Advances in Science and Technology Vol. 147

Abstract: The subject of the article is a description of the behaviour of a developed fully composite footbridge structure, with a focus on its subsidiary load-bearing elements. The bridge is built using a modular system, and is designed for temporary use. The load-bearing structure is composed of wall beams acting in the longitudinal plane of the footbridge, along with transversely oriented beam elements that form a basic structural module in the shape of the letter "U". The module's structure is supplemented with stiffening frames at the ends, which prevent horizontal deformations of the wall elements and contribute to the connection of additional modules. The connection of the individual modules is carried out by means of steel tabs in the tensioned and compressed parts of the wall beam and by bolting through the adjacent stiffening frames, thus transferring the shearing force. The walking bridge deck is made up of composite grates with an anti-slip coating, which are placed on pultruded profiles acting in the transverse direction. A numerical model was developed to predict the behaviour of the footbridge, the accuracy of which was verified by comparing the results from a load test that was carried out. The test specimen consisted of four modules, and the total length of the footbridge was approximately 8.0 m. For loading purposes, water tanks (tank capacity 1000 l) were distributed over the entire footbridge area to simulate a uniform area payload. Loading was carried out at three defined levels of design surface load. In addition to the uniform full-area loading, asymmetrically applied loading conditions were also performed.

Abstract: For bridges with a slender bridge deck, ensuring sufficient stability under external loads is one of the technical problems that must be addressed. This paper studies the stability of a flat arch under asymmetric loads. Flat arch structures can form a directly walkable bridge deck. These structures can be realized without external prestressing only up to certain spans due to the necessity of capturing significant horizontal forces. The paper includes a static study that analyses the possible arrangements of the prestressing cables. The study evaluates the stabilizing effect of external prestressing and the possibility of creating a self-anchored system. Based on the results of the static study, a suitable variant was chosen for the design of a physical experiment. The experimental measurements compare the increase of stability for an arch discretely connected to a prestressing cable and an arch structure with a tie without mutual connection.

Abstract: The monitoring of dynamic parameters of slender bridge structures is becoming of particular interest in terms of their possible use in determining their structural condition, or possibly as one of the parameters for their long-term monitoring. The method for monitoring dynamic parameters is relatively new and practically unexplored. First of all, it is necessary to find out with certainty how the dynamic parameters of slender bridge structures change, for example, with changes in temperature, the magnitude of the prestressing force, or how they change with changes in discontinuous mass (e.g. overlaying or stripping of pavement layers). The paper summarizes the important aspects that can affect the modal parameters - natural frequencies and their shapes. The above listed influences and their impact on the structure were investigated on real structures formed by stress ribbon.

Abstract: Determining the load-carrying capacity of existing bridges is a crucial task in assessing the current reliability and remaining service life of prestressed concrete structures and bridges. Nowadays, prestressed bridge structures that have been in operation for more than sixty years are proving to be problematic from the reliability point of view. If we want to comprehensively assess the reliability level of these structures, it is necessary to determine the current level of the prestressing as accurately as possible. This fact leads to the need to apply different methods that can determine these values. The paper is focused on the analysis of prestressing using indirect or analytical-experimental methods. Specifically, the Structural Response Method and the Saw-Cut Method. These techniques were tested both on prestressed members, in laboratory conditions, but mainly directly in-situ on a post-tensioned bridge. Finally, the experimental results are compared with the theoretically determined levels of prestressing.

Abstract: Slender concrete structures are often assembled from precast segments with concrete joints. Proper functioning of the joints, which are a source of discontinuity in prefabricated structures, is crucial in terms of the overall structure's serviceable life. They are typically cast between segments faces with formwork keys around their perimeter. This contribution compares the results from several numerical analyses of the joints with results obtained from experimental measurements. The analysis results were used in the design of stress ribbon footbridge recently constructed in Tyresta National Park in Sweden.

Abstract: The subject of the article is a summary of the results of inspection of 8 highway bridges, where the superstructure is made of prestressed precast girders. Standardized girders KA-73 for clear span of 9 - 18 meters are used since approximately 1975 for the construction of bridges in the Czech Republic. As part of the inspection, the corrosion of the prestressing reinforcement and the grouting of ducts were verified. Furthermore, actual strength class of concrete in relation to the design strength, a visual inspection of the outer surface and the internal chambers of the girders using a videoscope. At the end, the most common defects are summarized.

Abstract: The paper discusses the criteria of sustainability applicable in design of concrete structures, bridges in particular. It shows that old structures were usually sustainable, while todays trends supported by the technical progress provide more space for extravagant and unsustainable structures. The examples of bridges satisfying and unsatisfying criteria of sustainable design are presented. It is shown that the conceptual design is the stage, where the structure is defined and where it is decided on its sustainability.