TY - CHAP A1 - Niederleithinger, Ernst A1 - Wang, Xin A1 - Epple, Niklas A1 - Schumacher, T. A1 - Ahmend, S. A1 - Klikowicz, P. ED - Yokota, H. ED - Frangopol, D. W. T1 - Ultrasonic coda wave monitoring of concrete structures: First experiences with large-scale experiments and real structures N2 - Ultrasonic monitoring, making use of the sensitivity of the coda of repeated transmission meas-urements to changes in stress, temperature, moisture, as well as localized or distributed damage, has gotten at-tention in structural health monitoring (SHM) research recently. Analysis methods such as coda wave inter-ferometry (CWI), including its nonlinear extension, have been shown to be able to measure ultrasonic wave velocity changes with a 1∙10-5 resolution, while indicators such as cross-correlation or cross-coherence have been used to distinguish between reversible and irreversible changes. Several small- and large-scale laboratory experiments have demonstrated that stress changes in structures can be captured or damage detected in a very early stage. The use of this technique for pre-warning before failure are currently under investigation, as well as detailed research on the physical causes and the connection between ultrasonic wave properties and materi-al/structural behavior. Recently, several of large-scale laboratory and real structures have been instrumented with embedded ultrasonic transducers to gather experience and evidence on how to use this technology in re-al-world applications. Preliminary results from installations on a new bridge, an existing bridge, a tunnel, a la-boratory earthquake test as well as a historic stadium in Germany, Poland, and the United States, respectively, are presented. Environmental influences (mainly temperature) and validation by load tests are discussed. KW - Coda wave interferometry KW - Structural health monitoring KW - Ultrasound KW - Concrete KW - Bridges PY - 2021 SN - 978-0-367-23278-8 DO - https://doi.org/10.1201/9780429279119-345 SP - 2525 EP - 2531 PB - Taylor & Francis CY - London, UK AN - OPUS4-54168 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Niederleithinger, Ernst A1 - Hindersmann, I. A1 - Sodeikat, C. A1 - Groschup, R. T1 - Monitoring of a German Road Bridge Using Embedded Ultrasonic Transducers and Coda Waves N2 - The ‘G¨anstorbr¨ucke’ bridge between the cities of Ulm and Neu-Ulm is one of the best-monitored bridges all over Germany. In addition to an already active bride monitoring system, we have equipped the bridge with 30 ultrasonic transducers to explore the monitoring possibilities at an in-service large-scale reinforced concrete structure with continuous active ultrasonic measurements. The monitoring system is based on the detection of small changes in the entire signal, especially the multiply scattered parts of the recording, the so-called coda. Applying Coda Wave Interferometry (CWI), subtle changes in the signal can be detected and related to changing velocities in the area between source and receiver. A comparison of the results from coda wave interferometry with the strain measurements of the permanent monitoring system shows a correlation between strain measurements and CWI results. We discuss the challenges of changing environmental conditions, pose for interpretation of the results, and highlight the advantages of embedded versus externally attached ultrasonic transducers in permanent bridge monitoring, especially when coda wave interferometry is applied. T2 - EWSHM 2022 CY - Palermo, Italy DA - 04.07.2022 KW - Bridge monitoring KW - Ultrasound KW - Embedded sensors KW - Coda wave interferometry PY - 2022 AN - OPUS4-55383 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Niederleithinger, Ernst A1 - Hindersmann, I. A1 - Sodeikat, C. A1 - Groschup, R. ED - Rizzo, P. ED - Milazzo, A. T1 - From the Lab to the Structure: Monitoring of a German Road Bridge Using Embedded Ultrasonic Transducers and Coda Waves N2 - The ‘Gänstorbrücke’ bridge between the cities of Ulm and Neu-Ulm is one of the best-monitored bridges all over Germany. In addition to an already active bride monitoring system, we have equipped the bridge with 30 ultrasonic transducers to explore the monitoring possibilities at an in-service large-scale reinforced concrete structure with continuous active ultrasonic measurements. The monitoring system is based on the detection of small changes in the entire signal, especially the multiply scattered parts of the recording, the so-called coda. Applying Coda Wave Interferometry (CWI), subtle changes