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REAL-TIME BRIDGE HEALTH-MONITORING FOR MANAGEMENT

*A.E. Aktan1, F.N. Catbas1, M. Pervizpour1,E. Kulcu1, K. Grimmelsman1, R. Barrish1 and X. Qin1

Drexel Intelligent Infrastructure InstitutePhiladelphia, PA 19104

ABSTRACT

Effective management and renewal of civil infrastructure systems (CIS) are challengingproblems as well as critical societal concerns. Earthquake disaster mitigation and CISmanagement intersect with many common concerns and interactions. A coordinated, multi-disciplinary approach that integrates field, theoretical and laboratory research is proposed asnecessary for innovating both areas. Health monitoring (HM) of CIS is defined as an emergingparadigm for effective management, including emergency response and recovery management.Challenges and opportunities in health monitoring enabled by recent advances in informationtechnology are presented. An example of HM research on an actual CIS test-bed, whichnecessitated integration, is presented. Lessons learned from the conduct of field, laboratory andtheoretical research, carried out by a closely coordinated group of multi-disciplinary researchersare summarized.

INTRODUCTION

Relationship Between Disaster Mitigation and Infrastructure Health Monitoring Research

One of the topics addressed by the February 20-21, 1998 U.S.-Japan Workshop onAdvanced Technologies for Earthquake Disaster Mitigation was “Integrated disaster informationsystems: use of satellites in conjunction with various advanced sensors, wireless datatransmission techniques, radio telemetry, advanced signal processing techniques, globalpositioning systems for on-line real-time identification, reporting, diagnosis, and control ofhazardous events”. The Workshop participants identified “Real-time Earthquake DamageAssessment” as one of three topics relevant to and important for the development andapplications of the advanced technologies for future cooperative research programs.

A more recent March 2-3, 2000 workshop entitled “Mitigation of Earthquake Disaster byAdvanced Technologies (MEDAT-1)” and sponsored by the “Multidisciplinary Center forEarthquake Engineering Research” at Los Angeles provided examples of exploratory“Supervisory Control and Data Acquisition (SCADA) developments in Japan and in the US bywater, electric power and gas utilities, and the importance of SCADA systems for emergencypreparation and response in dense urban areas.

There are obvious connections between “Integrated Disaster Information Systems,”“SCADA systems” and the “Health-Monitoring (HM) systems” that are envisioned for long-spanbridges, tunnels and regional transportation networks in the realm of integrated operational,structural HM of intelligent transportation systems for their management, including “emergency

Paper to be Presented at the Second Workshop on Advanced Technologies in Urban Earthquake Disaster Mitigation, Kyoto Univ., July 9-14, 2000US-Japan Center to Center Cooperative Research in Urban Earthquake Disaster Mitigation between

Disaster Prevention Institute,Kyoto University and Southern California EQ Research Center under NSF.

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management.” In fact, the HM systems the writers envision for a network of large structureswithin a major metropolitan area integrate the disaster information systems that mainly takeadvantage of high-altitude sensing and the SCADA systems that mainly incorporate sensing andtransmission within an infrastructure system.

HM Systems for Intelligent Transportation Networks

Future HM systems for intelligent transportation networks will collect both satellite, aircraftand land-based data on weather, traffic, roadway and structural responses, integrate and displaythe data for on-line, real-time viewing by qualified officials for guiding the public, incidentresponse, enforcement, and management. The writers further envision that transportation HMsystems will take advantage of integrated information systems that will permit officials andengineers to access, review and analyze legacy and recent data and information in addition toreal-time data. The data will have many simultaneous modalities, such as satellite images and on-ground streaming-video of traffic and roadway conditions, weigh-in-motion information andcritical structural responses including temperatures, accelerations, displacements, tilts andstrains. Intermittent and continuous data should be sufficient to evaluate, in real-time, any criticalchanges in structural reliability due to aging, deterioration or damage due to accidents oroverloads. These are discussed further in the following. The similarities between transportationHM systems and the real-time earthquake damage assessment and disaster mitigation systemsenvisioned by earthquake disaster mitigation research community are obvious (Housner et al,1997).

