Advances in Science and Technology Vol. 176

Abstract: The application of high-strength prestressing steel represents a major step forward in the field of concrete structure design and construction. Prestressing steel with a tensile strength exceeding 1860 MPa enables more effective prestressing of structural elements, which in turn results in a substantial reduction in the required amount of reinforcement. At the same time, it allows for the design of more slender, lighter, and structurally optimized members. Due to these characteristics, this type of reinforcement finds wide application particularly in bridge engineering, prefabricated systems, high-rise buildings, and long-span structures. The paper focuses on analysing the principal advantages of employing high-strength prestressing reinforcement with regard to both structural behaviour and construction economy. From the structural design perspective, the main benefits include an increase in load-bearing capacity and a reduction of deformations, even when using smaller cross-sectional dimensions. From the economic viewpoint, advantages are primarily linked to reduced material consumption, lower self-weight of prefabricated elements, and significant cost savings in transport and erection. The concluding part of the paper addresses the anticipated direction of further development in high-strength materials, with particular emphasis on the possibilities of design optimization through nonlinear computational methods. High-strength prestressing reinforcement thus constitutes a promising means of improving the efficiency and sustainability of modern concrete structure design. The study provides a comprehensive summary of the main benefits of this technology, points out practical and design-related limitations, and indicates future development trends consistent with the objectives of sustainable and cost-effective construction.

Abstract: This article deals with increasing the load-bearing capacity of reinforced concrete panels by replacing the compressed part of the cross-section by a layer of ultra-high performance fiber reinforced concrete (UHPFRC). The geometry of the tested samples is based on a real example of a ceiling slab in a typical multi-storey car park. The load curves of the individual variants are compared using numerical simulation with nonlinear material models describing the specific behavior of concrete. In conclusion, the contribution of the UHPFRC layer to the properties and behavior of the investigated structure is evaluated.

Abstract: Large Panel System (LPS) Buildings represent a significant portion of the housing stock, with many structures approaching the end of their planned design service life. Given the ongoing local and uncoordinated reconstructions and modernisations of LPS buildings, it is crucial to expand knowledge in their structural assessment. This study analyses the most common defects within joints and investigates their impact on the load-bearing capacity and stiffness of panel connections. Both analytical and numerical calculations are used for the analysis. The analysis indicates that defects (whether from assembly or from later interventions) found during inspections of various structures affect the stiffness and load-bearing capacity of the joints. Therefore, the calculation of a joint's load-bearing capacity, which considers its current condition, plays a significant role in the structural assessment.

Abstract: The utilisation of concrete has significant environmental repercussions, including CO2 emissions (notably from cement production), the exhaustion of natural resources due to aggregate extraction, and the disposal of debris in landfills. In concrete production, recycled aggregate has a minimal direct effect on greenhouse gas emissions, as the predominant source of emissions is cement production. Its contribution is in diminishing the extraction of raw materials required for concrete production, hence decreasing waste and safeguarding natural resources. This paper examines the resistance of small columns constructed from concrete with recycled material. The essay outlines the results of experimental assessments of eccentrically loaded columns. The modulus of elasticity of concrete, including recycled aggregate, particularly when incorporating masonry and mixed material, markedly diminishes in comparison to concrete composed of natural aggregate or recycled concrete aggregate. Currently, recycled masonry or mixed aggregate is predominantly used in embankments, sub-base layers of roadways, and non-load-bearing structural components. To present, experiments have predominantly concentrated on its application in concrete components exposed to bending and shear forces. The utilisation of recycled masonry aggregate may have substantial applications in large piers, where the impact of a reduced modulus of elasticity would be minimal due to the primarily compressive load. In the experiment, following the normalisation of strengths, the samples exhibited comparable resistance; the sample with a 50% proportion of RA demonstrated nearly identical resistance to the reference column (0% RA proportion). The sample with a complete 100% share of RA exhibited a 6.57% increase in normalised resistance relative to the reference column.

