The study is devoted to a parametric analysis of the stability and load carrying capacity of prismatic segment shells built of rectangular sections of cylindrical shells and subjected to compression. Segment shells (columns) with a constant crosssectional area (weight) have been analysed and all the results obtained have been compared with the results obtained for the cylindrical shell with a radius R and a thickness c; First, an influence of geometrical parameters of the cross-section of single-layer isotropic shells has been analysed and such profiles have been sought for which the load carrying capacity is significantly higher than in the case of the cylindrical shell. Then, for a selected shape of the shell (apart from higher load carrying capacity, this choice could be influenced by other factors such as, e.g. easiness of manufacturing), an effect of the arrangement and thickness of orthotropic layers of the shell (laminate) on the stability and load carrying capacity has been investigated. The analysis has shown that one can design a segment shell made of the same orthotropic material and characterised by higher resistance to buckling and load carrying capacity than a single-layer cylindrical orthotropic shell. The results are depicted in the form of plots.

The paper deals with bifurcation and/or non-bifurcation post-buckling curves of composite plates under biaxial compression. For different lay-up sequences, a coupling, i.e. extension-bending (EB) is considered. The current investigations present distinct equilibrium paths describing when they have bifurcation-type and/or non-bifurcation-type responses. The novel parameter (i.e. EB coupling imperfection) is calculated to show the amount of non-bifurcation in the equilibrium path as a quantitative parameter. For the case of non-square plates, a novel mixed-mode analysis is conducted. The effects of different characters in laminated composites such as layer arrangement, loading ratio, aspect ratio, and boundary conditions are investigated. A novel result concluded in the numerical examples where there are some possibilities to have different mode shapes in linear and non-linear buckling analysis. FEM results of ANSYS software verify the results of analytical equations.

The essential problem in the process of technological prestressing is the imperfection of web sheets. These elements made of relatively large sheets (about 2 meters high) show significant imperfections of the shape and flatness. Initial deflections have the value equal several times the web thickness, but they tend to grow in the process of straightening. Such a case can particularly occur when stresses that compress the shield of the web sheet between diaphragms are close to the critical buckling stress. Experiments were carried out in a real object. The box girder having I I .Om span and 1.8 m in its height was prestressed by welding the straps on the bottom flange and on the web in the vicinity of the bottom llange. Results of performed investigations are the subject of the paper.

Aim: Assessment of the effectiveness and efficiency of three mobile (portable) rescue aspirators models in the opinion of state fire service officers. Comparison with the use of the medical simulation element.
Material and Methods: The study was conducted in organizational units of the State Fire Service (24-hour officers). The research consisted in carrying out the task with the use of three models of mobile rescue aspirators (manual, hand-foot, battery). Each participating firefighter had the task of sucking up an equal amount of fluid (100 ml, respectively) with each model of an aspirator. The test fluid was water at room temperature in a homogeneous 1:1 mixture with sugar (increased viscosity and density, simulated real conditions). Immediately after three suction attempts (with measured suction time), each officer completed a questionnaire on the three models used. Descriptive statistics were used to characterize the variables. The following measures were calculated for the variables: mean (M) and standard deviation (SD), minimum, maximum. The following measures were calculated for categorical variables: number (n) and frequency (%).
Results: 184 officers (182 M and 2 F) took part in the study, including commanders 18.43%, rescuers 65.22%, drivers 16.30%. In the study area 1,609 officers serve in the combat division as at the end of 2021. The studied group accounts for 11.43%. Age of respondents M 34.04 SD 8.24 Min 21 Max 52, length of service M 8.48, SD 7.20 Min 1, Max 25. The longest mean time of completing the task was recorded for model 2 (hand-foot) and it was 6.77 sec.
Conclusions: SFS officers highly appreciated the usefulness and effectiveness of the battery-operated automatic aspirator. This assessment may contribute to the widespread introduction of such a model to rescue sets in the SFS. Time of performing the task by mode 1 was significantly longer by elderly people. People with experience with the model 1 during rescue and firefighting operations had a significantly shorter time of performing the task with the use of the model 2. According to the subjective assessment of firefighters, the most effective is model 3, which is confirmed by the suction time obtained at the work station.