The senior writer has an earthquake structural engineering background. Following a BSdegree in civil engineering in 1967, he worked as an apprentice to several giants in the area ofintegrated analytical and experimental earthquake structural engineering research. Since 1984, hehas been researching “condition assessment and HM of infrastructure systems” together with hiscolleagues and students (Aktan et al, 1998). Experimental and analytical tools used byearthquake engineers were integrated, complemented by others such as modal analysis andmicro-structural analysis, and transformed for field applications. Researchers from civil,mechanical, materials, electrical engineering, computer science and information systemsbackgrounds joined forces for closely coordinated research intersecting the field, laboratory andtheoretical realms by taking advantage of operating and decommissioned highway bridges asreal-life test-beds.

During the last three years, Drexel University Intelligent Infrastructure Institute researchershave explored the issues, challenges and opportunities in the development and use of intelligenttransportation, HM and integrated information systems by constructing a prototype on theCommodore Barry Bridge in Philadelphia. In this paper, the writers are motivated to share theirexperiences in this ongoing project with their colleagues in the earthquake disaster mitigationfield.

INTEGRATION ISSUES IN INFRASTRUCTURE HM RESEARCH

A lack of tradition and designed incentive mechanisms for successful integrative research,technology development and education is currently the most critical barrier standing in front ofmeaningful HM applications for effective infrastructure management. Integration is amultidimensional problem encompassing: (a) academe, government, industry and the generalpublic; (b) various government agencies that support research, technology development and

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commercialization; (c) organizations or bureaus within the same organization having jurisdictionover different infrastructure systems and/or components; (d) engineering and non-engineeringacademic disciplines and sub-disciplines; (e) field, laboratory and analytical components ofresearch, development and education; (f) systems-integration of the experimental, analytical andinformation tools and technologies that are required for a HM application.

Close and optimal integration of the above for a successful “innovative technologydemonstration and its adaptation” poses a major challenge. Upon reviewing the advances inelectronics, communication, computation and information management technologies versus anyimprovements that may have occurred in infrastructure performance and disaster mitigation inthe last decade, it is clear that infrastructure stakeholders may be facing unusual challengesand/or missing certain elements necessary for successfully advancing the practice in their fields.

Integrating Field-Laboratory and Analytical Research

Significant benefits are expected from integration of recent advances in controlled testingand continuous monitoring of actual CIS with laboratory and theoretical approaches through asystems identification and integration framework. Presently, research is designed based on anincomplete understanding of all the issues and mechanisms that interact at the intersection ofnatural, social and constructed systems. Without a complete and accurate understanding of theparameters that impact CIS performance at the systems level, it will not be possible to definetrue-reality or the ground-truth measures that are needed for reliable management of CIS (NSF,1997).

Figure 1 illustrates the principal elements of field, theoretical and laboratory research thathave mostly remained disconnected in the past. For example, in the case of earthquakeengineering, many discoveries were made only after destructive earthquakes occurred. Observingdamage following a seismic event requires a forensic approach, and the conclusions are veryoften highly uncertain. In the past decade, researchers have been able to retrieve extensivestrong-motion data from the ground, soil and infrastructure during earthquakes, notably duringthe 1989 Loma Prieta and 1994 Northridge Earthquakes in California and the 1995 KobeEarthquake in Japan. However, whether or not the tools and experience exist to extract all of theavailable knowledge from such data, and especially if the maximum knowledge that can beextracted from the data would permit reliable simulation of the actual behavior of the natural,social and built systems before, during and after an earthquake remain valid questions.

It must be recognized that the challenges in reliably monitoring large spatial and decades-long temporal domains of infrastructure systems are daunting. To understand the complexphenomena that affect CIS performance requires acquiring, processing, synchronizing, fusing,archiving, mining and interpreting many different modes of data and information, collected atvarious frequencies and intervals for a very long time. At the same time, unless capabilities fordesigning observations and experiments to understand and measure phenomena that affect theperformance and management of large CIS are improved, it may not be possible to effectivelymanage CIS operation, maintenance or emergencies due to man-made or natural hazards.Furthermore, evaluating site and structural vulnerability, and that of hidden damage following aseismic event reliably often require more than just seismic instrumentation and measurementsduring an earthquake.

