W & auml;hrend zur Genauigkeit der Betondeckungsmessung sowohl Anforderungen als auch Erfahrungen vorliegen, ist die erzielbare Genauigkeit bei der Ermittlung des Durchmessers von Bewehrungsst & auml;ben weniger gut belegt. Dieser Beitrag greift bereits publizierte Erkenntnisse zur Genauigkeit von Messergebnissen in Abh & auml;ngigkeit von Durchmesser und Betondeckung sowie m & ouml;gliche Einflussgr & ouml;ss en wie Nachbarst & auml;be auf und f & uuml;hrt Ergebnisse mit Ger & auml;ten u. a. der neusten Generation an. Mit R & ouml;ntgen an Beton steht seit kurzem dem Markt ein Verfahren zur Verf & uuml;gung, mit dem Durchmesser auch jenseits der mit magnetisch-induktiv arbeitenden Ger & auml;te (MI-Ger & auml;te) bei & uuml;blichen Stababst & auml;nden messbaren Betondeckung von 6 bis 7 cm ermittelt werden k & ouml;nnen. So werden f & uuml;r zwei Verfahren M & ouml;glichkeiten und Grenzen zur Pr & uuml;faufgabe & bdquo;Ermittlung des Durchmessers" f & uuml;r Ger & auml;te aufgezeigt und Anwendungshinweise gegeben. Bar diameter measurement and achievable accuracy using magneto-inductive methods and X-rayThe application of concrete cover measurement and its accuracy is well known. This is not the case for the accuracy of the measurement of the rebar diameter. This article starts with known results in dependence of bar diameter, concrete cover and spacing presenting further results based on these parameters up to the latest devices on the market. X-ray is introduced as a relative new method that is now available on the market for rebar diameter measurement also applicable far beyond the 6 to 7 cm limitation of concrete cover for magneto-inductive devices (MI). Two methods with their strength and limitations are presented giving advice for practical application.

This contribution is intended to disseminate the contents of a national recommendation for action draft for the inspection-based reliability analysis of existing bridges. The focus is on the utilization of non-destructive testing methods for verifications in both the ultimate and the serviceability limit states. First, the contents of the developed recommendation for action are outlined. The guideline covers the process from the purposeful definition of inspection strategies via the quality assessment of measured information to the partial factor-based assessment under consideration of quality- evaluated on-site inspection results. Secondly, the concept of the drafted recommendation for action is demonstrated using a prestressed concrete bridge as a case study.

Probabilistic reliability analysis of a prestressed concrete bridge - Part 2 - Mechanical modelling and probabilistic reassessment of a single-span 6-webbed t-beam bridge In the second part of this article the limit state functions in the ultimate limit state for bending with axial force, shear with shear reinforcement and torsion are presented. The input variables of the mechanical resistance models are accompanied by numerous illustrations. The probabilistic verifications are carried out on the basis of the probabilistic models from the first part of this article and the mechanical models from this second part. In the subsequently compiled reliability analysis, reference is made to the semiprobabilistic calculation results. With the parameter studies it is shown which input variable measurable by non-destructive testing methods have the greatest influence on the calculated reliability. On this basis finally it is shown what opportunities arise for a reassessment from conducting non-destructive testing in the inspection.

The preservation of the degrading transport infrastructure is vital, as replacing it is impossible in view of limited budgets and environmental impacts. One component in overcoming this challenge is the evaluation of the reliability and the calculation of the remaining service life of existing structures. These structural reliability reassessments allow for the identification and utilization of load-bearing capacity reserves. The consideration of actual structural characteristics and environmental conditions, various of which can be gathered by means of numerous measurement and inspection techniques, has the potential for more realistic computation results and therefore more economic decisions about the operation as well as maintenance activities. This article attempts to shed light on the potential of nondestructive testing (NDT) methods for updating the input variables in the ultimate limit states during a recalculation. The approach of the NDT-supported reliability reassessment is demonstrated using a prestressed concrete bridge emphasizing the bending proof in transversal direction. As a result, the semi-probabilistic, probabilistic and NDT-based reassessment results are compared and the effects of NDT-supported structural analysis on the calculated reliability are highlighted.

This paper summarizes current developments and outlines essential teaching content in the field of non-destructive testing in civil engineering for academic education at German-speaking universities. This first memorandum on teaching and research in non-destructive testing in civil engineering (NDT-CE) at German-speaking universities provides an overview of academic education and identifies focal points in teaching and important developments and topics in NDT-CE research. Suggestions are given for the development and advancement of teaching curricula with regard to a comprehensive and sound professional education of students of civil engineering and related disciplines. In terms of content and form, the contribution deliberately borrows from the memorandum of university teachers in the adjacent subject “Building Materials” (Breit et al. Hochschullehrer-Memorandum Werkstoffe im Bauwesen—universitäre Lehre und Forschung, , , 72–80, 2012).

