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The article presents a comprehensive overview of a study investigating the influence of soil-foundation interaction on the natural frequencies and vibration safety of reinforced concrete cellular and frame buildings. Through numerical modelling and analysis, the researchers investigate the relationship between structural modes and soil-induced vibrations, emphasizing the sensitivity of vibration frequencies to soil composition. Findings reveal that alterations in foundation conditions can significantly affect building dynamics, particularly in mid-rise structures, highlighting the importance of targeted monitoring for early detection of potential issues. Furthermore, the study discusses the implications of vibrations on human comfort and safety, underscoring the need for effective vibration mitigation strategies. Various damping systems, including hydraulic, dry friction, and dynamic dampers, are proposed as practical solutions to minimize the adverse effects of vibrations on both structures and occupants. Overall, the study underscores the critical role of vibration safety in ensuring the resilience and well-being of buildings and their inhabitants.

The process of Structural Health Monitoring aims to detect changes in material and/or geometric properties, boundary conditions or member connectivity of a structural system in time. However, the transfer of research results into engineering practice poses several challenges, especially for stiff structures with very diverse geometry that could not be well dynamically exited like low and medium-rise structures under ambient vibration conditions. Noise in modal parameters from output-only modal analysis due to variable environmental and operational conditions is considered one of the most problematic aspects of detecting structural damage using a vibration-based method. This research proposes a new way to reduce environmental noise in vibration data and dynamic parameters by merging dynamic response data from two similar shear wall buildings. The object of the study is a three-story reinforced concrete building. First, the damage features as natural frequencies and zero-order temporal moment of the vibration response are studied. Further, those feature changes are explored by means of modelling wall removal/opening introduction into the finite element models. It is established that the variation in the base excitation spectrum has more impact on dynamic response than introduced structural changes. Therefore, a time-domain feature like a zero-order temporal moment of the vibration response is not applicable for the proposed method. The appropriate damage sensitive feature vector for this approach is the difference of natural frequencies from two monitored buildings. The proposed method for fusion of vibration information from several buildings that share the same environmental and operational conditions filter out environmental noise effectively and give a clear advantage in reducing false alarm possibility during continuous and automated structural health monitoring process.

Cement composite long-term property assessment usually is limited to the compression strain state due to the difficulty of performing long-term tests in tension and 3-point bending. This paper shows the difference in long-term properties in compression, tension, and 3-point bending for plain ordinary Portland cement mortar (OPC). The obtained results were compared to reinforced specimen results to determine whether the PVA refibres improve the long-term properties of OPC mortar in various stress-strain conditions. Cylinders, compact tension specimens (CT), and beams – plates were prepared to evaluate material properties and the role of fibre reinforcement in these different stress states. Additionally, to conventional surface-attached strain gauges, 2D-DIC was employed to observe the creep strain of specimens in tension. This paper aim to determine long-term property differences in compression, tension and 3-point bending and, also, to see if low amount PVA fibre incorporation improve long-term properties in previously stated stress-strain states. It was determined that the usage of 1 % of PVA fibres increases creep strains in compression on average by 15 % and reduced by 7 % in tension. It reduces shrinkage strain by 18 % in compression and 8 % in tension. The long-term deflection for the PVA fibre-reinforced specimens are, on average by 55 % higher than for plain OPC mortar specimens in 3-point bending.

High-performance fibre-reinforced concrete is gaining popularity due to fibres ability to improve the poor properties of high-performance concrete. High-performance materials make using of thin-wall structures possible. Square section with square hollow provides decreasing of non-renewable material consumption, column’s high stiffness in the both planes and possibility to integrate the engineering communication inside of columns. The current study focuses on the development of analytical simplified calculation method that approximate output results of finite elements calculations for columns under eccentric loading with complicate hollow square-section. Analytical simplified calculation method to determine column’s load-carrying capacity is developed as the second-degree polynomial equation which is based on response surface method. The variables of equation are column height and material consumptions of the high-performance fibre reinforced concrete and steel of the additional longitudinal reinforcement. Data set of 27 experiments calculations was used to get the coefficients of adequate equation. Based on the results, the obtained equation makes it possible to predict the load-carrying capacity of the column in selected the factors interval on which a function was defined with sufficient precision. The difference between load-carrying capacities determine by numerical model based on the finite element method and by obtained second-degree equation does not exceeds 3.3%.