For example, it can be argued that the discovery of connection weld failures in steelbuilding frames following the 1994 Northridge Earthquake (Rosenbaum, 1996) justifies HM ofat least selected samples of recurring soil-foundation-structural systems and certainly those that

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are critical for emergency response and recovery in areas of high seismic risk. Seismicinstrumentation that has now become quite common is only a small subset of technologiesrequired for lifecycle HM described earlier. In too many cases, it is not possible to assess post-earthquake structural reliability without an initial, as-constructed baseline and the pre-earthquakeconditions of the site, soil, foundation and structure. Therefore, advancing the ability to conductholistic and integrative research and education on actual, operating CIS, and being able toobserve, measure, model and simulate natural, social and structural phenomena reliably at thesystems level over the lifecycle should be the goal. A paradigm shift in the traditional approachesto civil and earthquake engineering research and education, and coordinated, integrative researchby participants from many different fields is necessary to achieve this goal.

Figure 1: Field, Theoretical, and Laboratory Research Integration

HEALTH MONITORING (HM) OF THE COMMODORE BARRY BRIDGE

A demonstration project that involves field research on a long-span structure integratedwith laboratory and theoretical research on simulation of large CIS is taking advantage of theCommodore Barry Bridge in Philadelphia. A pilot HM system for continuous and intermittentremote monitoring of the environmental and live load effects on the bridge and thecorresponding critical bridge responses has been installed on the bridge. A photograph of thecantilevered through-truss bridge is shown in Figure 2. The monitor system has been functioningsince 1998, and additional data has been obtained by many controlled tests. Data has beeninterpreted by the researchers for characterizing the mechanical characteristics and the loadingand response environment of the bridge structure in terms of a 3D finite-element model.Researchers continue recording and viewing data from continuous measurements in real-time,and from controlled load tests and ambient vibration tests that are conducted intermittently. Thedata is used for calibrating the analytical model and validating its reliability for simulating

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phenomena at the regional and element levels (Aktan et al, 2000, Catbas et al, 2000, Kulcu, et al,2000, Barrish et al, 2000).

Cantilevered Through Truss

Suspended SpanCantilever Arm

Cantilever Arm

Anchor Span Anchor Span

822 ft 411 ft 822 ft 411 ft 822 ft

3288 ft

Figure 2: Overview of the Commodore Barry Bridge

The current 145-channel monitoring system continuously measures ambient temperatures,and the wind speeds in three directions at several locations of the bridge at a frequency of 1 Hz.Tilt and displacement sensors for measuring the movement history and three-dimensionaldisplacement kinematics of the bridge are being installed on piers and at various locations of thestructure where relative displacements and tilts are expected due to designed or inadvertentmovement mechanisms. The corresponding changes in the long-term intrinsic strains andtemperatures are also measured at critical truss and floor system locations. In addition, thesystem intermittently monitors live load images and the corresponding strain and accelerationresponses in the critical truss and floor system members. A server located in a climate controlleddata acquisition cabinet on one of the bridge piers integrates the multiple data acquisitionsystems used in the bridge monitoring system.

The next-generation system that is being developed is schematized in Figure 3 and will takeadvantage of a high-speed fiber-optic local area network for collecting data from sensor-clustersdistributed throughout the bridge and wired to two data acquisition stations located at the towersof the bridge. The weigh-in-motion (WIM) and weather monitor systems are located distant fromthe bridge, and their data acquisition computer will maintain wireless communication with abridge data server. Integrated streams of data and image will be transmitted from the bridge dataserver through the Internet for remote control of data acquisition, viewing, processing andarchival. For example, truck images and weight information captured from WIM systems will besynchronized with the responses caused by the same truck at selected elements of the structure asit travels along the bridge. Video-camera images along the bridge will help synchronize truck

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positions and the corresponding member strains. Desired components of real-time data will bearchived in an Internet-based database system and integrated with the legacy documentationincluding bridge drawings and past inspection reports. In the longer term, global geometrymonitoring by GPS at milimeter-level resolution and local monitoring of fatigue sensitive weldsby acoustic emission sensors are planned. In addition, displacement measurements along anumber of critical truss elements will be monitored by “long” fiber-optic displacement gages.

Figure 3: Data Acquisition Systems and Sensor Modalities

REAL-TIME MONITORING AND CONTROLLED TESTS

Successful design and implementation of HM systems depend on how the data is convertedinto information and interpreted for decision making. Incident and damage detection from dataare major concerns for effective real-time emergency response management. The writers havebeen exploring the issues in effective data and information display, and the correspondinginterfaces for viewing and controlling the real-time data from the Commodore Barry Bridge. Theprincipal challenge is designing a multi-screen interface that would display and permit on-linecontrol of all the relevant real-time and recent data without overwhelming a manager. Variousanalysis, event and pattern search engines would be needed to assist in recovering and analyzinglegacy data and information and integrate this with real-time and recent data for decision-making. The interface development has been underway and several versions have been used for

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two years. The data is currently displayed by taking advantage of the LabView softwareprogram.