Abstract: The paper presents a research object of a portal realized using the method of 3D printing of cement composite. The object serves as an experimental portal redefining the relationship between a building element and ornament. The form of the portal is generated by a Möbius transformation of part of the load-bearing wall. This transformation allows the basic structural logic of the wall to be converted into an ornamental layer without losing material logic and continuity. The load-bearing material of the object is a cement composite, optimized for robotic printing without formwork. Printing enabled the production of complex elements with high geometric precision. Thanks to digital control, the shape can be deconstructed into a precise printing trajectory, eliminating the human factor and streamlining production even for complex segments. The resulting object combines the structural and visual roles of the elements without the need for secondary division into load-bearing and aesthetic parts. The aim of the research is to verify the possibilities of robotic printing in the production of architectural elements from cement composite that transcend the traditional dichotomy of structure and decoration. The process shows that even highly individualized elements can be produced efficiently, repeatedly, and with material savings. Special attention is paid to detailed parameterization of the mold, surface quality, and layering during printing, which fundamentally affects the resulting mechanical and aesthetic properties. The paper offers a practical view of the application of robotic 3D concrete printing in architectural and engineering applications and its potential for transforming current construction approaches.

Abstract: This paper deals with the multi-criteria optimization of reinforced concrete floor structures in terms of environmental impacts, costs, and durability. A software tool was developed and applied to three structural systems: one-way slabs with beams and girders, slabs supported by beams on all edges and flat slabs. The implemented optimization algorithm is presented, and the influence of span and imposed load on the environmental impacts and costs of the optimal solutions is analyzed. Selected scenarios illustrate the process of identifying the most suitable structural variant. Finally, the discussion highlights practical aspects of structural system selection, where additional criteria such as layout flexibility, acoustic performance, and construction time must be considered.

Abstract: Shear strength probabilistic assessment of concrete members with glass fibre reinforced polymers (GFRP) is performed in the paper. The aim of the analysis performed is to verify the existing code analytical formulas for shear strength calculation using stochastic models, to perform uncertainty propagation, sensitivity analysis and model uncertainty assessment. The study introduces a probabilistic framework that incorporates both model uncertainty and stochastic variability of input parameters into the assessment of shear resistance. The code models of Eurocode 2, ACI 440 and the fib Model Code 2010 are examined with respect to uncertainties involved and the reliability of the design value determination.

Abstract: The article addresses the issue of determining the dependence between the tensile strength of GFRP (Glass Fiber Reinforced Polymer) reinforcement and temperature. Figuring out this dependence is crucial for designing reinforced concrete structures exposed to fire. The newly published generation of standards does not specify any material characteristics of FRP reinforcement at elevated temperatures. The design equations are derived only for steel reinforcement, although this standard allows for the use of FRP reinforcement in the design of concrete structures. For this reason, and based on the available and published experimental data, a robust database of results expressing the decrease in GFRP reinforcement tensile strength as a function of temperature was created and supplemented by the results of our own tests. The characteristic value of the tensile strength was determined as 5% quantile according to the requirements of current a new standard by using two methods: data binning and quantile regression. The resulting (characteristic) dependence of the decreasing tensile strength of GFRP reinforcement on temperature shows zero strength at 550 °C and considers the effect of polymer matrix degradation on the behavior of the reinforcement. The determined curve can be used as a basis for the design of GFRP reinforcement in structures exposed to fire in accordance with EN standards.

Abstract: This paper deals with the stress analysis and prediction of crack formation caused by the development of hydration heat and shrinkage in the expansion block of the Nové Heřminovy dam. During the design of the concrete gravity dam, extensive analysis were carried out in order to predict the occurrence of cracks induced by hydration heat development and shrinkage within the first 10 years after the start of construction. The aim of the analysis was to predict the location, depth, and width of cracks under given conditions and to provide recommendations for minimizing crack formation in the structure. In the first stage, a parametric study on a sectional model was carried out, which led to the optimization of technological procedures and the concreting schedule. Subsequently, a global model of a typical gravity block of the dam was created to simulate the boundary conditions of the structure as accurately as possible during construction and subsequent operation, and to obtain results regarding stress distribution and areas with a risk of cracking. The analysis was performed using nonlinear numerical calculations in ATENA software, while also incorporating transport analysis of temperature and environmental humidity.