in the signal can be detected and related to changing velocities in the area between source and receiver. A comparison of the results from coda wave interferometry with the strain measurements of the permanent monitoring system shows a correlation between strain measurements and CWI results. We discuss the challenges of changing environmental conditions, pose for interpretation of the results, and highlight the advantages of embedded versus externally attached ultrasonic transducers in permanent bridge monitoring, especially when coda wave interferometry is applied. KW - Bridge monitoring KW - Ultrasound KW - Embedded sensors KW - Coda wave interferometry PY - 2022 SN - 978-3-031-07258-1 DO - https://doi.org/10.1007/978-3-031-07258-1_83 VL - 254 SP - 824 EP - 832 PB - Springer Cham CY - Cham AN - OPUS4-55385 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas T1 - Monitoring of bridges with coda waves - first steps towards an imaging strategy N2 - Monitoring of concrete structures is of utmost importance in maintenance and preservation of infrastructure. As a part of the DFG research group CoDA (Concrete Damage Assessment by Coda Waves), the works within this PhD project aim for identification of damage sensitive parameters extracted from ultrasonic measurements obtained with embedded sensors, the determination of environmental (reversible) influences on the signal and the localisation of damaged areas. The main technique used for the detection of changes in the monitored material is the so-called Coda Wave Interferometry (CWI). It uses the later part of the ultrasonic recording for the detection of small changes in the sensed area and the calculation of a relative velocity change. Using this technique we can show that we are able to detect changes in concrete temperature with ultrasound measurements. This enables temperature correction for ultrasound monitoring with embedded sensors. The crucial point for imaging and localisation with coda waves is the calculation of the so-called sensitivity kernels. We propose the application of numerical wave simulations for the kernel calculations instead of the commonly used diffusivity equation. Using finite-difference wave modelling code from our DFG project partners we are able to calculate those Kernels and first results are shown in this presentation. The major task for the second year will be the development and implementation of the inversion algorithm as well as the preparation of validation experiments. T2 - Doktorandenseminar BAM Abt. 8 CY - Berlin, Germany DA - 30.03.2020 KW - Ultrasound KW - Non-destructive testing KW - Numerical modelling KW - Structural health monitoring PY - 2020 AN - OPUS4-50624 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Clauß, F. A1 - Epple, Niklas A1 - Ahrens, M. A. A1 - Niederleithinger, Ernst A1 - Mark, P. T1 - Correlation of Load-Bearing Behavior of Reinforced Concrete Members and Velocity Changes of Coda Waves N2 - The integral collection of information such as strains, cracks, or temperatures by ultrasound offers the best prerequisites to monitor structures during their lifetime. In this paper, a novel approach is proposed which uses the collected information in the coda of ultrasonic signals to infer the condition of a structure. This approach is derived from component tests on a reinforced concrete beam subjected to four-point bending in the lab at Ruhr University Bochum. In addition to ultrasonic measurements, strain of the reinforcement is measured with fiber optic sensors. Approached by the methods of moment-curvature relations, the steel strains serve as a reference for velocity changes of the coda waves. In particular, a correlation between the relative velocity change and the average steel strain in the reinforcement is derived that covers 90% of the total bearing capacity. The purely empirical model yields a linear function with a high level of accuracy (R 2 =0.99, R2=0.99, RMSE≈90μ RMSE≈90μ strain). KW - Ultrasound KW - Coda Wave Interferometry (CWI) KW - Structural Health Monitoring KW - Reinforced Concrete KW - Embedded Sensors PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-542316 DO - https://doi.org/10.3390/ma15030738 VL - 15 IS - 3 SP - 738 PB - MDPI AN - OPUS4-54231 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Niederleithinger, Ernst ED - Rizzo, P. ED - Milazzo, A. T1 - Towards Monitoring of Concrete Structures with Embedded Ultrasound Sensors and Coda Waves – First Results of DFG for CoDA N2 - Due to the importance of reinforced concrete structures for modern