Im 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.

Probabilistic reliability analysis of a prestressed concrete bridge – part 1 – Semi-probabilistic reassessment and probabilistic modeling of a single-span 6-webbed t-beam bridge Maintaining the existing transportation infrastructure is a major challenge as the structures continue to age, the traffic loads increase and comprehensive replacement is impossible given limited budgets and resources. On existing structures present material characteristics, geometries or loads can be recorded on an object-specific basis. In Germany the reassessment of existing bridges is carried out in accordance with the reassessment guidelines at the stages 1 and 2 using the semi-probabilistic partial safety concept. Only in exceptional cases will a measurement-based assessment or a scientific analysis acc. to levels 3 and 4 be carried out. However the inclusion of additional information from condition assessment offers many advantages for a realistic reassessment. In probabilistic calculation methods, such information can be taken directly into account. The aim of this two-part article is to present the potentials and advantages of directly including the results of non-destructive testing methods when assessing the condition of bridge structures. The concept is presented on a prestressed concrete bridge. The first part deals with the possibilities for transferring the input values of the usual semi-probabilistic calculation into stochastic models. Starting from the semi-probabilistic reassessment acc. to current regulations, the probabilistic modeling of all relevant basic variables for the ultimate limit states of bending, shear and torsion is carried out.

Information about an existing structure can be collected at certain costs to evaluate the reliability and condition as realistically as necessary. This information can be relevant or irrelevant, true or biased, precise or imprecise. The incorporation of relevant and quality-assessed measured information into reliability reassessment offers the chance to extend remaining lifetimes and support decision making about optimal actions or maintenance strategies. This paper shows recent developments in a national research project that aims to produce a guideline on the NDT-based, structure-specific modification of partial safety factors. The general methodology, results from recalculations according to the Eurocodes and metrologically solvable testing tasks relevant in the recalculation of the concrete bridges are shown and compared with the non-destructive testing methods applicable to concrete bridges. A case study is used to demonstrate that as-built drawings, in this case of the positions of tendons and shear reinforcement, can be verified using the radar method.

Non-destructive testing in civil engineering is a fast-emerging field. This includes not only new devices, sensors, and techniques for the inspection of materials, components, and structures contributing to building information modeling (BIM) but also efficient concepts for structural health monitoring in the frame of digital twins. The paper highlights some of these new developments and examples for applications covering the design of new construction materials, quality control during construction, contributions to predictive maintenance, and finally the rehabilitation and repair of structures. The new demands and techniques require new training concepts for the qualification of experts for the construction industry but also well-structured courses for the academic education of students. Some new standards for training and education will be introduced. This paves the way for modern, efficient, and reliable applications of non-destructive testing and structural health methods.

Klassische Betondeckungsmessgeräte geraten bei Betondeckungen von mehr als 6 bis 7 cm und bei Objekten hinter oberflächennaher Bewehrung an ihre Grenzen. In diesem Beitrag wird für tiefere Objekte primär auf Ultraschall eingegangen und zunächst dessen Einsatzbereich von Radar abgegrenzt. Während die „Betondeckung“ mit max. 6 bis 7 cm nur für die Dauerhaftigkeit von Beton eine Rolle spielt, werden Radar und Ultraschallecho zur Ermittlung der „Einbautiefe“ von Hüllrohren und Bewehrung in deutlich größeren Tiefen verwendet, deren Kenntnis primär für den Nachweis der Standsicherheit von Konstruktionen notwendig ist (ZfPStatik). Dabei entscheiden Prüfaufgabe und Randbedingungen, welches Verfahren zum Einsatz kommt. Durch systematische Untersuchungen an Betonbauteilen und der Variation von Verlegedichte der Bewehrung an der Oberfläche, Einbautiefe, Stababstand der zu detektierenden Bewehrung und deren Durchmesser werden Leistungsfähigkeit und Grenzen von Ultraschall in Echo‐Anordnung (Sender und Empfänger eines Arrays auf einer Seite des Bauteils) hinsichtlich der Detektierbarkeit von Hüllrohren und Bewehrungsstäben aufgezeigt und die Genauigkeit der Messung der Einbautiefe ermittelt. Diese Erkenntnisse zu Ultraschall werden abschließend im Vergleich zur Leistungsfähigkeit von Radar und magnetisch induktiven Verfahren eingeordnet, die bereits in vorangegangenen Beiträgen behandelt wurden. Durch die zusammenfassende Betrachtung am Ende dieses Beitrags soll es dem Anwender erleichtert werden, das für seine Prüfaufgabe und Randbedingungen am besten geeignete Verfahren auszuwählen und realistische Erwartungen an die erzielbaren Ergebnisse zu stellen.

