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In a particular case of a hollow core floor subjected to a concentrated load, individual units forming the floor cooperate when loaded vertically due to the presence of cast in-situ joints. This phenomenon is studied numerically on a 400 mm floor which was investigated in a full scale experiment in Fin-land. Having obtained good fit with experimental data a parametric non-linear finite element analysis of the failure load is performed with various load locations. The analysis evidence that the capacity of a floor depends largely on the local effects in individual webs or flanges. It is therefore reasonable to limit the load values by local capacity criterions mentioned by EN 1168, which can however underes-timate the actual peak load value and do not take into account the effect of floors span. While peak loads obtained in the slender floor were lower than in the case of the stiffer floor, the redistribution obtained in the slender floor was significantly higher

Currently growing interest in use of timber-concrete composite (TCC) floor systems indicates thatthey can be an effective alternative to traditional concrete floors and an efficient solution for rehabilitatingexisting timber floors. This study aims to experimentally verify a novel sustainable timbersteel-concrete composite floor system implemented in a real building. The system's performance wasassessed under static and dynamic loads, with a particular focus on the impact of longitudinal joints,before and after they were grouted. Static tests used IBC water tanks to apply a 3 kN/m² load, anddeflections were measured with LVDTs and a levelling instrument. Dynamic tests involved measuringeigenfrequencies under self-weight and additional loads, and impact loads. The experimentsdemonstrate the effectiveness of grouting joints in enhancing the structural performance of the compositefloor system, reducing deflection, and improving dynamic response.

W artykule przedstawiono wyniki badań krótkotrwałych i reologicznych przyrostu odkształceń w teście wypychania (push-out test) w przypadku dwuzakładkowych połączeńklejonych. Łącznie przebadano 15 próbek złożonych z elementów wykonanych z drewna klejonego krzyżowo (CLT) oraz prefabrykowanych płyt betonowych. Połączenie między elementami wykonano jako klejone z użyciem innowacyjnych prefabrykowanych złączy podatnych o grubości 3 mm, w trzech konfiguracjach powierzchni klejenia. Celem badań było określeniewpływu geometrii połączenia klejonego na początkowy przyrostodkształceń w czasie. Wykazano, że pełzanie przebiega nieliniowo w czasie t1 = 800 s niezależnie od powierzchni klejenia, a następnie zwiększa się w sposób liniowy. W przeprowadzonych badaniach złączy pasmowych uzyskano przyrost początkowegopełzania o ok. 10% mniejszy w przypadku złączy ułożonychw kierunku obciążenia niż w kierunku prostopadłym. Wykazano również, że wartości pełzania nie są wprost proporcjonalnedo wielkości naprężenia ścinającego., This paper presents the results of a study of short-termrheological strain increments in a push-out test for double-lapglued joints. A total of 15 specimens consisting of crosslaminated timber (CLT) elements and precast concrete slabs weretested. The joint between the elements was made as a glued jointusing innovative 3 mm thick prefabricated flexible jointsin threebonding configurations. The aim of the study was to investigatethe influence of the adhesive joint geometry (typeAwith 600 cm2glue, B – 200 cm2 in strips parallel to the load axis and C – 200 cm2in strips in the perpendicular direction) on the initial deformationincrease over time. Creep phenomenon was shown to be nonlinear for an initial time range of t1 = 800 s regardless of theadhesive area, and then to increase in a linear manner. In the testscarried out on strip joints, the increments of initial creep wereobtained to be about 10% smaller for joints arranged in the loaddirection than for those arranged in the perpendicular one. It wasalso shown that the creep values are not directly proportional tothe magnitude of the shear stress.

As long-term investigations are often too time- and cost-consuming, short-term experimentsare introduced for investigating the behaviour of connections in timber-concrete-compositeelements. The paper presents a proposal for short-term double shear tests with adhesive andmechanical connections for investigating their time-dependent behaviour. The proposedevaluation method determines the elastic and visco-elastic parts of the slip modulus of theconnection. The validity of the identified parameters needs to be verified by long-term tests.