society, damage assessment during the entire life-cycle of such structures has become a special interest in non-destructive testing. Using embedded ultrasound sensors in combination with other measurement methods, numerical modeling and self-made data collectors, tailored specifically for monitoring tasks, the German research group DFG FOR CoDA aims to investigate and develop novel methods for damage detection and rapid model updating in reinforced concrete structures. In the first stage of the project, besides the development of custom-built, low-cost data collectors, ultrasonic transducers are embedded in a large, reinforced concrete specimen on a BAM test site near Berlin. In this experiment, the influence of changing environmental conditions (mainly temperature) on the ultrasound signal is investigated using coda-wave interferometry. The results show a correlation between changes in temperature and ultrasonic velocity. Such changes must be taken into consideration in a long-term monitoring setup to distinguish between reversible and permanent changes. By correcting the data using a linear relation between concrete temperature and velocity change to remove the seasonal trends and by low-pass filtering the data to remove daily variations can remove most of the temperature influence on the ultrasound measurements. KW - Ultrasound KW - Coda Wave Interferometry (CWI) KW - Embedded sensors KW - Structural health monitoring PY - 2021 SN - 978-3-030-64593-9 SN - 978-3-030-64594-6 DO - https://doi.org/10.1007/978-3-030-64594-6_27 VL - 127 SP - 266 EP - 275 PB - Springer Nature CY - Cham, Switzerland AN - OPUS4-52012 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Niederleithinger, Ernst T1 - Monitoring of Concrete with Embedded Ultrasound Sensors, Coda Waves and a Novel Measurement Device N2 - Using embedded ultrasound (US) sensors in civil engineering structures and Coda Wave Interferometry (CWI), DFG research group CoDA aims for developing methods of concrete damage assessment by combination of Micro and macro scale simulations and experiments. BAMs goal within the project is the provision of small and durable measurement equipment on the one hand, and the investigation of damage sensitive parameters and development of an imaging algorithm on the other hand. In this study we focus on the development of the measurement system and the influence of temperature variations on the measurements. T2 - Summer School DFG FOR CoDA CY - Berchtesgaden, Germany DA - 27.09.2020 KW - Ultrasound KW - Coda Wave Interferometry KW - Structural Health Monitoring PY - 2020 AN - OPUS4-51382 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Hau, Julia A1 - Niederleithinger, Ernst ED - Cunha, A. ED - Caetano, E. T1 - Accounting for Long Term Environmental Influences on Ultrasonic Monitoring Measurements of Reinforced Concrete Constructions with Embedded Transducers N2 - Ultrasound measurements in concrete are a well-known technique in civil engineering and non-destructive testing. For consistent monitoring of a concrete structure, the common techniques, using external sensors can often not provide the appropriate degree of repeatability, as the surface of structures changes, and comparable coupling conditions cannot be guaranteed when a measurement is repeated after some time. By embedding ultrasound transducers in concrete, we aim to develop a strategy for long-term monitoring of infrastructure, especially bridges, as a supplement and extension to other techniques. Applying the so-called coda wave interferometry to these measurements we can detect subtle changes in the medium far beyond the Resolution limit of traditional time of flight methods. A smart sensor layout enables cost-efficient sensing of the entire area of interest. Embedding the transducers might remove uncertainties like coupling or positioning changes, while other challenges remain. Temperature and moisture content influence the structure and the transducers. These drifts need to be recorded and removed and good coupling must be ensured while not being able to visually inspect the sensor. In a multidisciplinary research group funded by the German Research Foundation, we aim to solve these problems on the way towards an ultrasound monitoring system for reinforced concrete structures. In various experiments in the lab and field, we determine the influence of temperature variations on the measurements and the equipment. As the monitoring task is the detection of irreversible damages - not reversible changes - a smart system requires