Implementation of structural monitoring to assess the performance and serviceability of concrete and steel girder bridges

This research focuses on bridges and the development of structural monitoring systems used for both concrete and steel bridges. Parts of two bridges were built with a combination of sensors attached to a data acquisition system powered by a solar panel and battery, where data is transmitted wirelessly through cell phone technology. The research represents the first efforts to develop remote structural monitoring that is robust and reliable to survive through the construction of both concrete and steel bridges and continue to function from the beam fabrication through bridge construction and even now as the bridges have been in service for more than two years.Prestressed Concrete Bridge Beams were instrumented during beam fabrication. Concrete strains, concrete temperatures, and ambient temperatures are measured continuously from the time immediately before the casting of the beams, through fabrication, including detensioning of prestressing strands, through handling and storage, transportation, and erection, through bridge construction, and now during life-in-service. Sensors capture concrete strains and temperatures from early ages. These data are useful to assess important variables regarding the design and construction of prestressed concrete bridge beams and the bridges made with those beams. Specifically, prestress losses were assessed, and beam cambers were measured. Designs were varied to investigate different design choices to control and limit both prestress losses and cambers.In-situ load testing was performed on the completed concrete bridge structure. These data are used to investigate design parameters, specifically distribution factors for bridges' design and load rating and the dynamic amplification factor for bridges. Recommendations are made from the research.Findings from the research demonstrate the effectiveness of including fully tensioned top strands in prestressing strand patterns and mild horizontal steel as part of the primary reinforcement at midspans of bridge beams. The research shows that both of these design choices are effective in limiting prestress losses and beam cambers. These techniques can be employed nationwide and worldwide where precast, prestressed concrete bridge beams are used

Nondestructive testing of reinforced and prestressed concrete structures using acoustic waveguides

The main objective of this research is to develop both passive and active nondestructive testing techniques for reinforced and prestressed concrete structures using acoustic waveguides. The first technique introduces a two-dimensional surface waveguide to enlarge the acoustic emission (AE) monitoring area of a reinforced concrete structure. A two-dimensional steel wire system is developed as an acoustic waveguide to study the AE behavior of a reinforced concrete floor slab. AE sensors are mounted to the end of the waveguides to detect AE signals, which are generated by pencil-lead breaks at various locations on concrete surface. Results show that the use of the surface waveguides can significantly enlarge the AE monitoring area. In order to identify locations of AE sources, a neural network system is employed. Four data sets of AE parameters and their corresponding locations are used to train the neural network system. Satisfactory results in predicting the AE source locations are obtained when using the trained neural network system to identify AE source locations of a testing data set.;The second technique involves the measurement of tensile forces in a prestressing strand in prestressed concrete structures using ultrasonic stress waves. The commonly used 1/2-inch diameter seven-wire prestressing strands are studied. In this study, both experimental measurements and theoretical analysis are conducted. A stress wave is generated at one end of a prestressing strand and the wave is detected at the other end using an ultrasonic transducer. The stress waves due to tensile stresses of the strand up to 77% of its ultimate strength are investigated. The theoretical analysis is conducted by accounting for acoustoelasticity effect and the dispersion of waves. This analysis is used to calculate the traveling times of different frequency components of the wave propagating in the strand, which is subjected to prestress forces. The analysis provides a successful description of the behavior of a longitudinal transient wave traveling through a long, prestressed, circular strand. The Wigner-Ville Transform is used as a signal-processing tool in order to identify the arrival times of different frequency components of the detected waveforms. The analytical and experimental results correlate well, and good measurement accuracy is observed. Both experimental and analytical results indicate that the velocity (or traveling time) of each frequency component of the traveling wave can be related to tensile force level in the strand. This technique can effectively be used for measuring tensile forces in ungrouted post-tensioning strands of a prestressed concrete structure

Assessment of deteriorating post-tensioned concrete bridges.

A non-linear analytical model was developed to assess the residual strength of deteriorating post-tensioned concrete bridges containing integral grouted tendons. The damage mechanisms addressed were those due to failure of the prestressing tendon as a result of corrosion, and the presence of grout voids within the ducts. The model was based principally on the method of strain compatibility, but modified to accommodate unbonded tendons in regions of incomplete grouting in the ducts. The phenomenon of tendon reanchoring was also incorporated to estimate the distribution of residual prestress after tendon failure. This considered the distribution of grout voids along the beam and the quality of the grout surrounding the tendon. Once validated, the model was used to study the effect of tendon failure and regions of ungrouted tendons on the residual structural capacity of typical bridge beams incorporating a variety of defects. It was found that the presence of voids within the re-anchoring length of failed tendons will affect the ability of the tendon to re-anchor fully and may affect the residual strength of the beam. The distribution of grout voids along the beam is thus an important factor when considering loss of strength. It was also demonstrated that significant levels of deterioration do not always compromise ultimate strength to a significant degree, hence avoiding the need for costly replacement. In addition to the global analysis of beam strength due to failed tendons, the local effect of partial loss of tendon area was investigated with ANSYS finite element software. This enabled the level of stress enhancement in the corroded tendon and the amount of loss of prestressing force to be determined. Valid bond models were established based on results from available field observations. It was found that only a relatively small amount of prestressing force is lost as a result of partial loss of area in a tendon in part due to the redistribution of force to adjacent tendons