This study investigates the cyclic load application impact on fly-ash-based geopolymer composites that are reinforced with a low amount of fibre reinforcement. For reinforcement purposes, polyvinyl alcohol and steel fibres are used. For testing purposes, four geopolymer composite mixes were made, three of which had fibre reinforcement. Simultaneously, specimens were tested for shrinkage, static-load-induced creep, and cyclic-load-induced creep. For static and cyclic creep testing, specimens were loaded with 20% of their strength. For cyclic creep testing, load application and release cycles were seven days long. When each cycle was introduced, the load was applied in steps. Necessary load application or unloading lasted for 5 min and consisted of four steps, each 25% of the necessary load. From the long-term static and cyclic creep tests, it was seen that only the plain specimens showed that static creep strains are within cyclic creep strains. For all the other specimens, the static load was higher than the cyclic-load-induced creep amplitude. Also, 1% polyvinyl alcohol fibre-reinforced specimens showed the most elastic characteristics under cyclic load, and 1% steel fibre-reinforced specimens appeared to be the most resistant to the cyclic load introduction. [ABSTRACT FROM AUTHOR]

This study investigated the effect of a low amount of polyvinyl alcohol (PVA) and steel fiber reinforcement on fly ash-based geopolymer composite long-term deflection and its microstructure. For testing purposes, specimens with different amounts and types of fiber reinforcement as well as plain (reference) were prepared. The long-term deflection test was performed by loading specimens with 40% of the ultimate flexural strength. A microstructure analysis was performed using polished section specimens, and images were acquired at 25-times magnification on a scanning electron microscope. The results of the flexural strength test show that all geopolymer composites with fiber reinforcement have lower flexural strength than plain geopolymer composites. The long-term deflection tests show that the highest deflections exhibit 1% PVA fiber-reinforced specimens. The lowest amount of deflection is for 1% steel fiber-reinforced specimens. Specific creep shows similar results to plain, and 1% steel fiber-reinforced specimens, while 1% PVA and 0.5% PVA/0.5% steel fiber-reinforced specimen exhibits the same properties. The quantitative microanalysis of the polished section further confirms the deflection results. Specimens with 1% PVA fiber reinforcement have significantly higher porosity than all other specimens. They are followed by plain specimens and 1% steel fiber, and 0.5% PVA/0.5 steel fiber-reinforced specimens have almost the same porosity level. [ABSTRACT FROM AUTHOR]

One of the limitations of using glued connections in practice is related to the need for connection quality control. Still, the need for the non-destructive quality control of finished products to determine the compliance of the developed structure with the designed one still exists. Considering the small amount of research on timber–concrete composites with glued connections, there is a lack of research on non-destructive methods for the quality control of rigid connections in timber–concrete composite structures. During the literature analysis, no information was found on the possibilities of testing the quality of the rigid timber-to-concrete connection. Therefore, two well-known methods—operational modal analysis and ultrasonic testing—were tested to verify the possibilities of applying these methods in determining defects in the rigid glued connection between the concrete and timber layers in the timber–concrete composite structures. A series of small-scale specimens produced by the stone chips method with and without artificially made defects in the timber-to-concrete adhesive connection was tested by both methods. Operational modal analysis shows significant changes in mode shape, frequency values, and spectral density diagrams. Despite the sufficiently large reflection of the ultrasonic signal on the timber and concrete boundary, the transmitted signal is sufficient to perform local ultrasonic tests for detecting defects in the adhesive connection. Thus, it is concluded that the principles of both methods can be applied in practice, and further research is needed to develop testing technology. [ABSTRACT FROM AUTHOR]