a smart way of discrimination between permanent damages and reversible changes. With the data collected in these experiments, we present an approach to an environmental correction to ultrasound data to avoid a misinterpretation of these environmental changes as damage indicators. T2 - 10th International Conference on Structural Health Monitoring of Intelligent Infrastructure CY - Porto, Portugal DA - 30.06.2021 KW - Ultrasound KW - Coda Wave Interferometry (CWI) KW - Structural Health Monitoring KW - Embedded Sensors PY - 2021 SP - 1 EP - 7 AN - OPUS4-54007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Clauß, F. A1 - Epple, Niklas A1 - Ahrens, M. A. A1 - Niederleithinger, Ernst A1 - Mark, P. T1 - Comparison of Experimentally Determined Two-Dimensional Strain Fields and Mapped Ultrasonic Data Processed by Coda Wave Interferometry N2 - Due to the high sensitivity of coda waves to the smallest structural alterations such as strain, humidity or temperature changes, ultrasonic waves are a valid means to examine entire structures employing networks of ultrasonic transducers. In order to substantiate this ex ante assessment, the viability of measuring ultrasonic waves as a valid point of reference and inference for structural changes is to be further scrutinized in this work. In order to investigate the influence of mechanical strain on ultrasonic signals, a four-point bending test was carried out on a reinforced concrete beam at Ruhr University Bochum. Thus, measurements collected from a network of selected transducer pairings arranged across the central, shear-free segment of the test specimen, were correlated to their respective strain fields. Detected ultrasonic signals were evaluated employing Coda Wave Interferometry. Such analysis comprised the initial non-cracked state as well as later stages with incremental crack depth and quantity. It was to ascertain that the test specimen can in fact be qualitatively compartmentalized into areas of compression and tension identified via Relative Velocity Changes presented in Attribute Maps. However, since results did not entail a zero crossing, i.e., neither positive nor negative values were to be calculated, only relative changes in this work displayed staggered over the height of the object under test, are discussed. Under the given methodological premises, additional information is currently required to make quantitative assertions regarding this correlation of ultrasonic and strain results. This holds true for the comparability of the ultrasonic and strain results for both non-cracked and even the cracked state. KW - Digital image correlation KW - Fiber optic sensors KW - Coda Wave Interferometry KW - Ultrasound KW - Concrete PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-510501 DO - https://doi.org/10.3390/s20144023 SN - 1424-8220 VL - 20 IS - 14 SP - Paper 4023, 1 PB - MDPI CY - Basel AN - OPUS4-51050 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Diewald, F. A1 - Epple, Niklas A1 - Kraenkel, T. A1 - Gehlen, C. A1 - Niederleithinger, Ernst T1 - Impact of External Mechanical Loads on Coda Waves in Concrete N2 - During their life span, concrete structures interact with many kinds of external mechanical loads. Most of these loads are considered in advance and result in reversible deformations. Nevertheless, some of the loads cause irreversible, sometimes unnoticed changes below the macroscopic scale depending on the type and dimension of the impact. As the functionality of concrete structures is often relevant to safety and society, their condition must be known and, therefore, assessed on a regular basis. Out of the spectrum of non-destructive monitoring methods, Coda Wave Interferometry using embedded ultrasonic sensors is one particularly sensitive technique to evaluate changes to heterogeneous media. However, there are various influences on Coda waves in concrete, and the interpretation of their superimposed effect is ambiguous. In this study, we quantify the relations of uniaxial compression and uniaxial tension on Coda waves propagating in normal concrete. We found that both the signal correlation of ultrasonic signals as well as their velocity variation directly reflect the stress change in concrete structures in a laboratory environment. For the linear elastic range up to 30% of the strength, we calculated a velocity variation of −0.97‰/MPa for compression and 0.33%/MPa for tension using linear regression. In addition, these parameters revealed even weak irreversible changes after removal of the load. Furthermore, we