PSI - Issue 81

Volodymyr Romaniuk et al. / Procedia Structural Integrity 81 (2026) 234–239

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The essence of the prestressing method for steel structures is that, through insignificant one-time costs of material and labor, the necessary initial forces and deformations are created in the structure, which during operation allow the main structural elements to continue elastic operation. In construction practice, the following methods are used to create prestressing forces in structures: – prestressing using additional elements such as tensioners, struts, etc.; – preliminary deformation of individual cross-sectional elements (chords or webs) before manufacturing with subsequent execution of chord welds to connect them; – local thermal prestressing (LTP), which consists of heating individual sections of fully fabricated metal structures or their elements to a certain temperature (usually up to 850 –950°C) followed by their normal or intensive cooling. The first method of prestressing has become widely used in trusses, arches, frames, beams, and other structures and is the most well-known and well-studied. The second method of introducing prestressing forces is less common than the first but is also quite well-known. The third method is the least studied. It has been little used in scientific research and construction practice, and currently active scientific research is being carried out in this direction. The main principle of this method is to create the necessary residual stresses in individual elements of the structure or in its individual parts by heating them with subsequent cooling under a certain regime, which allows the desired strength and deformation parameters to be obtained. 2. Analysis of recent research and publications As specified in design standards DBN V.2.6-198 (2014) and EN 1993-1-8 (2005), the calculation of prestressed structures in engineering practice is performed by summing the stresses in the cross-sections of elements. These stresses include those arising from external loads, which develop as they would in a conventional structure without prestressing, and the stresses caused by prestressing, which have opposite signs at the most highly stressed design points of the cross-section. Theoretical and experimental aspects of the influence of initial stress on the condition of span structures of building coverings, in particular on perforated prestressed arches, were investigated in Romaniuk et al. (2024a, 2024b), Tsavdaridis and D’Mello (2011a, 2011b), Morkhade and Gupta (2015). It is also worth noting the influence of the actual stiffness of nodal bolted connections, where the magnitude of the bolt pre-tension also contributes to the emergence of initial forces in the structural elements, on the overall stress-strain state and the actual performance of structures under the action of external loads, as shown in Wang et al. (2018), Shardakov et al. (2018a, 2018b). 3. Research purpose and methods The aim of the research is to study the actual performance of elements of a steel perforated arch taking into account prestressing. The tasks are: determining the stresses in the elements of a prestressed arch; comparing theoretical and experimental stresses; and assessing the influence of prestressing on the bearing capacity of a steel arch with a perforated upper chord. The problems of calculating prestressed structures very often coincide with the problems of optimizing their stress state at different stages of loading in order to obtain the greatest effect at the lowest cost. It is no coincidence that from the very beginning of the new stage of development of prestressed steel structures, the main attention has been drawn to issues related to optimal material distribution, the search for the optimal stress state, optimal sequences of load action, and other aspects. 4. Main results For an arch with a perforated upper chord (Fig. 1), the following options for creating prestressing forces in its elements can be applied: 1) pre-tensioning of the strut; 2) displacement of one of the two support nodes of the arch outwards during its installation in the design position; 3) deformation of the ridge node; 4) use of additional tension mechanisms in the most stressed sections; 6) heating of metal in the most stressed sections. The option of creating initial forces by pre-tensioning the strut is considered in detail below. The creation of pre-stresses in the arch elements using strut prestressing is carried out by a tensioning mechanism, which is placed in one of the nodes where the strut fastens to the upper chord (Fig. 2). In this case, at the point of fastening these two elements to each other, a hinge adjacent to the upper chord is formed and the strut thus becomes an additional support for it. The prestressing of the arch is performed in the following sequence: 1) the chord elements are connected at the ridge node; 2) the tie rod is attached to the support nodes; 3) the upper part of the suspension is attached to the ridge node, and its lower part freely supports the tie rod, that is, the tie rod and the suspension are not connected to each other in any way;