[en] In the paper the dynamic analysis of a suspended reinforced concrete footbridge over a national road located in South Poland was carried out. Firstly, modes and values of natural frequencies of vibration of the structure were calculated. The results of the numerical modal investigation shown that the natural frequencies of the structure coincided with the frequency of human beings during motion steps (walking fast or running). Hence, to consider the comfort standards, the dynamic response of the footbridge to a runner dynamic motion should be calculated. Secondly, the dynamic response of the footbridge was calculated taking into consideration two models of dynamic forces produced by a single running pedestrian: a ‘sine’ and ‘half-sine’ model. It occurred that the values of accelerations and displacements obtained for the ‘half-sine’ model of dynamic forces were greater than those obtained for the ‘sine’ model up 20%. The ‘sine’ model is appropriate only for walking users of the walkways, because the nature of their motion has continues characteristic. In the case of running users of walkways this theory is unfitting, since the forces produced by a running pedestrian has a discontinuous nature. In this scenario of calculations, a ‘half-sine’ model seemed to be more effective. Finally, the comfort conditions for the footbridge were evaluated. The analysis proved that the vertical comfort criteria were not exceeded for a single user of footbridge running or walking fast. (paper)

[en] The construction and demolition waste constitute a quarter of all types of waste production. Recovery of this waste in other areas of the economy is a step in the right direction to achieve sustainable development. Department of Concrete and Masonry Structures at the Faculty of Civil Engineering of the Czech Technical University is concerned in the problematic of sustainable constructions by research on recycled materials. One of the focus is on replacing of natural aggregate by rubble concrete recycled from demolished concrete structures and use of the recycled aggregate in fibre-reinforced concrete with synthetic fibres. The research focused also on possibilities of the structural design of structures from investigated material. The investigations proved usability of fibre-concrete with recycled crushed concrete in certain applications. The composite has satisfactory material characteristics and its application would consume a great deal of recycled concrete aggregate. The paper will present the material parameters and its efficiency in examples of applications. (paper)

[en] Construction of facilities of cast in-situ reinforced concrete poses additional requirements to quality of material, peculiarities of the construction process may sometimes lead to appearance of lamination planes and inhomogeneity of concrete, which reduce strength of the material and structure as a whole. Technology compliance while working with cast in-situ concrete has a significant impact onto the concrete strength. Such process factors as concrete curing, vibration and compaction of the concrete mixture, temperature treatment, etc., when they are countered or inadequately followed lead to a significant reduction in concrete strength. Here, the authors experimentally quantitatively determine the loss of strength in in-situ cast concrete structures due to inadequate following of process requirements, in comparison with full compliance. (paper)

[en] There are various practical applications of dispersely reinforced concrete with polypropylene fibers; one of them could be achieving formworks for concrete columns. This paper presents some practical tests showing the combined effect of a lost shuttering made by dispersely reinforced concrete with fibers and a steel reinforced concrete core, for round and square shaped columns. The test results could be considered a contribution to the development of knowledge in the dispersely reinforcement area using one type of polypropylene fibers for which information on their application field are little or missing. (paper)

[en] This report presents the latest developments of the reliability analysis method for concrete containments. In specific, the tangential shear limit state for reinforced concrete containments is described in detail. Also, the flexure limit state has been modified such that the strain of tensile reinforcement is limited. Furthermore, the variations of material strength such as concrete compressive strength and reinforcement yield strength are included in the reliability analysis by using the Latin hypercube sampling technique. Then, the reliability analysis results and fragility curves for two containments are presented

[en] The available design rules for anchor channels with channel bolts were developed on the basis of the design rules for fasteners installed in conventional concrete. Recently, also more advanced reinforced concrete types became popular, e.g. fibre reinforced concrete for the production of prefabricated tunnel elements. The existing design rules for fasteners including anchor channels with channel bolts do not cover fibre reinforced concrete. To study the load-displacement behaviour in tension and shear, exploratory tests have been carried out on anchor channel-channel bolt-systems cast in plain and fibre reinforced concrete. The test results demonstrate a superior performance of channel bolts installed in anchor channels which were cast in fibre reinforced concrete if compared with systems cast in plain reinforced concrete. (paper)