Structural floor systems made of Timber-Concrete Composites (TCC) slabs are becoming more and more popular in office and residential buildings as well as in systems used for the renovation of old ceilings. Timber elements can be constructed as beams or solid slabs (massive CLT). Regardless of the main structural layout, individual components require using interlayer connections, which provide composite action in cross-sections. The most used connection types for TCC are mechanical fasteners, grooved or notched connections, and bonded shear joints. Bonded connections with rigid thin-layer adhesives provide high load capacity, but they are characterized by brittle failure due to their low ductility and introduced stress concentrations. An innovative flexible adhesive joint that ensures the transfer of high loads and high deformations simultaneously is presented in the paper. This connecting structural element, named PolyUrethane Flexible Joint (PUFJ) was examined experimentally in double shear lap tests of connections formed between two external CLT slabs of dimension 120 × 350 × 400 mm3 and a central concrete slab of dimension 100 × 250 × 400 mm3. Shear connections between the composite elements were made of a two-component polyurethane PS type adhesive layer of thickness 3 mm. The tested specimens were prepared in two variants of the application: wet application in the form of liquid adhesive and dry application in the form of prefabricated polyurethane layer glued to the elements by thin polyurethane adhesive. The effect of the adhesive application method on the stiffness and capacity of the TCC joint was investigated. In the paper, the analysis of the experimental tests’ results is presented.

Precast floors are gaining more and more popularity in modern construction, mainly due to their fast realization. However, the provisions of standards regarding floor design are often ambiguous and sometimes questionable. The article discusses selected issues of HC slabs design, which often pose problems in practice, with references to relevant scientific research in this field. Particular attention was paid to the principles of distribution of the concentrated load on adjacent slabs in the floor field, openings in the floors, support conditions and taking into account the slabfunction as an element of a floor.

Cross-laminated timber (CLT) slabs in residential buildings need additional weight, e.g., in the form of screeds or gravel layers, to fulfill the criterion for the highest impact-sound class. The additional mass is, however, not exploited for the load bearing behavior, but adds additional weight and leads to an increased height of the floor construction. In this study, such a CLT floor construction with a construction height of 380mm is compared with a composite slab consisting of a CLT plate with a concrete layer on top with a floor construction height of 330 mm. The timber concrete composite (TCC) slab has a different creep behavior than the CLT slab. Thus, the development of the time-dependent deflections over the service life are of interest. A straightforward hybrid approach is developed, which exploits advanced multiscale-based material models for the individual composite layers and a standardized structural analysis method for the structural slab to model its linear creep behavior. The introduced approach allows to investigate load redistribution between the layers of the composite structure and the evolution of the deflection of the slab during the service life. The investigated slab types show a similar deflection after 50 years, while the development of the deflections over time are different. The CLT slab has a smaller overall stiffness at the beginning but a smaller decrease in stiffness over time than the investigated TCC slab.

Research on the shear capacity of posttensioned, precast crane beams after more than 50 years of exploitation is presented in the paper. The tests simulated an emergency situation with the loss of one or two anchorages of the prestressing tendons. Due to the possible varying location of the concentrated force on the crane beams, tests were carried out for different shear span-to-depth ratios. The paper mainly presents experimental tests’ results. Studies have shown that loss of top cable anchorage does not significantly affect the behaviour of beam, but failure of bottom cable anchorage has a significant effect on reducing its shear capacity. The important conclusion is that even under very adverse emergency conditions the elements do not collapse in a brittle manner.

The issue of vertical load distribution in floor slabs made of hollow-core slabs, which is an important but not well-recognised design issue, is investigated in this paper. Various standards' provisions on load distribution are briefly presented. A comparative study has been performed which showed a large scatter of results, especially when the PCI Manual and EN 1168 provisions are compared for shear force distribution. Support reactions obtained from mentioned design models are also compared with experimental test results done in 1991 on six 400 mm deep and 12 meters long slabs.

Timber-Concrete-Composites (TCC) are a perfect symbiosis of two entirely different buildingmaterials, as the most favorable properties of both components are utilized. This ensures an efficient use of thenatural resources. As regards the long-term creep behavior however, only a rough estimation can be done basedon the current versions of the design standards (EN 1992-1-1 and EN 1995-1-1). The focus of this work is oncombining existing models for the individual time-dependent behavior of concrete and timber with commonstructural analysis methods to investigate composite structures, similar to Binder et al. (Buildings, 2022). Thehybrid model is applied to a simply supported TCC slab consisting of a cross-laminated timber (CLT) plateand a connected concrete layer on top. For comparison, two other floor constructions, namely a CLT slab andan in-situ concrete slab, are investigated as well, considering the same time-dependent material behavior. Allthree slab types fulfill the design requirements for long-term deformations and for stress limitation to avoidnon-linear creep. The time-dependent deflections of the slab types over 50 years are modelled and comparedwith the design according to the standards. This comparison shows that the hybrid approach for TCC and CLTfloor constructions yields smaller deflections than the calculation according to the design. standards. Modellingresults of the in-situ concrete slab were quite similar to the results of the design according to EN 1992-1-1.Comparing the modelled deflections of the TCC slab with the other two shows that the deflection of thecomposite slab changes the most over 50 years. At the beginning the behavior of the TCC is closer to theconcrete slab but develops more towards the CLT slab at the end of the investigated 50-years period. Herein,also the load redistribution within the cross-sections is shown based on the hybrid model and the axial stressesof the individual parts of the cross-sections.