show the time-dependent effects of shrinkage and creep on Coda waves by providing the development of the signal parameters over time during half a year together with creep recovery. Our observations showed that time-dependent material changes must be taken into account for any comparison of ultrasonic signals that are far apart in time. The study’s results demonstrate how Coda Wave Interferometry is capable of monitoring stress changes and detecting even small-size microstructural changes. By indicating the stated relations and their separation from further impacts, e.g., temperature and moisture, we anticipate our study to contribute to the qualification of Coda Wave Interferometry for its application as an early-warning system for concrete structures. KW - Ultrasound KW - Coda Wave Interferometry (CWI) KW - Mechanical Load KW - Microstructure KW - Concrete PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-556878 DO - https://doi.org/10.3390/ma15165482 SN - 1996-1944 VL - 15 IS - 16 SP - 1 EP - 15 PB - MDPI AN - OPUS4-55687 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Niederleithinger, Ernst A1 - Fontoura Barroso, Daniel T1 - Coda Wave Interferometry for Monitoring Bridges with Embedded Ultrasonic Transducers – Lessons Learned at the Gänstorbrücke Bridge Ulm, Germany N2 - Ultrasonic Coda Wave interferometry has the potential to detect minute changes in scattering materials like concrete. By permanently installing ultrasonic transducers in concrete, DFG Research unit CoDA aims to develop methods for concrete damage assessment in Germany's aging infrastructure. To test the methods developed in simulations and laboratory experiments on a large scale, we have implemented several ultrasonic transducers at the Gänstorbrücke Ulm, one of Germany's most monitored road bridges. Since fall 2020 we are monitoring parts of the center of the Bridge, as well as an abutment, and compare the results to the commercial monitoring system. All data is recorded with a self-made data collection device, the so-called W-Box, and analyzed with different coda wave-based algorithms to detect signal and volumetric velocity changes. The long-term measurements show that the influence of temperature changes on strains and therefore ultrasound velocity changes calculated with coda waves can be monitored. The capabilities and limitations of the coda wave-based monitoring system are tested in a controlled experiment. Static loading using a truck with varying loads at several positions allows the calibration of the system to improve the detectability of possibly damaging loads and changes induced by this loading. A map of velocity change analyzing data from this load experiment shows that the influence of load on the material and strain distribution can be detected with array measurements. T2 - NDT-CE 2022 - The International Symposium on Nondestructive Testing in Civil Engineering CY - Zurich, Switzerland DA - 16.08.2022 KW - Coda Wave Interferometry KW - Ultrasound KW - Embedded sensors KW - Bridge Monitoring KW - Load Experiment PY - 2022 AN - OPUS4-56454 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Niederleithinger, Ernst A1 - Fontoura Barroso, Daniel T1 - Coda Wave Interferometry for Monitoring Bridges with Embedded Ultrasonic Transducers – Lessons Learned at the Gänstorbrücke Bridge Ulm, Germany N2 - Ultrasonic Coda Wave interferometry has the potential to detect minute changes in scattering materials like concrete. By permanently installing ultrasonic transducers in concrete, DFG Research unit CoDA aims to develop methods for concrete damage assessment in Germany's aging infrastructure. To test the methods developed in simulations and laboratory experiments on a large scale, we have implemented several ultrasonic transducers at the Gänstorbrücke Ulm, one of Germany's most monitored road bridges. Since fall 2020 we are monitoring parts of the center of the Bridge, as well as an abutment, and compare the results to the commercial monitoring system. All data is recorded with a self-made data collection device, the so-called W-Box, and analyzed with different coda wave-based algorithms to detect signal and volumetric velocity changes. The long-term measurements show that the influence of temperature changes on strains and therefore ultrasound velocity changes calculated with coda waves can be monitored. The capabilities and limitations of the coda wave-based monitoring system are tested in a controlled experiment. Static loading using a truck with varying loads at several positions