Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology

INE/AUTC 10.0

Use of sensors in monitoring civil structures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004."September 2004."Includes bibliographical references (p. 141-145).This thesis surveys the use of sensors and sensor networks in monitoring civil structures, with particular emphasis on the monitoring of bridges and highways using fiber optic sensors. Following a brief review of the most widespread form of civil infrastructure inspection -- visual inspection -- the thesis describes the anatomy, mechanisms, and types of fiber optic sensors and characterizes the tradeoffs involved in choosing between fiber-optic and conventional sensor technologies. The thesis then presents a survey of contributions to this field, followed by a discussion of deployed applications of fiber-optic sensors, many of them in North America. The latter portion of the thesis first briefly discusses the emerging technology of wireless sensor networks and then presents an abbreviated case study comparing the costs and time required to deploy a fiber optic system to traditional visual inspection on the same structure. The case study suggests that the fiber optic sensors are a cost-effective technology, particularly when indirect savings are considered. The thesis concludes with some comments on the prospects and challenges for sensor technologies in civil infrastructure monitoring.by Bassam William Daher.S.M

Development of optical fibre distributed sensing for the structural health monitoring of bridges and large scale structures

Tesi per compendi de publicacionsPremi extraordinari doctorat UPC curs 2017-2018. Àmbit d’Enginyeria Civil i AmbientalIn this doctoral thesis it is proposed to research and assess the performance of the use of distributed optical fiber sensors (DOFS), more specifically the case of the optical backscattered reflectometry (OBR) based system, to the structural health monitoring (SHM) of bridges and large scale structures. This is a relatively recent technology that has demonstrated great promise for monitoring applications in a wide range of fields but due to its novelty, still presents several uncertainties which prevent its use in a more systematic and efficient way in civil engineering infrastructures. This is even more evident and relevant in the case of the application of this sensing technique to concrete structures. In this way, this thesis pretends to continue and further analyse this topic following the initial applications using the OBR system as a possible alternative/complementary monitoring tool in concrete structures. Therefore, in the present thesis, after an initial and thorough literature review on the use of DOFS in civil engineering applications, a set of experiments and analysis is planned and carried out. Firstly, different laboratory experimental campaigns are devised where multiple aspects of the instrumentation of DOFS technology in civil engineering applications are assessed and scrutinized. Consequently, the study of new implementation methods, comparison and performance analysis of different bonding adhesives and spatial resolution is performed through the conduction of load tests in reinforced concrete beam elements instrumented with OBR DOFS technology. Moreover, the long-term reliability of this sensing typology is also assessed through the conduction of a fatigue load test on two additional reinforced concrete beams. Afterwards, the use of the OBR system technology is assessed for the application in two real world structures in Barcelona, Spain. The first application corresponds to a previous monitoring work conducted in a historical masonry building and UNESCO World Heritage Site, which was subjected to rehabilitation works and where the collected data was analysed and interpreted in this thesis. The second real world structure application is an urban prestressed concrete viaduct that was exposed to major renovation actions, which included the widening of its deck and the introduction of new steel elements on the improved pedestrian sidewalks. This second application was conducted through a relatively extended period of time, which spanned from early summer to deep winter and therefore causing subsequent important thermal variations effects implications on the performance of the instrumented OBR system leading to the necessity of its compensation. Finally, taking into account the previous points, several conclusions are obtained related with the proficiency and limitations on the use of this particular type of optical sensing system in concrete structures. The advantages and disadvantages on the use of different types of bonding adhesives, implementation methodologies and spatial resolutions are described. Additionally, the performance of this technology in real world conditions is studied and characterized.En aquesta tesi doctoral es proposa investigar i avaluar la possibilitat d´aplicació de sensors de fibra òptica distribuïda (DOFS), més concretament un sistema del tipus OBR (Optical Backscattered Reflectometry), a la monitorització de la salut estructural (SHM) de ponts i estructures de grans dimensions. Es tracta d'una tecnologia relativament recent que ha demostrat una gran versatilitat i validesa en diferents aplicacions en un ampli ventall de camps, però que, a causa de la seva novetat, encara presenta diverses incerteses que impedeixen el seu ús d'una manera més sistemàtica i eficient en el cas de les infraestructures d'enginyeria civil. Sent això especialment cert i rellevant en el cas de l'aplicació d'aquesta tipologia de detecció en estructures de formigó. D'aquesta manera, aquesta tesi pretén continuar i analitzar aquest tema seguint les aplicacions inicials utilitzant el sistema OBR com una possible eina i de control alternatiu o complementari en estructures de formigó. Per tant, en aquesta tesi, després d'una revisió inicial i exhaustiva de la literatura sobre l'ús de DOFS en aplicacions d'enginyeria civil, es planifiquen i executen un conjunt d'assaigs experimentals i el seu posterior anàlisi. En primer lloc, es desenvolupen diferents campanyes experimentals de laboratori on s'avaluen i examinen múltiples aspectes de la tecnologia DOFS en aplicacions d'enginyeria civil. Com a conseqüència, s´estudien nous mètodes d'implementació, de comparació i anàlisi de rendiment de diferents adhesius de connexió i de resolució espaial mitjançant la realització de proves experimentals en elements a flexió a de formigó armat equipats amb tecnologia OBR DOFS. A més, la fiabilitat a llarg termini d'aquesta tipologia de sensors també s'avalua mitjançant la realització d'un assaig de fatiga en dos bigues de formigó armat addicionals. Posteriorment, l'ús de la tecnologia del sistema OBR s'avalua de cara a la seva aplicació en dues estructures reals a Barcelona, Espanya. La primera aplicació correspon a un treball de seguiment previ dut a terme en un edifici històric de maçoneria i que és Patrimoni de la Humanitat de la UNESCO (l´hospital de Sant Pau), que es va sotmetre a obres de rehabilitació i on es van analitzar i interpretar les dades recollides durant l´execució de les obres. La segona aplicació és un pont de formigó pretensat urbà que va estar exposat a una important intervenció de renovació, que va incloure l'ampliació de la coberta i la introducció de nous elements d'acer a les voreres de vianants. Aquesta segona aplicació es va dur a terme a través d'un període de temps relativament estès, que va des del començament de l'estiu fins a ben entrat l'hivern i, per tant, va provocar variacions tèrmiques importants tant als materials com als propis sensors, que van tenir conseqüències sobre el rendiment del sistema OBR instrumentat i que va comportar la necessitat de la seva compensació. Finalment, tenint en compte els punts anteriors, s'obtenen diverses conclusions relacionades amb la competència i les limitacions sobre l'ús d'aquest tipus particular de sistema de detecció òptica en estructures de formigó. Es descriuen els avantatges i desavantatges sobre l'ús de diferents tipus d'adhesius de connexió, metodologies d'implementació i resolucions espaials. Addicionalment, s'estudia i caracteritza l'acompliment d'aquesta tecnologia en condicions reals i no de laboratori.Award-winningPostprint (published version