[en] Experimental study aimed at evaluation of static preload impact on concrete strength and deformation characteristics had been carried out in 2014–2017 in laboratory of Strength of Materials Department of Moscow State Institute of Civil Engineering. The paper briefly presents the research technique, outcome and suggests its interpretation. Authors’ feature of the methodology is an absence of unloading when applying the dynamic load with stress growth rate of 450 MPa/sec and destruction time of approximately 0.8 sec after static preload with value of 0.3, 0.7 and 0.8 of prism strength. The use of portable dynamic module which was has been designed and built by Igor Bezgodov, engineer of Moscow State University of Civil Engineering, made it possible to complete the experiment. Investigation of samples under short- term static load of the same level and reference samples under static and dynamic load without preloading was carried out concurrently. The data obtained include strength values and stress-strain diagrams which allowed estimating the coefficients of longitudinal and transverse deformation and ultimate deformation. The authors suggest that long-term static preload does not affect the dynamic strengthening factor, which remained between 1.17 and 1.30 regardless of preload level. At the same time preloading changes stress-strain diagram significantly. Diagrams for various loading modes are combined on single figure to demonstrate their features. The coefficients of longitudinal and transverse deformation related to significant fragments of diagrams are presented in tables and compared to each other. Loading rate considerably lowers ultimate deformations under dynamic impact. Relatively low-level preloading does not modify longitudinal deformations perceptibly, however, at preloading level of 0.8 longitudinal deformations increase significantly and almost match the ones under static loading. The authors conclude that comparison of diagrams points out on necessity of taking deformation rate growth and static preload level into consideration in practical calculations of concrete and reinforced concrete constructions. Thus, the research contributes to the development of computational models of concrete and reinforced concrete. (paper)

[en] Steel bracing has proven to be a very powerful method to improve the seismic behaviour of reinforced concrete frame structures. In general the steel braces are indirectly connected to the RC frame via additional steel frames that are in turn fixed to the RC frame using post-installed anchors or reinforcing bars. However, this method comes with several shortcomings including increased weight and a disruption of the buildings function during installation. Therefore new connection approaches were developed where the braces are directly connected to the RC frame. One of the most promising solutions is the connection by means of post-installed anchors to connect the bracing to the frame corners. Using this type of connection allows an effective and low invasive strengthening of the structure. In this case the performance of the retrofitted structure is highly dominated by the performance of the post-installed anchors, since the imposed seismic demands are rather high. Therefore it is deemed necessary to assess the anchor performance under seismic actions, especially their displacement behaviour in the post-peak range. The current guidelines for seismic qualification of anchors only provide a force-controlled assessment procedure which is valid for non-structural connections but is not sufficient to obtain the information required for the assessment of their seismic performance in structural applications. A new displacement-controlled approach for the assessment of post-installed anchors under seismic conditions is presented. This approach allows the evaluation of the complete load-displacement behaviour as well as the hysteretic response of the anchors even in the post-peak range. A comparison with existing force-controlled assessment procedures shows that this approach is more suitable for the assessment of anchors used in structural strengthening applications under seismic actions. (paper)

[en] A novel method of testing reinforced concrete beams under impact using a drop tower is described. The method consists of configuring the support conditions and instrumenting both the loading end of the hammer and support points in such a way that a proper dynamic analysis of the impact event can be performed and rational data can be derived.

[en] This paper presents experimental program focused on determination of material properties of various types of fiber reinforced concrete exposed to elevated temperatures up to 1000° C. Material properties were measured by several methods which are described and compared. The resulting changes of material properties depending on temperature are presented. The values are compared with values from literature and standards. The aim of this paper is to provide a comprehensive overview of material properties of these types of concrete depending on elevated temperature and possibility of their measurement. (paper)