The acquisition and appropriate processing of relevant information about the considered system remains a major challenge in assessment of existing structures. Both the values and the validity of computed results such as failure probabilities essentially depend on the quantity and quality of the incorporated knowledge. One source of information are onsite measurements of structural or material characteristics to be modeled as basic variables in reliability assessment. The explicit use of (quantitative) measurement results in assessment requires the quantification of the quality of the measured information, i.e., the uncertainty associated with the information acquisition and processing. This uncertainty can be referred to as measurement uncertainty. Another crucial aspect is to ensure the comparability of the measurement results.This contribution attempts to outline the necessity and the advantages of measurement uncertainty calculations in modeling of measurement data-based random variables to be included in reliability assessment. It is shown, how measured data representing time-invariant characteristics, in this case non-destructively measured inner geometrical dimensions, can be transferred into measurement results that are both comparable and quality-evaluated. The calculations are based on the rules provided in the guide to the expression of uncertainty in measurement (GUM). The GUM-framework is internationally accepted in metrology and can serve as starting point for the appropriate processing of measured data to be used in assessment. In conclusion, the effects of incorporating the non-destructively measured data into reliability analysis are presented using a prestressed concrete bridge as case-study.

Classical covermeters come to their limits when the concrete cover exceeds 6 to 7 cm or beneath a mesh. Concrete cover measurement with these devices is performed up to 6 to 7 cm and is only of interest for durability. Concrete cover in greater depth is performed with Radar and Ultrasonic Echo with the focus on stability of structures (NOT-SC, static calculations). The decision of the appropriate method depends on the boundary conditions, given by the spacing of the rebars near the surface, the depth, diameter and spacing of the objects to be detected. These parameters have been varied systematically in different concrete members to quantify the accuracy as well as strength and limitations especially for Ultrasonic Echo. The obtained results will be set in the context of Radar and magnetic methods with results of former publications. This will help the operator to make the best decision to find the appropriate method according to his testing task or boundary conditions.

A multifunctional automatic scanning system for multiple nondestructive measurement methods was developed by BAM division IV.4. The modular, rail guided system can be used for the investigation of bridges or foundation slabs. Speed and accuracy are enhanced compared to conventional measurements, personnel costs reduced.

Recently, non-destructive testing in civil engineering (NDT-CE), in particular of concrete components, has successfully mastered the leap from research to practice. Several methods have been established for field inspections to determine the concrete cover of reinforcement or to estimate the compressive strength as well as other parameters related to the concrete material. In addition, the application of nondestructive testing is indispensable, if information about the inner structure - such as the location of rebars and tendon ducts or the damage-related condition assessment to detect grouting defects, honeycombs, delamination, or corrosion - is required. Besides the selection of a suitable NDT method and an appropriate inspection system, the reliability of the results depends largely on the person who applies the non-destructive inspection technique and evaluates the inspection results. To ensure a high quality of non-destructive concrete evaluation as well as to keep the uncertainty caused by the inspection personnel to a minimum, structured, consistent and regulated theoretical as well as practical training of inspection personnel is essential. To close this gap, the subcommittee of education (UA-A) within the committee for NDT-CE of the German Society for Nondestructive Testing (DGZfP) has been reactivated in 2018 to establish uniform training standards for nondestructive concrete inspections in the long term. The subcommittee consists of scientists, practitioners, authorities, and clients. So far, the national standard DIN 4871 “Non-destructive testing - Qualification and Certification of NDT personnel in Civil Engineering (NDT-CE)” was developed and is currently under review. This standard considers the civil-industry-specifics, for example, that standards for NDT of concrete, as well as related product standards with a few exceptions, still do not exist at the moment. Within this presentation, the concept, the connection to ISO 9712 and other standards as well as an overview of the developed German standard DIN 4871 will be presented.

This contribution summarizes actual developments and draft fundamental teaching topics in the field of non-destructive testing in civil engineering (NDTCE). It is based on the first memorandum on teaching and research in the field of NDTCE at Germanspeaking universities and provides an overview of the academic education and highlights possible focuses, especially in regards to teaching but also takes into account noteworthy developments and topics in research in the field of NDTCE. Suggestions are given for the development and advancement of the teaching curricula in regards to a comprehensive and sound professional education of students in civil engineering and adjacent disciplines. In terms of content and form, this contribution is based on the memorandum of university teachers in the sister field of “Building Materials”. Resulting parallels are therefore not by chance but rather intended. The memorandum was developed out of an initiative of the Subcommittee on Education – Workgroup Education in Universities – of the technical committee NDT in Civil Engineering of the German Society for Nondestructive Testing (DGZfP).