With the growing importance of the principle of sustainability, there is an increasing interest in the use of timber–concrete composite for floors, especially for medium and large span buildings. Timber–concrete composite combines the better properties of both materials and reduces their disadvantages. The most common choice is to use a cross-laminated timber panel as a base for a timber–concrete composite. But a timber–concrete composite solution with plywood rib panels with an adhesive connection between the timber base and fibre reinforced concrete layer is offered as the more cost-effective constructive solution. An algorithm for determining the rational parameters of the panel cross-section has been developed. The software was written based on the proposed algorithm to compare timber–concrete composite panels with cross-laminated timber and plywood rib panel bases. The developed algorithm includes recommendations of forthcoming Eurocode 5 for timber–concrete composite design and an innovative approach to vibration calculations. The obtained data conclude that the proposed structural solution has up to 73% lower cost and up to 71% smaller self-weight. Thus, the proposed timber–concrete composite construction can meet the needs of society for cost-effective and sustainable innovative floor solutions. [ABSTRACT FROM AUTHOR]

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Global vibration-based methods in the field of structural health monitoring are intended to capture structural stiffness changes of buildings or other civil engineering structures. Natural frequencies of buildings or bridges are commonly used parameters to monitor these stiffness changes. Therefore, it is essential to clarify the limit at which this method is no longer sensitive enough to be useful for structural health monitoring purposes. This paper numerically investigates the effect of structural damage and soil–structure interaction on cellular-type reinforced concrete buildings' natural frequencies. These buildings are a common housing stock of Eastern Europe but are rarely investigated in this context. Comparisons with a reinforced concrete frame and infill structure building are made. Finite element models representing three structural system types of nine-story reinforced concrete buildings were used for the numerical simulations. Furthermore, a five-story finite element model was used for a damage sensitivity comparison. It is established that, for cellular-type structure buildings to detect damage comparable to that investigated in the paper, structural health (fixed base model frequency) should be monitored directly. Then, a statistical significance level for frequency changes of no more than 0.1% should be adopted. Conversely, the rocking frequency is a very sensitive parameter to monitor building base condition changes. These changes are often a cause of the cracking of building elements. [ABSTRACT FROM AUTHOR]

Geopolymer composites have been around only for 40 years. Nowadays, they are used in buildings and infrastructures of various kinds. A geopolymer's main benefit is that it is a green material that is partially made by utilizing waste products. The carbon footprint from geopolymer matrix manufacturing is at least two times less than Portland cement manufacturing. Due to the nature of the geopolymer manufacturing process, there is a high risk of shrinkage that could develop unwanted micro-cracks that could reduce strength and create higher creep strains. Because of this concern, a common strategy to reduce long-term strains of the material, such as shrinkage and creep, is to add fiber reinforcement that would constrain crack development in the material. This article aims to determine how various kinds and amounts of different fiber reinforcement affect fly ash-based geopolymer composites' creep strains in compression. Specimen mixes were produced with 1% steel fibers, 1% polypropylene fibers, 5% polypropylene fibers, and without fibers (plain geopolymer). For creep and shrinkage testing, cylindrical specimens Ø46 × 190 mm were used. The highest creep resistance was observed in 5% polypropylene fiber specimens, followed by 1% polypropylene fiber, plain, and 1% steel fiber specimens. The highest compressive strength was observed in 1% polypropylene fiber specimens, followed by plain specimens, 1% steel fiber specimens, and 5% polypropylene fiber-reinforced specimens. The only fiber-reinforced geopolymer mix with improved long-term properties was observed with 1% polypropylene fiber inclusion, whereas other fiber-introduced mixes showed significant decreases in long-term properties. The geopolymer composite mix with 1% polypropylene fiber reinforcement showed a reduction in creep strains of 31% compared to the plain geopolymer composite. [ABSTRACT FROM AUTHOR]