on Princeton University campus, in USA. This framework aims to help the owner in quantifying the money saved by entrusting the evaluation of the state of the structure to the monitoring system, even if the manager's behaviour toward risk is different from the owner's own, and so are his or her management decisions. The results of the case study confirm the difference in the two ways to quantify the VoI of a monitoring system

Roadmap on measurement technologies for next generation structural health monitoring systems

Structural health monitoring (SHM) is the automation of the condition assessment process of an engineered system. When applied to geometrically large components or structures, such as those found in civil and aerospace infrastructure and systems, a critical challenge is in designing the sensing solution that could yield actionable information. This is a difficult task to conduct cost-effectively, because of the large surfaces under consideration and the localized nature of typical defects and damages. There have been significant research efforts in empowering conventional measurement technologies for applications to SHM in order to improve performance of the condition assessment process. Yet, the field implementation of these SHM solutions is still in its infancy, attributable to various economic and technical challenges. The objective of this Roadmap publication is to discuss modern measurement technologies that were developed for SHM purposes, along with their associated challenges and opportunities, and to provide a path to research and development efforts that could yield impactful field applications. The Roadmap is organized into four sections: distributed embedded sensing systems, distributed surface sensing systems, multifunctional materials, and remote sensing. Recognizing that many measurement technologies may overlap between sections, we define distributed sensing solutions as those that involve or imply the utilization of numbers of sensors geometrically organized within (embedded) or over (surface) the monitored component or system. Multi-functional materials are sensing solutions that combine multiple capabilities, for example those also serving structural functions. Remote sensing are solutions that are contactless, for example cell phones, drones, and satellites. It also includes the notion of remotely controlled robots

Concise Historic Overview of Strain Sensors Used in the Monitoring of Civil Structures: The First One Hundred Years

Strain is one of the most frequently monitored parameters in civil structural health monitoring (SHM) applications, and strain-based approaches were among the first to be explored and applied in SHM. There are multiple reasons why strain plays such an important role in SHM: strain is directly related to stress and deflection, which reflect structural performance, safety, and serviceability. Strain field anomalies are frequently indicators of unusual structural behaviors (e.g., damage or deterioration). Hence, the earliest concepts of strain sensing were explored in the mid-XIX century, the first effective strain sensor appeared in 1919, and the first onsite applications followed in the 1920′s. Today, one hundred years after the first developments, two generations of strain sensors, based on electrical and fiber-optic principles, firmly reached market maturity and established themselves as reliable tools applied in strain-based SHM. Along with sensor developments, the application methods evolved: the first generation of discrete sensors featured a short gauge length and provided a basis for local material monitoring; the second generation greatly extended the applicability and effectiveness of strain-based SHM by providing long gauge and one-dimensional (1D) distributed sensing, thus enabling global structural and integrity monitoring. Current research focuses on a third generation of strain sensors for two-dimensional (2D) distributed and quasi-distributed sensing, based on new advanced technologies. On the occasion of strain sensing centenary, and as an homage to all researchers, practitioners, and educators who contributed to strain-based SHM, this paper presents an overview of the first one hundred years of strain sensing technological progress, with the objective to identify relevant transformative milestones and indicate possible future research directions