allows the calibration of the system to improve the detectability of possibly damaging loads and changes induced by this loading. A map of velocity change analyzing data from this load experiment shows that the influence of load on the material and strain distribution can be detected with array measurements. T2 - NDT-CE 2022 - The International Symposium on Nondestructive Testing in Civil Engineering CY - Zurich, Switzerland DA - 16.08.2022 KW - Coda Wave Interferometry KW - Ultrasound KW - Embedded sensors KW - Bridge Monitoring KW - Load Experiment PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-564531 SP - 1 EP - 8 AN - OPUS4-56453 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, T. A1 - Sens-Schönfelder, C. A1 - Epple, Niklas A1 - Niederleithinger, Ernst T1 - Imaging of Small-Scale Heterogeneity and Absorption Using Adjoint Envelope Tomography: Results From Laboratory Experiments N2 - To complement the information provided by deterministic seismic imaging at length scales above a certain resolution limit we present the first application of adjoint envelope tomography (AET) to experimental data. AET uses the full envelopes of seismic records including scattered coda waves to obtain information about the distribution of absorption and small-scale heterogeneity which provide complementary information about the investigated medium. Being below the resolution limit this small-scale structure cannot be resolved by conventional tomography but still affects wave propagation by attenuating ballistic waves and generating scattered waves. Using ultrasound data from embedded sensors in a meter-sized concrete specimen we image the distribution of absorption and heterogeneity expressed by the intrinsic quality factor Q−1 and the fluctuation strength ɛ that characterizes the strength of the heterogeneity. The forward problem is solved by modeling the 2-D multiple nonisotropic scattering in an acoustic medium with spatially variable heterogeneity and attenuation using the Monte-Carlo method. Gradients for the model updates are obtained by convolution with the back-propagated envelope misfit using the adjoint formalism in analogy to full waveform inversion. We use a late coda time window to invert for absorption and an earlier time window to infer the distribution of heterogeneity. The results successfully locate an area of salt oncrete with increased scattering and concentric anomalies of intrinsic attenuation. The resolution test shows that the recovered anomalies constitute reasonable representations of internal structure of the specimen. KW - Ultrasound KW - Scattering KW - Tomography KW - Concrete KW - Heterogeneity PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-563163 DO - https://doi.org/10.1029/2022JB024972 SN - 2169-9313 VL - 127 IS - 11 SP - 1 EP - 21 PB - American Geophysical Union AN - OPUS4-56316 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Hau, Julia A1 - Niederleithinger, Ernst T1 - Monitoring Reinforced Concrete Structures with Coda Waves The Influence of Temperature on Ultrasound Velocity Changes calculated with Coda Wave Interferometry N2 - Monitoring of reinforced concrete structures to ensure their stability and increase their service-life is a crucial element of a modern infrastructural concept. With classical methods of non-destructive testing and inspection, repeated measurements under comparable conditions are difficult to conduct. Therefore, DFG research unit FOR 2825 CoDA researches the assessment of concrete damage using ultrasound coda wave interferometry and embedded sensors. Embedding the sensors into the monitoring target reduces human and non-human factors influencing repeatability. Using Coda Wave Interferometry (CWI), small velocity changes in the material can be detected by comparison of repeated measurements. The technique is sensitive to damaging changes like cracking as well as to reversible influences like material temperature. The understanding of these different influences on the signal is crucial for the analysis of long-term monitoring data to make an educated assessment of the structure and its integrity. With several laboratory experiments in a climate chamber and a long-term experiment recording an annual cycle in a large model on an outdoor test site in Horstwalde close to Berlin, we try to understand the influence of temperature on the CWI results. The results show that the velocity change calculated by CWI does closely follow the trend of concrete temperature. After one year of data recording with the large model being