Application of surrogate modeling methods in simulation-based reliability and performance assessment of civil structures

Structures and infrastructure systems are subjected to various deterioration processes due to environmental or mechanical stressors. Proper performance assessment approaches capable of detecting potential structural damage and quantifying the probability associated with structural failure are required to formulate optimal maintenance and retrofit plans that minimize the risk of failure and maximize the safety of structures. However, due to the presence of several sources of uncertainty that can affect the performance assessment and decision-making processes (e.g., uncertainties associated with loading conditions and performance prediction models), applying probabilistic methods, such as Monte Carlo simulation, is essential. In this context, a large number of simulations is generally required to quantify the low failure probability associated with civil structures. Executing the required number of simulations may be computationally expensive, especially if complex and/or nonlinear structural models (e.g., finite element models) are involved. The use of surrogate modeling tools such as artificial neural networks, polynomial chaos expansion, and kriging can help in reducing the computational costs associated with simulation-based probabilistic analysis. The research proposed herein aims to develop probabilistic approaches for performance assessment and damage detection of structures using advanced simulation-based techniques coupled with surrogate modeling. The proposed methodology is applied to quantify the risk of bridge failure due to flood events considering the impact of climate change. The approach was extended to establish the time-variant flood fragility surfaces for bridges under flood conditions. This approach (a) integrates deep learning neural networks into a simulation-based probabilistic approach to predict the future river streamflow necessary for assessing the flood hazard at the bridge location and (b) simulates the structural behavior of the bridge foundation under sour conditions. In addition, the proposed methodology is used to quantify the reliability of bolted and welded steel connections by integrating finite element analysis and surrogate models. Low-rank tensor approximation and polynomial chaos kriging surrogate models are adopted to perform Monte Carlo simulation and quantify the reliability of the investigated combination connection. Finally, artificial neural networks were used to develop a statistical damage detection and localization approach capable of evaluating the performance of prestressed concrete bridge girders using fiber optic sensors

A progressive collapse evaluation of steel structures in high temperature environment with optical fiber sensors