Two example screens from real-time monitoring of the Commodore Barry Bridge areshown in Figures 4 and 5. Figure 4 shows the live loads and corresponding selected bridgeresponses. Vehicles of interest are identified as they cross the WIM, and their positions arefollowed along the bridge while strains of desired elements and locations are selected for real-time viewing. WIM system will display vehicle geometry speed and weight in analog form.Bridge cameras will permit on-line viewing of the crossing of the vehicle along the bridge. Anyanomalies, for example due to high lateral wind gusts, reckless driving, overloads, etc. can becaptured.

The screen currently used for on-line monitoring of the environmental effects in real-time isshown in Figure 5. Wind speed and direction measurements at different locations are presentedin polar-graph format. Ambient and member temperatures and the corresponding strainmeasurements are integrated with image to interpret deck and driving conditions and trafficlevels.

Figure 4: Real time monitor screen for WIM and traffic strains

The writers will explore how an engineer and/or manager can take advantage of the real-time data describing the conditions on the bridge due to weather deck surface conditions, bridgemember responses, and traffic. This aggregate information in real-time offers promise to servefor operational decisions and control, provided that the screen requires only a brief time toabsorb the data, hence making it possible for bridge managers to react to incidents immediately.A related promise is assisting bridge operators by automatically detecting certain conditions andproviding alerts.

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Figure 5: Real time monitor screen for temperature, wind and environmental strains

A HM system should integrate real time monitoring with intermittent controlled tests.Certain response mechanisms that are not activated by regular traffic or are obscured by ambientvibrations due to traffic can be measured, and the HM system may be calibrated and verified bycontrolled crawl-speed or static positioning of proof-level test loads. Such input and responsedata collected under controlled conditions are important for reliable calibration of the analyticalbridge models at various resolutions of local detail. Taking advantage of such controlled testsshould also be a HM design and operation requirement. In addition to load tests, intermittentambient vibration and localized modal tests serve as essential complements to the real timemonitor. The opportunity to integrate millimeter-level GPS-based position measurements, longgage-length fiber-optic sensors, remote sensing measurements and local-sentry monitors such asultrasonic measurements for cracking of fatigue-sensitive details into the HM system as thesetechnologies further develop is another design requirement.

THE PHENOMENOLOGICAL LABORATORY MODEL

Drexel researchers have been attempting to construct and calibrate a finite element modelof Commodore Barry Bridge. They have recognized the challenges in analytical modeling,calibration and simulations while rationally incorporating the uncertainties due to scaling, anddue to the difficulties in observations and measurements with sufficient resolution, duration andaccuracy. To be able to study the fundamentals of the problem in a more controlled manner, a

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phenomenological physical model that further serves as an implementation and demonstrationtool has been developed.

The physical model shown in Figure 6 serves as a benchmark laboratory test-bed wherenatural systems and the associated uncertainties may be controlled. The physical modelincorporates sufficient inherent complexities and uncertainties at the material and structurallevels. The connection, continuity and boundary conditions may be controlled to some extent,enabling phenomenological sensitivity studies for structural and loading systems identificationand integration for simulation. Experimental and analytical tools and indices useful fordescribing performance, health, condition and damage may be explored prior to field studies.The model also serves for integration and calibration of the tools required for sensing, dataacquisition, processing and control, and, information management technologies and educationand training.

The loading system consists of a load frame and two servo-control electro-hydraulicactuators capable of applying both static and dynamic loads in the range of 0-20 Hertz at avariety of locations on the model. The actuators will also enable active structural-control studies.A measurement calibration system, consisting of a mechanically transparent beam, mechanicalcalibration jigs, and an environmental simulator are being developed for comprehensive studiesat component level and to help identify the errors and uncertainties that are inherent in sensorsand data acquisition systems. A prototype Graphical Internet Database (GID) has been developedfor real-time data viewing, archival and management. This system allows a user to access,review, process and visualize real-time and integrated legacy data.

