Structural health monitoring and bridge condition assessment

Thesis (Ph.D.) University of Alaska Fairbanks, 2016This research is mainly in the field of structural identification and model calibration, optimal sensor placement, and structural health monitoring application for large-scale structures. The ultimate goal of this study is to identify the structure behavior and evaluate the health condition by using structural health monitoring system. To achieve this goal, this research firstly established two fiber optic structural health monitoring systems for a two-span truss bridge and a five-span steel girder bridge. Secondly, this research examined the empirical mode decomposition (EMD) method’s application by using the portable accelerometer system for a long steel girder bridge, and identified the accelerometer number requirements for comprehensively record bridge modal frequencies and damping. Thirdly, it developed a multi-direction model updating method which can update the bridge model by using static and dynamic measurement. Finally, this research studied the optimal static strain sensor placement and established a new method for model parameter identification and damage detection.Chapter 1: Introduction -- Chapter 2: Structural Health Monitoring of the Klehini River Bridge -- Chapter 3: Ambient Loading and Modal Parameters for the Chulitna River Bridge -- Chapter 4: Multi-direction Bridge Model Updating using Static and Dynamic Measurement -- Chapter 5: Optimal Static Strain Sensor Placement for Bridge Model Parameter Identification by using Numerical Optimization Method -- Chapter 6: Conclusions and Future Work

On systematic approaches for interpreted information transfer of inspection data from bridge models to structural analysis

In conjunction with the improved methods of monitoring damage and degradation processes, the interest in reliability assessment of reinforced concrete bridges is increasing in recent years. Automated imagebased inspections of the structural surface provide valuable data to extract quantitative information about deteriorations, such as crack patterns. However, the knowledge gain results from processing this information in a structural context, i.e. relating the damage artifacts to building components. This way, transformation to structural analysis is enabled. This approach sets two further requirements: availability of structural bridge information and a standardized storage for interoperability with subsequent analysis tools. Since the involved large datasets are only efficiently processed in an automated manner, the implementation of the complete workflow from damage and building data to structural analysis is targeted in this work. First, domain concepts are derived from the back-end tasks: structural analysis, damage modeling, and life-cycle assessment. The common interoperability format, the Industry Foundation Class (IFC), and processes in these domains are further assessed. The need for usercontrolled interpretation steps is identified and the developed prototype thus allows interaction at subsequent model stages. The latter has the advantage that interpretation steps can be individually separated into either a structural analysis or a damage information model or a combination of both. This approach to damage information processing from the perspective of structural analysis is then validated in different case studies

Aging concrete structures: a review of mechanics and concepts

The safe and cost-efficient management of our built infrastructure is a challenging task considering the expected service life of at least 50 years. In spite of time-dependent changes in material properties, deterioration processes and changing demand by society, the structures need to satisfy many technical requirements related to serviceability, durability, sustainability and bearing capacity. This review paper summarizes the challenges associated with the safe design and maintenance of aging concrete structures and gives an overview of some concepts and approaches that are being developed to address these challenges

Cracking assessment in concrete structures by distributed optical fiber

In this paper, a method to obtain crack initiation, location and width in concrete structures subjected to bending and instrumented with an optical backscattered reflectometer (OBR) system is proposed. Continuous strain data with high spatial resolution and accuracy are the main advantages of the OBR system. These characteristics make this structural health monitoring technique a useful tool in early damage detection in important structural problems. In the specific case of reinforced concrete structures, which exhibit cracks even in-service loading, the possibility to obtain strain data with high spatial resolution is a main issue. In this way, this information is of paramount importance concerning the durability and long performance and management of concrete structures. The proposed method is based on the results of a test up to failure carried out on a reinforced concrete slab. Using test data and different crack modeling criteria in concrete structures, simple nonlinear finite element models were elaborated to validate its use in the localization and appraisal of the crack width in the testing slab.Peer ReviewedPostprint (author’s final draft

The Role of Shrinkage Strains Causing Early-Age Cracking in Cast-in-Place Concrete Bridge Decks

Early-age cracking in cast-in-place reinforced concrete bridge decks is occurring more frequently now than three decades ago and principle factors that lead to early-age deck cracking are not fully understood. A finite element (FE) simulation methodology for assessing the role of shrinkage-induced strains in generating early-age bridge deck cracking is described. The simulations conducted indicate that drying shrinkage appears to be capable of causing transverse (and possibly longitudinal) bridge deck cracks as early as 9 to II days after bridge deck placement. The drying-shrinkage induced stresses would result in transverse cracking over interior pier supports in a typical bridge superstructure considered in the finite element simulations conducted

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

INE/AUTC 10.0

3D-PhysNet: Learning the Intuitive Physics of Non-Rigid Object Deformations

The ability to interact and understand the environment is a fundamental prerequisite for a wide range of applications from robotics to augmented reality. In particular, predicting how deformable objects will react to applied forces in real time is a significant challenge. This is further confounded by the fact that shape information about encountered objects in the real world is often impaired by occlusions, noise and missing regions e.g. a robot manipulating an object will only be able to observe a partial view of the entire solid. In this work we present a framework, 3D-PhysNet, which is able to predict how a three-dimensional solid will deform under an applied force using intuitive physics modelling. In particular, we propose a new method to encode the physical properties of the material and the applied force, enabling generalisation over materials. The key is to combine deep variational autoencoders with adversarial training, conditioned on the applied force and the material properties. We further propose a cascaded architecture that takes a single 2.5D depth view of the object and predicts its deformation. Training data is provided by a physics simulator. The network is fast enough to be used in real-time applications from partial views. Experimental results show the viability and the generalisation properties of the proposed architecture.Comment: in IJCAI 201

Lattice Modeling of Early-Age Behavior of Structural Concrete.