In the process of a progressive failure of steel structures in a post-earthquake fire, real-time assessment and prediction of structural behaviors are of paramount significance to an emergency evacuation and rescue effort. However, existing measurement technologies cannot provide the needed critical data such as large strains at high temperature. To bridge this gap, a novel optical fiber sensor network and an adaptive multi-scale finite element model (FEM) are proposed and developed in this study. The sensor network consists of long period fiber gratings (LPFG) sensors and extrinsic Fabry-Perot interferometer (EFPI) sensors or their integration. Each sensor is designed with a three-tier structure for an accurate and reliable measurement of large strains and for ease of installation. To maintain a balance between the total cost of computation and instrumentation and the accuracy in numerical simulation, a structure is divided into representative/critical components instrumented densely and the remaining components simulated computationally. The critical components and the remaining were modeled in different scales with fiber elements and beam/plate elements, respectively, so that the material behavior and load information measured from the critical components are representative to the remaining components and can be used to update the temperature distribution of the structure in real time. Sensitivity studies on the number of sensors and the initial selection of an updating temperature parameter were conducted. Both the sensor network and the FEM were validated with laboratory tests of a single-bay, one-story steel frame under simulated post-earthquake fire conditions. The validated FEM was applied to a two-bay, four-story steel building under the 1995 Kobe earthquake excitations. Based on extensive tests and analyses, the proposed sensor can measure a strain of 12% at as high as 800⁰C (1472⁰F) in temperature. Within the application range, the LPFG wavelength and the EFPI gap change linearly with the applied strain and temperature. The proposed updating criterion and algorithm in the adaptive FEM are proven to be effective. The number of sensors is sufficient in engineering applications as long as the sensors can adequately represent the material behavior of the instrumented components. The predicted structural behavior is unaffected by any change in a low temperature range and thus insensitive to the initial selection of the updating parameter --Abstract, page iii

Strain Distribution and Crack Detection in Concrete Overlays with Pulse Pre-Pump Brillouin Optical Time Domain Analysis

This report is focused on the measurement of strain distributions and crack detection in unbonded and bonded pavement overlays. The main objectives of this study are: (a) to characterize the strain sensing properties of distributed fiber optic sensors with recently developed pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA), (b) to develop an installation method for real world applications, (c) to document the performance of the PPP-BOTDA technology in unbonded/bonded pavement applications, and (d) to develop a numerical model to facilitate the analysis of mechanical behavior of unbonded pavement overlay under vehicle wheel loads. A thin concrete layer can be cast on top of a severely deteriorated pavement layer with a fabric sheet in between to rapidly and cost effectively improve the driving condition of existing roadways. Once cured, the concrete layer is divided into many panels and often referred to as the unbonded Portland cement concrete (PCC) overlay. The service life of PCC overlays can be appreciably extended by appropriate rehabilitation strategies at early stages of deterioration based on the information provided by health monitoring. The strain distribution and crack detection are of interest to engineers in this application. Minor or moderately deteriorated existing concrete pavements can also be resurfaced with a thin concrete layer to improve their driving condition. In this case, potential cracks in the existing pavement may easily penetrate through the new concrete layer. The way the potential slip at their interface develops over time is an interesting question to answer. This study reports an application of a commercial single mode optical fiber to measure strain distributions in full-scale fiber reinforced unbonded overlays. Prefabricated cementitious mortar grid instrumented with distributed fiber optic sensors, namely smart grid, was developed and proposed to address the logistics of handling delicate optical fibers, and thus facilitate the in-situ construction. The smart grids can be laid on top of the fabric sheet and embedded in concrete overlay. With the proposed method, the pavement overlays instrumented with distributed sensors were successfully constructed in Minnesota\u27s Cold Weather Road Research Facility (MnROAD). The optical fibers were characterized on a precision load frame at room temperature. A Neubrescope was used to measure strain distributions based on the pulse pre-pump Brillouin optical time domain analysis (PPPBOTDA). The overlays were subjected to repeated truck loads and eventually cracked. Strain distributions were obtained from the distributed fiber optic sensor. Cracks were identified and localized by mapping the strain distribution in which the sharp peaks represent the cracks. The strain distribution was further investigated using a three-dimensional finite element model incorporating nonlinear boundary conditions. Opening between substrate and overlay concrete was demonstrated, and strain distributions in overlay and substrate concrete were determined with the numerical model. For the bonded concrete overlays on existing pavement, a delamination detection method was developed and implemented using the distributed fiber optic sensors. Delamination can be identified as sharp peaks in the measured strain distributions

Researching the non-linear geometrical effects caused by static flap-wise loading of a wind turbine blade

Many questions exist regarding the structural integrity of wind turbine blades, and this thesis aimed to answer some of these as a means to increase future reliability. One of the key problems with the blade structural response under high static loads was the occurrence of a geometrically non-linear bending phenomenon known as the Brazier effect. This research aimed to better understand the consequences of this effect on the lightweight material used, and this was achieved by performing laboratory scale specimen tests on representative material. A key outcome was that the box girder suction side web was identified as a critical component and most likely to fail via an interfacial disbond. A related finding was that the presence of an interlaminar delamination in the sandwich web material would significantly reduce the load bearing capacity of that section of web. The percentage reduction in load bearing ability appeared to be a function of skin to core thickness ratio and delamination size. Another key outcome was the identification that either the growth of matrix cracks or the presence of pre-existing delaminations were paramount in the development of interlaminar cracks in the laminate caps. This research has demonstrated that, should future blade flexibility be increased, reinforcing layers in the cap should be introduced. The suggested design of this reinforcement was a modification to the current layup that introduced transverse layers along the inner side of the cap. This was proven to increase the flexural rigidity by 107%. Additionally, for future blade certification and monitoring, web delaminations should be identified, potentially by use of digital image correlation or acoustic emissions monitoring, both of which were demonstrated as being capable techniques