exposed to environmental variations only, the calculated velocity change resembles the annual temperature curve. The data shows a linear dependency between velocity and temperature change in a range of -0.03 percent per °K to -0.06 percent per °K - regardless of specimen size. An approach to remove temperature influence from the yearly cycle recorded in the large-scale experiment using this linear relation is unable to remove high-frequency variations - especially daily influences. Low-pass filtering the data can eliminate these variations while preserving permanent shifts caused by damages. Although we have shown that the influence of temperature on long term monitoring can be removed to a significant extent, there is still an influence of environmental changes remaining in the data. Possible nonlinear effects and influences not related to temperature need to be investigated in the future. T2 - DGG 81. Jahrestagung 2021 CY - Online meeting DA - 01.03.2021 KW - Ultrasound KW - Bridge Monitoring KW - Coda Wave Interferometry KW - Structural health monitoring PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-522401 DO - https://doi.org/10.23689/fidgeo-3975 AN - OPUS4-52240 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fontoura Barroso, Daniel A1 - Epple, Niklas A1 - Niederleithinger, Ernst T1 - A Portable Low-Cost Ultrasound Measurement Device for Concrete Monitoring N2 - This paper describes a new ultrasonic measuring device called “W-Box”. It was developed based on the requirements of the DFG Forschergruppe (research unit) CoDA for a portable device for monitoring of concrete specimens, models and actual structures using embedded ultrasonic transducers as well as temperature and humidity sensors. The W-Box can send ultrasonic pulses with a variable frequency of 50–100 kHz to one selectable transducer and records signals from up to 75 multiplexed channels with a sample rate of 1 MHz and a resolution of 14 bits. In addition, it measures temperature and humidity with high accuracy, adjustable amplification, restarts automatically after a power failure and can be fully controlled remotely. The measured data are automatically stored locally on-site data quality checks and transferred to remote servers. The comparison of the W-Box with a laboratory setup using commercial devices proves that it is equally reliable and precise, at much lower cost. The W-Box also shows that their measurement capacities, with the used embedded ultrasonic transducers, can reach above 6 m in concrete. KW - Low-cost KW - Coda wave interferometry KW - Ultrasound KW - IoT KW - Non-destructive testing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-546756 DO - https://doi.org/10.3390/inventions6020036 SN - 2411-5134 VL - 6 IS - 2 SP - 1 EP - 17 PB - MDPI CY - Basel, Switzerland AN - OPUS4-54675 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Fontoura Barroso, Daniel A1 - Hau, Julia A1 - Niederleithinger, Ernst T1 - Accounting for Long Term Environmental Influences on Ultrasonic Monitoring Measurements of Reinforced Concrete Constructions with Embedded Transducers N2 - Ultrasound measurements in concrete are a well-known technique in civil engineering and non-destructive testing. For consistent monitoring of a concrete structure, the common techniques, using external sensors can often not provide the appropriate degree of repeatability, as the surface of structures changes, and comparable coupling conditions cannot be guaranteed when a measurement is repeated after some time. By embedding ultrasound transducers in concrete, we aim to develop a strategy for long-term monitoring of infrastructure, especially bridges, as a supplement and extension to other techniques. Applying the so-called coda wave interferometry to these measurements we can detect subtle changes in the medium far beyond the resolution limit of traditional time of flight methods. A smart sensor layout enables cost-efficient sensing of the entire area of interest. Embedding the transducers might remove uncertainties like coupling or positioning changes, while other challenges remain. Temperature and moisture content influence the structure and the transducers. These drifts need to be recorded and removed and good coupling must be ensured while not being able to visually inspect the sensor. In a multidisciplinary research group funded by the German Research Foundation, we aim to solve these problems on the way towards an ultrasound monitoring system for reinforced concrete structures. In various experiments in the lab and field, we