Ondrej Anton

This study explores the potential of non-destructive methods for diagnosing timber structures, with a primary focus on maximising the capabilities of the resistance-drilling technique. Laboratory tests were performed on spruce wood specimens, the most commonly used construction timber in Central Europe, prepared across a wide range of moisture contents (0–53%) to assess the influence of moisture on resistance-drilling characteristics. The resistance micro-drilling (RM) characteristic was found to be independent of moisture content (coefficient of determination close to zero), confirming that resistance drilling provides stable results under varying in situ moisture conditions. In contrast, wood density and the RM characteristic were strongly correlated, with coefficients of determination of R² = 0.87 for moisture contents between 0% and 30%, and R² = 0.90 for the 8–18% moisture range typical of timber in service. Based on these relationships, two linear conversion equations were developed (ρ = 1.685·RM + 183.85 and ρ = 1.982·RM + 135.15, respectively), enabling estimation of spruce wood density directly from RM values. Compressive strength parallel and perpendicular to grain decreased with increasing moisture content up to the fibre saturation point, beyond which the reduction in strength plateaued.

The field of diagnosis of structures has been experiencing a dynamic development in the last decades caused by the development and expansion of new NDT methods and instrumentation. At the same time, it is possible to observe changes in the focus of interest in this field, or more precisely, alternating waves of interest in specific types of diagnosis targeted at special types of structures. These waves of interest are always caused by a certain trend in the development of the society or building industry, and most often, by some major even in the field. In the last few years, particular attention has been paid to prestressed structures, especially to bridges, in connection with the recent accidents of bridges made from prestressed concrete in the Czech Republic and abroad. Considering the relatively large number of these bridges in the Czech Republic built in the second half of the 20th century, attention is paid to basic changes in the pre-construction condition surveys aimed at determining the condition and the remaining life of these structures. The paper focuses on the analysis of possibilities of assessing the condition of prestressing steel at the level of the present state of diagnosis of structures.

The current period in the development of building industry can be characterized as a period of rapid development in this field, not only in the area of new constructions, but also in the area of a new uses of old constructions which find a new use after restoration, and as regards traffic facilities, especially bridge structures, in the area of verification of the existing functional characteristics and prediction of the lifetime of structures. This puts a strain on the field of diagnosis of structures, the development of which can be observed in the last 10 years in the form of a new wave of innovations of the existing NDT (non-destructive testing) methods as well as of the development of completely new devices and technologies. In spite of these facts, it can be said that in a number of cases, the diagnosis of structures is performed in traditional ways without using modern techniques and technologies. The aim of this paper is to present an optimal way of using NDT methods in the diagnosis of reinforced concrete beam structures, specifically in the determination of the position of shear bends on the main load-bearing reinforcement. The paper deals with the current state of the issue and illustrates, on a number of examples from practice, the applicability of individual methods as well as their limitations given by their physical principles and technological solutions.

Steel fibre reinforced concrete is a widely used building material in the field of civil and military structures. To fully utilize its properties, it is very important to pay attention to the technological process of its production. The principle of steel fibre reinforced concrete consists in uniform distribution of steel fibres in the given volume of the structural element. The possibilities of checking uniformity are still discussed and examined in the field of NDT (non-destructive testing). The paper describes a radiographic NDT method allowing to evaluate the uniformity of steel fibre distribution in situ. The experiment results are compared with the results of testing performed using the standard destructive testing method.

The paper reacts to the contemporary situation in the field of determining the position of reinforcement in the reinforced concrete structures, in which the best method used so far – the Co 60 radiography – is significantly limited or even excluded due to the tightening of laws and regulations for management of radiation sources. In the article, the authors focus on the use of alternative NDT methods which, in an appropriate combination, can substitute the present radiographic method. They mention the advantages as well as technological and principle limitations of the methods of georadar and electromagnetic indicators, and on practical examples they demonstrate their usability when used separately or in a suitable combination.

Despite efforts to maintain quality during the construction of reinforced concrete structures, it is relatively common for improper reinforcement to be used, contradicting the project, which can lead to serious structural defects. It is then up to non-destructive testing methods to prove these defects. The key is the choice of the appropriate method and equipment, both in terms of achieving the necessary results and the possibility of their documentation. In recent years, there has been a significant progress in the development of non-destructive methods for the diagnosis of reinforcement and modernization of the technologies used so far, especially in the field of GPR and electromagnetic methods. At the same time, however, for a number of reasons, major limitations appear in the area of a conventional method of radiography. This contribution focuses on the current state of the problem, and it demonstrates the applicability of individual methods and their limitations given by their physical principles and technical solutions on a set of practical examples.

The principle of steel fibre reinforced concrete structures is a uniform distribution of steel fibers in the given volume (structure or structural element), which, however, is not always possible to guarantee in the production. This is closely related to a problem of performing diagnosis of the existing steel fibre reinforced concrete structures. Despite the fact that this material is not unknown, in the standards regulating quality control of the uniformity of fibre distribution, the assessment of distribution uniformity is still based on a destructive testing method. The paper describes a partial experiment which consisted in testing a proposed measuring device and in determining the depth of electromagnetic field range in the test specimens.

During restoration and maintenance of historical buildings, statues and sculptures are often neglected elements in the pre-construction condition surveys, especially in case they are not part of the supporting structure but only an ornamental and aesthetic complement of the architectural whole. The condition of a number of such artworks requires restoration or static assessment from the viewpoint of safety and durability. In the case of statues made of stone, artificial stone or concrete, an inseparable part of the pre-construction condition survey is determining the method of their reinforcement with steel elements, which is, considering the often complex spatial aspects of their surface, relatively complicated. The paper offers some possibilities of its solution on three examples. The diagnostic methods were proposed based on the authors' workplace's long-term experience with the diagnostics of reinforced concrete structures. During the past 10 years, about 1,000 such diagnostics have been performed. These experiences were subsequently experimentally applied to several historical sculptures with great success.

Correct reinforcement is an essential part of constructing reinforced concrete structures. Errors in positioning, diameter, or coverage may result in defects, which is why it is necessary to make sure the reinforcement is implemented well. Even though electromagnetic detection is the most common non-destructive method for locating reinforcement in reinforced concrete, science literary sources hardly discuss it. The main reason is a lack of graphic test results – thus far the most common research outcomes have been photographs of lines drawn on the concrete surface or additions to technical drawings of the reinforcement. Only modern detectors expanded the possibilities of the method's application including graphic measurement records and a more accurate estimation of reinforcement diameter including corrections for adjacent reinforcement spacing. The paper focuses on the principle of measurement and practical examples of determining the position and coverage of reinforcement in reinforced-concrete structures using a state-of-the-art electromagnetic rebar detector – a Profometer PM-630. Aside from data recording and statistical evaluation during coverage measurement, modern instruments also allow the data to be exported and visualised.