Figure 6: Physical Model, Loading System, Sensing, Data Acquisition and Networking

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HM AND EMERGENCY RESPONSE MANAGEMENT

Improving field research abilities and especially developing the technologies and know-how for controlled testing and continuous monitoring of actual operating CIS in the field iscritical to take greater advantage of observations and measurements before, during and followinga disaster. The experience gained from the integrated operational and structural HM of theCommodore Barry Bridge supports the feasibility and the intrinsic value of integrated high-altitude-and-land based HM systems for intelligent transportation networks. As envisioned by thedisaster mitigation community, such systems would collect multi-modal data on weather, ground,soil, traffic, roadway and structural responses of a regional highway transportation system,process, fuse and make the information available for on-line, real-time viewing by qualifiedofficials for guiding the public, incident response, enforcement, engineering and emergencymanagement. Web-based wide-band technologies are available to facilitate data acquisition andcontrol, communication, processing, integration, analysis. An example user interface engine for ahypothetical emergency-response information system is illustrated in Figure 7.

Figure 7: Emergency Response Information System

Information Technology Issues:

Since information technology itself is an emerging field, integrating many potentialapplications to CIS HM and management are pending. Some of the opportunities and challengesinclude:

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(a) Integrative information systems integrating both various hardware platforms and legacydatabases, heuristics and real-time data management engines. Information systemsshould permit the management of large amounts of real-time data and informationretrieved throughout the critical locations of an infrastructure system, such as a regionalhighway transportation system or an electric power grid. Such systems would beanalogous to the systems utilized by air traffic controllers, the US Navy and Air Force.

(b) Data and information management, abstraction and interpretation tools. Informationintegration (fusion) in HM is critical for reliable interpretation of data and informationand is closely dependent on how data is transformed to information. Some additionalchallenges relate to computer and information-science aspects of informationintegration and include the synchronization of data with varying formats and modalities,structural and architectural design of data-warehouses, interface and search engine andapplication software design, physical, phenomenological and heuristic tests for conflictevaluation and resolution, temporal-spatial-phenomenological correlation analysis, andmost importantly, presentation and display technologies for visualization,conceptualization and physical interpretation by engineers for management decisions.There is an additional challenge in the design of data collection and data managementstrategies so that the transformation from data-to-information-to-knowledge-to wisdommay be accomplished most effectively and economically.

(c) Decision-making by taking advantage of innovative information-management systems,especially for capitalizing on real-time data integrated with legacy information is achallenging research area in itself. Issues critical to the management of information tosupport decision making in complex, dynamic systems are described by Comfort (2000)as: Risk to interdependent infrastructure systems in metropolitan regions; distributedknowledge bases to support inter-organizational decision making among participatingorganizations at multiple jurisdictional levels; data review, collection, verification andformatting for a shared knowledge base for hazard reduction and response among theparticipating jurisdictions; personnel training for the operation and maintenance of thedistributed decision support system for the participating jurisdictions; testing throughsimulated operations exercises involving at least three jurisdictions.

SUMMARY AND CONCLUSIONS

A clear understanding of all the pertinent issues, and the data, information and knowledgeneeded for effective CIS management requires research at the intersection of natural, social andconstructed systems. Coordinated multi-disciplinary research that will effectively integrateobservations and experiments on real operating infrastructure in the field with controlledexperiments in the laboratory and theoretical research on simulation becomes the criticalchallenge. A paradigm shift in the traditional approaches to civil and earthquake engineeringresearch and education, and coordinated, integrative research by participants from many differentfields is necessary.

The ability to prepare for and to learn from disasters, especially in relation to theperformance and behavior of complex infrastructure systems can expand significantly if the HMsystems described in this paper are completely developed. Such systems will collect both satelliteand land-based multi-modal data on weather, ground, soil, traffic, roadway and structuralresponses of for example a highway transportation system throughout lifecycle. The data would

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be processed, fused and made available for on-line, real-time viewing by qualified officialsbefore archival for guiding the public, incident response, enforcement, engineering andemergency management.

The writers have taken advantage of a long-span bridge over the Delaware River inPhiladelphia, US as a test-bed to explore the most pressing challenges to realizing useful HMsystems that would assist bridge owners and emergency managers for planning, preparation andresponse to emergencies. The most relevant lessons have been:

(a) A virtual re-construction of the structure by 3D CAD tools was transformed into a finiteelement characterization true to the existing geometry and details. The global calibrationof the analytical model with more than forty thousand degrees of freedom was based onfifteen measured global frequencies and mode shapes. Ongoing studies aim at reliablymeasuring in excess of 30 lower modes. Fujino (2000) has reported excellent advances inthe area of ambient vibration monitoring of long-span bridges. Local calibration of thefinite element model of the Commodore Barry Bridge was based on controlled load tests.The calibrated model and the data used for its calibration serve as a baseline for long-term monitoring and damage evaluation, as well as for simulations for permit-load ratingand for maintenance management. For example, the impact of various repair and/orretrofit strategies and the related stresses in critical elements may be estimated bysimulation. The confidence in the simulation results, however, even after calibrating themodel, is estimated to be only within 80% for global responses, and less for localresponses due to many sources and complex mechanisms of uncertainty.

