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Extrusion based 3D concrete printing (3DCP) is a growing technology because of its high potential for automating construction and the new possibilities of design. In conventional construction methods, a sample is taken to be representative for one material batch. However, in 3DCP continuous mixing is used which results in variations during the mixing process. Therefore, one sample is not representative for the entire structure. This leads to the necessity of continuous and real-time process monitoring.
This study focuses on the variations of pressure and temperature which are caused by changes in the material due to the ongoing mixing process. Changes in material, which is transported downstream, are influencing sensor signals in different positions with a time delay. In the following, the data is analysed to investigate if the changing material and the so caused change in pressure can be used to calculate volume flow.
Extrusion based 3D concrete printing (3DCP) is a growing technology because of its high potential for automating construction and the new possibilities of design. In conventional construction methods, a sample is taken to be representative for one material batch. However, in 3DCP continuous mixing is used which results in variations during the mixing process. Therefore, one sample is not representative for the entire structure. This leads to the necessity of continuous and real-time process monitoring.
This study focuses on the variations of pressure and temperature which are caused by changes in the material due to the ongoing mixing process. Changes in material, which is transported downstream, are influencing sensor signals in different positions with a time delay. In the following, the data is analysed to investigate if the changing material and the so caused change in pressure can be used to calculate volume flow.
Implementation and validation of robot-enabled embedded sensors for structural health monitoring
(2024)
In the past decades, structural health monitoring (SHM) has matured into a viable supplement to regular inspections, facilitating the execution of repair and maintenance work in the early stages of structural damage. With the advent of wireless technologies and advancements in information and communication technologies, civil infrastructure has been increasingly instrumented with wireless sensor nodes to record, analyze, and communicate data relevant to SHM. A promising method for SHM is to embed sensors directly into concrete for recording SHM data from inside structural elements. In this paper, a sensor system for embedment into concrete is proposed, able to assess SHM data recorded from concrete. Power is supplied to the sensors on-demand by quadruped robots, which also collect the SHM data via radio-frequency identification (RFID), providing an automated and efficient SHM process. In laboratory experiments, the capability of the sensor system of automatically collecting the SHM data using quadruped robots is validated. In summary, the integration of RFID technology and robot-based inspection presented in this study demonstrates a vital approach to evolve current SHM practices towards more digitalized and automated SHM.
The ultrasonic echo technique is broadly applied in non‐destructive testing (NDT) of concrete structures involving tasks such as measuring thickness, determining geometry and locating built‐in elements. To address the challenge of enhancing ultrasonic imaging for complex concrete constructions, we adapted a seismic imaging algorithm – reverse time migration (RTM) – for NDT in civil engineering. Unlike the traditionally applied synthetic aperture focusing technique (SAFT), RTM takes into account the full wavefield including primary and reflected arrivals as well as multiples. This capability enables RTM to effectively handle all wave phenomena, unlimited by changes in velocity and reflector inclinations. This paper concentrates on applying and evaluating a two‐dimensional elastic RTM algorithm that specifically addresses horizontally polarized shear (SH) waves only, as these are predominantly used in ultrasonic NDT of concrete structures. The elastic SH RTM algorithm was deployed for imaging real ultrasonic echo SH‐wave data obtained at a concrete specimen exhibiting a complex back wall geometry and containing four tendon ducts. As these features are frequently encountered in practical NDT scenarios, their precise imaging holds significant importance. By applying the elastic SH RTM algorithm, we successfully reproduced nearly all reflectors within the concrete specimen. In particular, we were capable of accurately reconstructing all vertically oriented reflectors as well as the circular cross sections of three tendon ducts, which was not achievable with traditional SAFT imaging. These findings demonstrate that elastic SH RTM holds the ability to considerably improve the imaging of complex concrete geometries, marking a crucial advancement for accurate, high‐quality ultrasonic NDT in civil engineering.
This article presents two case studies for a full-probabilistic assessment of existing concrete bridges combined with the use of the finite element method for the evaluation of the internal forces. Since the structures already exist, additional information about material parameters and loading conditions can be collected. With a sensitivity analysis, the contribution of each parameter to the total uncertainty is examined and the relevance of their actual value and variation is shown. The first case study is a single-span reinforced concrete frame bridge on the German highway A92 constructed in the year 1985. With a span of around 5 m, but a width of 27 m and a skewness of 70 gon, the bridge is modelled as a three-dimensional finite element model. The second case study is a two-span reinforced concrete frame bridge from 1986 with span lengths of about 7,50 m each. The superstructure is a 45 cm thick slab and the base plate has a thickness of 80 cm. The assessment is performed based on the semi-probabilistic safety concept according to the codes first and secondly with a full-probabilistic calculation. In this article the selection of parameters for the relevant input data are presented and discussed. The results of the sensitivity analysis are used for the setup of measurements to acquire important data for the modelling in the critical limit states.