Modern composite materials based on non-metallic continuous fibres are increasingly used in civil engineering to strengthen building structures. In the strengthening of reinforced concrete (RC) structures, the utilisation of externally bonded fibre-reinforced polymer (FRP) composites is only up to 35% because of the pilling-off failure mechanism. This problem can be solved using pre-tensioned composite laminates. Due to more complex behaviour, the strengthening of structures by means of prestressing technology needs a careful design approach and a full understanding of the behaviour of both the materials and elements. The advantages and risks of the presented technology, which may determine the success of the entire project, will be highlighted in the paper. The possibility of using a flexible adhesive layer in carbon fibre reinforced polymer (CFRP) strengthening applications for flexural strengthening of RC elements, as an innovative solution in civil engineering, will also be presented. Parallel introduction of the flexible adhesive layer (made of polyurethane masses) and a traditional epoxy adhesive layer in one strengthening system was investigated in the laboratory tests. This solution was used for the repair and protection of a previously damaged RC beam against brittle failure.

The ageing engineering infrastructure is a growing problem in many countries and thus a challenge to make optimal decisions for their further safe operation. Therefore, effective diagnostic solutions are being sought to enable a reliable assessment of their technical condition. The article presents the results of static and high-frequency strain measurements of a 57-year-old post-tensioned crane girder, dismantled from one of the production halls. In particular, the anchorage zone and transmission length of the tendon related to the quality of cement injection around the prestressing tendon were analyzed. For this purpose, a distributed fibre optic sensing (DFOS) technique was applied, which allows performing strain measurements with a spatial resolution starting from2.6 mm (almost 385 measuring points per 1 m of the optical fibre). The application of such an approach allowed for detailed analysis in both longitudinal and transverse directions, including crack detection and estimation of their widths. The article describes in detail the sensing fibres and applied methodology, as well as the results of both static and high-frequency tests performed under laboratory conditions during cutting one of the tendon's anchorage off.

This paper presents the influence of overly stiff rail fasteners, which are used to stabilize rails on a ballastless track structure, on the mechanism of the occurrence of defects in concrete baseplates. During the analysis, there was a series of field tests performed on a real track, the purpose of which was the assessment of the technical condition of the ballastless track, the assessment of concrete baseplate strength and the verification of the correctness of the rail attachment by means of a fastener. In addition, there was a series of supplementary laboratory tests performed which assessed the relationship between the anchor clamping force and the torque at the assembly stage (the first tightening of the anchors) as well as after the adjustment of the fastening rigidity (loosening and tightening the fastening anchors again). On the basis of the obtained results, a three‐dimensional numerical model of a section of the ballastless track structure was prepared with the use of adaptive solid finite elements. The performed numerical analysis reflecting the real work of a fastener in a track structure was used to identify the causes of defects in concrete baseplates in the analyzed ballastless track structure.

The paper presents the authors’ model of calculating the shear capacity of prestressed concrete hollow core slabs in Slim Floor structures, the theoretical basis of which is Cholewicki’s two-beam model and the Finnish model by Pajari and Leskelӓ. The purpose of the model development was to find an alternative method for determining the horizontal tangential stress τzx which occurrence is decisive for reducing the shear resistance of channel slabs based on flexible supports. The model gives intermediate results between the Finnish model and the German model by Hegger and Roggendorf, which seems to be desirable, taking into account the conservative character of the Finnish model. The authors’ model is the first attempt to date at analytical consideration of the effect of web flexibility which may be important to maintaining an adequate capacity of the slab. In other models, the webs are treated as a rigid system, connecting the horizontal flanges of the slab. The model is a simple calculation tool, available to Slim Floor designers for engineering analysis.

Concrete floors constitute the vast majority of all types of floors erected worldwide. They do not require additional fire protection measures or periodical maintenance work that is necessary in the case of steel components, thus reducing the cost of their exploitation. Special concretes and prestressing technology are increasingly common in the production of concrete floors. The desire to de-load the structure is the driving force behind looking for ways of applying light-aggregate concretes in floor production. The application of fine-grain high performance concretes with textile carbon fibres reinforcement in concrete prefabrication processes seems an interesting solution, allowing for incomparably smaller cross-sections of the used elements than the components currently used in the traditional reinforced concrete technology. Although innovations in the area of on-site RC construction are not uncommon, prefabrication still constitutes a technology that is the most open to creating and implementing new and unconventional solutions in the construction industry.

Durability of mid-twentieth-century precast prestressed concrete structures has become an issue in many countries. In the 50s and 60s of the last century, a large number of post-tensioned and pre-tensioned concrete structures (e.g. bridges, crane beams, roof girders) were constructed throughout Europe. Design guidelines as well as materials and technologies applied in those days were significantly different from current ones. The rules of factory production control and on-site supervision differed from the ones applied today. Currently, these structures achieve (or have already achieved) the design life period. Owners or managers of such structures face the dilemma of whether these objects can still be safely operated, or certain intervention is needed or perhaps - in extreme cases - demolition is necessary. The procedure for assessment of technical state of old prestressed structures is briefly described in the paper. Based on numerous research of existing structures in Poland (which are representative of many European countries), their weak spots, which may determine safety of the whole object, are shown. The paper also provides ways of analysing the behaviour of such structures, allowing for more accurate determination of their load bearing capacity.

Research on posttensioned, precast crane beams after more than 50 years of exploitation is presented in the paper. Despite not secured tendons’ anchorages from corrosion as well as the use of the low amount of stirrups the beams are still successfully used in industrial facilities. The failure modes as well as results of the load, deflections, cracks width and strains measurements for tests in different static schemes are given. The first stage of tests contains four beams 60 cm in height. In the second stage, test were conducted on a beam 80 cm of height made of two precast segments. The role of the experiments in the decision-making process regarding further exploitation of the structure after the period of their designed durability is highlighted

The paper discusses the principles of precast concrete hollow-core slabs taking into account their spatial work. It is shown that consideration of spatial work makes it possible to determine the forces in individual floor slabs significantly more precise. The fact that strain redistribution between precast floor slabs depends on slabs’ bending and torsional stiffness is shown. The research has been mostly devoted to the determination of the bending stiffness with regard to the formation of cracks and the change in torsional stiffness, especially considering the presence of normal cracks, which is still unstudied. This paper presents the technique for determining the torsional stiffness of hollow-core slabs with normal cracks. In order to determine the components included in the resolving system of equations, it is proposed to use an approximation method based on the processing of numerical data using spatial finite elements.

An original concept of Slimfloor structure made of hollow-core slabs with structural concrete topping and post-tensioned delta-shaped beams is given in the paper. The technological assumptions and the results of computational analysis for this solution are also discussed. The multi-span continuous prestressed beam can significantly increase the length of the span of the Slimfloor ceiling and at the same time keeps its primary asset - almost flat bottom surface - creating the ideal solution for the demanding projects.

The real mechanical properties of concrete play an important role in the structural analysis of the behaviour of precast, thin-walled elements, especially those without passive reinforcement. The experimental research of pre-tensioned hollow-core slabs has shown that the actual strength and elasticity of concrete might be about 30 to 50 % lower than the so-called ”standard” properties assigned to a specific class of concrete. Reasons for the strength properties reduction in the narrow ribs of slabs with very heterogeneous structure subjected to the influence of interrelated hydrothermal fields, during the process of casting, are given in the paper.

In the paper, the physical and chemical parameters which are determining the durability of pre-tensioned concrete railway sleepers are presented. To the physical parameters the adhesion between prestressing reinforcement and concrete, which depends on the technology of pre-tensioned railway sleepers production was presented. The sleepers produced according to these technologies differ significantly in bearing capacity and cracking resistance. Experimental investigations have shown that the most advantageous properties are obtained when the button head anchorages of the prestressing wires are applied, according to the BBRV method; the bearing capacity of the rail seat zone for such railway sleepers exceeds the capacity of other types of sleepers even more than 35%. The most important chemical parameters is the content of soluble sodium and potassium in cement, which is assuring the concentration lower than 400 mmoles/L for heat treatment of concrete sleepers at a temperature not exceeding 70 °C. At a temperature not exceeding 50°C it should be 600 mmoles/L of concrete pore solution. It assures the stability of ettringite in concrete at a given temperature. These concentrations of sodium and potassium hydroxides should be calculated for known concrete composition and determining the content of soluble Na2Oe in concrete ingredients.