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

Dynamic performance of transmission pole structures under blasting induced ground vibration

Structural integrity of electric transmission poles is crucial for the reliability of power delivery. In some areas where blasting is used for mining or construction, these structures are endangered if they are located close to blasting sites. Through field study, numerical simulation and theoretical analysis, this research investigates blast induced ground vibration and its effects on structural performance of the transmission poles. It mainly involves: (1) Blast induced ground motion characterization; (2) Determination of modal behavior of transmission poles; (3) Investigation of dynamic responses of transmission poles under blast induced ground excitations; (4) Establishment of a reasonable blast limit for pole structures; and (5) Development of heath monitoring strategies for the electric transmission structures. The main technical contributions of this research include: (1) developed site specific spectra of blast induced ground vibration based on field measurement data; (2) studied modal behavior of pole structures systematically; (3) proposed simplified but relatively accurate finite element (FE) models that consider the structure-cable coupling; (4) obtained dynamic responses of transmission pole structures under blast caused ground vibration both by spectrum and time-history analysis; (5) established 2 in/s PPV blast limit for transmission pole structures; (6) developed two NDT techniques for quality control of direct embedment foundations; and (7) described an idea of vibration-based health monitoring strategy for electric transmission structures schematically

Viscoelastically prestressed composites : towards process optimisation and application to morphing structures

This thesis covers research that focuses on facilitating the industrial application of viscoelastically prestressed polymeric matrix composites (VPPMCs). With nylon 6,6 fibre as the reinforcement and polyester resin as the matrix material, unidirectional prestressed composite samples were produced and investigated, to expand the knowledge of existing VPPMC technology, and identify the potential application of viscoelastic fibre prestressing to morphing (shape-changing) structures.To produce a VPPMC, a tensile load is applied to polymeric fibre yarns to induce viscoelastically prestress; following load removal, the yarns are cut and moulded into a matrix. Previous research has shown that by using viscoelastic fibre prestressing within a composite, mechanical properties, such as tensile strength, flexural modulus and impact toughness can be increased by up to 50%. To further understand the underlying prestress mechanisms, the viscoelastic performance of nylon 6,6 fibre was investigated in terms of creep, recovery and recovery force measurement. By using various creep loading conditions, the viscoelastic behaviour of the fibre also provided the basis for investigations into the optimisation of load-time conditions for producing prestress. This provides the first step towards facilitating the production of VPPMCs for industrial application. Since there are increasing demands for using composites within morphing technology, the application of VPPMC principles to morphing structures was studied through both experimental and numerical investigations.The viscoelastic behaviour of nylon 6,6 fibre showed approximately linear viscoelasticity under 24 h creep conditions with up to 590 MPa stress. This was further verified through use of the time-stress superposition principle: instead of a nonlinear relationship as predicted by the well-known WLF equation, a linear relationship between the applied creep stress and the stress shift factor was found. By approaching the maximum creep potential of the fibre material, impact benefits from the prestressing effect were further improved by ~75% (at ~4.0% creep strain level). Charpy impact testing and recovery force measurement demonstrated that there was an optimum level of viscoelastic fibre prestressing to maximise the mechanical benefits. A viscoelastic deformation mechanism based on the three-phase microstructural model and latch-based mechanical model was then proposed.It was found that the fibre processing time for viscoelastically generated prestress could be significantly reduced from 24 h to tens of minutes. By employing the time-temperature superposition principle, the impact benefits from viscoelastically generated prestress under the standard 330 MPa, 24 h creep (at ~3.4% creep strain level), was found broadly to be the same as subjecting the yarns to 590 MPa for 37 min creep. Hence, there was no deterioration in prestress benefits from VPPMC samples produced under both creep conditions to an equivalent of 20,000 years at a constant 20˚C. Two viscoelastic creep strain levels (i.e. ~3.4% and ~4.0%) were evaluated through Charpy impact testing, the relationships between applied creep stress and the corresponding fibre processing time followed a logarithmic trend. This suggested that the fibre processing time for prestress could be reduced further, subjecting to avoiding fibre damage. The effects from increasing creep time were found to compare with increasing stress in terms of optimum VPPMC performance.Finally, the principle of viscoelastic fibre prestressing was successfully used to produce a bistable composite structure, which could snap from one stable cylindrical shape to another when subjected to external loading. The bistable structure was produced by bonding four prestressed strips to the sides of a thin, flexible resin-impregnated fibre-glass sheet. Here, bistability was achieved through pairs of strips orientated to give opposing cylindrical configurations within the sheet. Snap-through behaviour of the bistable structure was investigated through both experimental and numerical simulation; a snap-through mechanism was subsequently proposed based on these observations