In reliability assessment of existing bridges, collected information about the structure can be utilized to modify partial safety factors and to refine characteristic values individually. In this way, uncertainties covered in initial calculation models and arising from assumptions can be reduced as well as biases identified and corrected. This allows for more realistic assessments and more appropriate decisions on actions to be taken. However, the on-site observation of information is generally associated with certain costs. For this reason, an efficient data-supported reassessment requires that only the individually relevant testing tasks are solved. Additional sensitivity analyses can further be used to specify the requirements on certain inspections, such as the testing result quality to be achieved, in order to avoid too imprecise or too expensive measurements on-site. In this contribution, the methodology for the demand-actuated definition of measurement objectives is demonstrated using the example of non-destructive concrete testing methods and findings from reassessments of two prestressed concrete bridges. Each case study includes the semi-probabilistic identification of structural weak points in ultimate and serviceability limit states, a comparison with respective probabilistic sensitivity analyses, and the subsequent derivation of parameters that are a) measurable and b) highly relevant in the individual reliability analyses.
AbstractIm zweiten Teil dieses Beitrags werden die Grenzzustandsfunktionen für die Nachweise im Grenzzustand der Tragfähigkeit für Biegung mit Normalkraft, Querkraft mit Querkraftbewehrung und Torsion vorgestellt. Die Eingangsgrößen der mechanischen Widerstandsmodelle werden durch zahlreiche Abbildungen illustriert. Auf Grundlage der probabilistischen Modelle aus dem ersten Teil dieses Aufsatzes und der mechanischen Modelle aus diesem zweiten Teil werden die probabilistischen Nachweise geführt. Die Ergebnisse aus der Zuverlässigkeitsanalyse werden mit den semiprobabilistischen Berechnungsergebnissen verglichen. Mittels Parameterstudien wird gezeigt, welche Eingangsgrößen im Standsicherheitsnachweis die größten Einflüsse auf die Bauwerkszuverlässigkeit haben. Die Messung dieser Parameter ist entsprechend besonders nützlich. Auf dieser Basis wird abschließend gezeigt, welche Chancen sich aus der Durchführung von zerstörungsfreien Bauwerksprüfungen für die Nachrechnung ergeben.
AbstractDer Erhalt der bestehenden Verkehrsinfrastruktur ist eine große Herausforderung, da die Bauwerke fortwährend altern, die Verkehrsbeanspruchung zunehmend steigt und deren umfassender Ersatz mit Blick auf begrenzte Budgets und Ressourcen nicht möglich ist. An Bestandsbauten können tatsächliche Materialkennwerte, Geometrien oder Einwirkungen objektspezifisch erfasst werden. Die Nachrechnung von Bestandsbrücken erfolgt in Deutschland gemäß Nachrechnungsrichtlinie nach Stufen 1 und 2 mit dem semiprobabilistischen Teilsicherheitskonzept. Nur im Ausnahmefall wird eine messbasierte Bewertung oder eine wissenschaftliche Betrachtung gemäß Stufen 3 und 4 durchgeführt. Die Einbeziehung zusätzlicher Informationen aus der Zustandserfassung bietet jedoch viele Vorteile für eine realitätsnahe Bewertung. In probabilistischen Berechnungsmethoden können solche Kenntnisse direkt in der Berechnung berücksichtigt werden. Ziel dieses zweiteiligen Beitrags ist die Vorstellung der Potenziale und Vorteile bei der direkten Berücksichtigung der Ergebnisse von zerstörungsfreien Prüfverfahren bei der Zustandsbewertung von Brückenbauwerken. Das Konzept wird an einer Spannbetonbrücke vorgestellt. Der erste Teil befasst sich mit den Möglichkeiten zur Überführung der Eingangswerte der üblichen semiprobabilistischen Berechnung in stochastische Modelle. Ausgehend von der semiprobabilistischen Nachrechnung nach derzeitigem Regelwerk wird die probabilistische Modellierung aller relevanten Basisvariablen für die Grenzzustände der Tragfähigkeit Biegung, Querkraft und Torsion ausgeführt.
Moisture testing and mapping
(2024)
Most building materials are porous and hydrophilic. Thus, for condition assessment and damage detection a determination of the material moisture is required. In this lecture, a short overview is given regarding moisture transport in porous media in the hygroscopic range. Then, several non-destructive measurement techniques are introduced. Here, the focus lies on their practical application and limitations.
The design of bridges often overlooks the vertical component of earthquakes or considers it of secondary importance, despite compelling evidence indicating specific structural damage caused by primary earthquake waves. Conversely, during the operational phase, the combined influence of ground motion and moving loads from vehicles can significantly impact the structural health monitoring (SHM) of bridges. This study aims to evaluate the simultaneous effect of vertical earthquake vibrations and moving vehicle loads on simply supported bridges. The research employs a practical methodology based on the eigenfunction expansion method to analyze change of deflection due to the effect of these concurrent forces under seven different earthquake records. It is shown that within a realistic range of vehicle mass and velocity, the average of changing the maximum deflection at the mid-span of the main beam (denoted as M_n) reaches up to 163% under various scenarios. Subsequently, the seismic parameters influencing this phenomenon are identified through a statistical analysis of set of 100 different earthquake records with unique features. A linear regression equation is presented to predict the M_n based on the earthquake specific properties. Additionally, to control the vertical vibration of bridge systems, a novel vibration suppression system utilizing steel pipe dampers is introduced, and its reliability is examined across a broad spectrum of bridge flexural rigidity. The results indicate that the system's efficiency depends on M_n and the soil type of the bridge construction, enabling a reduction in structural sections (up to 27%) while achieving the same maximum target deflection in the initial state. This efficiency leads to a more economical design solution, emphasizing the potential benefits of the proposed system for practical application.