PSI - Issue 81

Svyatoslav Gomon et al. / Procedia Structural Integrity 81 (2026) 192–197

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structures, and trusses in particular, remains limited. The term “progressive collapse” and the development of building and structural protection systems emerged in the mid -20th century following the report of a commission that investigated the causes of the failure of a 22-storey residential building in London. After this report, numerical and theoretical studies on this issue were initiated in virtually all developed countries of Europe, Asia, and North America. In current international building codes, the concept of risk has been introduced (Eurocode 5:2004; NDS:2018), and various approaches to its assessment have been proposed. Design measures aimed at preventing progressive collapse are also evaluated, taking into account the vulnerability and importance of the respective structure. However, no economically justified measures can completely eliminate the risk of failure of any load-bearing element. Thus, it can be stated that every structure has an inherent probability of failure. Attempts to reduce this probability to near zero are accompanied by a substantial increase in construction costs. The development of additional protection measures for buildings under accidental situations should primarily focus on ensuring human safety and enabling evacuation by providing the necessary time margin. At present, there is no generally accepted, scientifically substantiated approach or design practice for buildings and structures that maintain structural integrity under various combinations of design loads and accidental actions. The difficulty of theoretically determining the potential for progressive collapse has been noted due to the lack of clear definitions, starting with the probability of occurrence and the magnitude of the anticipated hazard. In most cases, accidental actions cannot be quantified, and the extent of possible initial damage remains unknown. Analytical methods for determining initial damage and predicting the probability of subsequent progressive collapse of a structure due to assumed accidental actions have not been developed. The application of numerical analysis methods is also limited due to insufficient knowledge of structural behavior during progressive collapse, as well as the lack of adequate experience in developing comprehensive structural models and interpreting computational results. Therefore, further research is required to develop improved methodologies for assessing the vulnerability of structural systems and enhancing them to mitigate progressive collapse under various hazard scenarios. 2. Results and discussion The study of the behavior of elements of timber trapezoidal trusses, accounting for spatial action - namely, the presence of decking, purlins, and bracing - under the failure of a single element has demonstrated an influence on the stress-strain state of the remaining elements due to load redistribution. Let us consider the mechanisms by which a steel-timber trapezoidal truss prevents complete collapse, that is, conditions under which progressive collapse of the structure and the building as a whole does not occur. In standard design practice, such a structure is analyzed as a simply supported open-web beam resting on two supports, without considering the attached bracing system, decking with purlins, roof panels, or struts. In addition, the behavior of timber elements in such structures is typically assumed to be purely elastic (Eurocode 5:2004; DBN B.2.6-161:2017; NDS:2018). However, timber is an elastic-plastic material (Gomon et al. (2024); Janiak et al. (2023); Datsiuk et al. (2024); Roshchuk et al. (2024); Homon et al. (2024)). Moreover, in practice, structural systems are generally subjected to variable and repeated loading throughout their service life (Gomon et al. (2019); Pavluk et al. (2024); Aleksiievets et al. (2024)). To achieve the stated objective, a study was conducted on two steel-timber trapezoidal trusses with a span of 24 m, a depth of 2.8 m at the supports, and 4.0 m at the ridge, taking into account all the aforementioned effects (Figs. 1 and 2).

Fig.1. Geometric scheme of truss No. 1

The calculations were carried out using the LIRA software package. After forming the computational model of the truss under investigation, it is necessary to specify the stiffness of the elements. The top chord and the web of the truss consist of glued pine beams measuring 10 × 20 cm, while the bottom chord is made of two equal-angle steel sections, 100 × 10 mm. Three loads are applied to the computational model: a permanent load from the self-weight of the roof covering, and variable snow loads applied across the full span and half span. The loads are applied to the nodes of the top chord. After performing calculations for the intact truss, the actual selection of cross-sections for all truss members is performed in LIRA.