Review: optical fiber sensors for civil engineering applications

Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry

Concrete Box Beam Risk Assessment and Mitigation: Volume 2—Evaluation and Structural Behavior

Adjacent box beam bridges have a history of poor long-term performance including premature deterioration and failures. Leaking joints between box beams allow chloride-laden water to migrate through the superstructure and initiate corrosion. The nature of this deterioration leads to uncertainty of the extent and effect of deterioration on structural behavior. Due to limitations in previous research and understanding of the strength of deteriorated box beam bridges, conservative assumptions are made for the assessment and load rating of these bridges. Furthermore, the design of new box beam bridges, which can offer an efficient and economical solution, is often discouraged due to poor past performance. The objective of this research is to develop recommendations for inspection, load-rating, and design of adjacent box beam bridges. The research is presented in two volumes. Volume 1 focuses on the evolution of box beam design in Indiana to understand the lack of performance and durability. The Indiana Department of Transportation (INDOT) standards and bridge design manuals were reviewed to track the historical development of box beam bridges in the State. Two timelines were produced tracking important updates to box beam design. Adjacent box beam bridges within INDOT’s bridge database were also analyzed. Superstructure ratings were compared with bridge age as well as bridge characteristics to highlight possible causes for deterioration. Analyzing the INDOT inventory, data shows that the condition of adjacent box beam bridges may be affected by location, type of wearing surface, and the use of deck membranes. Six bridges were then inspected to identify common deficiencies and specific problems. Exterior beams and beams within the wheel load path tend to have higher levels of deterioration. Furthermore, leaking joints between beams leads to corrosion of reinforcement, ultimately resulting in spalling, fracture of prestressing strands, and loss of structural capacity. Volume 2 focuses on evaluating the capacity of deteriorated adjacent box beams, the development of improved load rating procedures, and new box beam design. Through a series of bridge inspections, deteriorated box beams were identified and acquired for experimental testing. The extent of corrosion was determined through visual inspection, non-destructive evaluation, and destructive evaluation. Non-destructive tests (NDT) included the use of connectionless electrical pulse response analysis (CEPRA), ground penetrating radar (GPR), and half-cell potentials. Deteriorated capacity was determined through structural testing, and an analysis procedure was developed to estimate deteriorated behavior. A rehabilitation procedure was also developed to restore load transfer of adjacent beams in cases where shear key failures are suspected. Based on the understanding of deterioration developed through study of deteriorated adjacent box beam bridges, improved inspection and load rating procedures are provided along with design recommendations for the next generation of box beam bridges

Dynamic performance of pre-cast prestressed beams – cast in-situ slab composite bridges

Most bridge management systems still rely on visual inspections for condition assessment of bridges; this means that damage in inaccessible parts of the structure such as shear connectors in concrete composite bridges remain undetected until catastrophic failure occurs. Localized non-destructive techniques such as ultrasonic techniques, radar method, impact testing, magnetic based methods and proof load tests are limited to small areas, time consuming and require prior knowledge of the damaged zone. These limitations can be overcome by using dynamics-based techniques. The main objective of this work is to investigate experimentally the effectiveness of dynamics-based techniques in assessing the condition of shear connectors in concrete composite bridges consisting of pre-cast prestressed beams and a cast in-situ slab based on measurements taken from the surface of the accessible deck slab. In this research, shear links of 8mm bars extended from beam to the slab are used to stimulate shear connectors in real bridges. The experimental work involved building five concrete composite beams each with different number of shear connectors. The testing procedure consisted of measuring the dynamic properties in both the undamaged and damaged beams. Damage was introduced by accelerating corrosion to a group of shear connectors near the supports in each composite beam. Push-off test was conducted in order to determine the shear capacity of the shear connectors in both undamaged and damaged state. The modal tests were successfully executed and from the modal analysis results it was observed that a beam with large number of shear connectors produce high frequencies and high amplitudes of frequency response functions (FRFs) compared to the one with less number of shear connectors. After the shear connectors were damaged all beams showed similar results. In the FRFs, the frequency peaks shifted to the left and the peaks amplitudes changed, the natural frequencies generally dropped indicating the existence of damage. In an attempt to locate regions with damaged shear connectors, the Coordinate Modal Assurance Criteria (COMAC), change of flexibility, change of curvature and strain energy method were used. All methods showed positive and negative results. The change of flexibility method showed minimum negative results compared to other methods in locating regions with damaged shear connectors. Generally, Results show that dynamics-based techniques can be used to detect and localize regions with damaged shear connectors in pre-cast prestressed beams - cast in-situ slab composite bridges by only taking vibration measurements from the surface of the accessible deck slab