The susceptibility of structural concrete to early-age cracking depends on material composition, methods of processing, structural boundary conditions, and a variety of environmental factors. Computational modeling offers a means for identifying primary factors and strategies for reducing cracking potential. Herein, lattice models are shown to be adept at simulating the thermal-hygral-mechanical phenomena that influence early-age cracking. In particular, this paper presents a lattice-based approach that utilizes a model of cementitious materials hydration to control the development of concrete properties, including stiffness, strength, and creep resistance. The approach is validated and used to simulate early-age cracking in concrete bridge decks. Structural configuration plays a key role in determining the magnitude and distribution of stresses caused by volume instabilities of the concrete material. Under restrained conditions, both thermal and hygral effects are found to be primary contributors to cracking potential

Damage Evaluation of Concrete Structures Using Acoustic Emission

The deterioration and aging of the infrastructure in the U.S. have become a crucial issue, especially for highway bridges and nuclear power plants. The reliability and safety of existing structures are affected by growing populations and limited resources. This issue has gained significant concern during the last two decades and efforts are being conducted to accelerate the improvement of nondestructive testing (NDT) and structural health monitoring (SHM) methods. Additional information regarding the condition of existing structures and the early detection of damage can aid in reducing overall maintenance costs. The studies presented in this dissertation employ acoustic emission (AE) as a non-destructive evaluation technique, leveraging its extreme sensitivity to mechanical waves generated by damage and progressive deterioration mechanisms within these structures. The objective of the research is to characterize damage conditions of existing structures using a stress wave-based approach including two cases of study: a) detect and identify the extent of microcrack initiation and progression occurring due to different compressive loading levels applied on small scale cement paste specimens using acoustic emission, and b) monitor and evaluate damage growth in a prestressed concrete girder bridge with shear cracks under truck loading and varying load positions. Three studies were performed in an effort to achieve the objectives and are presented in a series of journal articles as chapters in this dissertation. The first and second studies present a two-part paper which discusses damage mechanisms in cement paste under compression loading based on AE (Part I) and fracture mechanics (Part II). In this study, cement paste specimens having dimension of 38.1 mm x 38.1 mm x 152.4 mm (1.5 in. x 1.5 in. x 6 in.) were cast using Portland cement Type I/II and a water to cement ratio of 0.5, which was then cured for 28 days in lime water. Part I presents and discusses the results from compression tests while monitoring with AE. Active crack growth was detected and classified using amplitude and cumulative signal strength (CSS), and unsupervised pattern recognition was utilized to separate AE data into clusters. Then the source of AE data was verified using micro-CT scanning. Part II included a three-point bending test conducted on 38.1 mm × 38.1 mm × 152.4 mm (1.5 in. × 1.5 in. × 6 in.) cement paste specimens to measure the fracture toughness property. Also, the compression test of the cement paste prism was simulated using the Abaqus finite element program to determine the stress intensity factor (SIF) along a predefined crack tip at different levels of loading. The SIF is to be compared with the fracture toughness to define the limit at which a crack grows in an unstable manner. The results of this study show that under the conditions of unstable crack extension (defined in Part I by the AE method), the calculated SIF reached the fracture toughness of cement paste. This verifies the defined damage mechanisms described in part I. In the third study, acoustic emission (AE) data was investigated to better understand damage conditions in a three-span prestressed concrete girder bridge during a load test. The innovation lies in classification of crack extensions (stable or unstable) during the loading and holding processes. The gap in current literature addressed is a paucity of data and findings on bridges in operation and having inclined cracks. This study addresses the collection and processing of AE signals recorded by piezoelectric sensors attached on two interior girders toward the obtuse corner of an exterior span of the bridge while under loading. Results showed signs of crack propagation beyond the existing cracks. Damage classification procedures based on AE data recorded during one loading and holding step provided an indication of diminishing crack extensions as the load hold was continued in one girder. Concurrently, signs of unstable crack propagation were shown in the other girder. The use of previously developed AE analysis methods to evaluate the condition of each girder is discussed. Finally, shear strength analysis using modified compression field theory (MCFT) was performed to place the results in context. The outcomes of the studies described in this dissertation demonstrate the potential of using AE as a feasible technique for condition assessment and structural health monitoring through two main points including: a) stress wave-based data acquisition can be used to inform the microscale damage compression model as it relates to the degradation of cement paste, and b) a stress wave based approach may be used to define the level of shear damage in prestressed bridge girders due to applied loading