(b) Structural monitoring for several years is necessary for a clear understanding of theenvironmental and live load inputs, and the corresponding responses of the structure.Some of the notable findings from the data include an occasionally substantive verticalcomponent of wind pressure on the deck, local intrinsic stresses that exceed live loadeffects on elements exposed to sun radiation; the significant impacts of temperatureshocks on bridge movements and intrinsic member forces. Intrinsic stresses due totemperature shocks have exceeded live load stresses by an order of magnitude whentemperature changes in the order of 50 0F took place over a period of about six hours; thecomplexity of stress and deformation fields along so-called “uniaxial” truss elements.For example, measurements on the truss hanger elements that connect the 822 feet longsuspended span of the bridge to the cantilever spans indicated that they experiencesignificant levels of biaxial bending and torsion in spite of the pin and linear-movementsystems that were constructed to control the force in these hangers. The lack of symmetryin the radiation loading and other intrinsic effects were observed to lead to considerabledifference in the stress distribution of the hangers relative to those calculated from staticsfor these so-called “statically-determinate” elements.

(c) There are many remaining challenges in technology transfer, technology developmentand in the generation of new knowledge in order to accomplish real-time HM of bridgeswithin a regional highway transportation system for operational, maintenance andemergency management: (i) The integration of high-altitude and land-based sensing,data acquisition, networking and communication of data with many frequencies andmodalities along very large distances for a very long time; (ii) integration of numerousdynamic and static controlled test techniques with intermittent and continuous long-termmeasurements for structural identification and for an accurate characterization of theloading environment; (iii) decisions regarding sensor types, numbers and locations for

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the intermittent short-term high-frequency bursts, and long-term slow-speedmeasurement and monitoring of complex, coupled natural phenomena and responses; (iv)analytical modeling, computational and uncertainty management aspects of the structuralidentification for reliable simulation given the scale and complexity of the structures andloading environments; (v) assessment of vulnerability and tracking deterioration anddamage for the evaluation of their impact on structural reliability, given real-time data;(vi) data and information management issues, user interfaces, information display design;(v) intelligent agents for assisting human managers to absorb, understand interpret andtake advantage of integrated real-time and legacy data and information for decisionmaking. The writers have recognized that interpretation of measured data intoinformation and knowledge about the structural behavior as affected by nature andservice operations, followed by how the information and knowledge would be translatedto serve the needs of the bridge owner and help with management decisions, were majorchallenges requiring an integration of the heuristics of the researcher, of the consultingengineer, of the managers, and, extensive processing, statistical analysis, and displaydesign.

(d) The most critical challenge is that of financing, organizing, training, coordinating andmanagement of large, professional, multi-disciplinary research teams to integrate field,laboratory and analytical research for meaningful applications of real-time HM. Forming,successfully nurturing and maintaining a government, academe and industry partnershipis essential for research and technology demonstrations on actual infrastructure test-beds.This type of research requires a major investment and a Manhattan Project approach inits planning, organization and conduct. The key is in the transformation of the commonsingle-investigator or loosely coordinated, multi-investigator academic research cultureinto a closely coordinated and product-driven one without losing the motivational valuesand the highest possible peer-review standards of academic research. However, oncesuch a product becomes available, it may serve as the equivalent of the Hubble SpaceTelescope for transportation infrastructure systems, benefiting all stakeholders.

ACKNOWLEDGEMENTS

The research described in this paper has been funded by the National Science Foundation(CMS-9622259), FHWA (Cooperative Agreement HSR-20) and Delaware River Port Authority(DRPA) of PA and NJ. The writers are grateful for the support and the confidence of respectiveProgram Officers Drs. Liu, Chong, Chase, Ghasemi and DRPA Chief Engineer Mr. Box. Thewriters thank many graduate students who have participated and helped in the various researchprojects. Finally, support and encouragement from Drexel University is appreciated.

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