Each engineering decision is based on a number of more or less accurate information. In assessment of existing structures, additional relevant information collected with on-site inspections facilitate better decisions. However, observed data basically represents the physical characteristic of interest with an uncertainty. This uncertainty is a measure of the inspection quality and can be quantified by expressing the measurement uncertainty. The internationally accepted rules for calculating measurement uncertainty are well established and can be applied straightforwardly in many practical cases. Nevertheless, the calculations require the occasionally time-consuming development of an individually suitable measurement model. This contribution attempts to emphasize proposals for modelling the non-destructive depth measurement of tendons in concrete using the ultrasonic echo technique. The proposed model can serve as guideline for the determination of the quality of the measured information in future comparable inspection scenarios.

Concrete structures for sealing of tunnels in the host rock are an essential part of systems for nuclear waste storage. However, concretes based on blended cements or magnesium oxychloride cements, which are commonly considered for this application, can deteriorate severely due to a significant heat of hydration and associated deformation and cracking. Alkali-activated materials (AAMs) offer a potential solution to this problem because of their low heat release during hardening. To explore their suitability for the construction of sealing structures in evaporite rock, various AAMs with salt aggregate were studied regarding fresh properties, heat release, mechanical properties and microstructure. The heat of reaction of the AAMs was up to 55% lower than that of a blended cement designed for sealing structures, indicating significant benefits for the intended application. Other relevant properties such as mechanical strength and permeability depended strongly on the mix-design of the AAMs and curing conditions.

The reassessment of bridges continues to take great importance both nationally and internationally. A major challenge is to find computation models reflecting the actual properties of the considered structures sufficiently accurate. Besides regular inspections, the conduction of advanced measurements is suitable to generate reliable information about a structure to be assessed. Prior to incorporating measurement results in reassessment, the relevance, the trueness, and the precision of the measured information needs to be stated. On the one hand, the use of information whose quality has not been assessed can lead to errors with serious consequences. On the other, the measurement of irrelevant information is inefficient. Although the use of measured data in assessment is currently mostly unregulated, their appreciation in reliability analyses is beneficial since the built environment can be assessed more realistically. Utilizing NDT in reassessment has the potential to extend remaining lifetimes of a structure, save resources, and improve infrastructural availabilities. The power of judgment regarding the decision on the reliability of an existing structure can be increased. In this contribution, an approach is outlined to process non-destructively gathered measurement data in a comparable way in order to include the measured information in probabilistic reliability assessments of existing structures. An essential part is the calculation of measurement uncertainties. The effect of incorporating evaluated NDT-results is demonstrated by means of a prestressed concrete bridge and GPR measurements conducted on this bridge as a case-study. The bridge is assessed regarding SLS Decompression using the NDT-results.

Making optimal decisions about the reliability of existing structures requires that the information used in assessment adequately represents the properties and the condition of the structures. The knowledge gap regarding a structure to be assessed can be successively filled by individually purposeful observations on site. This paper gives an overview of an approach for utilizing nondestructively gathered measurement results in reliability assessment of existing structures. An essential part of measurement-based stochastic modeling of basic variables is the calculation of measurement uncertainties, which serves to establish confidence in measurement, to ensure the comparability of unambiguously expressed measurement results, and to quantify the quality of the measured information. Regarding the current discourse on how to treat information collected on-site in the context of assessment, the authors recommend that measurement uncertainty becomes an uncertainty component mandatorily to be represented in measurement-based stochastic models. The main steps of the proposed concept are presented, and the advantages of its application are emphasized by means of a prestressed concrete bridge as case study. The bridge is assessed regarding the serviceability limit state decompression using ultrasonic and radar data measured at the structure.

Every decision about the reliability of a structure is associated with uncertainties. The reassessment of existing structures remains a major challenge. The decisive difference compared to the design of new structures is the possibility and necessity to collect individual information about the actual condition and properties of the structure. Such knowledge should be appreciated in the reassessment in order to reduce uncertainties and increase the validity of the results. Reliability analyses using measured data require the comparability of measurement results and the evaluation of the quality of the measured information. Both requirements can be met by adequate measurement uncertainty considerations. Besides, the destructive interventions necessary for the measurements should be kept to a minimum. This paper shows how non-destructively gathered measurement results can be incorporated into probabilistic reassessments and which effects the implementation of measured data can have when evaluating existing structures, using a prestressed concrete bridge as a case-study.