determine the influence of temperature variations on the measurements and the equipment. As the monitoring task is the detection of irreversible damages - not reversible changes - a smart system requires a smart way of discrimination between permanent damages and reversible changes. With the data collected in these experiments, we present an approach to an environmental correction to ultrasound data to avoid a misinterpretation of these environmental changes as damage indicators. T2 - 10th International Conference on Structural Health Monitoring of Intelligent Infrastructure CY - Porto, Portugal DA - 30.06.2021 KW - Coda Wave Interferometry KW - Embedded sensors KW - Long-term monitoring KW - Ultrasound KW - Temperature Influence PY - 2021 AN - OPUS4-53404 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas A1 - Niederleithinger, Ernst A1 - Barroso, Daniel A1 - Lange, Marco A1 - Wöstmann, Jens T1 - Bridge Monitoring with Coda Waves - Embedding Ultrasonic Transducers in a Reinforced Concrete Bridge to Monitor Small Changes in Multiply Scattered Waves N2 - Within a DFG-funded research group, we investigate the possibility of concrete damage assessment with coda waves. Coda wave interferometry (CWI) can be a valuable asset to structural health monitoring (SHM) as we can detect small signal changes and quantify them with the calculation of relative velocity changes. By equipping an in-service road bridge with more than 24 embedded ultrasonic transducers, we want to analyze how methods developed within the research group perform in an uncontrollable environment. We evaluate individual source-receiver combinations for detection of temporal changes as well as the entire installed sensor array to create maps of material change comparing two distinct states of the bridge. T2 - Research Unit CoDA Summer School 2 CY - Garmisch-Partenkirchen, Germany DA - 19.07.2022 KW - Coda Wave Interferometry KW - Embedded sensors KW - Structural Health Monitoring KW - Ultrasound KW - Reinforced Concrete Structures PY - 2022 AN - OPUS4-55382 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Epple, Niklas T1 - Coda Measurements for monitoring infrastructure durability N2 - Presentation about the advancements in the DFG Research unit CoDA, with focus on Coda Wave Monitoring of Infrastructure. With some case studies, possibilities and challenges are discussed on the way towards infrastructural monitoring with CWI. T2 - PhD-Seminar Department 8.2 CY - Berlin, Germany DA - 07.09.2023 KW - CWI KW - Embedded Sensors KW - Ultrasound KW - Bridge Monitoring PY - 2023 AN - OPUS4-58196 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schumacher, T. A1 - Bertola, N. A1 - Epple, Niklas A1 - Bruehwiler, E. A1 - Niederleithinger, Ernst T1 - Combined Passive and Active Ultrasonic Stress Wave Monitoring of Concrete Structures: An Overview of Data Analysis Techniques and Their Applications and Limitations N2 - Combined passive ultrasonic (US) stress wave [better known as acoustic emission (AE)] and active US stress wave monitoring has been shown to provide a more holistic picture of ongoing fracture processes, damage progression, as well as slowly occurring aging and degradation mechanisms in concrete structures. Traditionally, different data analysis techniques have been used to analyze the data generated from these two monitoring techniques. For passive US stress wave monitoring, waveform amplitudes, hit rates, source localization, and b-value analysis, among others, have been used to detect and locate cracking. On the other hand, amplitude tracking, magnitude squared coherence (MSC), and coda wave interferometry (CWI) are examples of analyses that have been employed for active US stress wave monitoring. In this paper, we explore some of these data analysis techniques and show where their respective applications and limitations might be. After providing an overview of the monitoring approach and the different data analysis techniques, results and observations from selected laboratory experiments are discussed. Finally, suggestions for further work are proposed. T2 - 11th European Workshop on Structural Health Monitoring (EWSHM 2024) CY - Potsdam, Germany DA - 11.06.2024 KW - Ultrasound KW - Acoustic emission KW - Concrete KW - Stress PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-604687 UR - https://www.ndt.net/article/ewshm2024/papers/824_manuscript.pdf DO - https://doi.org/10.58286/29863 SN - 1435-4934 SP - 1 EP - 8 PB - NDT.net AN - OPUS4-60468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -