This article presents the results of tests conducted to identify the failure process and evaluate the deformation of axially compressed concrete specimens modified with polypropylene fibers (PP). The test specimens were previously stored at ambient temperature and subjected to fire temperatures of 300 °C, 450 °C, and 600 °C. Acoustic emission (AE) signals were recorded during loading, along with force and strain measurements. The recorded AE signals were analyzed using the k-means clustering method. The compilation of the test results made it possible to determine the classes of signals characteristic of different stages of the material failure process and to indicate the differences in the failure mechanisms of specimens stored under ambient conditions and subjected to fire temperatures. Digital image correlation (DIC) measurements were conducted during the strength tests. A numerical model of the material (FEM) was also prepared, and a comparison of the obtained results was carried out.

The optimisation of the design method for verification of slender steel beam-columns is still a current issue not only from scientific point of view, but also for design practice. Therefore, the main objective of this paper is comparison of the suitability of established design approaches, according to the European standards for steel and aluminium structures, on the basis of numerical simulations. Thus, a finite element model was validated on the basis of experimental analysis available in the scientific literature. To perform the comparison of accuracy of design approaches according to European standards, a commercial software program ANSYS was used for observation of the resistances of beam-columns. The resistance of european I beams with parallel flanges (IPE) and a rectangular hollow cross-section (RHS) were investigated for four load cases on a simply supported member and also on a pinned-fixed beam column with linear bending moment distribution, where the resistance of the cross-section governs. Finally, the conclusions for suitability of the respective design approaches are discussed, together with some findings that arose from this work.

During the years of bridge exploitation, many degradation processes and external influences attack its structure. Therefore, bridge reliability and durability is decreasing in time. On the other hand, the traffic load remains almost the same or even higher than in the past. However, bridges should not to become the limiting component of communication capacity and traffic reliability. Regarding to reliability, bridges should be assessed from the viewpoint of the Ultimate Limit States (ULS) and Serviceability Limit States (SLS). Within the ULS, cross-sections and members are verified for various types of stressing and their combinations, and also for fatigue at the same time. The cross-sectional verification, e.g., for bending stresses and fatigue, is done independently according to corresponding criteria of the ULS determined for strength verification a fatigue assessment separately. The presented article deals with the steel railway plate girder bridge with bottom member deck, in which there is an effort to prove the effect of the crack in tension bottom flange due to fatigue stressing on the change of bending resistance over time. The analytical calculation was derived and at the same time, the probabilistic approach of the influence of the fatigue crack size on the change of the cross-sectional resistance and reliability over time was used.

Transversely loaded beam grillages are quite often used in industrial construction. In order to produce a safe design of such structures, it is necessary to account for the lateral torsional buckling phenomenon, which reduces load-bearing capacity. To be able to calculate the relevant reduction factor, the elastic critical load must be determined. As regards the existing design practice for such structures, simplified conditions are assumed for the mutual restraint of the component beams. However, this approach does not correspond to reality. This study discusses the results of numerical investigations and analytical calculations concerning the effect of the elastic action of simple beam grillage (SBG) joints on the critical load, which results from the lateral torsional buckling (LTB) condition. The SBG was defined as a flat system of interconnected beams, unstiffened laterally and loaded perpendicularly to the grillage plane. The analysis covered H-shaped grillages with different span ratios of component beams, in which the main (coupling) beam was decisive for instability. The effectiveness of the use of closed-section stiffeners at the grillage joints was also investigated. The grillage elastic critical resistances (ECR) were determined for two variants of joint stiffening. The computations were performed by means of FEM numerical simulations. The spatial models were discretised with the following elements: (1) solid ones in Abaqus, (2) shell ones in ConSteel, and (3) thin-walled bars in ConSteel. The LTB critical moments of the weakest beam (critical beam), elastically restrained against warping and against lateral rotation (in the LTB plane), were computed using the analytical methods developed by the authors. To this end, the methods were proposed to determine the indexes of the critical beam elastic restraint in the adjacent stiffening beams. In the study, it was demonstrated that (1) taking into account the conditions of mutual elastic restraint and interaction of the component beams provides a more accurate assessment of the grillage ECR, (2) the use of closed-section stiffeners in the grillage joints increase the ECR compared with classic flat stiffeners, (3) the grillage ECR can be estimated based on the critical moment M_cr of the weakest beam (critical beam) when the conditions of its elastic restraint in joints are accounted for.

Steel girder bridges with member decks belong to the most frequently used types of superstructures of old riveted steel railway bridges. During their service life, the bridge deck members are affected by escalating effects of the traffic loads that significantly exceed those for which they were originally designed. As a result, these structures are often subject to the increased effects of fatigue degradation. One of the typical cases of fatigue damage on steel riveted bridges is a fatigue crack in the web of the stringer at the point of its connection to the cross girder. Such a connection used to be considered to transmit the axial and shear forces only, and so no fatigue crack was expected to develop in this detail during the bridge service life. However, the relatively frequent occurrence of fatigue cracks indicates the incorrectness of this assumption. This article is divided into two parts. Firstly, the bending stiffness of the stringer-to-cross-girder connection with different structural arrangements is analysed. Theoretical and experimental analyses of fictitious steel superstructures as well as of a real superstructure of an existing steel riveted bridge were performed to clarify the real stiffness behaviour of this detail. The results of the analyses confirm the assumption of a certain bending stiffness of the observed connection. Subsequently, attention is paid to the fatigue resistance of the riveted stringer-to-cross-girder connection in terms of the use of European standards. The results of fatigue tests performed on specially prepared test samples are presented with the aim to define the fatigue detail category.

In addition to traditional building materials, such as steel and concrete, wood has been gaining increasing prominence in recent years. In the past, the use of wood was limited due to its susceptibility to damage by fungi, insects, and temperature. These shortcomings were gradually eliminated as the quality of wood processing increased and thanks to modern high-quality insulating and protective materials. The return to the utilisation of this natural building material was also supported by the development of new wood-based materials, such as glued laminated wood, and new types of mechanical fasteners, as well as by the introduction of new design methods provided in the Eurocodes. Within this context, this paper focuses on using wood in transport infrastructure, especially as the basic material for footbridges and small road bridges. Combined timber–steel bridges emerge as a very effective type of superstructure in contemporary road bridges and footbridges, especially in areas with natural exposure. Usually, wood is used for the main bridge girders, while steel is preferred for bridge deck elements—stringers and cross-girders. The results of this parametric study offer optimal structural solutions for footbridges with spans of 12.0–24.0 m, reflecting satisfactory static and dynamic footbridge behaviour. Particular attention is paid to a problematic structural detail—the connection between the steel cross-girder and the timber main girder. Firstly, this connection’s characteristics were measured experimentally using nine laboratory samples made of two glued laminated timber blocks, simulating main girders connected with a hot-rolled steel cross-girder. The connection was prepared in three variants, with different heights of the end plates and different numbers of bolts. Subsequently, these characteristics were computed using two numerical FEM models. The first model was created using SCIA Engineer software with a combination of shell and beam finite elements. The second, more sophisticated model was created in the ANSYS software environment using 3D finite elements, allowing us to better take into account the plasticity and orthotropic properties of wood and the points of contact between the individual members. Finally, the experimental results produced by sample testing in the laboratory were compared to the outputs of FEM numerical studies.